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Uncle Bob · 20-10-2020, 18:00

Quote:

Originally Posted by Chotu

Ugh. You’re right!!!

418lbs (190kg) for 1/4” tempered glass

184lbs (83kg) for 1/4” Lexan.

If I’m going to fight Lexan again, I really need to ask a lot of questions about mounting it and sealing it.

Hi, have you had discussions with a good plastics supplier re product that is available and appropriate to your needs. As to fixing, consider a good structural glazing silicone, it is used to hold windows in place in highrise buildings and is supposedly good for 100 years. It has the ability to move 50% without breaking bond so it does need a thick bed.

Mr B · 20-10-2020, 18:02

Quote:

Originally Posted by Chotu

Ugh. You’re right!!!

418lbs (190kg) for 1/4” tempered glass

184lbs (83kg) for 1/4” Lexan.

If I’m going to fight Lexan again, I really need to ask a lot of questions about mounting it and sealing it.

Is Tempured glass the one that shatters into little bits if it get smashed, and leaves a big hole where the window used to be,

I have laminated glass in my windows in my home, I put my 3 ton tractor into it, Its still there 20 years later, It has a big crash spot in it, But its still there and water proof,
Its 2 sheets of thin glass with a plastic film between the sheets,
My windows are glued in with structural Silicone,
But you can get silicone sealant now thats adhesive as well, More adhesive, You cant pull it apart, Its incredible stuff,

Just some thing to think about,

Wish you well getting your boat finished,

Cheers, Brian,

Chotu · 20-10-2020, 18:20

Quote:

Originally Posted by Uncle Bob

Hi, have you had discussions with a good plastics supplier re product that is available and appropriate to your needs. As to fixing, consider a good structural glazing silicone, it is used to hold windows in place in highrise buildings and is supposedly good for 100 years. It has the ability to move 50% without breaking bond so it does need a thick bed.

The windows were attached with the thickest, most heavy duty 3M VHB tape they make (as suggested by 3m technical support). They also were prepped with 3m Primer 94.

Then, in addition to that, Dow 795 structural silicone adhesive was used.

Here was the result after a summer In Florida. I didn’t pull this window. It was already gone when I returned.

They all work loose due to the extreme thermal expansion in South Florida.

Chotu · 20-10-2020, 18:23

Tempered glass is what’s used on boats because it’s several times stronger than laminated glass on initial impact.

My thought was to put the ballistic 3m coating on the tempered glass. That holds it together even better than laminated.

However the weight as little wing pointed out.

I’m going to need to regroup with a new post.

Quote:

Originally Posted by Mr B

Is Tempured glass the one that shatters into little bits if it get smashed, and leaves a big hole where the window used to be,

I have laminated glass in my windows in my home, I put my 3 ton tractor into it, Its still there 20 years later, It has a big crash spot in it, But its still there and water proof,
Its 2 sheets of thin glass with a plastic film between the sheets,
My windows are glued in with structural Silicone,
But you can get silicone sealant now thats adhesive as well, More adhesive, You cant pull it apart, Its incredible stuff,

Just some thing to think about,

Wish you well getting your boat finished,

Cheers, Brian,

Matt Johnson · 20-10-2020, 18:25

3M VHB 4991 can be doubled up if used mostly as a spacer/sealer. Still bonds well and gives much more space for expansion.

-Matt

Chotu · 20-10-2020, 18:26

Needs in a glazing system:

1) visibility
2) tint/Uv blocking
3) longevity
4) weight
5) waterproof
6) modular design so a new piece can slide in if one breaks or goes bad.

These are not achievable in one single material.

Maybe I just need to get smoked Lexan and build aluminum tracks to hold it all in place, allowing it to move all around as it sees fit with the changes in temperature.

Chotu · 20-10-2020, 18:27

Quote:

Originally Posted by funjohnson

3M VHB 4991 can be doubled up if you need a thicker spacer. Still bonds well and gives much more space for expansion.

-Matt

Why didn’t 3m tech support tell me this?? Damn. If I knew, I would have done that for sure.

Matt Johnson · 20-10-2020, 18:34

Quote:

Originally Posted by Chotu

Why didn’t 3m tech support tell me this?? Damn. If I knew, I would have done that for sure.

I did edit my last post... it can be doubled if it's mostly being used as a spacer/sealer. The Dow 795 is the adhesive, but the VHB does a great job holding the panel at the correct spacing until the silicone cures.

Matt

fourlyons · 20-10-2020, 18:54

I would stay away from Lexan myself, it just doesn't hold up to the elements. I launched my boat 13 years ago. Lexan in all the hull and doghouse windows, it was toast within 6-7 years. The acrylic in the hard dodger still looks great, some scratches but totally serviceable. I steer from there so it has to be clear.

I replaced all the hull and doghouse windows, 16 of them, 5 different shapes, with 1/4" tempered. And three deck hatch glasses, with 1/2" tempered, two different shapes. All for about $800, mail-order from a company in Seattle, after I sent them plywood patterns, but they can cut from digital files.

I have never been able to get 5200 to reliably stick long term to acrylic or Lexan, I have had success with butyl tape, but you have to keep it from squeezing out.

Chotu · 20-10-2020, 19:04

Thanks, fourlyons.

That was my feeling too after seeing my Lexan turn to trash. But the weight.

This is one of the most difficult trade offs I’ve had to deal with on the boat.

Matt Johnson · 20-10-2020, 19:16

Did you use AR2 UV Polycarbonate - often called marine grade - or generic hardware store polycarbonate?

Matt

GRIT · 20-10-2020, 19:17

I used lexan on our last boat's dodger, and pilot house. I'm not a fan. It turns milky long before plexi starts to craze, and I'm pretty sure it has a higher rate of thermal expansion than does plexiglass. At least it seemed that way.

I checked with several cat manufacturers, and they all use plexi for their windows. I'd suggest you try plexi, it comes with a 20 year warranty against crazing, it's cheaper, and nearly as easy to shape as lexan. Cuts with a jigsaw, using a plexiglass blade, sands well, and is easier for silicone to stick to.

I used dow 795 too, though I'm not overly impressed. It's letting go in places.

Cheers.
Paul.

CarlF · 20-10-2020, 19:20

The trick to 795 is to have a thick glue line to allow for expansion. A thin layer will rip free quickly as the plexi expansion/contraction cycles.

The minimum 795 thickness is 1/4" but you can make it thicker to allow for more expansion. When placing a 2'x3' Plexiglas skylight I built a spacer of 1/4" wide by 3/8" high black foam tape to support the Plexiglass while the 795 next to it hardened.

That was 3 years ago and there's no sign of the 795 separating.

Here's a technical manual from Dow

https://www.dow.com/documents/en-us/...df?iframe=true

Also, be sure your Dow 795 is fresh. There's an expiration date on the tube. Don't use it after that date.

Uncle Bob · 20-10-2020, 19:37

Quote:

Originally Posted by GRIT

I used lexan on our last boat's dodger, and pilot house. I'm not a fan. It turns milky long before plexi starts to craze, and I'm pretty sure it has a higher rate of thermal expansion than does plexiglass. At least it seemed that way.

I checked with several cat manufacturers, and they all use plexi for their windows. I'd suggest you try plexi, it comes with a 20 year warranty against crazing, it's cheaper, and nearly as easy to shape as lexan. Cuts with a jigsaw, using a plexiglass blade, sands well, and is easier for silicone to stick to.

I used dow 795 too, though I'm not overly impressed. It's letting go in places.

Cheers.
Paul.

Hi, here in Aus the dow product pushed for structural glazing is 995, with the caveat that all surfaces must be scrupulously clean and the product must be used within its use by date. The minimum bed thickness is 5-6 mm.