Dow 795 Alternate?

dscribner · Apr 9, 2016

MS is right. McM ships so fast, you wonder if it's manned by elves. I used them often for work. I can't even begin to count the number of times I've placed the order online ,then before the end of the day I get an email confirming shipment with delivery the next day before noon. Incredible. They tend to be a little pricey but they have EVERYTHING.

Crazy Dave Condon · Apr 9, 2016

Dow 795 is a pure silicon archeticual grade which is why it is tenacious on holding and lasts a long time. Anytime silicones have added materials weakens the true nature of purity so as some had said to me. Not sure but wonder if that statement was correct.

Dan_Y · Apr 9, 2016

795 was a good choice by Hunter. Our 91 h30 got 22 years out of the factory 795 seal! I think another key is that 795 is a room temperature vulcanizing (RTV) silicone. The 795 data sheet states "One-part, neutral-cure, RTV silicone sealant". Apparently many RTVs are 2-part. 795 cures to what feels like rubber and does not seem to leave behind the "slippery slime" contamination characteristic of silicone sealant (maybe it does and I have just been super careful - ha). Maybe a chemist can help me out here!

A cool thing is that 795, like the Boat Life Caulk (I forget which one) cures through exposure to atmospheric moisture, and so does some of that expanding building insulating foam. It's a mystery to me how that works, but I have misted water over the material (795 and Boat Life calk) after applying to speed up the cure, especially if applied when the humidity is low. It seem to help speed up skimming and initial hardness. It's also useful to mist the insulating foam if you have to make several layers deep.

JamesG161 · Apr 9, 2016

Crazy Dave Condon said:
Anytime silicones have added materials weakens the true nature of purity so as some had said to me. Not sure but wonder if that statement was correct.

Correct!
Instructions on most adhesives....

"Thoroughly clean both surfaces before application!"

The last tip...

The adhesives contain a "Drying" agent. Once that agent leaves the adhesive, it doesn't adhere anymore (cured).
Speedy application give maximum bond.

This agent slowly permeates the container tube i.e. shelf life.
Jim..

Crazy Dave Condon · Apr 10, 2016

Other than the drying agent which I did not think of

kito · Apr 10, 2016

If anyone has any unopened, expired Dow 795 I will take it off your hands

I will not use it for structural purposes like installing 1/2 ton glass panels on a high rise but should work just fine for sealing purposes on a sailboat.

woodster · Apr 10, 2016

kito said:
If anyone has any unopened, expired Dow 795 I will take it off your hands I will not use it for structural purposes like installing 1/2 ton glass panels on a high rise but should work just fine for sealing purposes on a sailboat.

that's not a good idea the stuff loses it holding power when it starts to dry out and you will always second guess the work you have done

Pat · Apr 11, 2016

Rudy at D & R Marine told me that the 795 is able to withstand extreme changes in temperature, which may not be a big deal
in Louisiana....In Wichita I chose first to disregard the 795 suggestion and ended up having to replace the replacement hatches as they cracked into a thousand (maybe a hundred) pieces when the temperature fell below freezing.....I would suggest you contact a windshield shop..most of them use 795 due to it's ability to survive the freeze and thaw cycles...It is available in
several colors and clear from what I heard.

Maine Sail · Apr 28, 2016

kito said:
If anyone has any unopened, expired Dow 795 I will take it off your hands I will not use it for structural purposes like installing 1/2 ton glass panels on a high rise but should work just fine for sealing purposes on a sailboat.

It costs about $8.00 brand new.......... The ONLY thing it should be used for bedding is acrylic or polycarbonate and Beckson products. Silicone should be avoided otherwise unless you desire future adhesion/sealing problems due to silicone contamination..

woodster · Sep 22, 2016

looks good kloudie

SFS · Sep 22, 2016

@kloudie1 - What make and model are those vents just aft of the forward hatch? They look more robust than these Vent- O-Mates:

http://www.defender.com/product.jsp?path=-1|6880|2290139|2290145&id=46083

Pat · Sep 22, 2016

Check with an automotive window replacement company like Safelite....most of them use the Dow 795 due to it's ability to withstand material shrinkage and expansion due to thermal issues....Pat

gettinthere · Apr 19, 2018

I had an extra tube, unopened, of Dow 795 from an earlier project. I opened it a year later. Stored inside a cool locker. Still appeared fresh as a year ago...but it failed to cure properly. It definitely does have a limited shelf life!

thinwater · Apr 19, 2018

If you use a polyurethance for glazing (Sika 295 for example) you have to prime the plastic. This is because the polyurethane bond is quite vulnerable to UV and with glazing the UV strikes the bond surface. I've tested quite a few, bonding plastics and fabrics like sail cloth, and unless the material is truly opaque in the UV, the bond will fail in a year. Surprised me too, but that is what happens. This is true of epoxies and many other adhesives. Glazing is a unique application in this way.

For this reason, I would not fool with anything not rated for structural glazing, and I would follow ALL instructions, including priming, to the letter..

Mark Maulden · Apr 19, 2018

I’ve had three sets of cabin windows installed in the last six yrs..The first two were installed by the local yard who also is a Benny dealer. They used Sika 295 UV and primer. The second time, I was present on the boat when they were installed and “supervised”. Last summer, the second set fell out as did the first. Last fall , we cut every window out, cleaned all boat mating surfaces and installed new acrylic with 795. Different shipright who is very experienced..Sika is not allowed within eyesight. These are frameless windows inset into the cabin side. We’ll see what the next few yrs bring..

Dow 795 Alternate?

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SBO Weather and Forecasting Forum Jim & John

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