Best UV resistant sealant/caulk ?

[cooties]

Yes Gord, I saw his response. Won't silicone possibly cause problems later? In another thread, Jedi recommended it only "for windows, hatch lenses etc. i.e. glass, Lexan, Perspex etc"

I should add- I'm not needing anything structural, I don't need something that adheres too strongly (why I'm not really wanting 4000 UV, I have read it is tough to remove later), I'm not rebedding.. just sealing the long seam on each side of the boat as well as other seams when it becomes necessary.

Any other opinions for such a common job? I've read through the practical-sailor articles (what I could... it is difficult to find what you're looking for there, disjointed information). I feel like there must be some missing bit of information that would provide insight into why products that *should* last, aren't. I'm talking more than 2 years which shouldn't be asking for much.

I really don't have much frame of reference here, not having owned a boat more than a few years old. If I walk around the marina, I see that all boats have mold in their caulk, and a few do have some degradation, but none as bad as mine.

I've started to see some recommendations for LifeCalk polysulfide

[s/v Jedi]

Originally Posted by cooties

Yes Gord, I saw his response. Won't silicone possibly cause problems later? In another thread, Jedi recommended it only "for windows, hatch lenses etc. i.e. glass, Lexan, Perspex etc"

I should add- I'm not needing anything structural, I don't need something that adheres too strongly (why I'm not really wanting 4000 UV, I have read it is tough to remove later), I'm not rebedding.. just sealing the long seam on each side of the boat as well as other seams when it becomes necessary.

Any other opinions for such a common job? I've read through the practical-sailor articles (what I could... it is difficult to find what you're looking for there, disjointed information). I feel like there must be some missing bit of information that would provide insight into why products that *should* last, aren't. I'm talking more than 2 years which shouldn't be asking for much.

I really don't have much frame of reference here, not having owned a boat more than a few years old. If I walk around the marina, I see that all boats have mold in their caulk, and a few do have some degradation, but none as bad as mine.

I've started to see some recommendations for LifeCalk polysulfide

Polysulfide is not Uv resistant. It is a bedding compound, so needs to be between two surfaces, example: bedding of stanchion bases.

For this seam, Dow Corning 795 is the best option. You get a long working time (think 20 minutes) and very good UV resistance. To prevent getting it on your paint job, use wide masking tape below the seam.

Another option is to use thickened epoxy and paint that. I did this for a huge hatch in the cockpit to lift the engine out. If the day comes I need to lift the engine out, I’ll grind the epoxy away, but for now I have a zero maintenance seal

[Franziska]

Do not use silicone on board (there are very few, very special exceptions) but generally avoid it as the plague.

If you ever want to repaint and you just get a tiny spec of silicone onto your sandpaper you have big problems with pinholes in the new paint job because the silicone gets nicely distributed wherever you sand. And no, usually wiping down with silicone remover does not catch all of it (unless you use lots of silicone remover and lots of fresh rags).

Use anything but silicone based products. I am a trained boat builder and I have seen this happening numerous times....

What works on building is not always the best choice for boats.

[Thumbs Up]

3M 5200 has the reputation of being tough to remove. 4000 UV is medium strength.

[Fuss]

I use sika 295 uv for my windows...it’s ok but, I’m sort of looking for something longer lasting...in bright sunshine it goes off a bit after a couple of years...ok enough on this subject, so my question is....where in Europe can I get my hands on some Dowsil 795 to give it a go?

[GordMay]

Seneffe is the headquarters for Dow Corning's operations in Europe.
Parc Industriel - Zone C
Rue Jules Bordet
Seneffe, 7180 Belgium
PHONE: 32-6-488-80-00
➥ Www.dowcorning.de

Distributors Group Europe (DGE) B.V.
A. van Leeuwenhoekweg 38 C 12
2408 AN, Alphen aan den Rijn ,
ZUID-HOLLAND Netherlands
+31-172748200
➥ www.dge-europe.com
➥ https://dge-europe.com/brands/dowsil...one-solutions/

[CarlF]

I've been slowly switching over to Dow 795. Used it first for plexiglass but found it works just as well for general caulking of both fiberglass, stainless and aluminum above the waterline (don't know about wood).

Besides being absolutely color stable in sun it is much easier to apply neatly than 4000 or 4200. Tape the edges and use your finger to make a perfect bead. It doesn't get everywhere.

Comes in quite a few colors if you want to get fancy.

Warning 1 is that the tubes have an expiration date that you should take seriously.

Warning 2 is that it is best used with a bead that is at least 1/4" thick if you are caulking different materials with different coefficients of expansion (like stainless and fiberglass). The thick bead allows the different materials to move without ripping the bond loose. This is especially important with plexiglass. You have to support the plexiglass so that there's 1/4" of 795 between the surfaces.

[cooties]

I'm going to go with skipgundlach's recommendation to use TDS SIS-440. It's meant for teak, but seems appropriate for this application as well. Heat, UV, and chemical resistant, no primer needed, does come in white. Thanks all for comments.

[bbalan]

Hi All,
After using a variety of sealants over 30+ years on Migration (Butyl, 4000UV, 4200, 5200, various Sikas...), we've found that 4000UV has been incredibly inconsistent. We only use Mainesail's butyl on anything that is thru-bolted (awesome product), but when something is screwed in or we need an exposed bead to seal a joint, we've used 4000UV. It seems like it used to last longer but I could be wrong on that. Over the last 6 or so years, it tends to fail much sooner. Sometimes never curing completely and sometimes just turning to dust -- even when under a piece of hardware.


So very happy to have the alternatives suggested here. Thanks!
Bruce

[s/v Jedi]

Originally Posted by bbalan

Hi All,
After using a variety of sealants over 30+ years on Migration (Butyl, 4000UV, 4200, 5200, various Sikas...), we've found that 4000UV has been incredibly inconsistent. We only use Mainesail's butyl on anything that is thru-bolted (awesome product), but when something is screwed in or we need an exposed bead to seal a joint, we've used 4000UV. It seems like it used to last longer but I could be wrong on that. Over the last 6 or so years, it tends to fail much sooner. Sometimes never curing completely and sometimes just turning to dust -- even when under a piece of hardware.


So very happy to have the alternatives suggested here. Thanks!
Bruce

Yes, 4000UV cost me a day of my life removing it after a couple months. I never touched it again, but I have used it with great success in the past.

I got so upset that I actually epoxied that seam permanently. If I ever need to pull the engine, I’ll have to take the angle grinder or Fein Multimaster out to get the cockpit opened up for that.