Our "Diamond Seaglaze" windows in the work boat are sealed that way, with butyl. You can buy a brick of the stuff at Home Depot for $1.69.

 

Erps, did you use a spacer of some sort between the lense and the cabin sides? I'm just about to redo my windows with butyl and I'd love to hear the details of how you did yours (as I'm sure Weephee would as well). Thanks in advance.

 

No, I didn't use a spacer. I've used the spacer trick with silicone type caulks when trying to seal stanchion posts to give the caulk time to set and then squish it down the rest of the way without the spacer.

With this butyl material, it stays soft, so the more you crank down, the more of the material squeezes out.

 

So...

Can I just cut an appropriatly sized piece of lexan and screw/though-bolt it to the sides of the cabin with some butyl tape between the gelcoat and the lexan?

Is it that straight forward?

 

Unless through bolting, not just screwing, I would not personally use butyl for this application, and I sell the stuff.

If you have a wide enough portlight flange 1"+ a very thin bead of "shimmed" butyl, perhaps 1/4" wide on the inside edge, of 1/16" thick, works well as a spacer so you don't squish out all the other sealant out when drawing the bolts or screws down. It can also hold the port in place until the sealant cures, BUT, you need a wide interface flange which most applications do not have.

My general inclination is for mechanical spacers with proper thickness a jig to hold the ports in place while curing. If the ports are mechanically fastened, meaning through bolted, then you'd want at a minimum a "shimmed butyl" used for architectural glazing but I'd still opt for Dow 795, GE SG 4000 or Sikaflex 295 with the special primer.

There are good applications for butyl I just don't feel this is one of them just like a fuel fill flange is not. Butyl tape has very low adhesion so if you are relaying on it for bond then...well... I would not use it.. I don't consider screws into polycarbonate very strong as I have seen far to many strip out far to easily..

 

Mainsail, thanks for the tips (again). I don't want to hijack the thread, but something you wrote leads me to ask a few more questions. In my case, the portlights are throughbolted and have an ample overlap on the cabin sides. I was thinking of using some 2 sided automtive foam tape as a spacer around the portlight and using butyl to do the sealing part. After looking into the price of the Sika primer and Sikaflex 295UV I almost had a heart attack (EXPENSIVE in Brazil!). Do you think, in my case, the foam tape spacer and butyl is a good approach to getting watertight windows? I'm not relying on the butyl for any adhesion (the bolts do that). Thanks in advance.

 

Without mechanical spacers, as in "shimmed" butyl you'll like get a loot of ooozing out between the port and the cabin side as the foam continues to compress over time. These windows expand and contract a lot so they do need a decent thickness of butyl or silicone or PU between the deadlight and cabin sides.

 

Maine Sail, isn't there a verson of butyl tape available with a bead in the center to prevent displacement under pressure? Seems I heard of something like that. I have glass portlights to install on Lady J that are held against a mahogany lip by screws through mahogany rings.

 

Yes it will be an architectural grade "shimmed" product. I do not sell it but can get it. The problem is I need to order it in minimum case lot quantities and the demand is very small so I opt not to stock it. You might find a glazing specialist who is willing to break case lot quantity on-line. Most of the shimmed stuff is sold by the case.

Here's one.. Shimmed Butyl

 

I'm resealing the glass in the hatch over my V-berth. It is plexi in an aluminum frame, through-bolted. It was previously sealed in with silicone, but I don't think I want to go that route again. There are little standoffs probably 1/16" tall inside the frame to prevent the glass from going all the way down, so it would leave some room for the sealant. Do you think butyl would be good here?

 

I would not use butyl in that application unless also through bolted. It would seal but have minimal strength, if you were to get pooped. A product like Dow 795 or similar are the preferred sealants but the frame and glass must be 100% free and clear of all previous silicone before re-bedding it.

 

I have a similar question, slightly different application.

My head has a "rain drain" type of opening port in the middle of a plexiglas (acrylic) window:

I need to re-bed it because of a small leak. There are through-bolts from the inside to what I believe are molded threads in the outer flange. The flange is about an inch wide.

Is butyl tape an appropriate glaze for this, or is there some chemical incompatibility with the plastics?

 

reseat / replace ?

[as an aside, this forum is fantastic. However, searching is tough not to come up with less than pages of results...so, hope this is ok here...]

Bought my 1978 Mariner 28 last spring, launched her for 2010 season (Lake Michigan) doing what needed to be done. This spring I'm tackling some of the stuff that needs to be done, but doesn't stop me from sailing.

Any suggestions: