Pouring a concrete slab around a PVC floor sink.

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I'm installing some PVC floor sinks into a concrete slab.

We've cut the existing slab for the new drain pipes and the floor sinks. After the sinks and other drains are installed, we will backfill the trenches and pour concrete to fill the cuts in the existing slab.

I'm thinking it might be advantageous to decouple the edges of the PVC floor sinks from the concrete. Since PVC and concrete expand/contract and different rates, I believe that if the concrete were poured right up to the flange of the floor sink it will eventually develop a small crevice around the perimeter of the sink which will accumulate debris. If I could put a small spacer (~1/8") around the perimeter of the sink flange, that would allow me to create a small gap between the new concrete and the flange. After the concrete cures, I could remove the spacer and caulk the gap with construction sealant or epoxy crack filler.

The trick is coming up with a suitable spacer to create the gap during the concrete pour, but will also be easy to remove from the concrete. And it has to be able to stay in place on the thin edge (~3/16" thick) of the PVC flange.

Closet wrap foam is too thick (~3/8"). I considered cardboard, but that may get soggy and collapse during the concrete pour. I thought about cutting thin strips of Masonite board (hardboard tempered panel), and taping them on to the edge. But not sure if I'll be able to get them out after the concrete has cured.

Thoughts and ideas?

James Henry

In the Trades
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Billings, Montana.
I would go ahead and use the closet wrap and fill the gap with Vulkem seal. Coat the putty knife with dish soap to prevent it from sticking to the Vulkem seal.
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