DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   Flooring (
-   -   Another thread about subflooring & underlayment choices for a first timer DIY tiler (

pmergler 07-07-2010 04:07 PM

Another thread about subflooring & underlayment choices for a first timer DIY tiler
Hello...this is my first post here. I have read many threads (enough to think I have a pointed question that I didn't see answered anywhere else).

Background first (the usual suspect questions :)):
I have a kitchen I am remodeling from a 1941 home. The sub-flooring is 1" x 8" pine (seemingly) board planks run at 45 degree of joists installed with nails. They aren't T&G and do have approx. 1/8" gap between them. They were in pretty good condition, those that weren't we replaced and all loose nails either renailed or removed and the nail replaced. The joists are 2 x 10 anywhere between 14"-16" OC.

Using the deflecto gauge at it looks like I am boarderline for tile for floor deflection. Sistering the joists isn't an option due to lots of water lines, electrical and duct; so strength is something I need to gain where possible. Also my goal is to have the kitchen (space approx. 11' x 13') floor level with the adjoining dining room & hallway hardwood floors. This means I have 3/4" on top of the sub-flooring to work with. My tile is 3/8" (calculated factoring in 1/8" for thin set mortar), leaving me with 3/8" left for an underlayment material.

I did go out and purchase "construction" grade 3/8" plywood for the underlayment, but after reading here realized the quality of that construction grade wasn't very good (DD exposure 1) obviously that is going back....

From what I have read here are my options:
1) Not tile at wife would put me out of the house, so not an option :laughing:

2) Continue with current plan to lay 3/8" plywood of at least quality of CD but preferably AC, exposure 1 exterior plywood screwed to the sub-flooring and then lay the tile into thin set directly on the plywood (I know not the favored approach here) but this would give me 1 3/8" flooring base for the tile for strength purposes

3) Lay 3/8" concrete backer board screwed directly with concrete board screws to the sub-flooring and then lay tile with thin set mortar. Question I have is if I use a backer board...should I count this in the strength of my flooring would I consider having the 1" sub-florring + 3/8" concrete board for a total of 1 3/8" total flooring for the tile; or since I keep reading that backer board isn't for strength, do I not factor it into my calcuation for total flooring under the tile; which would leave me at only 1" of flooring and below the minimum?

4) Lay 1/4" CD or AC, exposure 1 exterior plywood screwed to the sub-flooring. This would give me 1 1/4" total flooring for stability. Then lay 1/8" Ditra with modified thinset to provide a tile friendly surface. Lastly, lay with unmodified thin set my ceramic tile?

Also, two other questions; when we pulled up the original 3/4" plywood underlayment and vinyl flooring, there was a thin, almost like a backing paper, layer between the planked sub-flooring and the underlayment. We didn't know what function this served? Just to keep debris from falling in to the basement level? My father thought a good idea might be to lay a thin moisture barrier (like a 2 MIL plastic sheathing material) just to reduce the risk of moisture from the basement (partially finished and partially unfinished, but does have finished plaster ceilings everywhere. Also it does get some minor moisture from exterior) getting into the underlayment. Is this a good idea? Maybe a good idea if using plywood but not necessary if using backer board?

Finally, the floor is pretty good on being flat, but there is a sligth downward slope from front to back of the kitchen of approx 1". It doesn't seem to be very noticable and it sounds like if the floor is flat we shouldn't worry about the slope? I looked like when the floor was originally installed they used asphalt (shingle like) strips about 3" wide that they laid under teh underlayment where the joists are to adjust the slope of the flooring. After my reading I am thinking this wouldn't be a good idea to re-use this approach as asphalt shingles could be more of a "spongy" material to further create variation in the floor plane; but I wanted to get the thoughts of the experts?

Thanks in advance for the advise and sorry for the long post

oh'mike 07-07-2010 08:19 PM

Wow--Long post!--First off---what would be the problem if the tiled floor was a bit higher than the hardwood?

The old 1x8 subfloor is to unstable to put Durrock on.(or anything else) At a minimum you need 1/2 inch of BC on top.

1/4 inch wonder board or Durrock fastened and mudded--(you are level with the hardwood without the tile.) Schluter makes a decoupling mat called Ditra--with that you don't need the cement board--

But you are still to high.----Make a nice wood reducer for the doorway ---you will get used to it.


pmergler 07-08-2010 07:58 AM

mike, thank you for the reply...I figures one long post rather than 3-4 back and forth of questions being asked about the floor :laughing:

Sounds like you think option 4 but instead of 1/4" BC use a thicker 1/2" BC that will bring me a 1/4" over the hardwood and use a reducer...I had a tile guy out to the house yesterday and he recommended the same thing..although the one thing he offered up was instead of the Ditra to use metal mesh lath? Any thoughts on this approach? This guy is HIGHLY reputatble...he does custom tile work in upper-upper end residential homes...$4MM + (our home is no where near that but we got a referral through my uncle). He said putting the 1/2" BC would also be more aligned with the newest recommendation from National Tile Association of America (sorry if acronym isn't correct) about having two layers of wood base and then a decoupling membrane...

oh'mike 07-09-2010 05:29 AM

The metal lath method is used only by a few old timers--that is a fine system in experienced hands.

I did not suggest that one ,as it is not a DIY--

pmergler 07-09-2010 07:31 AM

Thanks again Mike. Certainly I wouldn't attempt the metal lath as a DIY project, only if we decide to have this guy do it. As I was reading the metal lath the same method as scratch coating?

Just trying to get terminology straight...thanks again..

Branden 07-09-2010 10:05 AM


I don't mean to highjack your thread, but I have a question on the same subject (almost) that Mike might be able to help me out with.

I'm weighing my options for underlayment on an outdoor patio. right now I have 3/4" plywood down, supported great, no flexing. I have enough permabase cement board for the area and the thinset to set it down in and for use to set the tile.

Since this is readily available to me, I was planning on using this with Redgard over the cement board before the tile (I never used redgard before)

Someone suggested ditra instead of this, which would cost me a lot more money since I have the materials to do it the other way, and I do not think my thinset is meant for ditra.

Do you have any opinion on this, or does anyone else? Will this work? I've gotten one opinion from a separate post on here but am looking for more. The area is covered by a roof, but still will get wet from rain.

oh'mike 07-10-2010 06:20 PM

You will want to water proof that---I have never used Ditra--I believe that might be the product of choice here. Someone with Ditra experience will need to guide you on that.

For a paint on membrane--I use Hydroban by latacrete.---Their website has a video--also a technical help line.

I trust the product,it is used to waterproof pools and fountains,

I am not 'cutting edge' --I go with what works for me.--Mike--

oh'mike 07-10-2010 07:24 PM

pmergler---That is sometimes called a mud set.

tacomahardwood. 07-11-2010 02:00 AM

There's a new product ,wich I can't remember the name , But it's like vynil tile but looks like tile ,Has a textured surface , It can be grouted just like regular tile ,

All times are GMT -5. The time now is 04:18 AM.

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

Search Engine Friendly URLs by vBSEO 3.6.1