Fixed window replacement - Dow 795 still the sealant of choice?

[clockwork orange]

I have done dozens of acrylic or polycarbonate windows over the last 40 years, most with GE Silpruf silicone with never a problem, many were screwed also, I have always used countersunk holes and flathead screws and oversized the holes but nowhere near as much as some prescribe. I have never had a window crack for any reason. Then made new 1/4" acrylic windows for my catamaran which are larger than I am used to so I went without fasteners and unfortunately allowed myself to be talked into using Dow 795, I will never use it again, it took forever to cure and did not bond as well as the Silpruf. Unfortunately I did not have the time to allow it to fully cure before I had to get it out of the shop and make way for paying customers so I had to add a few screws.

[Cpt Pat]

Once you open the tube, any unused product will cure in the tube rather quickly.


I sealed my new portlights 4 years ago, and the 795 is still like new - even though it's exposed to sunlight, rain and sea water. Good stuff!

[Shoalbay]

I used Dow 795 last year to re-bed the plastic in a hatch frame. It was slow curing but over a period of time got less tacky but never really felt solid.
This year we had some hot weather when the temperature reached 32C (90F).
When I pushed the hatch open, the plastic separated from the frame; the 795 was gooey.

I consulted the yard where I have the boat out and they use Sikaflex 291 all the time and have no problems.

[TheOffice]

795 has a short shelf life. Sounds like your's expired.

[partyvi]

Originally Posted by mikereed100

Dow 795 is cheap, easy to use and well proven on boats. I believe, though that it is more suited to glass. If your windows are acrylic you are probably better off using Sika 295 uv, keeping in mind that you must use Sika primer 209 D in conjunction.
http://www.newbridge-owners.org/down...Data-Sheet.pdf

Two attempts to install Acrylic fixed window ports. Used in combination with primer. Works well for a year on Texas sun. Then boundary layer between acrylic and sealant loosing connection and window starts drip leaking.
I still fighting with these windows, next try DOW975. I hope it will be better.

[wholybee]

Originally Posted by partyvi

Two attempts to install Acrylic fixed window ports. Used in combination with primer. Works well for a year on Texas sun. Then boundary layer between acrylic and sealant loosing connection and window starts drip leaking.
I still fighting with these windows, next try DOW975. I hope it will be better.

I used Sika with primer 2x in 2 months, with a failure each time. For the 3rd attempt DOW795 worked fine.

[lateral]

Dow795 with VHB tape inside. 8yrs now no leaks. Slightly lighter colour and some leaching below on fg that wipes off though. Brutal uv here.

[deblen]

Bed-It tape https://bed-it.com/


https://marinehowto.com/bed-it-tape/

https://www.youtube.com/watch?v=KJTvnmGfBxc

[partyvi]

Originally Posted by lateral

Dow795 with VHB tape inside. 8yrs now no leaks. Slightly lighter colour and some leaching below on fg that wipes off though. Brutal uv here.

Going with Dow 795, screws and butyl

[s/v Jedi]

Originally Posted by partyvi

Going with Dow 795, screws and butyl

If there is one thing, only one thing to learn from this thread then it is to use VHB tape instead of screws.

Also, when you use Dow 795 then you don’t use butyl. You choose one or the other.

[marcjsmith]

did the VHB and Dow when I removed the old windows and went frameless on my moody...

that was three seasons ago...easy, looks great and it works... makes the boat look younger than it really is.


Edits. sheesh, don hurt your neck.... sorry the upside down pics...

[bstreep]

As others have said, be VERY aware of dates on these products. Also, removing old caulk that had silicone in it, is also VERY difficult. The only thing I've found that works is a product called ReMov.

[partyvi]

Originally Posted by bstreep

As others have said, be VERY aware of dates on these products. Also, removing old caulk that had silicone in it, is also VERY difficult. The only thing I've found that works is a product called ReMov.

Fortunately i did not use any silicons yet but this would be first and i do not want it to fail. Let's see.

[ithappens9889]

Originally Posted by Cpt Pat

I used 3M VHB tape, which provided a sufficiently tenacious watertight bond to install 1/2 inch thick acrylic on a cambered cabin surface without frames.

Details and photos are here: http://www.pearsonariel.org/discussion/showthread.php?2520-Portlight-replacement.

Hello! Any issues with the tape over the years? Much flex in the boat at all? Any leaks?

[s/v Jedi]

Originally Posted by ithappens9889

Hello! Any issues with the tape over the years? Much flex in the boat at all? Any leaks?

The tape is very good but most will recommend to use a sealant around the perimeter for waterproofing.

Dow 795 or GE silpruf SCS2000 are the common choices for that.