saw or not to saw?

[Streetbu]

I dont know the normal weather conditions where you live, but does it get below freezing in the winter? One of the cheapest ways, but the longest, is to build the shop, tamp the stone/dirt/soil down and let it go thru a full year, then pour your concrete. Lets it freeze and thaw and therefore settle naturally. Usually after one year it wont settle much more if any. Personally, I probably couldn't wait a year, so I would saw cut knowing there's a VERY strong chance with that size slab it will most likely crack.

 

[buzz4041]

24 x 48 here same as Falcon shrinkage cracks only after 15 years.

 

[600SL]

It is entirely possible to construct a crack free, 24 x 30 slab. Actually you can build them a lot larger than that.

There's more to it but basically you need to design the slab to avoid details like re-entrant corners and restraints against movement. Keep the aggregate size up, the slump low (use a mid range water reducer) and cure properly to minimize the possibility of shrinkage cracks. A solid base will prevent structural cracks.

Saw cut control joints are an admission that you're not willing or able to avoid cracks so you're going to hide them under nice straight saw cuts. Don't get me wrong, there is nothing wrong with that. It's a lot more work to do it the other way and if you don't nail it, you could end up with a random crack that will ruin your day.

Sound like good advice now actually getting a contractor to do that is the trick. My slab is 48x 30 with one cut at the partition as called for in the plans. It used 50 yards of concrete for a monolithic slab. So far no cracks in 1.5 years. My outside pad is about 35 yards of concrete poured by the same guy and had cracks all over the place by the next morning.

 

[Dajn]

I think a lot of people are missing an important point. If a concrete pad of any substantial size goes through any extreme heating and then cooling, it will crack. Garage slabs are more protected from this than outdoor slabs for obvious reasons. A normal green saw day during the summer goes like this if the paving crew starts dumping mud at seven a.m. and shuts down at seven p.m. paving one mile of mainline concrete 24 feet wide 10 inches thick. About 5000 yards. Of course temperature is a big factor so in this example it is 60 degrees at seven a.m. and reaches a high of 95 degrees before dropping down to a low of 55 at 5 a.m. no clouds. No rain. Depending on the mix, the beginning will be ready to saw at around 3 p.m. a cross joint every 15 feet and a centerline. I can saw one cross joint a minute on average with a good diamond blade. 354 cross joints in a mile. I will have something like 200 joints sawed by dark. And once the sun goes down and the temp drops the working joints begin. I will saw a few joints until it gets too green, then wait around an hour. Always keeping an eye on the working joints. The most dangerous time and when green saw guys get random cracks is right before the sun comes up when the temperature is at it lowest. Once the sun comes up and starts heating the slab it will begin to expand and then you are safe. I have had random cracks that were clear as day at night close up during the day when the slab heated up. I have gotten away with a few cracks in my day because most people don't have the eye to see a hairline crack. As far as garage slabs. I will always saw mine but it's fine to not saw it. Some people with no saw experience just end up making a mess anyway and should have left it alone. Goodluck either way any one decides to go