Sealant for Lexan/fiberglas/teak

jrd22 · #1 (**permalink**) 09-30-2010

I'm re-sealing the pilothouse windows because the PO used the wrong stuff and they are leaking. The windows are 1/2" thick Lexan or Plexi (I was told they were Lexan but don't know how to tell for sure) and they fit into cutouts in the fiberglas side walls. They are held in by SS rings and on the inside are butted up against teak (the screws that hold the SS ring on go into the teak). Boatlife Seal will adhere to the Lexan/Plexi and the SS and the fiberglas but I'm not sure if it will make a watertight bond to the teak. Are there other products that might work better than BL Seal? I DON'T want to do this again. Thanks.

Faster · #2 (**permalink**) 09-30-2010

John.. We've used the DC 795 with both screw-on and in-frame applications with good success. Just now I've had to remove a couple of lenses that cracked this year, and happy to say that these seals never leaked, and a very nice, soft "rubber" gasket-like layer was still easy to get off so I can redo them.

As far as the seal against the teak, won't the primary seal be between the lenses and the outer frame?.. still I think this stuff would work for you.

sailingdog · #3 (**permalink**) 09-30-2010

Boatlife lifeseal is a polysulfide sealant that should bond to teak fairly well. It is fairly compatible with Polycarbonate or Acrylic and should bond to the stainless steel fairly well too.

The question I have is how much expansion room you need for the ports. How big are the ports?

Dow Corning 795 is a sealant that is specifically designed for bedding glazing materials, and would be my choice over boatlife lifeseal.

jrd22 · #4 (**permalink**) 09-30-2010

Fast- you're right, the primary seal should be between the plastic and the fg, if that is good the seal against the teak shouldn't matter too much. I think the PO used 3M4200 or possibly 4000 to seal the plastic to the fg (which didn't work) and possibly BL Seal on the inside of the plastic up against the teak ( there is a clear sealant next to the teak and a white sealant everywhere else that is a very strong adhesive - peeled some gelcoat off with the SS ring). Where do you get the DC stuff?

Thanks SD.

Faster · #5 (**permalink**) 09-30-2010

Quote:

Originally Posted by jrd22

Where do you get the DC stuff?

I get DC 795 at a local wholesaler, Crossroads C&I nearby in Burnaby... bought 2 tubes today for $20 CDN. If you can't track it down I could pick some up and put it in the mail. Apparently you'll get 25 lineal feet of a 1/4 inch bead out of each 300ml tube (as a guide to how many you'll need)

Here's a link to a distributor search:
Find a Distributor

I found:

WASHINGTON LAKEWOOD
ATLAS SUPPLY INC
4425 100 ST SW BLDG 25 SUITE A
LAKEWOOD WASHINGTON 98499

WASHINGTON SEATTLE
ATLAS SUPPLY INC

TEL: +1 206 623 4697

611 SOUTH CHARLESTOWN STREET
SEATTLE WASHINGTON 98108

jrd22 · #6 (**permalink**) 09-30-2010

Thanks Ron, I'll give them a call. Do you think using butyl against the teak and the 795 to make the seal between the SS/Lexan/fiberglas would make sense? It sure would make the clean up on the inside around the teak easy.

SD- the windows are approx. 16"X32" ea.

Faster · #7 (**permalink**) 09-30-2010

Quote:

Originally Posted by jrd22

... Do you think using butyl against the teak and the 795 to make the seal between the SS/Lexan/fiberglas would make sense? It sure would make the clean up on the inside around the teak easy.
.

Should work and you're right about the cleanup.... another trick I use is to dry-fit the panes and mark the inside perimeter. With new acrylic I leave the backing on except where it mates to the sides, with old ones you could mask it and the inside of the inner frame leaving just enough space to form a fillet of any sealant that squishes out there. But using butyl inside might work.... however.... it occurs to me that a tight inner seal might hide an outer leak until too much damage was done by trapped moisture????

sailingdog · #8 (**permalink**) 09-30-2010

Sounds like a good plan. But Faster makes a good point about hiding a leak. However, if there is no exposed core, then that is less of an issue.

A 32" piece of plexiglass/acrylic will expand about .013" per 10˚ F or so. Given the temperature range in your neck of the woods, and making allowances for heating due to sunlight during the day, you're probably looking at a bit over an 100˚ temperature range, or a bit more... so say ±.125" overall for each port—assuming that you're installing the ports at a reasonable temperature—so having 0.0625" on each side for expansion should probably cover you.

Quote:

Originally Posted by jrd22

Thanks Ron, I'll give them a call. Do you think using butyl against the teak and the 795 to make the seal between the SS/Lexan/fiberglas would make sense? It sure would make the clean up on the inside around the teak easy.

SD- the windows are approx. 16"X32" ea.

Faster · #9 (**permalink**) 09-30-2010

Do the screws go through the ports, or just through the frames? If they go through the ports too they should be drilled rather seriously oversized to allow for SD's expansion quotient..... but if they've been fine so far you're probably OK..

jrd22 · #10 (**permalink**) 09-30-2010

Thanks SD, the screws do not go through the plastic and there is about 1/16" to 1/8" between the windows and fg so I should be OK. I'm going to call the outfit Faster found in the morning to see if they stock the 795.
Ron- thanks for the tip about the tape on the inside, that should make cleanup a lot easier.