Need to raise subfloor 1/4" - Ceramic Tile Advice Forums

Drydocked · 03-15-2003, 10:02 PM

Hi,

First of all I'd like to say that this site is great! I've been lurking here for a while gathering information on my first tile job that I started today, doing 2 baths and the kitchen on a new house, and have learned a lot from researching past posts. Based on my research, I decided to use Ditra for the project instead of the CBU that I originally planned but this has lead to another problem because the Ditra is much thinner than CBU, so I have to add 1/4" to the subfloor because I want the finished tile height to be the same as the adjacent floors. So I'm in need of advice on what type of material to use to add the extra layer. I don't need it for strength, only for height, and I'd like to use something as inexpensive as possible. It's going on top of 3/4" OSB and the Ditra will be going over top of whatever I decide to use. I thought about Luan but I think I'd probably be better off with regular 1/4" fir plywood. Any other suggestions? Would this have to be screwed down to the OSB or could it be nailed or stapled? If nailing is ok, would 15 guage finish nails be sufficient for this purpose?

Thanks for any advice.
Joe

stullis · 03-16-2003, 12:07 AM

Use a 1/4" exterior glue plywood and staple it down using a narrow crown stapler and a staple that has a 7/8" leg.
Staple it every 4" in the field and every 2" on the edges max.
Screwing it down would also work or using ring shank nails.
Finish nails are not recommended for this application.

Other option (less expensive) would be to use the 1/2" CBU

John Bridge · 03-16-2003, 07:47 AM

Hi Joe, Welcome.

I agree with Scott (stullis). No luan at all. The Ditra needs an approved surface to be bonded to, and luan is not approved. Use the fir/pine plywood and use a good modified thin set when you install the Ditra. Versa Bond works, and it is always easy to get. There are many others, though.

http://www.schluter.com

http://www.custombuildingproducts.com

I assume your floor framing passes muster.

Drydocked · 03-16-2003, 08:20 AM

Thank you for the quick responses. Yes the floor structure will is suitable for tile, it's a new house and was constructed knowing that tile was going down on some of the floors.

I figured staples were the better fastener but didn't have an air stapler and was exploring options using the tools I already have, now I've got an excuse to buy the stapler.

I'm on my way to get the plywood. Thanks again.

Joe

John Bridge · 03-16-2003, 08:31 AM

Not that everyone shouldn't have a floor stapler, but ring shank nails will work too.

tileguytodd · 03-16-2003, 08:32 AM

No arguments from me. Scott, you the man!!!
Thats exactly how i would do it.!!!

03-16-2003, 10:09 AM

John

Didn't Peter N. tell us at the Schluter School that a thin layer of extra plywood should be glued as well as mechanically fastened?

Cisco · 03-16-2003, 10:24 AM

I was always under the impression that the min underlayment thickness was 5/8. How could you possibly get 1/4 ply to sit flat and tight with nails. If you plywood over 1 small cumb of drywall your going to have flex in the 1/4". Gluing could be an option. I am not to savy on installing floors over plywood but I would thick if you needed to raise the floor 1/4 that a 1/4 CBU would be a better option under the Ditra.

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stullis · 03-16-2003, 11:39 AM

The 1/4" would be installed the same way as if I was going to install sheet vinyl over it.

That means the subfloor needs to be clean and flat. That may mean sanding or filling bad spots BEFORE installing the 1/4" plywood. Gluing the panel is not needed. Think stress as Dave G would say.

When it comes to vinyl, prep work is the key!

The problem with 1/4" CBU is by the time you put your thinset under it you are often up over 1/4". Don't know how much play he actually has to work with. If he has the extra play then yeah, CBU would probably be best.

Drydocked · 03-16-2003, 08:26 PM

Ok, here's what I did - I went over the entire floor with a sander so everything was nice and smooth just to make sure there weren't any uneven joints, high spots, or dabs of drywall mud that would keep the plywood from going down flat, then vacuumed thoroughly before laying the plywood. I fastened it down with 7/8" staples just as Scott said, every 2" on the edges and 4" everywhere else. It should be ready for the Ditra.

Joe

stullis · 03-16-2003, 08:32 PM

You are good to go!

flatfloor · 03-17-2003, 09:30 AM

Even tho this is a new house and the builder planned for tile I would still check the Deflectolater for compliance. You never know what someone's version of acceptable is.

John Bridge · 03-17-2003, 08:53 PM

Rob,

Did you note the nailing schedule being used here? They're putting a box of nails into every sheet.

I don't remember what Peter told me about plywood. I was too busy arguing about whether the cardboard box would hold water.

03-18-2003, 05:14 AM

John

I'm pretty sure Peter did say that. I'll call Big Larry and ask him.

Did I ever tell you about the trick we played on Larry?

I sponged some water on/under the corner of one of the cardboard boxes that was serving as a cooler, and then summoned Larry with a really "concerned" look on my face. We sure had him going for a minute!

John Bridge · 03-18-2003, 08:04 PM

Yeah, you told me. How many times did Larry whack you?

I still think if the plywood is nailed down really tight, it'll work. I don't see a lot of difference in that and going over any other plywood.