cracks in concrete

[crushers]

s***, all the studying i did and not once did i come across that tidbit.
no sand, 5" of 3500 over the slabs with rebar every 16"...
well, learn something new every day, thanks.

 

[splitshot]

Chad, never used it, but some of the sub contractors swear by this stuff..



Just like the jerky shooter.

 

[WarDamnEagle]

dang, did they keep the slab wet as it cooled? I would imagine the humidity was low when they poured.

I've poured pretty large slabs with no control joints and very minimal cracking. By pretty big I'm talking something like 20' on each side. The key is to keep the concrete moist while it's curing. Use polyurethane on top and wet the concrete at least twice per day for 10 days (or more). Even with perfect preparation you'll get shrinkage cracks unless you keep it wet.

I don't agree with the 2" of sand over the poly under the slab btw. That sounds like a good way to get too much moisture pull from underneath.

I will admit however that even with the best of everything it's difficult to keep concrete from at least getting hairline cracks. My father in law, the civil engineer with a PE, always called concrete a cracked structure. He said that's what rebar is for.

 

[bigndn]

Chad, never used it, but some of the sub contractors swear by this stuff..



Just like the jerky shooter.

Thanks! That looks like the stuff I need. Easy peasy!!

 

[PAToyota]

If you control the cracking with joints then yes, but solid slab will always crack.

We've done 50'x50' slabs for automated warehousing with no cracks other than the hairline drying cracks.

 

[pillguy]

I used this from HD Sikaflex 29 fl. oz. Self-Leveling Sealant - 106711 at The Home Depot
not cheap, but works very well on my 20yr old driveway.
It had a lot of existing cracks that were covered in this crappy vinly type patch.

Used my pressure washer to clean them out, then started pouring it in.

Very firm, and with some flexibility like gumby.

I used a different product that was more flexible, but I do not like it as I question the longevity.

 

[sparkplug]

Throw some blacktop over it.

 

[BattleWagon]

embrace the fxxxing cracks, they are not harming anything.

matter of fact, take a hot saw and slice a 2' grid lengthwise and widthwise, now you have a permeable paver driveway. Congrats, you just saved a dolphin, greener'n's***.

 

[nspctr1]

Man speak truth. shrinkage cracks will develop to some degree and control joints are always a good thing. There are still alot of variables that are not known so it's hard to give a good answer for what is causing the cracks bigndn but, if they are just hairline and less than 1/8" then I wouldn't worry about them.Especially since it's already been almost 20 yrs if I read the original post correctly.

FWIW, a foundation is designed for the soil it is going to be built upon and what is being built on it. for active soils such as clays that will expand and contract I would put at least a foot of base material down and then add grade beams every so often depending on the size of the slab and structure but at least around the perimeter. Even sandy soils will cause some issues with slabs because sand will suck the moisture from the concrete.
Finishing is another critical area, if concrete is in the truck for too long and it begins to set it loses its ability to bond together, like a cold joint, and if the finisher puts alot of water on top to achieve the finish then that is not a good thing either because alot of that paste will eventually break up. Lots of things to consider.

.02

I've poured pretty large slabs with no control joints and very minimal cracking. By pretty big I'm talking something like 20' on each side. The key is to keep the concrete moist while it's curing. Use polyurethane on top and wet the concrete at least twice per day for 10 days (or more). Even with perfect preparation you'll get shrinkage cracks unless you keep it wet.

I don't agree with the 2" of sand over the poly under the slab btw. That sounds like a good way to get too much moisture pull from underneath.

I will admit however that even with the best of everything it's difficult to keep concrete from at least getting hairline cracks. My father in law, the civil engineer with a PE, always called concrete a cracked structure. He said that's what rebar is for.

 

[bigndn]

Man speak truth. shrinkage cracks will develop to some degree and control joints are always a good thing. There are still alot of variables that are not known so it's hard to give a good answer for what is causing the cracks bigndn but, if they are just hairline and less than 1/8" then I wouldn't worry about them.Especially since it's already been almost 20 yrs if I read the original post correctly.

FWIW, a foundation is designed for the soil it is going to be built upon and what is being built on it. for active soils such as clays that will expand and contract I would put at least a foot of base material down and then add grade beams every so often depending on the size of the slab and structure but at least around the perimeter. Even sandy soils will cause some issues with slabs because sand will suck the moisture from the concrete.
Finishing is another critical area, if concrete is in the truck for too long and it begins to set it loses its ability to bond together, like a cold joint, and if the finisher puts alot of water on top to achieve the finish then that is not a good thing either because alot of that paste will eventually break up. Lots of things to consider.

.02

Good information, guys. Thanks, Kev!