Join Date: Apr 2003
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Rebedding leaking lexan ports
We just went through this exercise on 9 hatches and 11 portlights in our boat. (And two new hatches for a total of 22 openings). Though we were bedding into a metal frame. Experts recommended either 4200 or 101 for metal to fiberglass. They recommended structural silicone for lexan to fiberglass or to metal frame. This is not the stuff you get in the marine shops or home depot. The recommendation was for a GE structural silicone, which is the stuff they use to fasten glass into high-rises. Check the GE web site to get the product number. Any glass shop can order it, and you can probably get it from the major hatch manufacturers--Bowmar, etc. Bowmar definitely will sell it to you, though the price is somewhat high. No one recommended 5200, since it sticks to fiberglass so well that to remove it, you often damage the fiberglass. We have had mixed results with "Debond" to break the 5200 seal. Boatlife "Release" is excellent in cleaning up old silicon caulk, by the way. If there is old caulk, ALL of it must be removed before recaulking.
Also, the previous recommendation for a washer as a spacer to allow a 1/8" bead of caulk to form is vital. Otherwise, you may squeeze out all the caulk and it won''t hold. I have also successfully used small pieces of wooden popsicle stick or stir stick, which are 1/8" thick, to cut irregular pieces and epoxy them in place to form spacers, without interrupting the silicone seal. Either way, the spacers are essential.
This stuff is messy, by the way, so have lots of solvent nearby--like acetone--and test on an inconspicuous place on the lens to make sure it doesn''t hurt it (acetone was OK with all of ours).
By the way, not one of the 22 openings in our boat leaked.........