Hi all,
I have done a lot of floor tile to date but have always had a substrate that was either concrete or already prepared (for the most part). So here’s my question……
I am building a new house and am planning tile in all of the bathrooms. The current subfloors are OSB (3/4″). What do I need to put down before I lay my tile?
Should I be laying down Hardie backer? The thin stuff or the thick stuff? How should I attach it (I mean, I have done the screw every 2 inches or so before but I just recently saw somewhere suggested that this stuff should be set in thinset)?
I have had conversations with other new home builders who have said that they just use 2 layers of 3/4″ osb. That doesn’t really seem to me to be the best option.
So I know that the cement backer board makes a much better adhesion substrate than plywood or OSB but will it (does it) add enough thickness / strength for the floor to meet deflection ratings?
Thanks for any help.
Rob Kress
Replies
1/2 hardi or duroc
dryfit each sheet and then set it in bed of thinset
screws every 8" o.c. mesh tape and thinset the seems
then tile away
Edited 4/4/2004 10:13 am ET by hubcap
Several options. One I would say is to glue & screw at least a 3/8", better yet 1/2", underlayment to the OSB, then thinset down 1/2" cementboard then tile. Or 3/4" ply with 1/4" Hardee board. Some just put the 1/2" cementboard right on top of the first subfloor but I like the extra bit of meat in there.
I've always subscribed to the 1 1/4" minimum below the tile. If 3/4" subflooring is there now, I would re-fasten w/ screws, use 1/2" cementicious fiberboard set on a bed of thinset as suggested previously screwed every 8". If I'm starting fresh, 3/4" T&G U.L. followed by the backerboard seems a real sturdy application and haven't had any problems to date.
Good luck, Joe
As you can see, you'll get multiple opinions on this one.
I was taught that you should shoot for a minimum of 1 1/8" of underlayment NOT including backerboard. The backerboard is not structural and therefore should not be figured in in anyway when shooting for your L360 deflection.
Here's my system that been working to date:
3/4" subfloor
on top of that I like 1/2" ACX ply glued w/ ringshank 8's on a tight schedule
on top of that, 1/4" Hardibacker (or equivelant) on a bed of thinset (1/4" trowel) nailed down with roofing nails til the mud sets up.
Follow with your thinset and tile.
Personally I like using a CBU that is spec'd to be able to be used on exterior applications such as "Wonderboard". Just makes me feel better.
I always set it in thinset and use "wonderboard screws" that self sink just below the surface.
I've also used "Ditra" which I love other than the expense and availability around here.
I tried Hardiback on walls but I'd never use it on floors.
Just seems to me it feels like I'm puting sheetrock over my floors with a waterproof facing.
I could be wrong.
Its been known to happen......lol.
Be floored
andy
My life is my passion!
http://CLIFFORDRENOVATIONS.COM
Andy, you sure you are talking about the right product? Hardibacker's consistency doesn't even resemble sheetrock. No facing or backing on Hardi, it has the same consistency all the way through, not different layers like a sheetrock product.
Not trying to second guess you or sell you on Hardi, just wanted to make sure you weren't writing off a product that you may actually like.
Two layers of 3/4" OSB is a substandard job and will not hold up. Grout is not waterproof, it's more like a sponge. So any water sitting on the floor for a little while will soak into whatever's below. OSB will swell and pop your tile off.
Some type of cementitious backer board is needed. It must be set in thinset, then screwed down every 8 inches or so. Don't use construction adhesive. If you use construction adhesive you won't get even support, rather, a bunch of hollow spots between the beads of adhesive. Then when you walk on the finished floor, those spots will flex, eventually popping your tile off. The backer board needs to be fully supported, which is why thinset is needed.
There's many other things that go into a good tile job. Before spending all that money to tile all your bathrooms, spend $25 more and get a good book. Michael Byrne's Setting Tile is one of the best.
We use ½” cement underlayment over ¾” T&G subfloor in bathrooms in new construction. First, we clean the heck out of the subfloor, and then install additional 1-1/2” screws. We lay the cement board with the textured side up for thinset jobs, with the long seams perpendicular to the long seams in the subfloor.
We use a carbide-tipped laminate scribe score to the panels and break them. The laminate score works a lot better than a utility knife and one will last around four underlayment jobs. (Some people use a circular saw, but the dust is horrendous, even with a mask.) A good trick is to use a 3” X 8” piece of cement board sandwiched between two pieces of 1X4 as a sureform to smooth off the ragged edges that result when you score and break the board. We screw the underlayment panels down with 2” galvanized screws: 6” oc at the perimeter, 8” oc in the field, and then tape and float the joints with floor leveler. We leave a 1/8” gap at all joints. I see above that a few guys like to use thinset; we’ve never used it, and haven’t had a call-back yet. I reiterate though, we meticulously clean the subfloor. I don’t think the manufacturer of the type of underlayment we use recommends thinset—I almost always install per manufacturer’s direction, so I’ll check again.
We use pourable underlayment in bathrooms for remodeling and restoration work because it can save a lot of time trying to correct settlement or cutting around out-of-square conditions, and there’s usually heat of some sort available if needed on those types of projects. It can be placed directly over clean, well-fastened plywood subfloor or ¼” underlayment over old floor boards.
Most residential bathrooms are small enough to pour with just one plastic 50 gallon mixing drum. Mix it right in front of the doorway—a few guys with rubber boots can ease it over and slosh it around with a clean garden rake to general level. It will self-level from there. It takes about a week to cure before tile can be installed, so we generally install the stuff right after plaster.
We use USG products because they’re readily available in this area.
Wow guys!!!!!
Great replies. Thanks to all.
I can see that there are really a few ways to do it but really no short cuts. I am a little hesitant to do another 1/2" or so of wood then 1/4" of cement then tile. This to me seems like it will widely interfere with a smooth transition between flooring materials.
Makes a lot of sense to me to use the 1/2" backer in a thinset bed. And the floors that I will be covering already carry an L/360 deflection rating without anymore thickness (I also screwed the entire subfloor myself during installation).
Thanks again for all the replies,
Rob Kress
We've only put down 1/4" hardie board on top of the 3/4" sub floor and haven't had any problems. Normally just some liquid nails and a bunch of square drive screws (to get them to countersink). We also don't normally tape the seams on flooring, just on sidewalls. I haven't seen bathroom floors that were 1 1/4" higher than the hallways. That seems very high to me. I could be wrong, and I don't do tile for a living, but that's what I did in my house five years ago, and haven't had any problem yet. It's also what we've put into the custom houses here in New Mexico for the past six years that I've bee working here.
Jim
Rob:
I hate to rain on your party, and disagree with everyone here, but there is no, I repeat no, requirement that there be an inch and a quarter subfloor below tile. I have successfully tiles over five eighths, thank you very much. I have also tried to tile over 2" of solid plywood and have had the job fail. Boo Hoo.
What is important is the deflection of the subfloor. If you have 2x8 joists running 16 feet every 24 inches then I don't care how much OSB you have, the floor is going to flex and your tile job will crack, OK? If you have full 2x12's going 6 feet every 12 inches, then you can probably tile over cheap half inch ply. Got this concept?
So first things first. Tell me about the structure. What are the size of the joists? What is the unsupported span? What is the spacing of the joists?
Then we'll go from there.
Regards,
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
i'm with boris on this. too much overkill on the underlayment. the deflection is the key. if joists are properly sized and your 3/4 is cdx, i screw down the cdx to eliminate squeaks, plane uneven ply joints, floor leveller as needed, thinset, 1/4 hardi (cut with circ saw + hardi blade outside, hitachi makes it-$50-20 floors and counting-scoring is ridiculously tedious imo) nailed down with roofing gun (those screws are expensive and take forever, never sink flush, it's a scam, the thinset holds it fine), then tape seams and start your tile. i will sometimes use 1/2 hardi on osb because i don't trust osb flex-wise between joists. i always use flexi-thinset on floors.
with all that underlayment, how do you guys make a smooth tranny to the adjacent floor? riser and tread;)?
has anybody ever ripped up a hardi and tile floor? just asking, seems like it would be horrible, esp. with those screws. we may all be cursing it in 10 years.
Boris,
I totally dig what you are saying. Yes, I do understand that floor deflection is the single most important factor in guaranteeing a successful tile floor installation. And in that regard, I am covered. My floors are all joisted with 2 x 12s, 16" o.c. and spanning less than 14 ft.
I have however had tile floors fail because of improper substrate. In the one installation, I did not use a cement backer, nor did I treat the substrate to prevent dewatering of the grout. That installation failed within months (of course). Just one more curve on the road to better understanding.
That is really how my question has come up since I have been told that there are people out there who are tiling directly over OSB and plywood. In my experience (direct experience) that just doesn't work out.
Thanks for you input,
Rob Kress
Rob:
By my calculation, your floor is awesome, L833, which is fine for tile and even for stone. You are good to go, as is.
OSB did not used to be proper for tiling. The wet thinset under the CBU would swell and cause all sorts of problems. So, conventional wisdom was that OSB could not be used for tile, and one had to either apply a second layer of half inch EGP ply or membrane it. Membranes had issues too, because they were applied with thinset too. So EGP plywood it was. This was the way it was for the last 15 years in tile work.
The problem is that most of the conventional wisdom did not keep pace with current construction techniques. I am over 60, and remember when OSB was a cheap novelty. Now it is standard in most new construction that I see.
So backerboard and membrane manufactuers which previously would not warrant their product over OSB were losing business or contractors were ignoring the instructions and doing it anyway.
So in 2001, for example, James Hardie altered their warranty provision, and allowed the use of Hardibacker over OSB. Most manufactuers followed suit. I don't believe that the OSB changed, and I certainly know that the CBU's didn't change. Its just the case of the manufacturer realizing that it had to provide a warranty for its product over OSB.
So I think you are good to go. If I were you, I would install quarter inch Hardibacker over the OSB and call it a day. Follow the instructions to the "T" on the web site and photograph and document the construction and application of the tile. Make up a folder for the customer with this information and keep one yourself. Hardie is a good company, and will honor their warranties.
By the way, just so I am fair here, Schluter's Ditra is a fine membrane as well, and is only an eighth of an inch. It is approved over OSB as well. It is significantly more expensive than Hardibacker, however.
Good Luck.
Regards,
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
Absolutely the framing structure is the first thing, I thought that was pretty much a given. No sub standards there, and if there are any, start by fixing them. I learned floor tiling by setting into a wetbed of mud and still do it on occasion.
Boris,
You've obviously set a lot more tile than most of us here. However, this is a quote from page 80 of Michael Byrne's revised and updated "Setting Tile"
"The American National Standards Institute (ANSI) recommends that a plywood setting bed for a floor or countertop be a minimum thickness of 1 1/8" (on wall installations plywood must be at least 5/8" thick....."
Soooo, I'm not the only one who considers this to be a good guideline. Before you go blowing your stack at me and writing one of your self-righteous, "everyone is an idiot but me" posts, just consider that maybe it is a decent rule of thumb. Some of us, like the original poster, don't have the vast past experiences you have with installations. That is what standards like this are for. It probably isn't what is needed in EVERY situation, but it is a good rule of thumb to use and a place to start.
Next time someone's opinion differs from yours, don't take it so personal. Go back and re-read the first paragraph of your first post to Rob Kress.....it's obnoxious. Everyone here respects your experience, there is no reason to belittle advice that has been given and is different from yours.
I have the new (2003-04) TCA installation handbook.
They have several dozen different systems for floors, every thing from exterior over membrane, to chemical resistant, to over sub-floor without any backer board.
He are a couple. All of them are based on the requirement of a maximum 1/360 deflection with 300lb concentrated load.
- F150-03 Wood sub-floor -
5/8" EGP (exterior glue plywood) subloor on 16" OC joist.
Plus 5/8" (light commerical) or 1/2" (residential) EGP underlayment
Install using latex-portland cement mortar
This is a 1 1/4" total sub-floor.
- F144-03 CBU/Fiber Cement Underlayment -
5/8" EGP on 16" OC joist.
Backer installed with thin-set and tile set with thin-set or latex modified. No mention of thickness of backer board so the net floor could be a little as 7/8"
- F149-03 Wood subfloor on 24" OC joist -
This is similar to F150-3 but limits it to miniumum of 8" sq tiles and
3/4" EGP subfloor
5/8" EGP underlayment
- F155-03 OSB sub-floor on 24 OC joist -
Limit minimum of 8" sq tiles.
3/4" T&G OSB
5/8" EGP underlayment.
Tile set with latex modified.
Note this is the ONLY one that I have seen that mentioned OSB and none of them mention OSB in contact with either thin-set or latex modified.
Bill's comment is dead on, and that was my original point.
The inch and a quarter standard is dead. The TCA works WITH manufacturers not against them. Indeed the TCA is a trade group in which manufacturers are represented and are invited to write standards, so that tile installation has some objective guidelines.
So if a particular manufacturer believes that a 5/8" subfloor is fine for their product (Schluter's Ditra, for example) then the TCA will write a spec for it. Actually the manufacturer writes it and the TCA adopts it. Mr. Byrnes's book is currently out of date with the TCA specs. I think his last revision was about 2-3 years ago, and the TCA revolution was in 2001-2 if I recall correctly.
I repeat, it matters not what kind of subfloor one has, whether it is a skinny five eighths or a massive 2 inches. The floor has to be L360 for tile and a whopping L720 for stone. This whole discussion about an inch and quarter misses the point. The point is that L360 is what you are shooting for. You either have L360 or you don't. If you have an L360 floor, then by all means, add all the plywood you want per manufactuers instructions. But to say that inch and quarter is the minimum is wrong.
The TCA has a floor wear machine, in which manufacturers install their tile to various specs and then this machine rolls over it for days and they check the wear and cracks. So presumably Schluter is fine with 5/8 and it worked for them. Hardi isn't, and requires 3/4. But these are objective standards, not subject to debate. You either have L360 or not.
And OSB is fine for a subfloor on tile. Didn't used to be, and nothing has changed, except that manufacturers will warrant it. Do I like putting sloppy wet thinset on thirsty OSB after 20 years of preaching that it was terrible? No. Do I now do it, because the TCA and the manufactuers warrant it? Reluctantly yes.
And this is the only difference that Bill and I have is the thinset on OSB thing. If you go to Ditra's Web Site or Hardi's Web site their instructions will call out unmodified thinset under their products. Actually Ditra changed their instructions last month, and I forget if they are now calling for modified under the membrane and unmodified above. I dunno. But in any event, one must have thinset under the products, so wet sloppy thinset over thirsty OSB is now the order of the day. Go figure.
Regards,
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
1 1/4" minimum underlayment under tile set in thinset over 16" O.C. framing will not fail. That was easy. Thanks, JoeG.