Flooring and Carpeting/Tile Substrate


Hi Chris,

I have a question regarding tile substrates.  I am doing a bathroom remodel and installing porcelain tile.  I have a couple of questions around that:

1) I have already removed the original tile (1" square), which was installed directly to a layer of 3/8" ply over the original subfloor.  Should I remove the 3/8" ply and replace it with something more substantial (say 5/8")?  The tile going in is 12" square.
2) The original tile was fastened with some sort of thinset that contained 1% chrysotile asbestos.  I had it tested (unfortunately) only after having it removed.  That is apparently a very low content, but...  Have you ever dealt with such mortar? Would it change your opinion on #1 above?
3) I am planning on using hardi-backer on top of the ply.  Do I need to thinset the hardi into place or will screws alone be enough?


Mark ,

You don't have to remove the 3/8 ply unless you feel it is a health concern...you can just add to it, as long as it is sound structurally and isn't damaged. The goal would be to have about 3/4" thickness of plywood, then add a cement board ...then tile.

The hardi backer instructions are very clear ...use thinset and screws to adhere the cement board to the plywood..they have a web site dedicated to the install.

I have no idea what mortar you demo'd, never heard of it. I am still kicking after 28 years of demo and install??? crosses fingers


Flooring and Carpeting

All Answers

Answers by Expert:

Ask Experts




20+ years flooring installation ...carpet,wood,tile and vinyl. Residential and commercial. I do not sell the products , just install what ever the shop / customer has purchased. I actually love seeing the finished project completed and it gives me great satisfaction to help others acheive that goal. If I don't know the answer I will say so, and then I will recommend another expert for you. I may even research the subject and answer to the best of my ability ...including links to my sources. I wish you all success Chris


20 years as an independant contractor

H.S. diploma A.S. agriculture Mt San Antonio JR. College

Past/Present Clients
Gene Bonas and Kevin Churnock Inc. Sheward&Son&Sons Century 21 Forte Const. Famous Footwear BOSE Corporation Homebodies General Contractor Perry Floors, Tri Cord Flooring T.J.'S Supplies

©2016 About.com. All rights reserved.