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Old 06-02-2020, 08:32 PM   #1
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Window caulking question

Hello all,

I have glass front windows on my pilot house. The caulking has worn away and I need to replace it. What do you recommend?

I will caulk it where the glass meets the gelcoat. Thanks in advance!
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Old 06-02-2020, 08:50 PM   #2
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Greetings,
My ONLY recommendation: Do NOT use silicone sealant!
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Old 06-02-2020, 10:33 PM   #3
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I used Sika 295UV but it was on the plexiglass windscreen on the flybridge a couple of years ago. So far it is holding up very well without any problems. I also would not use silicone. Someday you will have to do it again.
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Old 06-02-2020, 10:39 PM   #4
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Sikaflex 291. I replaced a broken front wheelhouse window last year. The original window was sealed with a 1980 sealer that was still in very good condition. It felt, looked and sealed the same as the Sika 291. After a year, you can't tell which window I replaced.
NEVER allow Silicone aboard.
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Old 06-02-2020, 10:42 PM   #5
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Quote:
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Sikaflex 291. I replaced a broken front wheelhouse window last year. The original window was sealed with a 1980 sealer that was still in very good condition. It felt, looked and sealed the same as the Sika 291. After a year, you can't tell which window I replaced.
NEVER allow Silicone aboard.
291 LOT gives you more time to mess with it. One advice, clean the excess or any mess using WD40 degreaser, works like charm and clean it very nicely.

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Old 06-03-2020, 12:46 AM   #6
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Roof & Gutter versions of silicone will often take paint. But others will not.
I have sealed rubber/glass successfully with silicone sealant. Twice. 2 boats I bought, incl the current one, had leaks where the glass surround gasket had shrunk creating one or more gaps, and the POs could not work out why there was a leak
For ease of use, and use of remaining product, without the need to freeze, silicones have their uses. But not where gelcoat or paint abut sealant.
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Old 06-03-2020, 07:27 AM   #7
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I used Sika (291 I think) 14 years ago on my front windows and they are still watertight.
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Old 06-03-2020, 08:20 AM   #8
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I used to use 3M products but since I have gone to Sika, it just seems to work better than the 3M. No actual testing just a gut feeling.
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Old 06-03-2020, 08:53 AM   #9
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I appreciate all of the responses. I have researched Sikaflex 291 and it seems it is listed as an "Adhesive" rather than a sealer. I want to confirm that this is the appropriate caulk for windows. I certainly like that it's going to last a while, but I have concerns in the event it needs to be redone.

Thanks again for all of your responses.
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Old 06-03-2020, 10:20 AM   #10
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Quote:
Originally Posted by Freespool View Post
I appreciate all of the responses. I have researched Sikaflex 291 and it seems it is listed as an "Adhesive" rather than a sealer. I want to confirm that this is the appropriate caulk for windows. I certainly like that it's going to last a while, but I have concerns in the event it needs to be redone.

Thanks again for all of your responses.
I will expand on my post #4. Sika 291 may be called an adhesive, but in this application an adhesive, if used properly, will do the job of caulking, very well. If it ever needs to be redone, which is exactly what I had to do when my front wheelhouse window cracked and needed to be taken out and replaced, the 39 yr old adhesive holding it in had to be made to release the old glass. A sharp knife was effective to cut through the adhesive, a sharp scraper was effective to remove it where it needed removal, once the glass was removed.

As for Silicone, I found silicone in several places when this boat was new to me, at age 14 yrs. It would release itself from whatever surface it had been used on, but the areas released were difficult to locate, as it would continue to adhere to itself and disguise its lack of adhesion to the very places it was applied. Water intrusion, that it was used to fight, was the direct result of its use. It will NEVER be allowed on my boat, nor on anything that spends any time outdoors.
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Old 06-03-2020, 11:36 AM   #11
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Lots of products can work, but mostly it’s not about the product. You talk about “caulking”, a verb that usually means smooging product on the outside of two surfaces and pretending that the adhesion of the material alone will magically seal the imperfect surfaces along their entire surface area in the absence of a mechanical clamping force.

Windows are often challenging and sometimes are even designed to be “sealed” using a product applied as caulk. However, On most boat windows, the sealing surfaces are actually captured between two surfaces. That mechanical capturing forcing the material between two surfaces means the product does not have to rely on its adhesive properties alone and keeps the product in place mitigating movement. You need to inspect how your windows go together and hopefully find this area where the seal is mechanically captured between surfaces. That is where you need to remove and reinstall with new product. In which case we call this sealant, not caulk. Only caulk if you have absolutely no other alternative.
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Old 06-03-2020, 11:39 AM   #12
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Has anybody used Sika 295UV for this application ?
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Old 06-03-2020, 04:40 PM   #13
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I truly hate 100% silicone for the fact that (a) it is /never/ paintable, (b) its residue is /never/ paintable, (c) sanding silcone residue often just drives it more stubbornly into the surface vs removing it, and (d) even silicone doesn't want to stick to silicone residue if something needs to be redone.

Having said that, I no use it on any window, hatch, or port that I expect to be problematic. Quite simply, it /never/ fails. It seems that even 30 years later it is just like new. It seems things can expand a bit, contract a bit, buckle or shift a bit, and it has the flexibility to can accommodate it without losing adhesion or seal or integrity, even decades later.

So, I 100% agree with the warnings everyone here is giving. I'll just say that there are exceptions to every rule. I think 100% silicone has its rare place, even on a boat.
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Old 06-03-2020, 05:05 PM   #14
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Has anybody used Sika 295UV for this application ?
See post #3.
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Old 06-03-2020, 05:07 PM   #15
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I truly hate 100% silicone for the fact that (a) it is /never/ paintable, (b) its residue is /never/ paintable, (c) sanding silcone residue often just drives it more stubbornly into the surface vs removing it, and (d) even silicone doesn't want to stick to silicone residue if something needs to be redone.

Having said that, I no use it on any window, hatch, or port that I expect to be problematic. Quite simply, it /never/ fails. It seems that even 30 years later it is just like new. It seems things can expand a bit, contract a bit, buckle or shift a bit, and it has the flexibility to can accommodate it without losing adhesion or seal or integrity, even decades later.

So, I 100% agree with the warnings everyone here is giving. I'll just say that there are exceptions to every rule. I think 100% silicone has its rare place, even on a boat.
Well I have seen silicone come “unstuck” in places. Then the problem is getting the replacement caulk to stick where the silicone was. And you are correct that it is almost impossible to get it all off.
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Old 06-04-2020, 08:35 AM   #16
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Before using any caulk or sealant the surface needs to be cleaned and degreased. I use alcohol to wipe down the glass and the frame after removing the old sealant and masking with tape. I then use a gloved finger and a scribe or dental pick to force sealant under any gasket, followed by smoothing and shaping the excess and removing the tape before the sealant is cured. Be sure to allow the sealant to overlap the window frame by 1/32” to help ensure a good bond.

I learned this technique during a 40 hour class in sealing while at McDonnell-Douglas and it has served me well.
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