Why is everyone stuck on Dow 795 When Cars use this?

[zeehag]

for glass in hatch covers made of wood we use car windshield sealant. yes goood stuff.
nothing else seems to actually work well. formosa side windows we use sikaflex. but overhead we use the black stuff.. is awesome and does work well. no rain on my pillow at all.

[Wallaby]

Having used various sealants/adhesives over the years, I suspect the problem also has to do with different rates of expansion/contraction and the ability of the sealant to allow this. One product, often used for aluminum hatch-plexi replacements, applied according to manufacturer instructions, ripped four plexi-panels apart within months--fractures all over. The next install with Dow 795 is still going strong after several years. Product shelf-life is another issue--it doesn't last long in the tube.

[svfinlandia]

Originally Posted by glcalahan

Following

+1.

Al, S/V Finlandia

[Chotu]

Originally Posted by tamicatana

It is quite disingenuous to denigrate the common wisdom and especially the product.

In the prior thread, and indeed on the label itself, directions were given that the OP did not follow. Please be sure to peruse the OP other threads before passing judgment on the statements made.

When you become a glazier with a 4.9 rating on google maps and over 1000 reviewed and completed jobs, you can talk like this.

My dude has stock in Dow apparently. Ha ha ha.

What, are you glazing up ports the size of a pop tart to test out your Dow 795 on polycarbonate? Or are you really frightened to hear what a highly respected, professional glazier has to say about this incorrect product usage that’s been accepted as fact in the marine world?

Wouldn’t be the first time.

[Chotu]

IMPORTANT

In these discussions, very few people can distinguish between an adhesive and a sealant.

Adhesive:. Holds the glazing material in place structurally keeping it from falling off the boat. May provide sealing qualities as well.

Sealant: . Keeps water from entering cracks. Does not hold the glazing material in place.

Please be sure to keep these very distinct definitions in mind while discussing since they seem to get mixed up constantly.

[Chotu]

Originally Posted by Mlp48

I'd be interested in any new sealant but would worry about a sealant being too hard to remove like some polyurethanes. The popular hatch repairer in Norwalk, CT is the 1st place I'd heard say, "We use nothing but 795..-- and you should too". I've sent a number of hatches there and they come back looking great but the sealing material has eventually failed. The charge to re-condition with this service is not inexpensive but they do a very thorough with it, replacing the lens too. It has sometimes been as cheap to buy new hatches when they can be found on sale. To be fair, the hatches I've sent most often for repair are SS-framed and Chinese and these do get very hot, in my case, from having sliding light blocking shade tightly closed -- which makes the space between hatch glass and slider an "oven" or one very hot space. This is in the MidAtlantic to Northeast. In the Tropics, exterior hatch covers are often more sensible to worry about any new sealant.

I don’t think these windshield adhesives could be used as sealants on hatches anyway. 795 is probably the best for that. These are very specific in usage. They have to be protected by a frit and are mostly an adhesive with secondary sealing often applied in addition to the adhesive bead.

They are useful in structurally bonding very large pieces of glass to a substrate on a moving vehicle.

[CarlF]

The primary reason you don't see Dow 795 on cars is that cars don't have windows made of plexiglass or lexan that expands and contracts much more than the aluminum or fiberglass frame material.

If Dow 795 if applied at least 1/4" thick as instructed it has the flexibility to handle large amounts of expansion without ripping loose. Auto adhesives are put on thin because the auto glass is selected to match the expansion coefficient of the steel car frame.

Dow 795 is primarily used in building construction where it holds large window curtain walls onto 50 story buildings in high winds, sun, ice, and rain. They never use auto adhesive either.

[Thumbs Up]

Chotu, if this is really your seventh time installing these windows you should be an expert by now. Go ahead and use polyurethane if you want. If you ignore the proper procedure again, you will end up with the same failed results as before.

[geoleo]

Originally Posted by Chotu

These products are what is used to hold car windshields in place.

Why are all boat people stuck on Dow 795 then, when there are proven, existing products for bonding glass to moving vehicles?

https://www.3m.com/3M/en_US/company-...3242009&rt=rud

https://www.dupont.com/products/betaseal.html

I can’t understand why all these half a dozen or so stationary construction minded glazing products are so recommended on this forum and throughout the boating world are suggested when this stuff has been properly holding windshields in cars for decades and never leaks, never comes unbounded, never reveals its existence unless you smash a windshield and have to replace it.

Seriously questioning the collective wisdom on this one.

Did some guy use 795 once and it spread like a rumor?

Who here has used industry standard windshield bonding adhesives? Anyone?

I’m blown away these products aren’t in the discussion when we talk about glazing on moving vehicles

Note: My glazier (4.9 stars on google maps, over 1000 reviews) said my mistake was using Dow 795 on polycarbonate in the sun. That it was the Dow 795 or ANY silicone was the incorrect method that caused the problems I had with the large windows. He suggested an entirely different adhesive for polycarbonate.

I was PM on a 15 story rise building in late 70s . 1 1/4 inch thick granite slabs were glued to galvanized roof deck with Dow 795 for the buildings walls. Its never had a problem in oast 30 years.

[mvweebles]

Installing both glass and acrylic windows right now. After extensive research, I went with Sika 296 (acrylic) and 295 (glass) with their Primer. Expensive materials - seven windows run over $400 for the sealants and Primer alone. They have very specific instructions on installation, gap around edge, and the thickness of the bead (generally over 1/4").

[boatpoker]

We have a 24" square aluminum frame hatch with a polycarbonate (Lexan) pane right over our bed.

Four times it was re-bedded with the common products mentioned here and they all failed.

Then I found this stuff .... and it has not leaked or degraded since.

https://www.amazon.com/s?k=Titebond+...ref=nb_sb_noss

[Chotu]

Originally Posted by Thumbs Up

Chotu, if this is really your seventh time installing these windows you should be an expert by now. Go ahead and use polyurethane if you want. If you ignore the proper procedure again, you will end up with the same failed results as before.

I’m not installing anything.

I’m relating information form a professional glazier putting tempered safety glass on my boat with a 4.9 rating and 1000 jobs rated.

795 was the wrong material for the job of real normal size so windows made from polycarbonate in Florida. Not or ya. Big windows.

Tiny little bits of polycarbonate or acrylic? Sure. It’ll probably hold up.

But I’ll let you all know what the pros use as soon as he’s out here and I chat him up again about what to use on polycarbonate.

[Chotu]

Originally Posted by geoleo

I was PM on a 15 story rise building in late 70s . 1 1/4 inch thick granite slabs were glued to galvanized roof deck with Dow 795 for the buildings walls. Its never had a problem in oast 30 years.

Then again, it’s not a vehicle, nor is it undergoing massive thermal expansion

[AKA-None]

It’s all about the right material for the right application. Certainly wouldn’t use the high expansion stuff I use for the log house on a window on a boat or the other way around

[StuM]

Originally Posted by Chotu

I’m relating information form a professional glazier putting tempered safety glass on my boat with a 4.9 rating and 1000 jobs rated.

You keep repeating these numbers.
How many of those 1000 jobs were in a marine environment?

"Glaziers specialize in installing different glass products."
"Glazier: one who sets glass"
What's his experience with non-glass products?