Hi,

I'm looking for advice on getting the proper product for the underlayment on my main floor.

We are replacing approx. 1000sq. ft of existing tile. The current installation is 12x12 porcelain tile on 1/2" plywood underlayment, over 5/8 T&G OSB subfloor. the subfloor is glued and screwed(I can see the glue from the basement)
Joists are solid pine, 2x10, 16" O.C., 13' max span. the house was built in 1996 in Ottawa, Ontario, Canada

The current installation has failed at multiple places where large cracks across multiple tiles are seen. no new cracks have former over the years, but these cracks have been there as long as I remember(7 years) Of course the grout is cracking at multiple places as well.

Now we are at the point where we are going to replace the entire floor. This floor goes into the kitchen, hallway, mudroom/laundry room, front entrance/foyer.

The installer advised he would use 1/2" ply over the OSB, but hasn't looked at the specific details I know to look for. He stated he would use whatever products I wanted. Now I know from reading this site, it all depends on the type of tile being used.

We have not chosen the tile yet, but we'll say stone as I think it would need the most re-enforcement.

I'm trying to avoid increasing the overall height of the floor.

Rather than 1/2" ply, ditra, thinset, tile, I remember reading about a plywood that is 3/8" or 3/16" but is as strong as 1/2".

This would allow the overall height to be reduced or not increased by a large amount.

Can anyone advise what this special underlayment is? I searched and came up with Halex 3/8"m but it stated that it is only to replace 3/8" and is not suitable for 1/2" substitution.

Any help is appreciated

Thanks

Eric

Hi Eric,
I'm sure the regular members will be able to provide you with plenty of advice. Have you read information regarding "movement joints"? Sounds like you have a multiple room installation. The lack of movement joints in your current tiled floor might be the reason for the cracks. Movement joints will be something you will want to consider before installing your new tiles.

I'll look into the movement joints. I def. do not have any in the current installation. I imagine the movement joints are put in at the room to room thresholds(doorways)

I'll search this some more and post up a floor plan for you guys to look at.

Thanks
Eric

Hi Eric,

There may be several reasons your installation failed. Some could be the lack of expansion joints both in the field and at the perimeter at all walls. I think the biggest problem likely is the installation direct over plywood though.

The birch plywood Harry (the owner here) referred to in the past was indeed Halex. I've seen it, but never used it. The plywood thickness for your floor may depend on whether you go with porcelain or stone. Actually I'd go with min. 1/2" but think 5/8" is more like it. Your 5/8" OSB subfloor is really an inferior product, love those cheap ass builders.

But again go with as much plywood as possible. Since you're gonna use Ditra you'll be saving some height there over 1/4" CBU's.

You should also check your joists to be sure you don't have too much deflection. Use the "Maximum Span Calculator" above left. You need no more deflection than L360 for ceramic or porcelain and L720 for stone tiles. (lower numbers = more deflection).

Jaz

Thanks Jaz,

I ordered the Halex in 3/8". not too cheap either. it works out to approx. $2 a sq/ft.

I'm not installing stone for sure. We will install porcelain or ceramic.

My deflecto comes out to L/458. so stone is out of the question.

I can't believe the builder cheaped out on OSB. This is an expensive custom home.(I wasn't the original owner). I can't lift the entire floor. Too much involved.

At this point I feel very confident that this 3/8" halex, Ditra combo will be more than enough for a proper long lasting tile installation.

Thanks again for all the help,

Eric