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Old 19-02-2022, 18:28   #1
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Resealing perspex hatches - help needed

Hi all,

I am currently trying to re seal the Perspex hatches. The frame is alloy. I have tried SIKALFLEX 295 UV but it doesn't seem to be adhering to the Perspex properly and some leaks still occur.

What is the best surface prep? I have removed all old sealant, sanded it and wiped it down with alcohol. (I do not have access to buying the proper Sikaflex primer where I am located and it cannot get delivered).

Any tips?

Thank you.
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Old 21-02-2022, 12:22   #2
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Re: Resealing perspex hatches - help needed

I have similar hatches: aluminum frame and acrylic lenses. Nothing worked until I started using Dow Corning 795. It lasts until the plastic itself needs changing.

Gotchas:
1. I’ve used nothing but black 795. Can’t speak to other colors.
2. Don’t buy more 795 than you need. When it’s past it expiration date, it might take months to set up.
3. Clean all the old adhesive away on the frame. Clean with pure alcohol before you sand. Then sand with 80-100 sandpaper and clean again, until the rag shows no dirt.
4. Make sure you have enough free space for at least 1/8” bead of caulk on all surfaces. I separate the plastic from the frame with pieces of 1/8” wooden dowel until the 795 is set.
5. Sand every place on the plastic where there will be caulk. Especially around the edges. Clean with alcohol.
6. Mask surfaces where required.
7. Put on enough caulk so that it will squeeze out of all the seams.
8. Put the lense into the frame and leave it alone until the caulk sets completely, then trim the excess with a razor blade.

That’s worked for 5 hatches up to 24x24 in full time tropical conditions.
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Old 22-02-2022, 04:30   #3
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Re: Resealing perspex hatches - help needed

The other approach that gets good recommendations on the forum is to use butyl tape, following very closely to bycrick's clear step-by-step.
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Old 22-02-2022, 04:52   #4
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Re: Resealing perspex hatches - help needed

Quote:
Originally Posted by fraser123 View Post
Hi all,

I am currently trying to re seal the Perspex hatches. The frame is alloy. I have tried SIKALFLEX 295 UV but it doesn't seem to be adhering to the Perspex properly and some leaks still occur.

What is the best surface prep? I have removed all old sealant, sanded it and wiped it down with alcohol. (I do not have access to buying the proper Sikaflex primer where I am located and it cannot get delivered).

Any tips?

Thank you.

The old sealant was probably silicone. Try DeBond. Much better than alcohol at removing the silicone residue. Lack of primer will reduce UV durability (the UV attacks the bond area on glazing), but that is not the adhesion problem, at least not for 6 month or so.


If it loosing it's grip after 6 months, it is the lack of primer. Sorry, no cure for that. Use DOW 795 or get the right primer.
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Old 22-02-2022, 09:36   #5
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Re: Resealing perspex hatches - help needed

Butyl tape is a good sealant, but a lousy adhesive. If you use it, the plastic must be mechanically secured. Drilling holes in acrylic is not nearly as simple as one would think and produces its own set of problems. Some people have suggested VHB tape in combination with 795, but I’ve not tried it.
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