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best material for sealing cedar siding to stone?

Posted by ctjohn (My Page) on
Mon, Oct 25, 10 at 20:20

The exterior of my house (in the north-east USA) is cedar siding and stone. The gap where they meet was filled originally with mortar, but this has cracked and partially come away over time. The gap is about 1/8 to 1/2 inch. My question is what should I use to seal this gap? Presumably some sort of flexible caulk, but I would really appreciate specific recommendations.
Thanks


Follow-Up Postings:

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RE: best material for sealing cedar siding to stone?

Such a wide joint between such dissimilar materials that will move so differently present an extreme test for any sealant both for adhesion and elongation. Traditionally such joints were carefully avoided by lapping one material over the other so your situation is unusual.

Silicone sealant is the most flexible but adheres poorly to porous materials and cannot be painted.

Urethane sealant adheres much better but is less flexible and can be painted.

You might try one tube of each and see how it works. I would favor the urethane for the narrower joints. The widest joints will probably fail no matter what you use.


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RE: best material for sealing cedar siding to stone?

Use backer rod - a foam tubular material intended for just these uses - before you caulk. Its purpose is to fill large gaps and compensate for different rates of expansion. Best caulking material I know of is Lexel.


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RE: best material for sealing cedar siding to stone?

The purpose of a compressible foam backer rod is to form the back side of sealant so the finished section resembles an hourglass. This allows the maximum stretching of the sealant at the thin middle and the maximum adhesion at the wider edges. Of course, the joint has to be deep enough and narrow enough for the rod to be compressed to half it's diameter and still leave enough room for the sealant. A half inch joint would need to be about 1 1/4" deep.


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