question about subfloor


  #1  
Old 04-29-02, 10:30 AM
EdgarF
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question about subfloor

I am getting ready to prep the subfloor in my house for a tile guy who is going to come in and lay the tile. The area consists of a large kitchen area, which runs into a foyer and also a small bathroom. The house is fairly new about 8 years old. I am pulling up linoleum and ww carpeting in this area that will be tiled. The existing floor underneath is plywood which is 3/4 inch thick. The tile guy told me to buy commercial grade plywood 1/2 inch thick and to place that on top of the existing plywood. The total thickness of the plywood that is already down plus this plywood I am laying will be one and a half inches. I asked him about wonderboard and he said that the plywood would be just as good if not better and said I could use the wonderboard in the bathroom if I preferred since it is needed in areas where water would be on the tile. I decided for the bathroom area that I would use the wonder board. I called my local lumber yard and asked them for commercial grade plywood - the guy asked what are you using for..I said for a subfloor under tile. The guy on the phone said you want the plugged and sanded plywood - this is what is used under tile. I said fine. They have already delivered it to my house. I spoke with the tile guy last nite and told him about the plugged and sanded plywood and he told me that when I install it to put the plugged and sanded side DOWN since he wants the rougher side up so that the tile will adhere better. My question is do I even need the plugged and sanded plywood? What benefit is it if he has me lay it with the plugged side down? I assumed the plugged side would go up since the large knot holes have been plugged up and that would make a better surface for laying the tile. I called the lumber yard back and asked the guy that I spoke to and he said that it has to be plugged and sanded or the tile warranty would not apply. He also said that it still will be a benefit if the sanded side goes down as there will be less pockets between the two layers of plywood. Does this make sense? Any help you can provide will be appreciated. I am doing the prep work to cut down on the cost of the job. Thanks! Ed
 
  #2  
Old 04-29-02, 11:35 AM
diemeto
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I am not a pro but I am not sure why you needed the extra plywood. 3/4 on an inch on 16in oc rafter I think is fine. You should have instead spent the money on the tile guy doing a mud job on top of the plywood and then laying the tiles.
 
  #3  
Old 04-29-02, 11:53 AM
diemeto
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I should further clarify, you should have approximately 1 1/8 inch as a sub floor with tile, generally this is 3/4 inch plywood 16inch on center of 2x10 rafters. Then 1/4 inch cbu and 1/8 inch thin set. the tile. alternatives is 3/4 plywood and then 1 inch mud and then tile but you need the be able to handle the addtional height. I think most pros avoid laying tile directly on plywood though it is done
 
  #4  
Old 04-29-02, 03:23 PM
A
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Hi
The concrete board would have been a better idea than the plywood.....concrete board doesn't expand and contract with changes in temperature and humidity, like the plywood does. The tile installation will have a limited warranty on top of plywood..no matter which side is up or down. Your best bet(if you have 2x10 joists, 16 inches on center) would be this product.

http://www.schluter.com/english/prod...601-index.html

It can go over your existing 3/4 plywood, is only 1/8 thick, and is a crack isolation membrane, made for this application. Great stuff.
 
  #5  
Old 04-29-02, 05:05 PM
AGC
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The sanded and plugged side should be up. Gaps in the plywood are "plugged" which means filled. These areas can create hazards by leaving a gap under the tile. Finally, cement board such as durock or hardi backer is far superior to plywood. If you haven't already installed the plywood I would bail on it and can some 1/2" cement board. Finally, and I mean it this time, why would one even get sanded and plugged plywood only to turn it down? If your tile guy is that concerned about the smooth surface tell him to get out his belt sander and rough it up a little.
 
  #6  
Old 04-30-02, 08:32 PM
T
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Underlayment for ceramic tile

Concrete underlayment for tile is recommended. Any movement in wood subfloor will result in grout failure and possibly cracked tile.
 
  #7  
Old 05-01-02, 10:44 AM
Dave Gobis
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I agree with the other posters, Ditra or a backerboard would be preferable but I applaud your lumber yard for knowing the right plywood which your "tilesetter" didn't. There is a special thinset formulated for that type of installation called EGP thinset mortar. Here is part of an article on that installation.

All wooden flooring, when placed over conventional floor joist or other systems, should be of a design and thickness so as to maintain a substrate deflection not to exceed 1/360th of span, including live and dead load. Further, the area to receive the Latex Portland Cement Mortar should be exterior or exposure 1 grade plywood only, secured with screw-type nails and glued where possible. Locate nails or screws at 6 inch centers along panel edges and 8 inch centers each way throughout the panel: offset joints of subfloor and underlayment. Underlayment fasteners should not penetrate the framing below. A gap of 1/8th” shall be left between sheets of plywood and ¼" at all other surfaces which they abut to allow for expansion. Most manufacturers require the gaps to remain empty when the installation is complete. The installation of the ceramic tile should be performed in accordance to ANSI A108.12. The subfloor should be 19/32” thick plywood or 1" by 6" tongue and groove boards on joists spaced 16” o.c. The overlay surface should be 15/32” minimum (19/32 commercial floors) C-C plugged exterior grade, non-fire treated plywood. Additionally the substrate should be dry, clean, free of oil, grease, dirt, old adhesive residues, gypsum patches, curing compounds, sealers, waxes and paints including overspray. Tongue and groove plywood sheets butted up, not gaping plywood sheets, and/or filling the gaps between sheets and abutting surfaces with the dry-set latex-Portland cement mortar DOES NOT ALLOW FOR EXPANSION/CONTRACTION OF PLYWOOD SHEETS and will likely result in bond failure. Many manufacturers have their own specific recommendations on spacing and treatment of plywood joints. Problems can occur in plywood substrates when subjected to moisture. Installation of ceramic tile using EGP mortar is recommended only in interior dry or limited water exposure areas. All wood floor structures should be designed with proper ventilation on the underside and thorough protection from water vapor or moisture. In the case of homes built with crawl-spaces, an effective moisture barrier must be provided.
 
  #8  
Old 05-02-02, 10:21 AM
EdgarF
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David, thanks for your reply. This is basically the information I needed. I appreciate all the other posters telling me that cement board is better but they didn't really help answer my question. The area being tiled is definately a dry area with no water exposure. My tile setter
was recommended to me by a local tile retailer and has been said to do excellent work. I am not sure why he would have steered my towards the plywood if it wasn't the right thing to do. He is definately doing the thinset installation as he told me that. From what I gather from this article the plugged side should be face up..do you agree? He did explain to me about leaving enough room for expansion as your articel states. Thank you for the information - it is greatly appreciated. Ed
 
  #9  
Old 05-02-02, 12:45 PM
Dave Gobis
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Plugged side up.
 
  #10  
Old 05-02-02, 01:24 PM
EdgarF
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David, one more question: what does this mean -

"Underlayment fasteners should not penetrate the framing below."

This sounds like you are saying when screwing down the underlayment to the subfloor that you do not want to hit the joists with the screws? Example, I was planning to use longer (2-1/2 inch) screws so that I could hit the joists. Can you explain why this is not desirable....? It sounds like your article is not recommending this if I am reading it correctly.

Thank you. Ed
 
  #11  
Old 05-02-02, 02:32 PM
A
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Hi Ed
You don't want to screw it down into the joists...you want the new subfloor to be as independent as possible..so that if your house moves, your floor doesn't go with it. This is why we were all recommending either cement board or Ditra..they are both isolated from your subfloor.(as much as possible) You'll notice that Dave Gobis said a "special thin set" is used . You might want to check with your installer(he may be using ordinary modified thin set) which is ok...it will stick just fine....but you may notice some hairline cracks in the grout joints in the future.
 
  #12  
Old 05-03-02, 06:07 AM
Dave Gobis
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Ed, what he said. The recommendation comes from the EWS (Engineered Wood Association) who is the trade group for manufacturers of plywood. 2" offset, minimum. Unless you get an educated installer he will never have heard of it. The theory which also applies to backerboards, is to avoid transfering addtional movement, compressive, and tensile stress to the installation system.
 
  #13  
Old 05-03-02, 11:36 AM
EdgarF
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Adanac / Dave - thanks for the help.
I understand now. I am also going to speak to the installer tonite and mention the special type of thinset and see what he says. I am going to go with the plywood. I think the cement board would have been good, but don't have the time, will or patience to return all this and start over. I think this will work out fine..will let you all know once the job is done. Thanks again. Ed
 
 

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