# How to bridge between wood and concrete subfloors for tile



## leadhead (Jan 20, 2017)

I am remodeling a kitchen and removing the old tile. What I found was on top of the floor joists (18"OC) was a 1"x8" on diagonal with 3/4 inch hardwood floors on top of that. Now half of the kitchen floor is like that the other half is on a concrete slab with a crawl space underneath. My though was to rip out the hardwood floors and put in 3/4 inch plywood to come flush with the concrete slab then install Ditra over both the plywood and concrete before tiling the whole thing. 

Does that seem to be sufficient to cover the transition between the wood sub-floor and the concrete slab, preventing future cracking? 

Also the concrete has old black linoleum glue on it, does that mater for installing the Ditra? 

Thanks,

G


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## Dan_Watson (Mar 1, 2008)

leadhead said:


> I am remodeling a kitchen and removing the old tile. What I found was on top of the floor joists (18"OC) was a 1"x8" on diagonal with 3/4 inch hardwood floors on top of that. Now half of the kitchen floor is like that the other half is on a concrete slab with a crawl space underneath. My though was to rip out the hardwood floors and put in 3/4 inch plywood to come flush with the concrete slab then install Ditra over both the plywood and concrete before tiling the whole thing.
> 
> Does that seem to be sufficient to cover the transition between the wood sub-floor and the concrete slab, preventing future cracking?
> 
> ...


That black glue may have asbestos in it.

We just did this, but the vast majority of the floor was concrete, only a very small wood section. We hit the entire floor with EcoPrim, then feather finished the transition, then used I think Kerabond over the entire floor. 

Ditra would be a great solution, but be careful with that black glue! Because of the asbestos and adhesion.


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## leadhead (Jan 20, 2017)

Thanks Dan! So you think if i paint over the cutback residue with Ecoprim, then I should be good to go with an unmodified thinset under the Ditra?

Is the Ditra enough to not give me cracking issues where the wood and concrete meet?


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## leadhead (Jan 20, 2017)

I could also pull the hardwood floor and put down a 1/2' sheet of plywood and 1/4" CBU then tile, but what would be the best way to deal with the wood/concrete interface?

Would that be enough underlayment? 3/4" subfloor+1/2" plywood+1/4" CBU=1 1/2" underlayment.

Thoughts?


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## 91782 (Sep 6, 2012)

subscribed.


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## Dan_Watson (Mar 1, 2008)

leadhead said:


> I could also pull the hardwood floor and put down a 1/2' sheet of plywood and 1/4" CBU then tile, but what would be the best way to deal with the wood/concrete interface?
> 
> Would that be enough underlayment? 3/4" subfloor+1/2" plywood+1/4" CBU=1 1/2" underlayment.
> 
> Thoughts?


I would use Ditra if there are no height restrictions. We could not use it, that's why we went with the Keralastic directly over the Ecoprim. Our transition between wood and concrete was small and not in a walking surface, so we were less worried with the bridging. 

We use the Bostik Ditra-Set thinset for Ditra and Kerdi, but there are a couple out there, Ardex makes a good one as well.


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## leadhead (Jan 20, 2017)

I just talked to Ditra, they will not approve there material over the black adhesive, nor will Mapei with the EPG. 

I am leaning toward removing the hard wood floors and adding 1/2" ply and 1/4 cement board. Then bridging the wood concrete transition (7 feet long) with Mapei Mapelastic with the fiberglass mat rolled into it. I would still use EPG over the black adhesive before then tiling. 

Any thoughts on Proflex vs Mapelastic for the transition? My guy at Shoreline likes the Mapei product better.


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## TNTRenovate (Aug 19, 2010)

You will need to grind the concrete down clean. Prime and then it's ready for thinset.

The plank subfloor needs to either come up or be covered with plywood. The plywood SHOULD NOT be secured to the structure (joists).

The transition can be handled in a few ways. If you are tiling the wood and concrete you will need an expansion joint of some kind. You can use a Schluter Transfer joint or just a grout line that is filled with a foam backer rod and flexible sealant. But you must maintain the joint. You cannot just use Ditra over the joint and think you are good.


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