Tiling over osb subfloor, [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


View Full Version : Tiling over osb subfloor,

10-08-2016, 04:38 PM
Good day, I am new to this forum I am about to undertake a large shower project for my daughter. It is large, 8 x 6. I plan to preslope and then pvc liner and mud. Should this shower pan have some kind of expansion joints or any special considerations ? I have done 3 or 4 showers but smaller size. thanks

Sponsored Links

10-08-2016, 05:34 PM
I never have. I build them all the same.

10-08-2016, 07:27 PM
Welcome, mont2049. Please change that permanent signature line to a first name for us to use. :)

The ceramic tile industry's ANSI standards consider all showers of 65 square feet or less to be the same and requiring no special treatment except for the change in deck mud mixture from the more customary 5:1 to a 4:1. Many of us still use the same 5:1 mixture we use for any other deck mud application.

When the shower floor is larger than 65 square feet, the use of welded wire mesh reinforcement in the final mud bed is required.

My opinion; worth price charged.

10-08-2016, 08:12 PM
thanks for the quick information

10-08-2016, 08:45 PM
You might want to get you a helper to mix up the mud. That's a lot for one guy to mix and pack all by himself.

10-08-2016, 09:20 PM
Thanks, I do plan to have a helper to mix mud. I also am concerned about having to seam a liner that large. (should I start a new thread about seaming a pan liner?)

10-09-2016, 08:42 AM
You could skip the liner and use a surface applied membrane like Kerdi.

Houston Remodeler
10-09-2016, 09:11 AM
add one vote for the surface applied membrane

10-09-2016, 10:12 AM
With the surface applied membrane, then the drain needs to be a match drain, right?

Houston Remodeler
10-09-2016, 10:27 AM
Not sure what you mean there, but the drain must be bonded to the waterproofing, no matter which system you select.

10-09-2016, 10:35 AM
I was thinking about the kerdi system, they require their own drain with their membrane

Houston Remodeler
10-09-2016, 10:38 AM
Its possible to use another drain manufacturer with the kerdi system. We often use a laticrete linear drain and kerdi walls and nobleseal floor. Its called a hybrid, and voids all the warranties, but makes life easier for me.

10-09-2016, 12:05 PM
I think the warranty doesn't matter as long as you can warranty your work by yourself.

10-11-2016, 04:22 PM
I am about to tackle a large shower, mud pan and pvc liner, and would like advice on waterproofing from outside of the curb transitioning to wood floor. I think the wood floor will also get tile. Also considering using brick for initial curb as opposed to 2 x 2s . appreciate all advice

10-11-2016, 04:27 PM
What is the substrate? Wood or a slab? If it's a wooden subfloor, you can use kiln dried 2x4's, but you should avoid them if it is a slab and probably use bricks or concrete pavers (or you could use a foam product on either).

You can waterproof the area outside of the shower with one of the various membranes. If you choose Schluter products, you'd use Ditra outside of the shower and Kerdiband to make the seam between the curb and the Ditra, and then along any seams in the Ditra, and again, at the room perimeter behind the moulding. That won't do anything about excess water pouring out into the hallway, though, but will keep any from getting into the walls.

10-11-2016, 05:38 PM
thanks for reply. The sub floor is wood and have not decided on substrate, possibly something like wonderboard. If I use ditra, would this second floor be rigid enough for tile ? (or would ditra go over wonderboard) thanks

10-11-2016, 05:58 PM
Download the Ditra handbook at www.schluter.com - it gives all of the details on how to install it and get a warranty. Ditra, in your case, would normally be installed directly over the plywood (assuming your subfloor meets the specs for installing tile), then you install the tile on top of the Ditra.

11-11-2016, 01:33 PM
good day, I am doing a tile project that involves tiling ( 12 x 24 ceramic) over osb subfloor. The question is whether or not to use 1/4 hardieboard over 1 inch osb subfloor or 1/4 concrete board. It seems that ditra is about 2 bucks per sq foot, and I am not sure we would add that expense. Also like ideas on thinset to use from box stores. Any opinions are appreciated. thanks

11-11-2016, 01:44 PM
I am not a pro, they will surely address your questions in more detail.
Have you checked your floors deflection to see if tile is appropriate? I don't think any tile setting is approved directly to OSB, 1/4" backerboard with thinset under I believe would be the minimum if your subfloor is within deflection limits.

11-11-2016, 03:13 PM
Monte, I've again combined your new thread with your existing thread for this project. It'll help if you'll keep all your project questions here so folks can see what you're working on and what's been previously asked and answered. We can give it a more generic title any time you'd like to suggest one.

11-11-2016, 05:22 PM
Some thinset manufacturers allow use over osb, some do not. Plus, not all osb boards are created equal. Some are definitely better than others.

Hardiebacker or a different type of cbu, your choice...they all will work if you install them properly. If you shop around, Ditra may not be all that much more expensive and certainly is easier to install, carry, and cut. By the time you add in the costs of all of the screws required to anchor the cbu, the tape to reinforce the seams, and the time it takes along with the thinset underneath it, Ditra begins to look much better! Watch out for creating speed bumps when you add the tape to the seams on cbu (the tape helps make the various sheets act as one, monolithic sheet).

11-13-2016, 10:03 PM
I am finished with another shower project that has preslope and pvc liner and
finished pan. I am going to redgard shower walls (cement board) but unsure whether or not to redgard floor since it has the liner. Any suggestions help, thanks

11-13-2016, 10:06 PM
You should definitely not do that.

My opinion; worth price charged.

11-13-2016, 10:12 PM
Isn't that creating two moisture barriers and the old moisture barrier sandwich. I believe that is frowned upon as is mixing many different systems of waterproofing. A pvc liner is a method of waterproofing. Redgard is a method of waterproofing. Pick a method and go with that one exclusively.

11-14-2016, 09:13 AM
Thanks for the information. I suppose I still should waterproof the walls using redgard or hydro ban, (on cement board) but should I tape where the walls transition to the floor and redgard that ? thanks again

11-14-2016, 09:19 AM
I've never used redgard but I'm sure there's many threads covering the proper use with a liner.

11-14-2016, 09:46 AM
No need to tape that joint. Just cover the walls and leave the floor alone.

11-15-2016, 08:13 AM
I am going to tile porcelain and ceramic 12 x 24 over OSB subfloor, probably using ditra on top of that. I am asking advice on thinsets. Some say use modified under ditra then unmodified on top of that. Need advice uncluding brand names please. (one told me to use kerabond t for all of it) I am a little confused. (not a pro) thanks

11-15-2016, 08:24 AM
For stuff that's easily available, many of us like Versabond for under which is available at the orange store and TEC makes an "uncoupling mat" unmodified mortar that is specifically made for Schluter products and available at the blue store for around $16/bag.

11-15-2016, 09:46 AM
Monte, you wanna visit the Schluter website (http://www.schluter.com/schluter-us/en_US/Membranes/Uncoupling-(DITRA)/Schluter%C2%AE-DITRA-&-DITRA-XL/p/DITRA) and download the Installation Instructions for the Ditra. They are very clear on what they want you to use for bonding their products and bonding to their products.

For Ditra over plywood or OSB you must use a thinset mortar meeting the standards of ANSI A118.11 to bond the Ditra to the wood. And read the mortar manufacturer's instructions, too, as some do not recommend bonding to OSB.

For all other applications, Schluter will generally recommend an un-modified thinset mortar.

11-15-2016, 02:40 PM
If you want to possibly simplify your life, you could buy a quality unmodified and their specific liquid modifier. You'd then mix the thinset with their modifier per the instructions to get a modified thinset, and only with water to get an unmodified. This will mean no half bags of one left over, or having to go buy another bag to complete something when you have a bunch of the other one sitting around. Once opened, they're toast fairly quickly, so it's not like you can save it for your next project.

11-15-2016, 07:04 PM
Jim makes a good point and now that I think about it, Lowes also carries the TEC Skill Set admix for their uncoupling mortar. So you could go with a single solution for the whole job. Of course the TEC brand with the admix meets ANSI 118.11 as suggested by CX.

11-15-2016, 08:25 PM
If your Lowes carries Mapei and not TEC (like my Lowes stores), Mapei has a list of thinsets approved for use on OSB and/or Advantec. Shoot them an email with your question, Ive found them extremely responsive and helpful in planning out my tiling project (including Ditra to Advantec).

11-16-2016, 08:53 PM
Thanks for all the information. Trying to determine the correct thinset to use to bond ditra to osb is about impossible. Many modified thinsets do list A118.11 as their standard, then I see that the thinsets say it is not recommended over osb. Interestingly enough Schluters very own video installing ditra show it going down on osb. My project meets all the deflection requirements etc.. but no thinset I find can recommend use over osb. I need more advice.....thanks

Steve in Denver
11-17-2016, 08:57 AM
I ran into the exact same issue on my OSB (advantech) install. I hadn't anticipated how difficult it would be to find a thin set approved for use over OSB - if I had I would have just used plywood instead. In the end I decided to add a layer of 1/2" plywood on top of the OSB.

I have wondered if the reason "no one" approves their thinset for use over OSB is more about tiling directly to OSB as opposed to installing Ditra. I suspect it is done all the time with acceptable results, but I didn't want to risk it.

Good luck, and let us know if you find a thinset approved for OSB.

11-17-2016, 09:14 AM
Mapei has products approved for use on advantech (along with their own technical bulletin extending the warranty to them) but I'm not sure if that covers OSB in general.

I have advantech subfloor and plan on using kerabond+keralastic to bond DitraHeat to it

Sent from my Nexus 6P using Tapatalk

11-17-2016, 09:54 AM
Well some anecdotal evidence for you. I got about 12 sq ft of Ditra XL laid with Versabond over OSB. I had laid just a bit to tie it into the kerdi shower and tub enclosure. My wife decides a week ago that she now wants heated floors that were an extravagance a month ago. :crazy:

I pulled that Ditra up last night, or let me say I tried to pull it up. Every bit of fleece separated from the Ditra. And that Versabond will not come up from that OSB without some serious work. I just ordered a diamond cup wheel and dust shroud for my grinder to get it up so I can start with a smooth surface for the Ditra Heat. So my small sample size suggests that Versabond is well suited for installing Ditra to OSB.

11-17-2016, 02:05 PM
Some OSB has a sealer like material applied to it that can become a bond-breaker with thinset. THen, not all OSB is made in the same manner. Advantec is made with the chips alternating layers similar to plywood, but in a nominal 3/4" sheet, they alternate about 20x which makes it much stiffer than just one that may keep them all in line or use fewer alternating layers. You can see the result in their stiffness - about 10-20% stiffer than the typical underlayment grade plywood (and a pain to screw into!). In my limited experience, since my Advantec floors were down for a bit before being covered, they got some surface abrasion, and anything that might have been on the surface was gone...things stuck quite well!

11-18-2016, 07:42 AM
The subfloor I am going to lay tile on is durastrand osb. About 1 inch thick on 16 in center. Exceeds deflection criteria. I still am unable to find a thinset that mfg will admit to being ok for use on osb for installing ditra. I think I will use laticrete 253 gold. Any comments or suggestions are appreciated....thanks

11-19-2016, 09:43 AM
Check with Ardex, I know they just came out with info about using their products over osb. Their Af207 would most likely be their first choice, but I believe they approved a few of their thinsets for osb as well.

11-21-2016, 09:48 AM
I now have a shower having cbu treated with redgard. I would like opinions for the thinset to use here, for tiling porcelain. The tiles are 12 x 24....so a little heavy. thanks

11-21-2016, 09:58 AM
I believe they say to use a modified thinset.

11-21-2016, 02:44 PM
I like using this for large tiles. Home Depot has it.

11-28-2016, 12:05 PM
thanks for all the advice. Now working on a shower with cbu only on walls. I want to seal the shower valve and pipe with schluter product. Can I their pipe seal on this wall that is not covered in kerdi ? Also modified or unmodified thinset ? thanks

11-28-2016, 01:36 PM
You can, but it won't do much good if you don't seal the rest of the walls. You have abandoned the RedGard plan?

I'd use modified thinset mortar as required by the CBU manufacturer.

My opinion; worth price charged.

Dave Gobis
11-28-2016, 02:44 PM
I am a little late on this one, but, I am doing a claim right now with a modified thinset over AdvanTech. Not all thinsets and OSB panels are created equal. We did NOT scrape the floor, just vacuumed.

11-28-2016, 02:47 PM
Any idea what thinset was used?

Mapei says Keraband+Keralastic is approved, as are a few other of their products. I was planning on using Keraband so I can use it w/admix under Ditra and as unmod for both sides of Kerdi and on top of Ditra.

Dave Gobis
11-28-2016, 06:21 PM
It wasn't bottom of the barrel but not anything near Kerabond/Keralastic performance wise. Think the chances of that working are very good, even more so if they warrant it. With AdvanTech your bonding to resin, not wood.

11-28-2016, 11:23 PM
thanks cx for the reply. I am on another shower now. It was my understanding to keep all my posts on one thread. In both cases I will use redgard or other brand waterproofing. Not using kerdi on this one. I have a couple of pipe seals I thought I would use..thanks

12-04-2016, 11:30 AM
Davy, somewhere I think I read that your favorite thinset for shower walls was the prolite thinset. Is this accurate or do you use another for shower walls ? (I can't find that particular post)