Windows.....

Looking for opinions as to the best chalking/bedding compound to use on installing new glass. These are the forward quarter windows on our trawlers salon. The laminated glass is sandwiched between inner and outer teak frames.

Ever plan on taking them out again...?

I have just repainted my aluminum window frames and re-applied caulking to the outside of the windows. The caulk between the outside of the frame and the glass had "shrunk" away. I refilled the "groove" in front of the glass with Sikaflex 291 Black. Kind of messy to apply, especially as it turned out the best tool is the finger. Used lots of disposable gloves (not the real cheap ones!!). You do need to mask off the wood frames-- this stuff is next to impossible to remove, except from the glass. For your application, you might want to look up the Sikaflex 295UV. Also Sika has a pretty good web site and tech service email.
Chris

Take them out? Not unless the get broken or scratched. Had not planned on it this time but the wife got a little carried away with the heat gun, now she knows.

We have rebuilt most of the 21 windows on our GB. For bedding glass we use white Sikaflex. For bedding new window track we use the Sikaflex as well. For bedding the wood window frames to the fiberglass cabin sides and sills we use whilte Dolfinite.

Some of the shipwrights on the GB owners forum recommend Dolfinite for bedding glass as well but we have stayed with the Sikaflex recommendation.

Dolfinite has no adhesive properties-- it is only a bedding compound. As such, if a window frame ever has to be removed it will be very easy to do so. The downside of Dolfinite is that it dries out over time where it is exposed to air. For that reason we follow the recommendation to run a faired bead of white Polyseamseal around the joint between the window frame and the cabin side. This prevents air from getting at the edge of the Dolfinite bedding.

When we first started rebuilding windows we used 3M 4200 to bed the glass and track. But after doing a couple of windows we switched to the Sikaflex.

There are other sealants that will probably work as well and most shipwirghts have their favorites. So it's probalby easier to tell you what not to use than what to use. Don't use 3M 5200 on anything you might want to remove again. If you do need to remove something bedded/adhered with 5200, a heat gun is the solution.

And never, ever, EVER use silicone. Silicone should be outlawed for marine use except perhaps to seal the joints of things like raw water pump covers on the engine. Other than that it has no place on a boat.

3M 5200 if you do not wnat to take it appart again and 3M 4200 if you wnat to be able to take it apart. Most of the time I use 5200 quick dry.

The Sika 291 is great for what your doing.3M 4200 is my other choice. Both will yellow in a few weeks in sunlight.
If it's exposed to sunlight use the Sika 295UV or 3M 4000UV as they are more tolerant to the UV.

Most glass shop will tell you they use silicone for all their glass work. I have used Dow Corning 795 for years to bed glass and plexi. This is the material used to bed the glass in skyscrapers. We have never had a leak with this.
http://trawler-beach-house.blogspot.com/2010/05/window-frame-rebuild.html . Chuck

The issue with silcone is not that it doesn't work as a sealant but what the residue does on the boat. It is almost impossible to clean off even if you can't see it and even the tiniest bit of silcone residue will prevent paint or other finishes from sticking to wood, fiberglass, you name it.

It is also a bitch to remove a frame or something sealed down with silicone in our experience. Sikaflex, while as good or better an adhesive/sealant as silicone, for whatever reason makes a bond that we have found to be far easier to separate. Which makes it far less likely that something like a wood window frame will be damaged in the process. Of course, Dolfinite makes removal of a frame even easier.

But the real problem with silicone is that once it gets on something, particularly somehting porous like gel coat or paint or whatever, it is a MAJOR effort to get rid of it. Far, far easier to avoid the potential problem altogether and simply not use it. Particularly since there are plenty of adhesive sealants on the market that are as effective or better than silicone but without the non-stick residue problem.

AH! the debates go on... which anchors, which sealant.. seems we'll always have an active forum as long as men of various backgrounds and experience continue to differ. My only personal experience with this window issue was replacing a cracked plexiglass panel in an aluminum-frame Bomar hatch on a sailboat. Horizontal placement, so leak prevention was paramount. The instructions said clean everything out, bed it in silicone (mask off the glass, of course) and when it was over, it was watertight. At least for fixed frames like that, silicone is probably OK..

In bedding a windowframe in a deckhouse, with attendant expansion, contraction maybe there are better alternatives. Moral: there are no absolute "right" answers.

I hate silicone too for the reasons stated by Marin. Plus, silicone seems to have an innate ability to attract black, unsightly mold. I spent a couple of weeks last year and a couple more this year removing old, ragged, moldy silicone caulking beads from around all of our window frames, repainting the frames and re-beading with 3M 4000. Next projects: removing the @*#@ blasted, unsightly beads of silicone from around the chain locker and flybridge dash doors, the cockpit door and the caprail to bulwark joints the length of the boat on both sides. Who put this stuff on our boat anyway? The builder's yard? A PO? Why?

The manufacturer's window replacement instruction sheet for a GB, at least an older GB like ours, calls for silicone as the sealant. However...... this was back when there were not as many choices of sealants as there are today. Silicone was probably regarded as a "miracle" product back then.

Today there is no reason to use it since there are a bunch of equally good or better products on the market. And the residue issue--- particularly for people with boats that are painted or there is a chance the silcone could get on brightwork--- is a huge pain in the butt when it's time to repaint or refinish.

Plus all the other issues Dave mentions above.

Silicone was a good choice if not the only choice "back in the day." But it's not anymore.

I have been using Lexel and like it a lot. Paintable, comes in white or clear. Stays clear. Sticks to everything dry or wet. Even sticks to teak.

Sikaflex. Maintains a seal on the glass but easy to remove by cutting if you need.
Previous boat, we re-bedded the windows twice because we did not realize that nothing sticks to old silicone -- had to sand the wood and Scotch-brite the glass.

All my boat windows leak - they're 40 years old. I'm gonna pull them out and rebed with this stuff.
Need Butyl Tape ?? Photo Gallery by Compass Marine at pbase.com
I'll blog the process/results.

Recommend the black Sikaflex. The white turns "dirty" within weeks. Hopefully the black holds up better. I just spent a lot of time putting it in and do not want to take it out again anytime soon!!
Chris

jeffnick said:

Need Butyl Tape ?? Photo Gallery by Compass Marine at pbase.com
I'll blog the process/results.

Click to expand...

I really like the Butyl tape for bedding everything above the waterline. Deck hardware too, just chamfer the holes a little and your golden.

When I reglazed the windows on our GulfStar, I used Sika's 295UV. It was a little messy to work with....but that is part of the fun. Its good stuff...and it is UV proof.