Which silicone for portlight glass?

[sailingdog]

Actually, part of the problem with brass in a salt-water marine environment, is that it will dezincify, leaving behind basically a porous copper sponge. It also has galvanic corrosion issues with Bronze, which is much more noble IIRC.

[Sapperwhite]

Thanks John.

[Faster]

We've had good results with plexiglass and Dow Corning 795 sealant, both for bolt/screw down portlights and those inside (aluminum) frames.

[GBurton]

Thanks John

Gary

[alanl]

Strongly advise NOT to use silicon and especially beware of the acetic version that has etch properties. Sikaflex and other polyurethanes are much more expensive but will do a better job without any of the problems of silicon. There are various grades, some mainly designed as sealants and others as bonding agents. Look at the www.SIKA.com website for further advice

Cheers

Alan
www.handymariner.com.au

[JohnRPollard]

Alan,

Thanks for the heads up. In my notes above, I mentioned that a non-acidic silicone was important because of the silicone bronze composition of the portlights in question. Also, I am aware that silicone is not the most UV-resistant bedding, but in the case of the Whitewater MArine bronze portlights, the bedding (whether it be silicone or whatever) is not exposed to sunlight due to the design of the portlights.

However, I do not by any means claim that silicone is the best solution for re-bedding the portlight lenses. I invite others to post recommendations here, remembering of course that there are a lot of variables in play, e.g. lens material (glass, acrylic, polycarbonate, etc), and portlight material (silicone bronze, stainless, aluminum, plastic, etc). So the best solution in one insatance may not recommend to another.

Also, apologies to all for the wordy post above. If I had some digitial photos it would have been much easier to explain, but that was pre-digicam for me.

[trantor12020]

Originally Posted by speciald

C&C used Sikaflex (?sp). DON"T use 5200. When I replaced the plastic windows,the yard used 5200 and the windows fell off in 3 weeks and they had to grind the 5200 off to re-replace the windows.

Sikaflex 295 UV ?

[alanl]

John

Yes it is a complex issue. I did some work with the Australian Sika company a few years ago and became convinced about the bonding properties but as you and others infer, there are various grades and that is why I suggested the website for further information.

The problems with silicone go beyond what have already been mentioned - one of the main issues is the inability to remove traces of it wherever it gets - and it will get everywhere, no matter how careful - this makes a nighmare for painting. Conversely, uncured polyurethane can be easily wiped off with a paper towel or rag soaked in turps and can be painted over.

The second problem is longevity. Silocon seems to work fine, but over time the bond lets go. That does not happen with polyurethane, especially if the substrate is treated with the appropriate primer. Homeowners have found this out the hard way in shower stalls and other areas wher the plumber has used the cheap method

You have now exhausted my knowledge of the subject, but so far, it has worked as described

Cheers

Alan [/i]