After a contractor moved some plumbing and electricity lines in my chalet I started to tile and misfortunately, with a bit of pressure, the toilet tipped back. Floor tiles around toilet popped off and from there, one this led to another. There was this huge square hole under air jet tub and toilet. Found the construction term for this hole is a 'dap out'. Makes sense but my chalet concrete slab rests on the ground with pillar foundation columns going six feet under. The tub is beside an exterior wall. I have recommenations to fill it with concrete, but but but... what if something happens to the city drain pipes or if there is a huge water leak in the bathroom. The square hole has no ledge to rest wood on. Even so, regular wood does not seem to be the best to withstand mould, frost heat and condensation. I am guessing, the previous owner did the same reno two years prior (found an empty yogurt container lid with expiry date on it). Any suggestions with all the new construction materials out there?

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Originally Posted by Mishiyoyo

After a contractor moved some plumbing and electricity lines in my chalet I started to tile and misfortunately, with a bit of pressure, the toilet tipped back. Floor tiles around toilet popped off and from there, one this led to another. There was this huge square hole under air jet tub and toilet. Found the construction term for this hole is a 'dap out'. Makes sense but my chalet concrete slab rests on the ground with pillar foundation columns going six feet under. The tub is beside an exterior wall. I have recommenations to fill it with concrete, but but but..... what if something happens to the city drain pipes or if there is a huge water leak in the bathroom. The square hole has no ledge to rest wood on. Even so, regular wood does not seem to be the best to withstand mould, frost heat and condensation. I am guessing, the previous owner did the same reno two years prior (found an empty yogurt container lid with expiry date on it). Any suggestions with all the new construction materials out there?

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By the looks of the picture self leveling concrete in my option is the best way to go, it will give you a nice flat solid base to tile on and finish grade will sit level with the toilet flange. Any other way you will have to build it up to make it level and it would be as solid, I would go concrete.

Josh