Caulking

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Zeeuw

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Hello everyone,
I have a problem: I want to use Sikaflex 291 to caulk my hull under the waterline. But Sika told me that I never may use a one-component paint on Sikaflex. I have to use a two-component paint. But I always learned that you can't use two-component paints on a wooden hull. (the paint is not flexible enough) What's the solution for my problem?
 
Can't see any problem painting cured Sikaflex with oil based single pack paint, perhaps they mean you cannot apply Sikaflex to a recently painted single pack oil based substrate which is probably true as the adhesion will be only as good as the underlying paint, which when soft, will not be very good. Usually a Sikaflex primer is advised for oily timber to get good results, helps for high adhesion.

John Lilley
 
johnlilley said:
Can't see any problem painting cured Sikaflex with oil based single pack paint, perhaps they mean you cannot apply Sikaflex to a recently painted single pack oil based substrate which is probably true as the adhesion will be only as good as the underlying paint, which when soft, will not be very good. Usually a Sikaflex primer is advised for oily timber to get good results, helps for high adhesion.

John Lilley
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Sorry, you cannot successfully paint or varnish over Sika for at least a year, as Isocyanates continue to leach out and the paint will stay tacky.


Paying seams below the waterline rarely works in the long term unless done from new. It is almost impossible to decontaminate the seam to a level where the primer, and subsequentialy the sika, will stick.

If you hull is 'moving' so mush you think sika will cure it, then address your structural problems.

If your huul dries out easily, then paint well inside and out.

All cheaper than a box of Sika!
 
Sika is a bad idea for caulking under the waterline. If for some reason the bond to the wood fails and the caulking starts coming out then you could potentially run the risk of the caulking along the entire seam pulling out, which would sink you very quickly.

Red lead putty is one good option. It always worked before after all. Just remember to wash your hands afterwards. We however use a form of thick pine tar in our seams under water, which is easy to apply by just smearing it into any gaps and cracks. Paint also adheres to it well enough after it's started to dry on the surface. It's only available from Norway though as far as I know so obtaining it might be a problem.

As for painting over fresh Sika, I've found that if you paint over the newly cured sika with the sikaflex primer then single part paints will work just fine.
 
Caulking below waterline

Don't use Sika on wood with a high moisture content.

Speak to John at Trad boats in Suffolk. He's very knowledgable and extremely helpful. He helped me with a similar problem on my 60 year old motor sailer and will always make time to talk to you. If you don't get an answer when you phone, leave a message and he will come back to you. You can get hold of him on 01502 712311 or visit his website at www.tradboats.com

I have no connection to John except as a customer. I thoroughly recommend him.
 
Ok, I prefer red lead putty also, but then I have to wait till next year to caulk. The boat will be launched in april 2011. I like to finish the hull this spring. If not, I leave her unprotected another year.
 
Do you mean paying with Sika rather than caulking?

Cotton caulking driven into the seams stiffens the hull when she takes up. If you just use mastic, be it red lead or Sika, it will get squeezed out. You mustn't overdo the caulking though or you'll end up with split planks and fractured ribs.

FWIW I recommend conventional caulking payed with white or red lead.
 
No, first I will use cotton. But after that i'm intent to use sikaflex instead of red lead putty because of the time till launching.
Some say I can use 1c on Sikaflex, others say I can't (including Sika)
 
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