Concrete slab expansion question

[ineedagarage]

Hello all


I have a situation where my new slab will **** up to the walls. Should I install something between the slab and wall? Will the expansion of the concrete cause it to crack if I don't?

 

[pstnbly]

No and no, if it's a radiant slab there should be a thermal break (insulation) but if not not necessary

 

[ConCretin]

It is standard practice in commercial construction to use an expansion material around the perimeter of slabs on grade that abut foundation walls. All materials including concrete expand and contract with temperature changes.

With that said, cracks are much more likely to result from contraction and most residential slabs aren't big enough to create expansion related problems. Expansion material around the perimeter won't hurt anything but it isn't necessary.

 

[Fastback]

If you live in a cold climate it could help as a thermal break. I would also do it so that if the slab wants to move it will not be fused to the foundation wall and crack. Get some 6" tall expansion joint material and pin it to the block, it's cheap insurance.

 

[ConCretin]

Fastback, we've found that a spray on adhesive works best and doesn't requires nails or pins that can bind the slab mitigating the value of the expansion material.

 

[Fastback]

Fastback, we've found that a spray on adhesive works best and doesn't requires nails or pins that can bind the slab mitigating the value of the expansion material.

I like that idea, it only needs to hold till the pour.
I just used 2 or 4 thin tension pins because they were handy,but the pins do not protrude outside of the material, they are countersunk to some degree and will not cause the slab to stick to the fiberboard.