Gap in concrete floor from xps?

[Mrs.maintenance]

I am seeking advise on what product to use to fill at least a 4 inch gap all the way around the parameter of a concrete floor. It had foam blocks in it but the foam is causing problems with flooring and the gap under is causing moisture issues.

 

[ConCretin]

Welcome to the GJ. We're always willing to help. Your reference to 4" gaps raises major red flags. Maybe you could start from the beginning and describe your existing conditions and slab set up.

 

[Mrs.maintenance]

This is

Welcome to the GJ. We're always willing to help. Your reference to 4" gaps raises major red flags. Maybe you could start from the beginning and describe your existing conditions and slab set up.

I'm working in a 3 story apartment complex with multiple buildings. They used the blue foam board under the slab. The problem I'm having is the foam pieces that were around the slab are allowing the flooring to sink and crack. It's 4inch x 4inch strips of foam board to fill the space that's the issue. The foam board under the slab is great but the foam pieces the are under the actual flooring is not great. So far one contractor used concrete to fill and one used mortar mix. I have a few of these apartments to do as they come up vacant so I'm trying to find the best answer to this problem.

 

[LopezBart]

I've seen this insulation used this way before, but the foam at the edge is usually 1" or so wide, and didn't cause issues w/ the finish floor (something like Pergo). I'm no expert, but I'd be inclined to cut some 1" EPS foam, put it at the edge of the room as a thermal break, and fill the remaining 3" gap with concrete, finishing to meet the requirements of whatever finish flooring is used, which should be able to bridge the 1" foam gap.

 

[lmg]

Mrs.maintenance, I am not qualified to give legal advise, but I have been involved in similar situations.

Looks like you are contracting the new floor covering installation, and this problem was unexpected by you and/or your company. If that is the case, and if you just go ahead and fix it on your own, you will own the results, good or bad. I suggest you let the owner propose a fix, and you will need to submit a cost for that fix as it appears to be additional and unexpected work. You should expect to be paid for any work not in your contract, and additional days added to your schedule for the extra work.

Your mention of moisture issues complicates the issue.

Good luck.

 

[ConCretin]

I can't imagine why anybody thought that was a good idea but the question at this point is how to deal with it.

The problem I'm having is the foam pieces that were around the slab are allowing the flooring to sink and crack.

I'll start by suggesting that the foam isn't causing the floor to sink and crack. It's the apparently inadequate base under the slab that's likely causing that to occur. Nor is the foam causing moisture issues, which are probably the result of improper drainage and/or the lack of a vapor barrier. Whatever you do to fill the void left by removing the foam won't solve the underlying problems. Correcting those issues is a LOT more involved and will probably require removal and replacement of the slab.

If you want to just fill the void, a simple concrete or mortar infill might work as long as the existing slab does not continue to move. You could try to install some dowels, pins or tapcon screws to hold the patch in place but there's not much room to work.

 

[LopezBart]

I think the problem the op was describing was the motion of the foam used to fill the 4" thermal barrier, rather than motion of the floating slab.

 

[The Cobbler]

I think I would be tempted to get the owners or management company involved ... and probably get an engineered report for a fix.
now, if it was my house, I would probably fill it with concrete , trying to get some rebar or something to tie both sides together

 

[Kpaige]

First structural spray foam jacking of the slab to stabilize it then jack hammer the edges so they are not smooth install a 1/2 expansion piece between wall and new fortified concrete poured in to fill the gap.