Hello sir. Good video. Ive been diy building these furnaces for about 8 months now. I used to use the diy recipes for refractory getting material from local stores. Perlite was the main material i used all the time. Ive noticed from doing about 25 different recipes which utilized different ratios of cement to perlite to sand to bentonite clay to water glass, etc etc, that it never held up to the heat that is needed to melt brass and copper. It would break down just as yours did. I even coated the diy refractory cements with green patch 421 and/or Girtech mortars which are rated at 3200’f. They held up better but behind the coating the diy refractorys would still breakdown. The only thing holding it in place was the strength of the coating which as time and usage went on eventually you develop cracks and the diy refractory cements would fall out like sand in an hour glass. Water glass ( sodium silicate) was the worst ingredient to use because i found out it melts to a liquid glass at 1900’f and above. Had a furnace lid completely fail and melt into the crucible when temperatures exceeded 1900’f. Ive since decided to use kaowool with the Girtech mortar coating which has done extremely excellent. Holds up and lasts a looooong time. From time to time putting a maintenance coating of the Girtech mortar on it as it develops tiny cracks, which doesn’t hinder the efficiency and usage of the furnace at all. I have also just recently made a mixture of perlite and water glass ( home made water glass, easy to make) and made a 2.5” x 4” x 9” fire brick with it and attached kaowool to one side of it covering that entire side. Then used a 1” furnace burner, secured the burner in a vice and aimed it at the perlite/water glass fire brick on the kaowool covered side. Fired it for 15 minutes reaching 2500”+f on the kaowool side for 15+ minutes. No melting or damage to the perlite/water glass mix fire brick. So in doing this test I’ve decided that when i build a 16” round furnace with 3” walls, bottom and lid that i would make the first 2” with the perlite/water glass mix then line it with the kaowool, then coat the kaowool with the Girtech mortar. The perlite/water glass mix is an awesome insulator while the kaowool coated with the Girtech mortar is not only a good insulator but an efficient refractory of heat. Anytime i build a furnace with 2” or more of walls/bottom/top i will use at least 1” of the perlite/water glass mix refractory to cut down on a little expense of using just kaowool material. I built a kaowool/Girtech coated propane tank furnace and with a 1” frosty T burner with a .035 mig tip Ive melted a #6 crucible of copper in under 20 minutes using about 18 psig of propane gas pressure. With the 2” of kaowool used for the sides, bottom and lid the sides of the propane built furnace gets about 180-210’ f. I made a small 12” furnace using only 1” of kaowool on the sides and 3” on lid and bottom and the sides get around 300’+f after my first copper melt which is not bad at all. Anyways hope maybe some of my info here can help anyone reading it who builds these furnaces. Cheers smelters.
Wow, thanks for the in depth comments. Much appreciated. Yes, my furnace lining is deteriorating same as everyone else will and your comments are very interesting. One good thing is that it should be easy to restore, but a cheap longer lasting solution is what we all want. Best bang for buck ? Cheers Rob
Used to fix up older style cooking stoves. Mainly replacing refractory tiles. Good quality tiles have very little expansion, so you could cut them into wedges to sit loosely inside the tank. A single cut to suit one on the bottom, another to be held loosely on the top. It does work, having done this myself. Out of this job many years, so you have to look for these tiles, can't be too hard.
love that you show us the bad stuff.. This is what most want.. we see the good.. Thank you mate, top video;; was wondering if I should try to use perlite or buy refectory cement..
Hi Dave, I would use a mix of both. Perlite should be the better insulator. It's your call and largely depends upon how much heat the lining has to withstand. It's all suck it and see time really and largely comes down to price. I'm a cheapskate, so that's the basis of my builds. Cheers Rob
@@Xynudu I bought some 1600AR casting Refractory cement, 4.8kg.. Going to try that, 1st on my lid without mixing any perlite, then make a brick with perlite and test it out.. Its all mostly "lets just try it and see" mostly hay!! Cheers Rob and Thanks for the reply..
Enjoyed your series on the build Rob. I used a glazed tube garden pot surrounded by sand inside an old hot water tank. It's had many fires over probably 4 years or more. Some of the glaze has melted to the bottom and the clay pot is definately cracked. It melts brass no worries. I looked at the cement versions but was always concerned about the breaking down. My lid consists of a Hebel block that does detioriate but easy to replace. It's heavy for sure. Thought I'd share for you to ponder. Btw it ain't pretty lol. Cheers George
I made a furnace using a popular online recipe (Portland cement, sand, fire clay and perlite). Of course being the sort of person who likes to test the limits, I was soon trying to cast bronze with it. I found that the perlite actually melted at high temperatures and acted as a 'flux' for the surrounding material, which glazed as a result. A bigger issue was the pedastal for the crucible, along with the region of furnace wall directly opposite the burner. Both of these melted into a greenish glassy substance. It seems that the Portland cement melts at such temperatures and once again acts as a flux, once it goes the remainder of the material goes too. I subsequently made a new pedastal from fire clay and sand, and fired it in the furnace as if it were pottery. This held up far better, remaining perfectly solid even when melting pure copper. I then covered the hot spots on the furnace lining with fireclay only. It resists the heat well but tends to flake off, I think I actually need a small amount of the 'flux' to melt and bind the clay more thoroughly to the wall for best results. If I were to try again I think I would set out to find a mix with less cement content, maybe just enough to provide sufficient green strength.
It might make sense to separate the two functions: insulation vs. heat shield. It seems like the pearlite/mortar mix is a good insulator, but its inside surface won't hold up to the direct blast. Suppose you coat the inside with just mortar--with no pearlite--to make a layer of, say, 1/4" over the pearlite/mortar mix? You could probably just scrape the loosest material that's there now and then line it with 100% mortar. Same for the lid. I've seen this done over that light-weight fire brick (which provides the insulation). Youe already have the insulation in place.
Hi Todd. I had a layer of refractory mortar over the exposed areas, but it didn't last long. The issue is the temperature exceeds the heat limit rating of the binding agent. Cheers Rob
What if you lined the inside with a refractory firebrick. I've seen some which are fairly thin possibly a little less than half the thickness of a normal brick. So you use a thinner layer of your perlite/cement mixture and then line with firebrick. The brick might hold up better to the direct flame which protects the mixture and the mixture holds the bricks in place. Possibly a more expensive process though. Thanks for your videos. I am looking at building a furnace for exactly the same reasons you have. Your videos are most helpful. Thanks again..
I did consider that, but didn't have the right sized SS pot. It should be OK if thin SS is used. I originally lined my earlier paint tin furnace with a mild steel liner but it eventually burnt away. I have relined the gas bottle furnace with sand and refractory mortar, has set rock hard, but have yet to test it with high heat. Cheers Rob
I saw this mix on the honeydo carpenter channel 1 part Portland, 1 part silica sand, 2 parts vermiculite, 2 parts fire clay, 1/2 part water, 1/2 part sodium silicate.
hd carp has way too many videos to single out the exact one you refer to,....unless you can provide link to that particular one. I purchased his refractory mix recipe but it is not same as one you posted. Thanks
makes me realise how well the kaowool lasts, i've got 3 years out of mine so far, forging for 3 or 4 hours 2 or 3 times a month - recently i covered in in satanite as the kaowool was finally starting to look a little ratty, before that i just used rigidiser, recoating it every 6 months or so,.
Hi Rob. Very interesting. I didn't expect it to start breaking down so quickly. The only things I could think of have already been mentioned in other comments. Coat the inside with a layer of just refractory cement and or use a stainless steel liner. I suppose you could use a layer of firebricks on the inside, they might last longer than the pearlite mix. A tricky problem. Cheers, Alan.
When making refractory mix you should coach your Pro-Lite lightly in shampoo or dish soap then add a small amount of Portland cement just enough to barely coat let that dry now when you use it you'll need much less water in your mix Yoli matchless time to cure it and you'll get much less cracking in your finished product
Hi Rob, at the begining of this you tube you mentioned that you used heat bricks in one of your furnaces. Do you have a link to this as I do have bricks for mine and was wondering how good did it work? By the way how is the Subi as we have had them for a few years now and greatest resale value of any car we have had. Regards Merv.
Hi Merv. The outside wood fired furnace uses old recycled cement incinerator bricks. I don't know what they are made of as regards heat resistance. Some are getting cracks in them now. The Subaru is going great. Super happy with it. Goes in for the first service tomorrow. All good with nothing to report. My niece has the current Forester and loves it. It's surprising how many Subbies are on the road when you take note. Yes, they have excellent resale value. Cheers Rob
better still line with ceramic fibre matt insulation first then cover the insulation with refractory cement that will never crumble away even under brass smelting conditions
Thanks for putting the video out, I made my furnace about 5 years ago and used perlite and Portland cement at 4 to 1 ratio. the wear on my unit looked exactly as your looks. I thought I may have done something wrong, but it would seem the crumbling is just the nature of the beast. Mine is made from two five-gallon water pails turned top to top. That way the unit splits in the middle and just set off the top half off the furnace and the crucible is about halfway out before you even try to grab it. You don't have to reach down into the furnace. Not saying it's any better or worse than any other unit it's just the way I did it
Thanks for the info. Your design is a good take on the issue. The problem of durability as I see it is that the temperatures are higher than the cement and mortar as designed for. Perlite is volcanic rock and remains intact. It's the binder that breaks down. Whether varying the mix ratio will help is debatable. I have reservations on that. Cheers Rob
And a bit of Fireclay... Dont be afraid to by a 20kg bag from Bunnings.. Fuck refractory ..cements.. True your honesty Rob! Not quite the brass yet ole mate. Cool vid. Down to earth
Good one Rob appreciate honestly. I'm guessing for myself I'm going to be using it the same as you for material I can machine. But kinda the cost factor I can spend a lot for fire brick and wool. Or cheaper refractory cement but having to repair more often. Kinda big toss up
Hi Jim. It's a mind bender. Gotta try the cheap options first I guess ;) You can always move on to something more expensive next time. The trouble is that you rarely hear back on how well these home made furnaces last. Cheers Rob
It is very interesting , good to see the wear on what happens I use hebel aerated block easy to replace I get about 8 copper burns out , great video mate
Glad you enjoyed it. Interesting subject. I've done a couple of brass burns recently and the sand and refractory mortar mix have stood up very well. I have some ceramic wool and hardener to install if/when the insulation thickness gets reduced significantly. Still a cheap option if you buy it off of Ebay. Cheers Rob
G'day Rob. Thanks for sharing. My current furnace is 4:1 perlite/normal cement and it performs similar to yours but I have continued to use it up to about 20 burns by now but it should be replaced. One day I'm going to make clay bricks to line it with perlite mix behind it but that won't be for a while. Cheers Peter
Hi Peter. I thought about Bentonite clay as the binder. I have a 20 kg bag of that and may try it next. So many possibilities, it's a bit of a mind bender. As long as it's cheap I don't really care ;) Cheers Rob
@@Xynudu A quick google for fire brick kiln lining here in the UK = well over £100 to build a furnace as big as yours. The home brew linings seem to be the way to go.
Wow. I'm a bit surprised at that Lee. I will have to research the subject some more. I can only assume most home brew Perlite mixes will suffer the same fate as mine eventually. Cheers Rob
I have both of those Peter and may reline it with something similar once it wears down some more (to get a decent thickness). I have been keen to try Bentonite from day one. Cheers Rob
Thank you, Rob, for the video and the information update. Remember you are heating the new one much more then before. As you say the mixture thing is a bit of a question, and I suppose more important with the higher temperatures you are using. I am interested in the work you do. Thanks again.
Hi Glenn, the heat output of the larger burner is pushing the mix temperature well above what the refractory mortar is rated at. Pizza ovens don't get this hot ;) I'm not surprised at the outcome. Whether refractory cement will cope better is questionable. There is very little information on durability at these temperatures. Cheers Rob
I just found this post, very interesting. I built one (using a 9 kg propane tank) but lined it with firebricks from Littlehampton Bricks. I dug down in the garden until I hit clay and used that, mixed with some Perlite - not much - and added kitty litter (Bentonite clay). This was mixed to a stiff consistency, lined the tank with it then stood the bricks against it and pushed more of the mix between the bricks. The bricks were cut with an angle grinder (DUSTY!!) so they fitted close together. It seems to be working ok so far, other than a chunk just fell out of the lid! I've melted brass with it but damaged my crucible getting it out, I've just melted some aluminium (from BMW suspension arms, good stuff) using a pot made from steel tube. I built a gas forge and managed to get hold of some Kaowool, but I didn't have enough left for the forge and couldn't get any more from the guy. It's the best thing to use but difficult to locate here in Adelaide. Good fun, isn't it.😄
Hi Richard. The firebricks are a good idea. Lots of options to try out ;) My crucibles are thick steel and pretty much indestructable. Melting brass was no problem. The fumes are toxic so take precautions. Lots of fun and a good money saver. Cheers Rob
@@Xynudu My "pot" is thick steel tube with a steel plate welded to the bottom. The original one was used in my coke forge to melt brass but it got a bit hot, melted the bottom and the brass flowed out into the tuyere and blocked the airflow!!! It's easier to control the heat in the foundry. Cheers, Richard.
I have the same issue with my perlite mix. I had some sand in it, but is still becomes flaky and brittle after a while. I have soaked the bricks with liquid glass. We'll see what happens.
Hi, Thanks for sharing your ideas in this informative video. Given that you have a very good insulation lining, I think that you could coat the old eroded surface with a thin layer of render that could withstand the heat. Pure commercial refractory mortar, that you use with the perlite, may do the trick. My supply of Lanko 156 refractory mortar is only good to ~1,000C). I expect you need a bit higher temperature. Sodium silicate mixed with suitable refractory minerals is another that can be good for 1,200+ (My thermocouple will not measure above this temperature and I expect that the probe wires get destroyed at this temperature). Sodium silicate and aluminium oxide make a bulletproof DIY refractory render. It is easy to use and very cheap. I have found that the aluminium oxide can be substituted with finely ground and sifted clay-free loam soil (from farm post hole digging or crab hole towers) and it is literally 'dirt-cheap'. The link to my rambling post on DIY REFRACTORY FROM SODIUM SILICATE “BORN IN FIRE TO SURVIVE IN FIRE” is below. I will be interested to see how your liner repair goes. Lastly, I am curious to know what the little metal-lined notch in the lower portion is for? Tim timtinker.com/diy-refractory/
Thanks for the update Rob. Is the heavier erosion because you've upped the heat by going to brass from aluminium? I've never tried any melting but you never know, I might make a similar unit and try it.
Hi Mart. Yes, brass requires a lot more heat. The much bigger burner really puts out the heat and I suspect it exceeds the limit of the binding agent (mortar or cement). Cheers Rob
Hi Rob, another good video. It is a shame to see the flaking so soon on your foundry. However, you are getting it a lot hotter there with melting brass so maybe the heat is just a bit too much? My foundry has a 1.5/1 ratio of perlite to cement. I have not run it up much because I'm still working on the hossfeld bender build, but it would be good to see how it holds up with melting brass. I saw your other video on melting brass which again is a great video. I have a bunch of brass so that is on the list to do. All the best.
Hi Jon. I'm keenly awaiting the outcome of your mix under duress. I firmly believe the temperature is exceeding the limit of the binding agent (Pizza ovens don't get this hot). Next time I will try some Bentonite clay to re-line it. Nothing to lose as I have 20 Kg of the stuff. All very interesting. Cheers Rob
Hello Rob, A very good video... I was a little surprised how it has broken down so quickly... I was wondering if you could make a runny (for want of a better description) solution of the Perlite / Refractory Mortar and try and seal it now... I would be an interesting exercise to see if it extends the life somewhat. Take care. Paul,,
Hi mate, check out Foseco Pyrocrete 165 AFT. It’s a commercial cast-able refractory. You can get it in Brisbane. I went monolithic for my furnace for durability (it’ll last longer than I live) but many use ceramic wool then 2” of cast-able refractory for the hot face. Also, Pyrocrete is very dense and does not use much water. I need 1.5 bags for my 9kg gas bottle furnace.
What a great thread. I ,m retired & have spent the Last three days reading everything I could on this. Every time I think I have this figured out I Find some where it fails.I must check out the Girtech mordar. Thanks
It's a very varied subject. If money is no object it's going to be a better end result, but for the pittance this cost it works pretty well. Cheers Rob
Out of my league with that rob as i have never done any melting of metal using a home made furnace but i keep thinking of a sacrificial liner . Maybe something like a big coffee can that you can insert to protect the lining ? When it is stuffed just replace it and it may keep the lining from degrading- just a thought . .
Hi Ian . Food for thought. I'm obviously not alone with this issue, but you see very little reference to it happening. After what happened to the coffee tin furnace I was not surprised. Now I just have to find a cheap solution. Cheers Rob
As the video proceeded, I thought what if you could line the walls of the furnace with ceramic tiles using refractory cement like thin set. I have no idea how well or not this might keep the furnace from disintegrating. Do you think it would be worth a try? Thanks for the video.
They don't last. I had a metal liner in the smaller furnace and it just burnt away quite quickly. Given the much greater heat of the new torch it would be even worse. Cheers Rob
Thanks Rob, that was quite "illuminating" :). The nature of the flakiness where the flame front is suggests a stringy addition might help near the surface. I have no idea what material that can be, maybe a fibreglass weave although that will melt at around 1100oC, but that might be ok if its buried a little under the refractory mortar mix?
Hi Benny. I'm going to have to give some more thought to this. I had a steel liner in the paint tin furnace, but it soon burnt away. I'm not sure how stainless steel would go. Interesting subject. Cheers Rob
Stainless grade 304 is apparently ok for up to 870 Celcius for intermittent service, or 925 Celcius in continuous service. So it seems like a stainless lining might do for melting aluminium, but wouldn't be much good if you were working with brass or bronze.
Try 100% refractory cement putting a veneer layer on the existing insulation, I reckon that would give excellent thermal properties and stabilise what you have already done
Perlite is great insulation but not suitable for hot faces. Fire clay works, wants to be an inch thick, it wil crack all over but is expected. Coat it with a layer of alumina and sodium sillicate binder.
Hi Stavros. I might try that next when I re-line it. I have 20 kg of Bentonite clay and may give that a go with some Perlite at about 50/50. Cheers Rob
Hay Rob, I found this clip and recipie, he also test it. ua-cam.com/video/KZyUcYhYVgU/v-deo.html and another clip testing different mixes. ua-cam.com/video/xV51Om1Mv_o/v-deo.html
Thanks for the links Mick. I see that Perlite comes out on top. I have a few home brew mixes to try next. The one most likely is Perlite and Bentonite clay binder with a dash of high temp mortar or sand. I have all that and nothing to lose ;) Cheers Rob
@@XynuduHay Rob, I'm going to use his fire brick recipe in the first vid. I'm in the middle of building an oil fired gas bottle furnace and had a look at your build videos. One question I had is did you put any reo or mesh in the lid to hold it in and to stop it falling apart?
Hi Mick, I put two pieces of reo across the lid - one each side of the square vent and added two cross links between them. That keeps the insulation mix well in place. You could use weldmesh as an alternative, so long as you can weld that small a diameter. Cheers Rob
Perhaps the most exhaustive research into this type of material was undertaken by NASA for the Space Shuttle protective 'Ceramic Tiles'. Maybe a mixture of the tile material (given in the attached link) used as a bonding agent with your 'Perlite' would provide the answer you seek. www.nasa.gov/sites/default/files/atoms/files/shuttle_tiles_9_12v2.pdf. Best regards.
How long does it take for that mix to cure? I'm making a pizza oven and did the first 8" or so of the "igloo" with perlite and refractory cement, then the rest with perlite and portland cement. The portland cement and perlie is rock hard, but the refractory mix isn't. It's set, but still kind of "damp" and not solid. Been three days...
I didn't use refractory cement. Refractory mortar is different, so I can't comment on your mix or the ratio you used. It sounds like there wasn't enough cement. Cheers Rob
That mix sounds about right. Too much water could do it. I don't use a water ratio, just add enough to get the consistency how I want it. If it is a water issue, it should dry out when warmed in the sun (but could hairline crack the surface slightly). Cheers Rob
Hello sir. Good video. Ive been diy building these furnaces for about 8 months now. I used to use the diy recipes for refractory getting material from local stores. Perlite was the main material i used all the time. Ive noticed from doing about 25 different recipes which utilized different ratios of cement to perlite to sand to bentonite clay to water glass, etc etc, that it never held up to the heat that is needed to melt brass and copper. It would break down just as yours did. I even coated the diy refractory cements with green patch 421 and/or Girtech mortars which are rated at 3200’f. They held up better but behind the coating the diy refractorys would still breakdown. The only thing holding it in place was the strength of the coating which as time and usage went on eventually you develop cracks and the diy refractory cements would fall out like sand in an hour glass. Water glass ( sodium silicate) was the worst ingredient to use because i found out it melts to a liquid glass at 1900’f and above. Had a furnace lid completely fail and melt into the crucible when temperatures exceeded 1900’f. Ive since decided to use kaowool with the Girtech mortar coating which has done extremely excellent. Holds up and lasts a looooong time. From time to time putting a maintenance coating of the Girtech mortar on it as it develops tiny cracks, which doesn’t hinder the efficiency and usage of the furnace at all. I have also just recently made a mixture of perlite and water glass ( home made water glass, easy to make) and made a 2.5” x 4” x 9” fire brick with it and attached kaowool to one side of it covering that entire side. Then used a 1” furnace burner, secured the burner in a vice and aimed it at the perlite/water glass fire brick on the kaowool covered side. Fired it for 15 minutes reaching 2500”+f on the kaowool side for 15+ minutes. No melting or damage to the perlite/water glass mix fire brick. So in doing this test I’ve decided that when i build a 16” round furnace with 3” walls, bottom and lid that i would make the first 2” with the perlite/water glass mix then line it with the kaowool, then coat the kaowool with the Girtech mortar. The perlite/water glass mix is an awesome insulator while the kaowool coated with the Girtech mortar is not only a good insulator but an efficient refractory of heat. Anytime i build a furnace with 2” or more of walls/bottom/top i will use at least 1” of the perlite/water glass mix refractory to cut down on a little expense of using just kaowool material. I built a kaowool/Girtech coated propane tank furnace and with a 1” frosty T burner with a .035 mig tip Ive melted a #6 crucible of copper in under 20 minutes using about 18 psig of propane gas pressure. With the 2” of kaowool used for the sides, bottom and lid the sides of the propane built furnace gets about 180-210’ f. I made a small 12” furnace using only 1” of kaowool on the sides and 3” on lid and bottom and the sides get around 300’+f after my first copper melt which is not bad at all. Anyways hope maybe some of my info here can help anyone reading it who builds these furnaces. Cheers smelters.
Wow, thanks for the in depth comments. Much appreciated. Yes, my furnace lining is deteriorating same as everyone else will and your comments are very interesting. One good thing is that it should be easy to restore, but a cheap longer lasting solution is what we all want. Best bang for buck ? Cheers Rob
Used to fix up older style cooking stoves. Mainly replacing refractory tiles. Good quality tiles have very little expansion, so you could cut them into wedges to sit loosely inside the tank. A single cut to suit one on the bottom, another to be held loosely on the top. It does work, having done this myself. Out of this job many years, so you have to look for these tiles, can't be too hard.
Hi Rob. Wow, that was an eye opener. Food for thought. Thank you for sharing. Andrew 👍😀
love that you show us the bad stuff.. This is what most want.. we see the good.. Thank you mate, top video;; was wondering if I should try to use perlite or buy refectory cement..
Hi Dave, I would use a mix of both. Perlite should be the better insulator. It's your call and largely depends upon how much heat the lining has to withstand. It's all suck it and see time really and largely comes down to price. I'm a cheapskate, so that's the basis of my builds. Cheers Rob
@@Xynudu I bought some 1600AR casting Refractory cement, 4.8kg.. Going to try that, 1st on my lid without mixing any perlite, then make a brick with perlite and test it out.. Its all mostly "lets just try it and see" mostly hay!! Cheers Rob and Thanks for the reply..
Enjoyed your series on the build Rob. I used a glazed tube garden pot surrounded by sand inside an old hot water tank. It's had many fires over probably 4 years or more. Some of the glaze has melted to the bottom and the clay pot is definately cracked. It melts brass no worries. I looked at the cement versions but was always concerned about the breaking down. My lid consists of a Hebel block that does detioriate but easy to replace. It's heavy for sure. Thought I'd share for you to ponder. Btw it ain't pretty lol. Cheers George
Thanks George. Cheers Rob
I made a furnace using a popular online recipe (Portland cement, sand, fire clay and perlite). Of course being the sort of person who likes to test the limits, I was soon trying to cast bronze with it. I found that the perlite actually melted at high temperatures and acted as a 'flux' for the surrounding material, which glazed as a result. A bigger issue was the pedastal for the crucible, along with the region of furnace wall directly opposite the burner. Both of these melted into a greenish glassy substance. It seems that the Portland cement melts at such temperatures and once again acts as a flux, once it goes the remainder of the material goes too.
I subsequently made a new pedastal from fire clay and sand, and fired it in the furnace as if it were pottery. This held up far better, remaining perfectly solid even when melting pure copper. I then covered the hot spots on the furnace lining with fireclay only. It resists the heat well but tends to flake off, I think I actually need a small amount of the 'flux' to melt and bind the clay more thoroughly to the wall for best results.
If I were to try again I think I would set out to find a mix with less cement content, maybe just enough to provide sufficient green strength.
It might make sense to separate the two functions: insulation vs. heat shield. It seems like the pearlite/mortar mix is a good insulator, but its inside surface won't hold up to the direct blast. Suppose you coat the inside with just mortar--with no pearlite--to make a layer of, say, 1/4" over the pearlite/mortar mix? You could probably just scrape the loosest material that's there now and then line it with 100% mortar. Same for the lid. I've seen this done over that light-weight fire brick (which provides the insulation). Youe already have the insulation in place.
Hi Todd. I had a layer of refractory mortar over the exposed areas, but it didn't last long. The issue is the temperature exceeds the heat limit rating of the binding agent. Cheers Rob
Just another reason why I enjoy your videos sir, you’re showing the good and the bad. Keep it up, you’ll get it just right like your brass melts 😎
What if you lined the inside with a refractory firebrick. I've seen some which are fairly thin possibly a little less than half the thickness of a normal brick. So you use a thinner layer of your perlite/cement mixture and then line with firebrick. The brick might hold up better to the direct flame which protects the mixture and the mixture holds the bricks in place. Possibly a more expensive process though. Thanks for your videos. I am looking at building a furnace for exactly the same reasons you have. Your videos are most helpful. Thanks again..
Hi Kegan. All doable. The bricks could be sliced with a friction disc to fit cleanly. Worth investigating. Cheers Rob
@@Xynudu That indeed would be an interesting solution.
Would putting a replaceable rolled steel or stainless (or pipe section) sitting inside the refractory lining protect it without robbing too much heat?
I did consider that, but didn't have the right sized SS pot. It should be OK if thin SS is used. I originally lined my earlier paint tin furnace with a mild steel liner but it eventually burnt away. I have relined the gas bottle furnace with sand and refractory mortar, has set rock hard, but have yet to test it with high heat. Cheers Rob
I saw this mix on the honeydo carpenter channel 1 part Portland, 1 part silica sand, 2 parts vermiculite, 2 parts fire clay, 1/2 part water, 1/2 part sodium silicate.
hd carp has way too many videos to single out the exact one you refer to,....unless you can provide link to that particular one. I purchased his refractory mix recipe but it is not same as one you posted. Thanks
This is interesting, I can't help but thank you for sharing your experience.
Thanks for watching!
makes me realise how well the kaowool lasts, i've got 3 years out of mine so far, forging for 3 or 4 hours 2 or 3 times a month - recently i covered in in satanite as the kaowool was finally starting to look a little ratty, before that i just used rigidiser, recoating it every 6 months or so,.
Hi Rob. Very interesting. I didn't expect it to start breaking down so quickly. The only things I could think of have already been mentioned in other comments. Coat the inside with a layer of just refractory cement and or use a stainless steel liner. I suppose you could use a layer of firebricks on the inside, they might last longer than the pearlite mix. A tricky problem. Cheers, Alan.
Hi Alan. I'm not really surprised given the massive heat involved. I will give it some more thought when the time comes to replace it. Cheers Rob
Great content as usual thanks. Yeah, I wish more people in the makerverse were so sharing with long term issues.
Yes, it would help a lot. Cheers Rob
When making refractory mix you should coach your Pro-Lite lightly in shampoo or dish soap then add a small amount of Portland cement just enough to barely coat let that dry now when you use it you'll need much less water in your mix Yoli matchless time to cure it and you'll get much less cracking in your finished product
Hi Rob, at the begining of this you tube you mentioned that you used heat bricks in one of your furnaces. Do you have a link to this as I do have bricks for mine and was wondering how good did it work? By the way how is the Subi as we have had them for a few years now and greatest resale value of any car we have had. Regards Merv.
Hi Merv. The outside wood fired furnace uses old recycled cement incinerator bricks. I don't know what they are made of as regards heat resistance. Some are getting cracks in them now. The Subaru is going great. Super happy with it. Goes in for the first service tomorrow. All good with nothing to report. My niece has the current Forester and loves it. It's surprising how many Subbies are on the road when you take note. Yes, they have excellent resale value. Cheers Rob
Thank you for this, very helpful.
better still line with ceramic fibre matt insulation first then cover the insulation with refractory cement that will never crumble away even under brass smelting conditions
Thanks for putting the video out, I made my furnace about 5 years ago and used perlite and Portland cement at 4 to 1 ratio. the wear on my unit looked exactly as your looks. I thought I may have done something wrong, but it would seem the crumbling is just the nature of the beast. Mine is made from two five-gallon water pails turned top to top. That way the unit splits in the middle and just set off the top half off the furnace and the crucible is about halfway out before you even try to grab it. You don't have to reach down into the furnace. Not saying it's any better or worse than any other unit it's just the way I did it
Thanks for the info. Your design is a good take on the issue. The problem of durability as I see it is that the temperatures are higher than the cement and mortar as designed for. Perlite is volcanic rock and remains intact. It's the binder that breaks down. Whether varying the mix ratio will help is debatable. I have reservations on that. Cheers Rob
@@Xynudu Portland cement at a small ratio... Silica sand and perlite
And a bit of Fireclay... Dont be afraid to by a 20kg bag from Bunnings..
Fuck refractory ..cements..
True your honesty Rob!
Not quite the brass yet ole mate.
Cool vid. Down to earth
The secret is fireclay
@@djpaulk And a small amount of water glass.
Good one Rob appreciate honestly. I'm guessing for myself I'm going to be using it the same as you for material I can machine. But kinda the cost factor I can spend a lot for fire brick and wool. Or cheaper refractory cement but having to repair more often. Kinda big toss up
Hi Jim. It's a mind bender. Gotta try the cheap options first I guess ;) You can always move on to something more expensive next time. The trouble is that you rarely hear back on how well these home made furnaces last. Cheers Rob
Perlite has half the fahrenheit resistance of vermiculite.
It is very interesting , good to see the wear on what happens I use hebel aerated block easy to replace I get about 8 copper burns out , great video mate
Glad you enjoyed it. Interesting subject. I've done a couple of brass burns recently and the sand and refractory mortar mix have stood up very well. I have some ceramic wool and hardener to install if/when the insulation thickness gets reduced significantly. Still a cheap option if you buy it off of Ebay. Cheers Rob
G'day Rob. Thanks for sharing. My current furnace is 4:1 perlite/normal cement and it performs similar to yours but I have continued to use it up to about 20 burns by now but it should be replaced. One day I'm going to make clay bricks to line it with perlite mix behind it but that won't be for a while. Cheers Peter
Hi Peter. I thought about Bentonite clay as the binder. I have a 20 kg bag of that and may try it next. So many possibilities, it's a bit of a mind bender. As long as it's cheap I don't really care ;) Cheers Rob
@@Xynudu A quick google for fire brick kiln lining here in the UK = well over £100 to build a furnace as big as yours. The home brew linings seem to be the way to go.
Wow. I'm a bit surprised at that Lee. I will have to research the subject some more. I can only assume most home brew Perlite mixes will suffer the same fate as mine eventually. Cheers Rob
@@Xynudu you reminded me that my very first mix was 10:1 sand/bentonite it worked just as well
I have both of those Peter and may reline it with something similar once it wears down some more (to get a decent thickness). I have been keen to try Bentonite from day one. Cheers Rob
My perlite failed after ten or so melts, I put koawool in a fixed that problem got fifty melts on it it's fine,it cost more but lasts forever.
It's a very expensive option in Australia. Did you coat it with anything ? Cheers Rob
Just cut to length and rolled it in,you can't even tell it's been hot and it three years old, amazing stuff.
Thank you, Rob, for the video and the information update. Remember you are heating the new one much more then before. As you say the mixture thing is a bit of a question, and I suppose more important with the higher temperatures you are using. I am interested in the work you do. Thanks again.
Hi Glenn, the heat output of the larger burner is pushing the mix temperature well above what the refractory mortar is rated at. Pizza ovens don't get this hot ;) I'm not surprised at the outcome. Whether refractory cement will cope better is questionable. There is very little information on durability at these temperatures. Cheers Rob
Interesting….enjoyed
line with straight refractory mortar on its own, on top of your perlite you have already lined with to stop it crumbling away
I just found this post, very interesting. I built one (using a 9 kg propane tank) but lined it with firebricks from Littlehampton Bricks. I dug down in the garden until I hit clay and used that, mixed with some Perlite - not much - and added kitty litter (Bentonite clay). This was mixed to a stiff consistency, lined the tank with it then stood the bricks against it and pushed more of the mix between the bricks. The bricks were cut with an angle grinder (DUSTY!!) so they fitted close together. It seems to be working ok so far, other than a chunk just fell out of the lid!
I've melted brass with it but damaged my crucible getting it out, I've just melted some aluminium (from BMW suspension arms, good stuff) using a pot made from steel tube. I built a gas forge and managed to get hold of some Kaowool, but I didn't have enough left for the forge and couldn't get any more from the guy. It's the best thing to use but difficult to locate here in Adelaide.
Good fun, isn't it.😄
Hi Richard. The firebricks are a good idea. Lots of options to try out ;) My crucibles are thick steel and pretty much indestructable. Melting brass was no problem. The fumes are toxic so take precautions. Lots of fun and a good money saver. Cheers Rob
@@Xynudu My "pot" is thick steel tube with a steel plate welded to the bottom. The original one was used in my coke forge to melt brass but it got a bit hot, melted the bottom and the brass flowed out into the tuyere and blocked the airflow!!! It's easier to control the heat in the foundry.
Cheers, Richard.
Brian from Ma.Always love your vids MR.Robbie THANKS Besafe
I have the same issue with my perlite mix. I had some sand in it, but is still becomes flaky and brittle after a while. I have soaked the bricks with liquid glass. We'll see what happens.
Hi, Thanks for sharing your ideas in this informative video. Given that you have a very good insulation lining, I think that you could coat the old eroded surface with a thin layer of render that could withstand the heat. Pure commercial refractory mortar, that you use with the perlite, may do the trick. My supply of Lanko 156 refractory mortar is only good to ~1,000C). I expect you need a bit higher temperature. Sodium silicate mixed with suitable refractory minerals is another that can be good for 1,200+ (My thermocouple will not measure above this temperature and I expect that the probe wires get destroyed at this temperature).
Sodium silicate and aluminium oxide make a bulletproof DIY refractory render. It is easy to use and very cheap. I have found that the aluminium oxide can be substituted with finely ground and sifted clay-free loam soil (from farm post hole digging or crab hole towers) and it is literally 'dirt-cheap'. The link to my rambling post on DIY REFRACTORY FROM SODIUM SILICATE “BORN IN FIRE TO SURVIVE IN FIRE” is below. I will be interested to see how your liner repair goes.
Lastly, I am curious to know what the little metal-lined notch in the lower portion is for? Tim
timtinker.com/diy-refractory/
How much gas does this thing use to do an average 1kilogram melt??
Stavros again
It's hard to say. It's certainly not excessive. I guess it probably uses about the same weight in gas. Cheers Rob
Thanks for the warts and all review
My pleasure. Cheers Rob
I am wondering if the insulation would last longer if there was a liner (i.e. sheet metal) to protect it from the current of burning gas ?
I did originally have a steel liner in my previous furnace, but it burnt away. I think stainless steel may last longer.
Thanks for the update Rob. Is the heavier erosion because you've upped the heat by going to brass from aluminium? I've never tried any melting but you never know, I might make a similar unit and try it.
Hi Mart. Yes, brass requires a lot more heat. The much bigger burner really puts out the heat and I suspect it exceeds the limit of the binding agent (mortar or cement). Cheers Rob
I wonder if lining this with Satanite could slow down the decay on the insulation. Gameco often has some good specials on it if you're not aware.
Hi Rob, another good video. It is a shame to see the flaking so soon on your foundry. However, you are getting it a lot hotter there with melting brass so maybe the heat is just a bit too much? My foundry has a 1.5/1 ratio of perlite to cement. I have not run it up much because I'm still working on the hossfeld bender build, but it would be good to see how it holds up with melting brass. I saw your other video on melting brass which again is a great video. I have a bunch of brass so that is on the list to do. All the best.
Hi Jon. I'm keenly awaiting the outcome of your mix under duress. I firmly believe the temperature is exceeding the limit of the binding agent (Pizza ovens don't get this hot). Next time I will try some Bentonite clay to re-line it. Nothing to lose as I have 20 Kg of the stuff. All very interesting. Cheers Rob
Hello Rob,
A very good video... I was a little surprised how it has broken down so quickly... I was wondering if you could make a runny (for want of a better description) solution of the Perlite / Refractory Mortar and try and seal it now... I would be an interesting exercise to see if it extends the life somewhat.
Take care.
Paul,,
Skip the perlite on the lining, get some firebox repair or relining compound, comes in tubs. Many brands
The ratios you mention, that is by volume?
Yes.
Hi mate, check out Foseco Pyrocrete 165 AFT. It’s a commercial cast-able refractory. You can get it in Brisbane. I went monolithic for my furnace for durability (it’ll last longer than I live) but many use ceramic wool then 2” of cast-able refractory for the hot face.
Also, Pyrocrete is very dense and does not use much water. I need 1.5 bags for my 9kg gas bottle furnace.
Thanks for the suggestion. I will check it out. Cheers Rob
you might be old, but you always ask the right questions
You might want to put a high density liner in it. That might last a bit longer.
What a great thread. I ,m retired & have spent the
Last three days reading everything I could on this. Every time I think I have this figured out I
Find some where it fails.I must check out the
Girtech mordar. Thanks
It's a very varied subject. If money is no object it's going to be a better end result, but for the pittance this cost it works pretty well. Cheers Rob
Out of my league with that rob as i have never done any melting of metal using a home made furnace but i keep thinking of a sacrificial liner .
Maybe something like a big coffee can that you can insert to protect the lining ? When it is stuffed just replace it and it may keep the lining from degrading- just a thought . .
Hi Ian . Food for thought. I'm obviously not alone with this issue, but you see very little reference to it happening. After what happened to the coffee tin furnace I was not surprised. Now I just have to find a cheap solution. Cheers Rob
As the video proceeded, I thought what if you could line the walls of the furnace with ceramic tiles using refractory cement like thin set. I have no idea how well or not this might keep the furnace from disintegrating. Do you think it would be worth a try? Thanks for the video.
Hi James. I have no idea how that would go. A lot of this is suck it and see. Cheers Rob
What about using a big coffee can indsigt. To reflect the heat from the blower..
They don't last. I had a metal liner in the smaller furnace and it just burnt away quite quickly. Given the much greater heat of the new torch it would be even worse. Cheers Rob
I've been thinking about making a smelter. I need a large capacity one as I want to cast intake manifolds.
That will require a big furnace and heavy lifting gear to handle/pour the hot melt. It's a major undertaking. Cheers Rob
Thanks for sharing 👍
Thanks Rob, that was quite "illuminating" :). The nature of the flakiness where the flame front is suggests a stringy addition might help near the surface. I have no idea what material that can be, maybe a fibreglass weave although that will melt at around 1100oC, but that might be ok if its buried a little under the refractory mortar mix?
Hi Benny. I'm going to have to give some more thought to this. I had a steel liner in the paint tin furnace, but it soon burnt away. I'm not sure how stainless steel would go. Interesting subject. Cheers Rob
Stainless grade 304 is apparently ok for up to 870 Celcius for intermittent service, or 925 Celcius in continuous service. So it seems like a stainless lining might do for melting aluminium, but wouldn't be much good if you were working with brass or bronze.
Bloody hell, I didn’t think it would deteriorate so fast, it’s a shame
Such is life. Learn by destruction ;) Cheers Rob
Try 100% refractory cement putting a veneer layer on the existing insulation, I reckon that would give excellent thermal properties and stabilise what you have already done
Worth a try Don. I will let it wear away a bit more before I re-do it. Cheers Rob
Perlite is great insulation but not suitable for hot faces. Fire clay works, wants to be an inch thick, it wil crack all over but is expected. Coat it with a layer of alumina and sodium sillicate binder.
Has anyone tried using good old clay, the stuff we have in all our backyards and which bogs your car if you drive on it???
Stavros
Hi Stavros. I might try that next when I re-line it. I have 20 kg of Bentonite clay and may give that a go with some Perlite at about 50/50. Cheers Rob
perlite + sodium silicate
Hay Rob, I found this clip and recipie, he also test it. ua-cam.com/video/KZyUcYhYVgU/v-deo.html and another clip testing different mixes. ua-cam.com/video/xV51Om1Mv_o/v-deo.html
Thanks for the links Mick. I see that Perlite comes out on top. I have a few home brew mixes to try next. The one most likely is Perlite and Bentonite clay binder with a dash of high temp mortar or sand. I have all that and nothing to lose ;) Cheers Rob
@@XynuduHay Rob, I'm going to use his fire brick recipe in the first vid. I'm in the middle of building an oil fired gas bottle furnace and had a look at your build videos. One question I had is did you put any reo or mesh in the lid to hold it in and to stop it falling apart?
Hi Mick, I put two pieces of reo across the lid - one each side of the square vent and added two cross links between them. That keeps the insulation mix well in place. You could use weldmesh as an alternative, so long as you can weld that small a diameter. Cheers Rob
@@Xynudu Yea I thought you needed something in there, I'll do something simmilar.
Perhaps the most exhaustive research into this type of material was undertaken by NASA for the Space Shuttle protective 'Ceramic Tiles'.
Maybe a mixture of the tile material (given in the attached link) used as a bonding agent with your 'Perlite' would provide the answer you seek. www.nasa.gov/sites/default/files/atoms/files/shuttle_tiles_9_12v2.pdf. Best regards.
How long does it take for that mix to cure? I'm making a pizza oven and did the first 8" or so of the "igloo" with perlite and refractory cement, then the rest with perlite and portland cement. The portland cement and perlie is rock hard, but the refractory mix isn't. It's set, but still kind of "damp" and not solid. Been three days...
I didn't use refractory cement. Refractory mortar is different, so I can't comment on your mix or the ratio you used. It sounds like there wasn't enough cement. Cheers Rob
@@Xynudu I used castable refractory cement at a ratio of 3-1-1 perlite/cement/water.
Thinking too much water.
That mix sounds about right. Too much water could do it. I don't use a water ratio, just add enough to get the consistency how I want it. If it is a water issue, it should dry out when warmed in the sun (but could hairline crack the surface slightly). Cheers Rob