New window sealing question.

[Hoohaa]

I have very similar Windows to this boat and I want to remove the existing perspex.
Seal and glue it back in. Or?
I am wondering why you wouldn't just glue a new panel in. Without using screws.
They seem a bit pointless and just a source of future leaks.

[Neptune's Gear]

Yep, that is exactly what you'd do. No need for screws/bolts with modern adhesives. I've done a few boats with this adhesive - SINTEX MS-35 SEALING AND BONDING | Quilosa
It works great, high initial bond, no primers needed.
DONT do it in direct sunlight though, the suff goes off too fast on a hot day!
Remove the old windows, clean the frames, fill and fair the bolt holes, mask, apply adhesive, fit window. Not hard at all, but easier with 2 people if the windows are long.

[Hoohaa]

Originally Posted by Neptune's Gear

Yep, that is exactly what you'd do. No need for screws/bolts with modern adhesives. I've done a few boats with this adhesive - SINTEX MS-35 SEALING AND BONDING | Quilosa
It works great, high initial bond, no primers needed.
DONT do it in direct sunlight though, the suff goes off too fast on a hot day!
Remove the old windows, clean the frames, fill and fair the bolt holes, mask, apply adhesive, fit window. Not hard at all, but easier with 2 people if the windows are long.

Thanks Neptune. Great advice.

[GordMay]

C&C used (late 70'2-80's) a 2-part methacrylate glue* on their glued-in (no fasteners) plexiglass windows.
* PLEXUS MA590 ➥ Window Glue w/ mixing tube - South Shore Yachts - Yacht Brokers - Yacht and Boat Repair and Parts - Niagara-on-the-Lake
➥ http://itwplexus.co.uk/media/17270/tds-plexus-ma590.pdf

Sikaflex 295-UV is an exc ellent 1-part alternative for bonding acrylicand polycarbonate windows.
➥ https://www.sika.com/sikamarine/en/i...lex-295UV.html

[Franziska]

Just as an aside, use the proper primer for the SIKA.
It's black for the glass and cuts the UV even more down.

[Hoohaa]

All sounds good.
I have been watching "Boatworks Today" and he is recommending the "3M VHB Tape".
Do you have any thoughts on this? Would it be easier to apply?

Also. The existing widows are still in good condition but have holes drilled into them. If they come through the removal process ok. Do you think there would anything wrong with reusing them and filling the holes with Sikaflex 295?

[Ilina]

Sealing windows can be a complicated or simple issue to deal with,
Depending on a number of factors.

Firstly, 3m VHB tape 4991, works. As long as the window is of correct proportion to be able to manage the expansion/contraction ( which the tape hates ). Also don’t consider tape on windows which have previously been sealed with an adhesive, you are just setting yourself up for failure. Too much curvature in the window and you have to overcome the peel effect that’s constantly acting against the tape.
So in short, tape is a tough gig unless you really know wht you are doing.

Sika ( polyurethane liquid adhesive “PU” ) works fine if you can block out the UV, because most PU sealants are not UV stabilised, so they harden and break down over time with UV exposure. This is why Sims have a black out primer..
look into the expansion rates for PU sealants and compare that with potential for window expansion rates. If you use a PU, it’s advisable to use a foam soccer tape or other method to maintain a uniform sealant thickness. Remember if there is no sealant thickness, there is no flexability, so it will split and leak !

Silicone - the old GE silicone company ( now Momentive ) produce a sealant called Ultraglaze SSG4000. It is a true Structural grade high performance silicone with 50% movement capability. It skins and cures slowly, giving plenty of working time.
Glass, acrylic or polycarbonate are no problem for adhesion.
Same rule applies - no thickness, no flexibility or strength, so it’s advisable to try and maintain at least 4 to 6mm of sealant depth for best results.
Understand that this silicone is moisture cured at approx 1mm of depth per day, so if you gun down a sealant bed 50mm wide then squeeze a window into it, the sealant will cure from either exposed face of the sealant at 1mm per day. So the middle of that 50mm sealant may take 25or more days to cure.

Regardless of what sealant you choose to use, is all about knowing how to set up the sealant depth, how to prep both surfaces for a perfect bond strength, and how to hold your window in shape until sealant cures.

I have sold Ultraglaze for more than 28 years, and know that it’s difficult for many people to find, but still believe it’s an option that done correctly the first time, will last longer than the window material.

Good luck and happy black sticky fingers !

[Seabeau]

If you use adhesives, what happens if you break the glazing? Use butyl rubber tape and mechanical fasteners. Much, much easier to repair.

[Ilina]

Mechanical fastners, like sealants, have their own issues if not used correctly. No idea how many polycarbonate windows I have seen, peppered with a neat row of countersunk screws or thru-bolts around the edge. Polycarb by nature loves to expand and contract, so a snug fitting csk fixing is only go to end up with stress cracks to the edge of the window. Assuming the vessel is subject to some heat.

A good old external metal perimeter compression cap with less fixings, and oversized holes through the window material, will overcome the problem above.

A good quality closed cell PVC double sided adhesive foam tape is 100% watertight at 25% compression. So it’s a good solution. BUT, everyone seems to want that slick finish of the windows stuck on flush. Not saying I think it’s the best option..

[ArmyDaveNY]

Originally Posted by Ilina

I have sold Ultraglaze for more than 28 years, and know that it’s difficult for many people to find, but still believe it’s an option that done correctly the first time, will last longer than the window material.

Thank you for some excellent insights. When you say "will last longer than the window material, roughly how long should I expect a new acrylic window to last?

On a different note, do you have any websites you like that show and describe good practices for prepping and installing new windows?

[Captain Bucknut]

Originally Posted by Hoohaa

All sounds good.
I have been watching "Boatworks Today" and he is recommending the "3M VHB Tape".
Do you have any thoughts on this? Would it be easier to apply?

Also. The existing widows are still in good condition but have holes drilled into them. If they come through the removal process ok. Do you think there would anything wrong with reusing them and filling the holes with Sikaflex 295?

I've seen the video and am going to utilize the same method to install new lenses in my Catalina 25. Use the VHB tape and then the Dow 795 to seal in the edges.

I would not recommend reusing the old windows. Sounds like more hassle and more possibilities for water intrusion.

[anacapaisland42]

Does anyone have any suggestions for sloping opening rectangular ports/windows that accumulate rain water before either letting it drip thru onto my bunk or drenching it when opened.....other than replacing the whole darn thing.

Bill

[QUOTE=Hoohaa;2617570]I have very similar Windows to this boat and I want to remove the existing perspex.

[bcboomer]

The 3M VHB 4991 in 2.3mm thickness, finished off with Dow 795 is quick, easy and bullet proof.

https://www.sailmagazine.com/diy/rep...xed-portlights

This is Don Casey's method. It works and looks great when it's finished.

[Captain Bucknut]

Originally Posted by bcboomer

The 3M VHB 4991 in 2.3mm thickness, finished off with Dow 795 is quick, easy and bullet proof.

https://www.sailmagazine.com/diy/rep...xed-portlights

This is Don Casey's method. It works and looks great when it's finished.

here is a video for installing fixed lights

https://youtu.be/MQyjxVUskd8

[ArmyDaveNY]

Originally Posted by Hoohaa

All sounds good.
I have been watching "Boatworks Today" and he is recommending the "3M VHB Tape".

Which episode?