Thinset Below Backer Board for Floor Tile Install?

[teamextreme]

Looking for some opinions from tile installers. I'm re-tiling kitchen in g/f's rental. Existing tile was placed directly on plywood subfloor. They did a **** job, thinset not spread well, tiles all cracking, areas with no thinset contact, etc.
I'll be laying down 1/4" backer board on the new install. We've torn all the old tile out and spent hours chiseling, hammering and scraping all the old thinset from the plywood. This task has been a total PITA and taken more time than I thought the whole job would take. With this in mind, it occurs to me that it would make any future tile removal way easier if you just screwed the new backer board down without using thinset, but every how-to guide I've found calls for that method. I found one old GJ post were a tile pro said he doesn't use thinset. What's the drawback of not using thinset? Seems like it would provide a stable base if just screwed in place.

 

[Angelfire]

Not a professional so I'll let them join and comment, but simply screwing down won't give as much rigidity to the base such that the tile could still be affected. The thinset underneath fills all the voids/etc...and provides a more stable base. I would also look at using a good thinset to allow for any movement. Personally I'd prefer a 1/2" backer but not sure if it really matters.

Cheers.

 

[cgrutt]

I'd skip the backer board all together and use an isolation membrane such as Ditra. The isolation membrane needs to be set into modified thinset then tiles set with non modified thinset. Many advantages over backer board including creating isolation barrier to prevent cracked tiles during seasonal movements, creating waterproof barrier and creating vapor barrier that will let subfloor breathe. You could put this over 1/4 subfloor if you are thinking about replacing tile down the road. Downside is it cost a bit more than cement board. I also wouldn't recommend 1/4 cement board for floor if you go that route use 1/2. The 1/4 is used on countertops.

 

[Kaizen]

Only time I have used thinset under backer was if floor was dipped. Put a four foot level on the area and see what you have. Any idea of what thickness ply is? Is it screwed down?
Start with screwing the heck out of it then the backer also screwed with correct fasteners. If it’s an old house and the ply flexes I’d add the thinset to give it rigidity.


Sent from my iPhone using Tapatalk

 

[thammel]

I did my only tile floor about 8 years ago and it has held up perfectly.

I used hardie board (1/4") as the backer board. I used thinset under it and put screws in a matrix every 8 inches. Then I taped and thinset all the seams. Actually the biggest pain was the grouting and getting it all up. BUt this job worked out great - a mudroom about 9' x 20'. Another trick was to use something that looks like a plastic hockey puck (from Lowes, I believe). What you do is move this from tile to til when setting them and it's an easy way of getting all the tiles to the same height. If the puck doesn't get hung up on a tile edge, then they're even.

Tom

 

[jdsac]

Video from James Hardy, makers of Hardiboard showing correct installation. They seem to know what works- video @ 1:00 mark. Screw on pattern provided .Do it their way & you won't have to worry about doing it over at a later date

https://www.youtube.com/watch?time_continue=5&v=HX_RdK-9fxo

 

[b-boy]

I'd skip the backer board all together and use an isolation membrane such as Ditra. The isolation membrane needs to be set into modified thinset then tiles set with non modified thinset.

I agree with using the DITRA. It's really good stuff.

Remember, use modified thinset to attach Ditra if you're using plywood or OSB as a substrate. Use unmodified thinset if you're using cement or backer board.

 

[Negen]

One thing I would like to mention is that I just went through this in my bathroom. Your removal job although already done would have been a million times faster if you would have bought a decent multitool and used the scraper and a couple of wilde pry bars. Along with a decent masonry chisel and 1lb steel mallet. These few tools would have down right made the removal process down right fun.

My subfloor was two layers of 3/4" I moved the top layer and replaced it with 1/2" hardi board. I used thin set and cement screws. I am not sure if this was proper or not because every website I went through seem to have multiple answers that were all slightly different in regards to how thick the subfloor needed to be. If I had to do it again I would do the ditra system. And add heat coils.

As far as spacers next time i tile I am going to use the spin doctor type of spacers. The only real tip I can give you is to read and follow the manufactures instructions of what ever system you use. Another thing I learned is that pre-mixed thinset is not thinset at all and is really just mastik type of glue. I wouldn't use it again. Also I learned that thinset with the higher amounts of portland cement is higher quality. I also learned that you should only mix the amount of thinset you can use in a 15-20 minute period. One last thing is that it seems best to start at the center of the room and lay from the center out seems to keep lines straighter.

 

[jkuro]

Go by the tile manufactures guidelines. If on 16" floor joists you need a minimum of 1 1/4" thick of flooring to stop deflection, 3/4" subfloor plus 1/2" underlayment. Underlayment if done properly can be plywood (exterior glued) or cement board. Apply underlayment to tile manufactures guidelines. Good luck.

 

[bugnut]

Do a search on https://www.johnbridge.com/
when i did tile shower and ceramic tile entry they are the garage journal of tile

good luck

 

[BlindViper]

 

[901man]

I've done several DIY tile jobs and always use thinset under the cement board. Depending on the substrate you use modified (for porous) and unmodified (non-pourous). A close relative (who will go unnamed) didn't use thinset on his first tile job and he had cracking of the grout everywhere. A friend of mine did the same thing and put slate down and it too cracked within months after install. The point of the thinset is to fill the voids that will exist under that backer board. The board thickness itself is irrelevant as it doesn't add any structural strength (1/2" board is made just so that it meets up flush with 1/2" drywall).

 

[PoorOwner]

The manufacturer instructions says you have to, e.g. "glue and screw"

I caught my contractor just screwing it down had to argue with him. He told me they have never used thinset below backerboard, I send him the instructions and he finally agreed.

last time I have installed the hardibacker myself, I was taught to mix the thinset a little thinner (not too much) for the portion under the board. For ditra as well.

 

[engineer2]

You'll see where the plywood is nailed into the floor joists. It's a good idea to put a screw in between every pair of nails.
Rule of thumb for thinset:
If air can't reach it use unmodified thinset.
If air can reach it, it's OK to use modified thinset.

 

[KenC]

My method is this;
Place a layer of 15lb felt directly on the plywood. Staple it really well, no wrinkles at all.

spread thinset.

screw the backer down with it's special screws.

Proceed with tile

That provides an isolation barrier to keep any wood movement from being transferred to the tile. And, provides a rigid, flat base for the last layer of thinset under the tile. That makes getting the tile even, without lipage easier.

I use a 2x wood block with a scrap of thick rubber glued on to set the tile. It's big enough to span several tiles so rapping it with a mallet really helps with even tile also.

 

[teamextreme]

Thanks for all the replies. I haven't been back to post, cause I've been too busy tiling! (and skiing)

I decided since the directions, and almost all the directional videos, etc. recommended it, I went ahead and laid the backer down using thinset. I'm not sure what kind I used (modified vs unmodified), I just used what the tile place recommended, but they certainly didn't ask any questions that seem like should have been asked to determine that and they didn't impress me with a couple of other things (the counter guy claimed he's never sold the fiber tape for the seams, never heard of anyone using it (yet they sell it)).

The subfloor was nailed in place (not sure size, but likely 3/4" plywood). I added screws into the joists to reduce deflection.

The old thinset removal was the worst part of the process. I learned the easy way to do it, which I waited til the very end to try, unfortunately, because I didn't want to make a god-awful mess. I finally had enough of the scraping and chiseling and realized even that was making a dusty mess, so I said screw it, and got out the grinder. My 4" angle grinder with a floor grinding wheel took care of it in no time, but made quite a mess.

Everything turned out great, it's all complete and grouted now. With all the steps I took I think it will hold up well. The best video I found demonstrating techniques, especially thinset application, was this one. Interesting how important the combing technique is. The swirl pattern doesn't work, which is how the old tiles were installed, and they were all cracking.

 

[tcianci]

Video from James Hardy, makers of Hardiboard showing correct installation. They seem to know what works- video @ 1:00 mark. Screw on pattern provided .Do it their way & you won't have to worry about doing it over at a later date

https://www.youtube.com/watch?time_continue=5&v=HX_RdK-9fxo

This is the most sound advice. Follow the instructions for this or any other manufacturers products for the desired result. If you have a non standard situation, they will have technical support as well. Once you're well heeled at setting tile, you may be able to save a few bucks by sourcing your supplies from a box store but if you're a noob, take advantage of the wealth of knowledge available about products and technique from a local tile supplier.