Tile floor with particleboard subfloor and hardibacker... am I hosed?

**aavguy** · 09-22-2010, 07:59 PM

Pulled out some old hardwood floor in a closet to convert to a bathroom. Beneath what was wood laid diagonally. Over that, I placed 3/4 particleboard.... yeah, I meant to buy plywood, but the store was out of stock and didn't realize this was a significant mistake. Over that, I screwed in 1/4 hardibacker, no thinset beneath.

I've done some reading that particleboard and tile is a no no do to flex. However, shouldn't the solid floor beneath the particleboard provide durability?

At this point, the tile is already down. I guess I just need to wait and see what happens. Thankfully, its a tiny bathroom, so replacing the floor would be a weekend job.

Unfortunately my toilet tank leaked and the floor beneath the particleboard got wet. Strangely, it looks like the particleboard is dry except for right around the toilet flange. Think I'm hosed or might the floor actually hold up?

**jadnashua** · 09-22-2010, 11:09 PM

Particleboard (you sure it isn't OSB?) is a real no-no under tile. If it gets wet, it swells up like a sponge. That movement will cause the tile to break loose. OSB, although not the first choice, may survive. But, as you've discovered, not putting thinset UNDER the cbu is also not good. The idea of the thinset is not to hold the cbu down, but to fill in any (hopefully) minor imperfections (the screws hold it in place), and ensure that the tile are 100% supported. Did you use the special mesh tape on the cbu seams? BTW, while more ply is never a deterrent underneath a tile install, over planks, the minimum is 1/2". For your next project involving tile, check out www.johnbridge.com.

**aavguy** · 09-23-2010, 05:09 AM

yep.. its "environmentally friendly particleboard" for $18 a sheet.. OSB, which I intended to buy, was only $8.. but out of stock. After reading about OSB, it seems that real plywood would be the best choice next time?

Floor seems solid this morning, I bounced up an down on it and it appears very firm. Room is so small, it may help... its only 40" x 48". I suspect I will be replacing it at some point, but it would be happy to get even 2 years out of it. My wife likes to remodel constantly.

**geniescience** · 09-23-2010, 07:21 AM

It's so small that most of the caveats don't apply. It all fits in less than one panel so there are no seams.

In this discussion you have not yet mentioned the joists. In the future, pay more attention to this.

**NSfirefighter** · 02-18-2013, 04:51 PM

I agree with what everyone said in regards to putting tile over particleboard. I had a dishwasher that leaked when I had linoleum flooring throughout my mainfloor, which caused the lino in that area to lift off the particleboard. when I ripped all the lino up, I realized that the particleboard was glued to the 3/4" subfloor. I really wanted to tile my mainfloor but soon learned that this wasn't an ideal situation. Tearing up my particle board meant tearing up the entire subfloor. I really wanted to tile and looked for ways around how to tile over particleboard. I had a few recommendations. One was to screw down 3/8 plywood overtop and tile onto the plywood. One tiler came in to do a home estimate after my little incident and said he was going to tile right over the particleboard. He mentioned he would use a subfloor sealer on the particleboard so the thinset would properly adhere to the particle board. I wasn't too keen on that idea. Finally I met up with a 35 year tiler who told me he use to just screw down cementboard right over top of particleboard without putting down thinset between the particleboard and the cementboard. I liked that idea so I decided to just use 1/4 cement board and screw it down right over top of the particle board and then just tile over top. My joists were 16" on center so I was good for spacing. One thing I did before screwing down rockboard was screw 2" deck screws into my joists every 6 inches. That took care of all the squeaks in the floor and made everything solid. The other thing I did was instead of screwing the rockboard in every 6 inches, I screwed in every 3 inches to make up for having no thinset underneath my rockboard. It's been almost 2 years since I've completed this project and I have no cracks in my tile or grout and everything is as it was the day I finished installing everything. I know this is not what is considered the proper way to install tile, but it has worked for me, and for other professional tilers who have done it in the past. I'm not recommending this as a way to install tile either, but just saying it can be done with no problems. I also had a coworker who installed the schluter membrane right over particleboard, and he has had no problems either with his tile, and it's been over 4 years. I can't quote how he prepared his subfloor because I have no idea, but that option has worked for him as well!