Quote:
Originally Posted by SafariBen
Excellent information. I'll add my preference for professional polyurethane sealants such as Sika, Vulkem etc. Nasty to work with, but work good once applied.
Wetting is especially important in repair work. On the assembly line, the temperature is controlled and the surfaces are clean, and they still don't get it right all the time. Once the surface is weathered and dirty, getting the surface fully wetted for good contact and adhesion is critical. Applying the sealant in several passes is one technique, with each "caulk bead" forced into the surface with pressure and the nozzle held tight to smear flat, not apply a round bead. Then apply the bead over the smeared surface. Kind of like brushing in paint vs spraying paint on to the surface.
Nothing will adhere to silicone, you can use that to your advantage if a joint moves then silicone can be the backer rod, as the polyurethane will flex over the silicone rather than crack. It must be adhered on both sides of the silicone and form a flexible seal over the silicone, as it will not adhere to the silicone.
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Well said.
I just wanted to comment when you stated that the silicone can be the backer rod - unfortunately, most RVers do not understand what the backer rod terminology means. We use backer rod when applying sealant to an open joint that is usually wider than 1/4 to 1/2 inch. The backer rod acts as a backstop preventing the sealant from going into a joint that is usually wider than 1/4 to 1/2 inch. The backer rod is a polyethylene or polyurethane foam rod which sealants will not bond to, now making it a bond breaker which allows the sealant to perform as is intended. We then apply the sealants over the backer rod and on to both sides of the joint, to approximately 3/8". This will now leave you with a wide seal of approximately 3/4", plus the actual joint width. Now, you may ask, "why not just stuff more sealant into these wide joints and seal over top of the joint as stated above?" Well, this will cause something that we call 'three sided adhesion'. You will have a bond on the outer sides of the joint, but the inside as well. This will cause the sealant to stretch and pull the sealant in directions that will cause a seal failure. So, the silicone referred to above, is a bond breaker as stated above, which is good when resealing. One other comment, ONLY silicone will adhere to silicone, so be careful when you are attempting to use silicone as a bond breaker and reapplying silicone over the existing as stated above. This won't work and last for long.
I hope that I have not stepped on any ones with my additional comments to this thread.
I am surprised that my old posts are still being read on sealants repair and use. I have since retired from both my job and from RVing. I wish you all the best in our future projects.
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