Plumbing / Concrete Expert Question

[I-Hate-Hulse]

So the renos are continuing to the basement bedroom / bathroom. The plumber came in and had to bust up concrete floors to get at the trap / flange / vents, so there's 4-6" holes (4" deep) holes around the PVC pipes coming up from the floor. I'll be laying a 2x4 + 1/2" plywood subfloor over top of the concrete.

My question is: do I have to fill in the holes surrounding the pipes/trap with concrete? Especially since I have the 2x4 grid on top of it that will structure the subfloor nicely? Will they be prone to leak more or something?

I'd rather not mix concrete if I don't have to...

[ken0042]

I'm no expert, but when I did mine I backfilled the pipes in the ground with some of the gravel I pulled out, then poured concrete over top. Main reason was to have a bit of resistance against ground water.

[IGGYRULES]

Why are you laying down a subfloor? Typically you don't need any type of subfloor on a concrete slab.

[I-Hate-Hulse]

Hmmm good point... this is 1/2 basement where half of it is above ground, so I don't think I need to worry about ground water too much. Then again... this is Kensington. Was it hard to mix concrete, or was it a simple mix from Home Depot?

I'm laying a subfloor for warmth, and to level the place out. I'd have gone with the plastic cleated tiles they have now but I didn't tear out all the old sub floor from the last owner and am just redoing the bathroom area.

[ken0042]

Mixing the Home Depot bags of concrete is easy. I just took the wheelbarrow downstairs and ran the hose through the window.

The one mistake I made- next time I would make the concrete about 1/4 inch below the level of the existing concrete floor, then finnish it with the self leveling concrete.

And I'm doing a subfloor as well. Get yourself off the concrete- make it just that much warmer.