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Old 27-11-2012, 19:00   #1
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Fixed window replacement - Dow 795 still the sealant of choice?

We are soon going to tackle replacing our acrylic windows. Fairly easy process, just pull them and duplicate them on a router table and reinstall.

However, as I recall from prior threads, the sealant of choice is (was) Dow Corning 795. Is this still the case? As I recall, that's what Tony from Hatchmasters recommends.

Or is butyl caulk a better choice? It's so freakin' messy.

TIA,
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Old 27-11-2012, 19:31   #2
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Re: Fixed window replacement - Dow 795 still the sealant of choice?

Bill, yes your are right - Dow is still recommended as far as I know.
I did my ports with cast acrylic this summer and used Dow 795. Before I applied, I cleaned the lens with 50/50 mix of water and alcohol. I did a test piece and tried to pull the caulking off after it was cured - it did not come off easy and I was pleasantly surprised.
I used butyl to caulk the frames to the hull.

Good luck.
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Old 27-11-2012, 19:35   #3
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Re: Fixed window replacement - Dow 795 still the sealant of choice?

Thanks for the quick reply. I do need to note that these windows are to be sealed to the fiberglass, not a frame.
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Old 27-11-2012, 19:44   #4
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Re: Fixed window replacement - Dow 795 still the sealant of choice?

Others may think differently but if it was me I would still use Dow 795 simply because it stuck to the plastic so well and Butyl has no adhesion strength.
I know its messy, but if you tape it carefully...
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Old 28-11-2012, 06:53   #5
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Re: Fixed window replacement - Dow 795 still the sealant of choice?

It works great. Did my hatch lenses with it.
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Old 28-11-2012, 07:28   #6
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Re: Fixed window replacement - Dow 795 still the sealant of choice?

3M makes structural glazing tapes that are used to mount skyscraper windows and steel panels with no other fasteners, adhesives or caulking needed. If we need to remount our windows, I am looking into using that over caulks - much simpler installation and much less mess.

Mark
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Old 28-11-2012, 08:52   #7
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Re: Fixed window replacement - Dow 795 still the sealant of choice?

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
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Old 28-11-2012, 09:12   #8
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Re: Fixed window replacement - Dow 795 still the sealant of choice?


Dow Corning 795 uses:
Weather sealing of most common construction materials including glass, aluminum, steel, painted metal, EIFS, granite and other stone, concrete, brick and plastics

http://www1.dowcorning.com/DataFiles...c8802a267c.pdf
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Old 28-11-2012, 12:09   #9
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Re: Fixed window replacement - Dow 795 still the sealant of choice?

Bill, We're still using 795 after many years, including up to a few months ago. It's the only sealant I have used on plastic or glass that I have never had leak. So it gets my recommendation. Chuck
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Old 28-11-2012, 12:25   #10
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Re: Fixed window replacement - Dow 795 still the sealant of choice?

Quote:
I do need to note that these windows are to be sealed to the fiberglass, not a frame.
I think it is important to consider all the details of the port.

795 is a great sealant and a pretty good adhesive; However, if you need an adhesive there are better things to use.

Are your acrylic ports recessed into the hull ? No exposed edges that could hook a sheet or be stepped on ? I don't think 795 is strong enough in shear.

Are they perfectly flat ? Not too big ?

If yes to all the above then 795 alone should work.

If no to any of those questions then some other approach may be warranted.

Cheers,
JM
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Old 28-11-2012, 12:46   #11
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Re: Fixed window replacement - Dow 795 still the sealant of choice?

I use butyl tape for rebeds. I don't think it's messy at all. That's why I use it.
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Old 28-11-2012, 12:50   #12
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Re: Fixed window replacement - Dow 795 still the sealant of choice?

One of the things that I like about Dow 795 is that it has a very high elasticity. This is great because plastics stretch both by heat and by flex of the boat.

Another +1 for Dow.
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Old 28-11-2012, 14:31   #13
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Re: Fixed window replacement - Dow 795 still the sealant of choice?

Quote:
Originally Posted by colemj View Post
3M makes structural glazing tapes that are used to mount skyscraper windows and steel panels with no other fasteners, adhesives or caulking needed. If we need to remount our windows, I am looking into using that over caulks - much simpler installation and much less mess.

Mark
I tried using tape but had better results with 795 and small pieces of tape used to space and hold window in place until 795 sets. 795 fills any bumps , tape will pull the acrylic to the shape of the bump.
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Old 28-11-2012, 15:41   #14
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Re: Fixed window replacement - Dow 795 still the sealant of choice?

Watching this thread with INTEREST! Just about to do my new recessed no fastener acrylic windows.
I beleive there is a paint you apply the same colour as the 795 to inside face of window to blank out any visible voids. Whats the trade name of this? Tips for new players?
795 must have to be applied accurately to get no squeeze out in the gap around window. (expansion clearance)
I guess the 3m tape will co$t 3 arms & legs?
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Old 28-11-2012, 19:11   #15
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Re: Fixed window replacement - Dow 795 still the sealant of choice?

I painted the inner border (bonding surface) of my Acrylic ports with KRYLON FUSION paint (black).

I made up some samples of the acrylic and 795 with and without the paint and found no appreciable difference in the strength of the bond.

The ports I have installed so far are bolted onto the flat cabin sides, not recessed. They replace some aluminum frames that would have been difficult to seal and not as strong.

One thing to keep in mind is that the elasticity of the 795 is a percentage of it's thickness, so, don't squeeze it all out. I used a piece of rubber trim to cap the rough opening in the cabin after removing the aluminum frames.

I applied the 795 liberally, the opening was masked on both sides, scraped up the excess and tooled the joint smooth.

I have some recessed ports that I am planning to replace; for those I am thinking of putting a 45deg. bevel on the outside edge of the acrylic and tooling the 795 flush with the outside surface of the acrylic. The idea being to wrap the 795 around the edge of the acrylic so that it can not be pushed outward.
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