DIY cutting concrete expansion joints

Cutting expansion joints on a week old concrete slab using a circular saw with a diamond tippied blade. Saw rested on thin aluminium sheets. Gentle trickle of water from a hose to cool the blade. Air, from a compressor, to blow the water away from the line. The line was drawn with a chinagraph pencil (wax based). Chalk washed off.
Cracks appeared in the slab a couple of days after being poured. Seems the expansion joints should be done the following day. The area was 60m² and quite thick. The joints were cut a week later in this video. Due to days of severe weather here we were unable to get the tools sooner.
We're going to paint the concrete and use a special epoxy filler afterwards.

[@renejackson7652]

Actually these are control joints. Used to control where the concrete cracks. An expansion joint goes through the whole depth of the concrete to allow for expansion. Thanks for the video.

[@MoneyManHolmes]

You are the only other person on UA-cam I’ve seen who knows the difference. Is there a formula you use to determine how far apart EXPANSION joints should be?

[@renejackson7652]

@@MoneyManHolmes No hard and fast rule. Usually one breaks it up into 10x10 squares, taking care to catch as many inside corners as you can. On narrow areas, make the squares or rectangles as large as the narrowest point. For example a 4' walkway is best cut every 4'. On thicker concrete, 6" or more, you can spread the cuts out further...up to 20' apart. Roads, walkways and inside corners are most apt to crack.
Some concrete suppliers use a square footage rule to advise how far apart to make the cuts, usually between 100 and 150 square feet.

[@MoneyManHolmes]

I was wondering about expansion joints. I noticed the local city puts one expansion joint for about every 4 control joints when installing sidewalks.

[@joeyR1CBR1000RR]

Can you please tell me what is this power tool called? is it a normal circular saw for cutting timber with a diamond blade in it?

[@mariapage4753]

Yes it is.

[@joeyR1CBR1000RR]

@@mariapage4753 thank you for that

[@christopherhaak9824]

If you are going to cut in control joints - which these are, they should be cut in within 12-24 hours after the concrete is finished. Then all the cracking will occur at the cuts, not in the middle of the slab like you have.

[@irishtino1595]

Ummm... really don't recommend water and electric saws. This could and has killed people.

[@mariapage4753]

Thanks... wasn't aware of this.

[@approots]

Concrete dust also kills and a wet cut will chip less. Wet tile saws are electric. Must use a GFCI outlet of course. I just wet cut my 1600 sqft patio and I'm still alive.