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jhoover3468 05-22-2003 11:01 AM

Rebedding leaking lexan ports
I have a 83 Jouet sailboat with lexan ports (leaking) set into the fiberglass. What is the best way to rebed these ports, (they are long and narrow)?

fourknots 05-23-2003 03:59 AM

Rebedding leaking lexan ports
From recent experience, I can tell you that you should use only silicone. Polysulphide sealants will eventually cause crazing along the edges and though the poly/silicone stuff won''t, you can''t get it off of Lexan without damaging it.

Use lots of sealant and don''t tighten down all the way until it has set - gives you a good gasket seal

jhoover3468 05-23-2003 11:29 AM

Rebedding leaking lexan ports
Fourknots, Thanks for the input. JH

Koene 05-25-2003 03:45 PM

Rebedding leaking lexan ports
A long time ago I used to own a catalina 30. Up front in the V berth they have a small sky light which was leaking. I tried many different methods with final result a leaking sky-light. One day I decided to use 3 m 5200. Never had a problem again. 3 m 5200 did an excellent job attaching to lexan and the gelcoat arround it. I would use 3 m 5200 if i were in your shoes.


Silmaril 05-26-2003 05:15 AM

Rebedding leaking lexan ports
Never is a pretty long time, and I always am hesitant using 5200 where you may for some reason want to remove the portlight.

I would use 4200, a strong adhesive, but not the "permanant" bond of 5200.

One thing you will want to do, after making sure ALL the old bedding compound is removed, is use small washers, spaced about 1 every 10" or so around the perimiter of the bedding area. They should be small enough to not reveal themselves when the portlight is in place, but not so small that they don''t do their job...which is to hold the light away from the cabin surface just enough to keep a nice bead of bedding compound to remain. You see, if you don''t have some spacers in between the light and the hull, when you push the light into place, you will squeeze most of the bedding compound out of the critical area between the light and the hull. And then if you used 5200 and no spacers, you would have "permanant" leaks!

tsenator 05-27-2003 12:15 PM

Rebedding leaking lexan ports
5200 would probably would 4200. Which is basically the same thing with a bit less adhesion.

One note (of caution?) is that 4200/5200 - polyurethanes are not really recommended for Lexan. Neither are Polysulfides (i.e. Life Caulk).

(here is a chart for compatabilities --

Personally I am a big fan of LIFE-SEAL which has the flexibility properties of a silicon but the adhesion of a polysulfide and has worked great for me in the past.
Its rated VeryGood for use on Lexan by Westmarine

mlc101 06-02-2003 12:43 PM

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).

Peace. M.

By the way, not one of the 22 openings in our boat leaked.........

musicmkr 06-24-2003 01:12 PM

Rebedding leaking lexan ports
You want to use Dow Corning 795 (NOT 791) structural sealant. I work for a glazing company and we use the stuff for absolutely everything including lexan (lexan is incorperated in bullet proof glass). It will easily hold a 400# piece of glass for over 20 years, so a porthole is not a problem. (You do need at least 1/8" of silicone between surfaces to function properly)

namaste04 07-10-2003 04:39 AM

Rebedding leaking lexan ports
I just called Bomar about this. (Ours are aluminum with Lexan). They recommended GE Ultraglaze (structural silicone). I mentioned the washer trick and she said, "We don''t do that."

Hope this helps.

Stacey (our boat refit)

mcain 07-10-2003 10:19 AM

Rebedding leaking lexan ports
Per the previous post from namaste04, this GE Ultraglaze is great stuff (in black). Bowmar will also sell you the GE Ultraglaze directly, however the cost is about 2-3 times what you can get it from a glazier, and Bowmar is slow as mollasses north of the Mason-Dixon line. But it is great stuff.
Bowmar said not to do the washer, because their method is entirely different (we just re-bedded the lenses of all of our Bowmar hatches, and bedded the hatches themselves into the boat, with advice and guidance from Bowmar. we also put in 11 new portlights). Bowmar coats the aluminum hatch frames with the sealer. Then they "float" the lexan into the sealer, making sure that they do NOT squeeze all of it out--leaving perhaps 1/8" or so of caulk between the aluminum and the lexan. This is an excellent seal and works well. We did this same process in resealing the lexan in our hatches.
The time to use the washer or some spacer is when you are using bolts to tighten down a hatch or portlight. For instance, most portlights have an outter ring and an inner ring, with bolts that join and squeeze them together. If you squeeze all the caulk out (which can easily happen), the seal can easily leak.
In practice, it is easier done than said. Once you do it, you''ll know how.
I do still prefer 3M 101 for metal to fiberglass seals, and the structural silicone for lexan to fiberglass or metal seals.

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