Installing Lexan Windows

[fraser36]

I am building a blue water cruiser and just joined SailNet. Wished I had found this site 2 years ago.

I am installing Lexan windows into recesses I glassed into the cabin top.

Do I have to use fasteners or can I "glue" them in with 3M 4200?

With either method, how do I protect the sealant from UV light? Paint 2" around perimeter?

If I use fasteners, how close should they be spaced?

[SEMIJim]

Coincidentally, this was posted just a week ago or so: Surface-mounted ports. Perhaps it'll be of some use to you.

Good luck,
Jim

[danjarch]

I would recomend that you use fastners with a resonable caulking. Space your fasteners about 1 inch apart. I recomend this because, if the lenses ever get scratched or broken they will be easier to replace. I've seen alot of older boats with scratched up windows, it looks bad, but so many are over glued into place that no one is willing to replace them.

[sailingdog]

fraser36-

If you're building a bluewater cruiser, you will want to use both a good sealant, like 3m 4200 and mechanical fasteners. The holes on the lexan itself should be a bit oversized, compared to the bolts or screws you use, since it will expand and contract at different rates, compared with the hull beneath. For the same reason, the Lexan probably shouldn't be cut to the exact size of the recess in question, but have a bead of sealant around the outside edge.

BTW, IMHO, an inch apart between fasteners is far to close together in terms of spacing. I'd go two-and-a-half to four inches, depending on the thickness of the lexan glazing material.

[hellosailor]

Whenever you use the words "glue" and "plastic" in the same sentence (4200 and Lexan) your *only* safe bet is to get the engineering data sheets from the manufacturer of the specific plastic that you are using (and GE has the data for genuine Lexan all online) and then confirm you are using the right adhesives/sealants.

When in doubt you can also usually call them (GE is very good about routing calls) to find out how much room you need to allow for expansion, material compatibilities, etc.

There's a lot of good information on the internet, and some bad, and more confused. Going directly to the source is always a good idea.

[NOLAsailing]

Lexan is very sensitive to solvents, I would do some serious checking to be sure that 4200 will not harm the plastic.

However, even if it is safe, I would advise against the 4200. If you install it and find a leak after it has cured, it will be a difficult job to remove the 4200. Not nearly so bad as 5200, of course, but it will be a challenge.

I would suggest butyl caulk for plastic ports and hatches. It is very flexible and maintains its pliability for a long time. It will not harm the plastic and makes a very effective watertight seal. As a bonus, you can buy it at Home Depot or any hardware store for just a few bucks a tube. It commonly comes in black, white, or grey.

As a downside, it is a bit messy. However, taking care with the installation will make cleanup far easier.

[snorphinj]

You may also want to reconsider the use of Lexan. A good discussion of Lexan or polycarbonate vs. acrylic for hatches can be found on Select Plastics FAQ's in the second question. The link is Select Plastics, LLC
they also sell sealents and are a good source of information.

[Valiente]

Originally Posted by NOLAsailing

I would suggest butyl caulk for plastic ports and hatches. It is very flexible and maintains its pliability for a long time. It will not harm the plastic and makes a very effective watertight seal. As a bonus, you can buy it at Home Depot or any hardware store for just a few bucks a tube. It commonly comes in black, white, or grey.

I agree with this. You want the caulk or tape purely for sealant purposes...sealant under compression. The fasteners are for mechanical bonding. The two do a different job, and if one fails, you can deal easily with the other without having to essentially provide a key for two separate "locks".

I removed an aluminum extrusion from my stern quarter last year and found "live" 33 year old butyl tape as a bedding/sealing compound. It's great stuff, but a butter knife or exacto cleans it up.

[sailingdog]

Checked with 3m...and 4000 would be better than 4200 for use with lexan. The butyl tapes used in the automotive glazing would work quite nicely and be easier than caulk to apply.

[Cruisingdad]

Hi Fraser,

Just a thought that came up as I read this: Have you sized the thichness appropriately? If not, have you designed storm boards? This would be the time to think about how/where to install them.

Just thoughts. Post pics.

- CD