Specific application of sealant

[Stan in Oly, WA]

If I'd known I was going to get such good information in response to my question about silicone caulk, I'd have been more careful about what I asked. I haven't yet read all the information provided in the links which people included because I want to post another question first. Since people are giving such specific information, it seems like it might be a good idea for me to describe exactly what I need to use the caulk for.

A small but important part of the fence I'm building is on top of a short, wide retaining wall which was poured with 5' high lengths of 1" rebar sticking up every six feet. I welded horizontal lengths of 3/4" rebar 6" from the top and 6" from the bottom between each pair of uprights. Then I boxed everything in with vertical 2X6's and horizontal 2X4's separated by full length 1" spacers so that the frame appears to be 4X6 uprights and 4X4 cross members. An interior frame for each section of cedar fencing and a decorative 1X4 trim piece on top of each upper (nominal) 4X4, and post caps, will hide the spacers and joints.

The rebar was all sanded and painted but I still consider it the most likely trouble spot in this design. If water can get to it and it rusts, I could get rust staining the retaining wall, with no way for me to get at the location of the problem. That's why I would like to use the best type of caulk available to waterproof all the joints before I cover them with 1X4 trim pieces. I do not want to caulk any of the joints between the trim and the framing---places where the caulk would be visible and/or interfere with the painting or staining of the wood.

I hope that's clear. It's certainly long.

Stan

 

[retired farmer]

Clear as mud. How about a picture?

 

[Stan in Oly, WA]

Sorry, no picture. I'll put it more simply. I need to permanently seal joints in wood to keep water out. The sealed joints will never be exposed to direct sunlight or weather. What should I use?

There are people on this forum who have the expertise to provide very specific advice to a very specific question. When I ask a simplified, non-specific question, that's the kind of answer I can expect to get.

Stan

 

[MarkB_MI]

When it comes to sealing joints in wood, the standard by which all other caulks are judged is 3M 5200 Marine Sealant. Just don't use it on anything you'll ever want to take apart.
3M 5200

 

[dpendzic]

Actually Stan moisture will migrate thru wood, and also condensation will occur inside the sealed timber box. It might have been better to use galvanized or epoxy coated rebar, at the very least a good quality 3 coat paint job--but it may all be too late for that if you have it built already.

 

[Billy NY]

I have an idea of what you did here, sounds like you boxed in deformed metal bars embedded in the concrete, that rise up to form an internal frame that you clad or boxed in with wood. I assume the frame is what provides the structure.

It sounds like the substrate is wood to wood, so you need a material compatible, that will bond to wood, that is also elastomeric, so it can expand, contract etc.

With the rebar, epoxy coated may have well sufficed, but you would have to field apply it to any areas cut, or welded etc. Galvanized would have been nice too, but you may have had to build the grid, then send it out before you embed it, just some thoughts. However, its not helpful to state "well you could have done this, or done this or that way" LOL !!!!!

Bituminous materials (asphaltic) may have also been a good coating, but I think the biggest concern would be where rebar meets the concrete, thats where rust will likely want to occur and that is where liquid, ie; water could settle unless its pitched, hence your concern with rust staining.

Bituminous material is in no way compatible with silicone, FYI.

In any event a photo or two would be extremely helpful, but it sounds like a wood to wood joint, one that you may be able to poke a small backer rod into, make the joint concave, place the sealant, then strike or tool it to a smooth finish.

The wood will likely need to be cleaned of any surface latence, sort of like mill scale on steel, if new material, likely not an issue, should bond fine. Best material will give longest service, though you do want periodically look at it to see if any has delaminated.

 

[Ellis Kinney]

EPOXY PAINT Ellis

 

[Anonymous-0]

Silicone will make stuff rust and no paint will stick to it.

 

[Anonymous-0]

Maybe some tar like roof repair or even undercoating on the rebar would stop it from rusting?

 

[Anonymous-0]

Just thought of something else. Spray or brush the rebar with rust converter.

 

[Frank (N.Mi.)]

I would still use the Lexel to caulk the wood, because it does so well at stretching without cracking and will not peel off.( i have dozens of jobs that I used it on without any callbacks) Because of what dpendzic says ( the re-bar inside the box WILL be subject to condensation) I would paint the re-bar with three or four coats of "rust bullet" and then a coat or two of good outside oil base enamel or epoxy.
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