Need Sealant suggestion

[Onajourney]

After much research and planning I chose a trimlock seal for my stargazer window. Well, I need to go to plan B. After adding the aluminum to the plywood, it's too wide for the trimlok. I knew this was potentially a problem and I could sand the ply down. Really not a good solution, I returned the trimlok and now just want to mount the Polycarbonate down flat to the roof. I am sure someone has done this but I could not find anyone here.

Question is, what would be the best method of sealing? Poly chalk, butyl tape? Seems like there are countless chalks and methods. I have seen some sailors use just poly sealant for frameless windows but that seems like a mess. I am probably overthinking this one too.

[tony.latham]

I don't think you are overthinking this since they do like to leak. You might take a look and see how John tackled this issue: https://www.tnttt.com/viewtopic.php?f=50&t=73779

Tony

[Capebuild]

I saw your post. I had cut the aluminum back from the ply opening so the thickness for the seal was just the thickness of the ply, NOT both the ply and the aluminum. If you look at my build journal somewhere there it should explain what I did.

[MickinOz]

If I was doing it, and it is under consideration for the next build, I would cut my hole, cut my Lexan, drill and bolt down. Once all holes are drilled. I'd lift it all, run in a bead of black silicone and reinstall, with the appropriate solvents and scrapers on hand to clean off squeeze-out. With regard to squeeze-out I find carefully applied electrical tape is great. If you run it right, you can peel it off as soon as you've installed the silicone and instant clean up ensues. as long as you have the will-power to resist the urge to fiddle before the silicone sets.
So basically, form a gasket, in-situ.
Using lexan or other plastic bolted directly to the body, I might have to take into consideration expansion.
I haven't completely though this through yet, but as a first pass I'm thinking the holes should be a little bigger than the screws, and the silicone gasket should be a few mm thick to allow things to move.

[Philip]

Another small suggestion. If you are using plywood in the roof. Drill the holes oversize. Then fill those holes with epoxy. Let it dry. Then redrill after epoxy sets for the correct size screws. If those screws ever leak. The epoxy plug keeps the ply from becoming a sponge.

[Onajourney]

If I was doing it, and it is under consideration for the next build, I would cut my hole, cut my Lexan, drill and bolt down. Once all holes are drilled. I'd lift it all, run in a bead of black silicone and reinstall, with the appropriate solvents and scrapers on hand to clean off squeeze-out. With regard to squeeze-out I find carefully applied electrical tape is great. If you run it right, you can peel it off as soon as you've installed the silicone and instant clean up ensues. as long as you have the will-power to resist the urge to fiddle before the silicone sets.
So basically, form a gasket, in-situ.
Using lexan or other plastic bolted directly to the body, I might have to take into consideration expansion.
I haven't completely though this through yet, but as a first pass I'm thinking the holes should be a little bigger than the screws, and the silicone gasket should be a few mm thick to allow things to move.

I am going to go this route. I am going to use Butyl Rubber Sealant in a chalk tube.

[jimrab]

Another small suggestion. If you are using plywood in the roof. Drill the holes oversize. Then fill those holes with epoxy. Let it dry. Then redrill after epoxy sets for the correct size screws. If those screws ever leak. The epoxy plug keeps the ply from becoming a sponge.

Good suggestion, I totally agree with you, the epoxy plug really keeps the ply from becoming a sponge.

[John61CT]

Caulk

The sailing forums have the experts, have to withstand heavy pounding seas, full submersion life and death mission critical.

even high end yachts DIYers do it like this, they come out looking very clean and professional

Butyl rubber is old school, great for the inner seal under the glass but spacer needed so bolting firm does not squeeze it all out. Then a purpose designed outer sealant for the trim facing edge.

But most just use the latter 3M and Sika make some incredible modern products that are strong adhesive (but you do not want "fully permanent") but also great sealant, firms up but retains eternal flexibility

CruisersForum is my go to

[Onajourney]

Caulk

The sailing forums have the experts, have to withstand heavy pounding seas, full submersion life and death mission critical.

even high end yachts DIYers do it like this, they come out looking very clean and professional

Butyl rubber is old school, great for the inner seal under the glass but spacer needed so bolting firm does not squeeze it all out. Then a purpose designed outer sealant for the trim facing edge.

But most just use the latter 3M and Sika make some incredible modern products that are strong adhesive (but you do not want "fully permanent") but also great sealant, firms up but retains eternal flexibility

CruisersForum is my go to

Thanks John.

[DJ Davis]

I was told about something called Dicor. I used it figuratively everywhere there was something to seal or a hole made. So far, so good.

[Graniterich]

I swear by lexel!

Sent from my KFTRWI using Tapatalk

[KCStudly]

For a professional look, I would consider painting a border around the inside perimeter of the "glass" to show an even width border. That way the inevitable messy look of the sealant squeeze out won't show through to the outside. Probably need to mask and scuff the area to be painted in order to promote good adhesion, without scuffing up the field. Black paint should look clossy from the unpainted side, just like in modern automotive glass applications.



But what I would more likely consider would be fashioning a trim frame out of aluminum or stainless steel to clamp the plastic to the wood. Otherwise the screw heads can cause uneven point loads on the plastic (point loads) causing it to crack much more easily. It may be "impact resistant", but it's still breakable. (Much experience with this stuff in high speed packaging machines... frequent failure mode.) If the installation is super flat and the trim frame would tend to cause water to pool, you could make the low side a separate strip and leave gaps (instead of butting tightly) so that water can drain in a couple of places. IMO, rubber washers alone won't provide enough clamping force between screws for a thin panel to pull down evenly.

Another good practice is to apply the sealant, bed and screw the "glass" down gently... just enough to get the sealant to spread some, but not so much that it runs down hard and squeeze sit all out. wait for it to cure, and then snug the screws up finally. That way you form a cured gasket than has some spring back.

[Onajourney]

Thank you KC for the detailed suggestions. I like the painting idea but I am going with white butyl tape on a white aluminum roof so I think it will look ok. I too thought about a aluminum trim ring but after I mocked a small piece up, I really don't think I will get uneven point loads with the 1/4" polycarbonate and 3" spacing. It's pretty rigid stuff that I will definitely not over tighten. I am planning on running a bead od white chalk around the outside for good measure. I definitely don't want a messy look like a see way to often even on pro builds. The main reason I feel confident is I had a hard time prying apart the mock up. The butyl tape clearly had 100% contact with excellent adhesion. I think Twistedlines did something similar. Perhaps he can chime in.

[KCStudly]

Test results trump speculative design concepts every time.

Build on.

[tony.latham]

...but I am going with white butyl tape...

I think there are much better sealants, but here's the deal: If the butyl doesn't work, it's easy to clean with paint thinner followed by alcohol and you can use something else such as a polyurethane sealant.



Just make dang sure to upgrade this thread in a year or two and tell us how it's performing.

Tony