installing ceramic tile over old plywood subfloor

Reply

  #1  
Old 07-26-08, 06:27 PM
T
Member
Thread Starter
Join Date: Jul 2008
Location: USA
Posts: 22
Received 0 Votes on 0 Posts
installing ceramic tile over old plywood subfloor

I am putting down ceramic tile on a bathroom floor. I stripped the bathroom of toilet and sink (no tub ) room is completely empty. I stripped the old tile from the plywood floor and removed the old adhesive. The plywood subfloor is 5/8 and has a seam in it. The old tile 12X12 one inch pieces on a mesh. This old tile grout was cracked along the seam in the plywood subfloor. The bathroom is small 25 sq. ft. The plywood floor does have a few gouges in the surface from pulling up the old tile. I am very new to laying tile a beginner to say the least. The question should I try to patch the gouges and the seam or install backer board? If I install backer board 1/4 " my floor level will be 1/4 " higher then before raising the toilet by 1/4" . Will this effect the proper mounting of the toilet and cause it to leak? If I were to fill in the hole and seam of the subfloor then lay the tile (ceramic) the floor would be at the same height as before and there should be no problem. Please advise Thank you Torque1
 
  #2  
Old 07-26-08, 07:36 PM
J
Member
Join Date: May 2007
Location: USA
Posts: 1,604
Received 0 Votes on 0 Posts
As you now know, your old floor was not installed correctly. You should NOT install tile direct to a subfloor. That goes for any tile. You can install 1/4" backer board on fresh thinset mortar over your 5/8" ply subfloor, but be aware that 5/8" is bare bones minimum. Check back with us when you've determined what specific materials you've chosen.

Raising the floor 1/4" will be easy to work with when re installing the toilet. At what level will the new floor be in relations to the top of the toilet flange?

Jaz
 
  #3  
Old 07-27-08, 05:38 AM
H
Member
Join Date: Jan 2006
Location: USA
Posts: 3,525
Received 8 Votes on 8 Posts
Is the 5/8" plywood tongue and groove or square edge? If it's square edge, it doesn't meet minimum standards. If square edge, you either need to add blocking under the seems of the plywood between the joists or add another layer of plywood. If it's t&g, as already said you are at bare bones minimum.

Its likely your old tile lasted as long as it did because you had 1" mosaics. You probably had other cracks in your grout that were less noticeable. Larger tiles on a subfloor like that would not have survived for very long.

Consider adding another layer of plywood. You could add 3/8" plywood and then an isolation membrane instead of cement board. The total added height would be 1/2" or less depending on what membrane you choose. You will end up with a much stronger floor with less chance for failure. Ceramic tile is a different type of flooring than other floor coverings. What's underneath the tile will determine how long it will last. Done right it can last a life time.

You can use a flange extender or thicker wax ring for the toilet, depending on your situation.
 
  #4  
Old 07-27-08, 03:23 PM
T
Member
Thread Starter
Join Date: Jul 2008
Location: USA
Posts: 22
Received 0 Votes on 0 Posts
Hi John The plywood is square cut it is 5/8" but there appears to be a subfloor below it. I could see the 3" copper pipe coming up to the flange thru plywood. I went down into my basement beneath the toilet and checked the 3" pipe going up thru the subfloor plywood. so there is a subfloor beneath the 5/8" plywood above it. The 5/8" was cut around the flange. From the lower plywood the height to the top of the flange is 1" There is also 2x4 support between the joists. The floor feels very solid, however the large crack in the old tile grout was directly above the seam in the 5/8" same direction as seam
 
  #5  
Old 07-27-08, 03:36 PM
T
Member
Thread Starter
Join Date: Jul 2008
Location: USA
Posts: 22
Received 0 Votes on 0 Posts
I have filled in the gap in the seam with Henry 549 feather finish. I have other gouges in the plywood not many from where i removed the old tile and adhesive. I wanted to fill in these gouges with the henry 549 material and lay tile. This tile is same thickness as old tile so the floor will be at same level. I do not want to risk this new tile cracking any suggestions or advice? I keep hearing I cannot lay ceramic tile on plywood. Should I put down backer board 1/4" and deal with the extra height of 1/4????
 
  #6  
Old 07-27-08, 06:05 PM
HotxxxxxxxOKC's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2006
Location: USA
Posts: 8,034
Received 0 Votes on 0 Posts
You can use a Schluter Ditra product. It's 1/8" thickness and gets thinsetted down to the plywood. This serves as a good isolation membrane to prevent cracking.
 
  #7  
Old 07-28-08, 04:32 PM
H
Member
Join Date: Jan 2006
Location: USA
Posts: 3,525
Received 8 Votes on 8 Posts
Torgue

You say you have 1" of plywood and the top layer is 5/8". That would make your subfloor 3/8" plywood, very unusual, are you sure thats the case?

Can you check to see if the seem on the 5/8" underlayment lines up with the subfloor seem as well? It should not. You also mention that you have blocking between the joists. Is that blocking underneath the plywood seems, cause thats where you need it. There should be 1/8" gap between the plywood sheets so that there is room for expansion. If you don't have that, you can use a circular saw to make cuts accordingly. You can fill the gaps between the plywood sheets with a cheap caulk that will allow the plywood to move.

Adding cement board or an isolation membrane will also help to isolate joist and subfloor movement from the tile. Don't set the tile directly to the plywood.

Short and sweet, you know that seem was a problem with the old tile floor. That movement, is vertical movement and you have to fix it before you go any further. Underlayment and isolation membranes wont fix vertical movement. Make sure you add blocking between the joists under that seem and screws into the blocking from above. Make sure there is a gap between the plywood sheets per above and caulk it with a flexible caulk to allow for movement. An isolation membrane will be better for you than the cement board and won't give you as much height either.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: