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bmancanfly 09-22-2009 12:22 PM

Wood to Concrete Block
I have a concrete block house in FL. I'm replacing some windows and had to removed the plaster around the window returns - it's just bare concrete block now.

Is it ok to attach wood directly to the concrete block and paint it, using it as the finished surface of the return. This is all above ground and indoors.

I noticed that some of the other windows seem to have been done this way without is seeming to be a problem.

It wood make life a lot easier if I could just attach a wood frame around the inside of the window opening, inside the room, to finish the return off.

Scuba_Dave 09-22-2009 12:25 PM

Any wood in contact with concrete must be PT wood

Gary in WA 09-22-2009 12:43 PM

In this application, you would be fine. I suggest putting a piece of builder's paper or even plastic behind the wood, in case the block transmits water from the exterior.
Be safe, Gary

bmancanfly 09-22-2009 01:34 PM

Thanks for the input.

I was thinking of putting some sort of "paint on" moisture block on the concrete block (to prevent moisture intrusion), then prime the wood, then glue wood to block.

I know code calls for PT but in this application PT won't work - too instable for finish work.

Another thought is to use mastic to apply strips of cement board to cover the returns, and then spackle over that.

Any other suggestions would be appreciated

ARI001 09-22-2009 01:47 PM

It does not need to be treated if you provide a barrier between the wood and the concrete. Roofing felt is an acceptable barrier.

bmancanfly 09-22-2009 02:17 PM


Originally Posted by ARI001 (Post 330981)
It does not need to be treated if you provide a barrier between the wood and the concrete. Roofing felt is an acceptable barrier.

Thanks that's very helpful

The appeal of attaching the wood with adhesive though is that the concrete surface is very uneven. The adhesive will allow me to even out the imperfections of the concrete blocks.

Gary in WA 09-22-2009 02:51 PM

Correct me if I'm wrong... the code requires p.t./concrete only on:

1.sill plate to concrete (structural)

2. beam pocket in concrete if no 1/2" air space (structural)

3. posts on concrete piers closer than 8" to soil. (structural)

I would protect the wood from moisture coming from exterior, with the method you stated is fine. And with a thermal break. I don't know of a code requiring p.t. to concrete block above grade that high up. Maybe someone else could state the code # please? Back priming is also a good idea, especially for trim wood with a lower moisture content than framing lumber.
Be safe, Gary

concretemasonry 09-22-2009 03:45 PM

The "old wives tale" of P.T. must be used when the wood in contact with concrete is easily misunderstood.

It really applies to wood that is attached to the concrete that is in contact with the soil. A separate pour or concretemasonry unit does no need P.T. unless it is exposed to the elements. - There might be some unique situations.


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