16 replies to this topic

[chnlisle]

I guess I'm confused here. I am looking to re-sael the screws on top of my '86 Grandby.
I have a tube of 3M Marine Grade Silicone Sealant. It is specified for sealing glass, metal vinyl, etc. above the waterline. Is this a bad idea?

http://solutions.3m.com/wps/portal/3M/en_US/Marine/Home/Products/Catalog/?PC_7_RJH9U5230GE3E02LECIE20S4K7_nid=P3RNM39V14gsQH8HT14PGTgl52WHRRXV4Bbl

If it's 3M 5200 and you ever want to take the screws out again don't use it.

[gandhii]

I'd like to interject in the hopes of a real answer of why silicone is so evil?
I've used it for years without complaints for aquariums and more recently my old ass fwc.

The only complaint about it that I've heard so far is that it doesn't stick very well to already cured silicone. Which in my experience is only partially true. Yes, when it comes to silicone that has been around for a while, but I've used silicone that touches silicone that has cured within the previous month or so with out any noticeable difference in stickiness. Both for aquariums and more recently in resealing the roof of the '82 fwc I recently bought. The camper had several layers of various kinds of caulks that previous owners had applied to the roof over the decades. For the most part they had decomposed into various levels of uselessness. Not to mention the fact that it should be a given that what ever you use it isn't going to work very well if you just stick it on top of something bad without cleaning it out first. You should have seen what the seal looked like. Various types of caulk all laid on top of each. No wonder it was leaking. Someone had previously squirted some silicone on top of parts of it. Which didn't help any considering what it was laying on, but the silicone was the only stuff there that didn't look like it was turning into mud.

So I cleaned the whole thing out of old caulk and silicone and applied new silicone. It now stays dry as a dog's nose. The silicone sticks as solid as I've ever seen silicone stick, even to itself. Cleaning caulk/silicone is not a fast job. I did one side at a time over a space of a month. And where I continued one side from the other is not noticeable in any way. It certainly sticks to itself.

So where am I wrong? Is it common to reapply caulk onto old caulk? Is that why I'm not understanding? Or is the extra dry desert conditions on the west coast the variable that I'm not experiencing? Please don't take my rant personally and set me straight. Thanks.

[LuckyDan]

Me personally, any long straight seam gets eternabond.

I too hate silicone sealant except in gasketing applications.

I too give eternabond two thumbs up. Not Cheap, but good stuff.

[leadsled9]

I recently made a trip to the FWC factory for a rear awning install. While I was there I asked Terry what FWC uses for roof sealing and other external sealing. He said they've tried a lot of different sealants....and the one they settled on as the best one is this (he gave me a tube):

[craig333]

For professionals only. Darn. Maybe I can get the industrial exception

[leadsled9]

For professionals only. Darn. Maybe I can get the industrial exception

I've seen your wiring drawer....you ARE a professional!

[JohnF]

So where am I wrong? ... Thanks.

Wrong is sort of the wrong word to use here. If you go to the effort to get all of the old silicone off then silicone sticks great. Silicone will peel off due to flex and thermal expansion/contraction cycles. You have to get it all off. To the point that you can wet (with water) the substrate that you are sticking it to. And I don't think there is a solvent that can help here. I've tried many.

You worked on it a little at a time for a month. I can do mine in a couple of hours on an afternoon. No, I do not just caulk over the bad; I take a razor blade and cut out the failed/failing caulk line and then apply new caulk. If you used a urethane (Could be other, my experience is here) product like the PL I mentioned then everywhere the adhesion is good will still be good and the new caulk will stick to the old. So you don't need to get it all off. If you feel you want to get it all off, then solvents will do it.

It is the effort to get the old off and that silicone peels that is the issue.