Replacing Ceramic tile floor

handy andy

I have just finished tearing out a ceramic tile floor in the entry foyer of a 30 year old house. The area is about 10' by 14', over a crawl space. The original tile was installed over expanded metal lath imbedded in thinset. The base is 5/8" t&g plywood over 2x10 joists spaced at 16". The floor was in fairly good shape with no cracked tile and a few areas with cracked mortar.

The plan is to replace the old tile with 12" square porcelain tile. I know that the new tile should not be installed on the plywood without another layer of plywood and concrete board. The problem is that this would raise the floor level above that of the other rooms which are recently redone with 3/4" hardwood or 10 mil laminate. Also the outside deck at the front door is level with the old tile floor. This is a wheelchair 'accesible' home where transitions have to be kept to a minimum.

I think I can get away with 3/8" backer board under the new tile, but not an extra layer of plywood. As the crawl space is accessible, the idea I'm considering is to glue and screw a layer of 5/8" plywood to the underside of the current subfloor between the floor joists to give this floor more stiffness.

Will this work?

Bud Cline

Why do you need another layer of plywood?

Have you seen Schluter System's DITRA Mat underlayment?

handy andy

1. I thought that a single layer of 5/8" plywood is not stiff enough. Some of the advice I've seen leaves me with the impression that plywood subfloor should be a minimum of 1 1/8". I thought that the concrete board provides a 'tile friendly' surface but does not add strength!
2. I have seen schluter's ditra but not 'ditra mat'! Does this replace the old 'mortar and metal lath' process?

Bud Cline

More plywood would always be better but if you were to check the specifications of the cement board products (I think) you would find they are all suitable for use over a 5/8" subfloor. A subfloor of 5/8" inch is the minimum the building codes allow and of course a lot of builders build to minimums.

Same thing.
There is no such process that has ever been recognized or sanctioned by any tile installation governing authority. Mortar and metal lath is not an acceptable installation method.

handy andy

Thanks for the help Bud. The ditra mat would result in the new floor level the same as the old. Unfortunatly I have now asked a question that I should have asked earlier. One of the doors from the entry is into a Kitchen that has lino on 3/8" plywood underlay. I thought this would remain. But the owner is planning a future kitchen reno at which time she will want ceramic tile! Now is the time to plan for that reno. Using the same tile throughout would be logical. She can buy the tile for the kitchen now and store them for 2 years or whatever.

Two choices now are:
1. Install the entry tile over ditra now and then tear out the kitchen underlay for the tile install when the kitchen reno happens.
2. Install underlay in the front entry to match the kitchen underlay now and install the ditra over this. Then install ditra and tile over the Kitchen underlay when the kitchen reno happens. This would save a lot of work during the kitchen reno. (The kitchen is 3 times the size of the entry foyer). Is ditra over plywood underlay plywood acceptable?

I will go to the Schluter web site to see what they say. I did not look for this on my last visit.

Background: The last time I was involved in removing kitchen underlay, we found it easier to remove all the subfloor with the underlay as it was glued down so tight that chiselling it off was the only way it would come off.