Question from Marilyn

I’m planning to redo a bathroom with an open shower. The contractor tells me it involves some kind of hot tar layer to make the floor water proof before laying tile. Do you know of a non-toxic option that meets California code?

I am not familiar with California code so you will need to work with your contractor on that.  I have used Hardibacker Board or another water-resistant cementitious board as an underlayment for the tile.  I recommend the book “Prescriptions for a Healthy Home, 3rd edition” for any building or remodel project that you have.