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bad urethene adhesion

I've been seeing alot of urthene that is not bonding to trimed down urthene left on body. I start to trim after cut out,(I use a very sharp 1" putty knife), and when I start pulling up to help the cutting, the whole new bead pulls off, it does not adhere to old bead. any ideas why I'm seeing this? Urthene I'm removing does not have a high tensile strenght, and it seems to be fairly elastic. I use asap for my installs, but it would seems that the urthene I'm removing is not safe. I just want to make sure that People are safe.

Re: bad urethene adhesion

If I am reading your post right, you are saying the urethane to urethane bond is bad? Can't say we are seeing much of that. What we do see a LOT is Bond failure from factory of the paint to the e-coat. More and more VW's, chryslers and some others.

Re: bad urethene adhesion

I have also run into this .Quite often too.It could only be caused by two things.Not cleaning the old bead good enough,or some bad urethane.Contamination must be the deciding factor.And we all know that contamination can be caused by just about anything.

Re: bad urethene adhesion

my guess is that maybe they cleaned the old bed with 3m or some other solvent that reacted with the new urethane.

Re: bad urethene adhesion

I think there is more out there than we know! We have seen Audi's that urethane peels off the body,I also cut out a Mercedes S-Class and under the urethane was masking tape and the urethane was applied right over it and That was a factory set. We all have seen problems with all models of Jeeps! How about the older S-10's with the guardian w/shields that the bottom of the shields, the frit came right off the glass you could see that from the outside, but was that the glass or the preps that caused that problem.

Re: bad urethene adhesion

The poor bond that you are describing could be from incorrect priming. Most urethane specs call for you to just prime the spots that are scratched and not prime over your trimmed thane. But I have heard of techs that will just run there dauber over the pinchweld covering the old urethane bed with a coat of primer. This will cause poor adhesion, that will just peel away.

HH

Re: bad urethene adhesion

I see alot of guys wiping down the dash, which has armor all, etc, then wiping the pinchweld thus contaminating the surface. Glass cleaner on the urethane could even contaminate the bed and cause poor adhesion.

Re: Re: bad urethene adhesion

Another thought might be the base urethane was installed wrong.Many people dont understand if clear coat is on pinchweld the urethane will not stick.We see many vehicles with factory installed ws,that base urethane failed to hold.

Re: bad urethene adhesion

the problem is urthene pulling away from urthene. I was always told this is the strongest bond. I shouldn't be albe to pull new bead off of old bead. also Ive seen no real sign of over priming or dirt. the urthene just pulls off

Re: bad urethene adhesion

Well then I'd have to say it is a contamination problem. Can't say as to what because it could be any number of things. These are probably installs from different glass shops correct? So it is hard to say what is going on. Bad batch of urethane distributed to different glass shops in your area by the same vendor? Could also be the culprit.

Re: bad urethene adhesion

"Most urethane specs call for you to just prime the spots that are scratched and not prime over your trimmed thane." I have heard of this also. It makes you wonder if the primer won't stick to the urethane, why are we using it????

Re: bad urethene adhesion

first and foremost you are using primer on just the scratches on the pichweld to keep it from rusting. we occassionally get a failed urethane to urethane bond. but we get more factory urethane adhesion failure than you would think. dodge and chrysler used to be really bad, here lately is has been chevy/gmc pickups.

Re: bad urethene adhesion

If it's a rust preventive why do they call it urethane primer? If it is urethane primer don't you think urethane sealer should stick to it? If it is so important to not mix urethanes and primers why don't the Manufactures tell us what they use, so we can use the correct sealant system? One other question, does urethane primer stop rust?

Re: bad urethene adhesion

We have worked closely with Sika on the rust issue. The correct term for them is rust "inhibitor", meaning it will protect from rust starting, but WILL NOT 'stop' existing rust. Only way to stop rust is to COMPLETELY remove it, including all pitting. This is one reason it has been given the nickname 'cancer'. Products like Rust Bullet are designed to stop existing rust but the problem is that I don't know of any adhesive mfgs that will give the OK in writing proving its compatibility. Until then, off to the body shop they go.

Re: bad urethene adhesion

again this is urethene to urethene bond. I'm in the phoenix area, and wondering if high temps, 100+, heating pinchweld bead is affecting bond.

Re: bad urethene adhesion

Just had another one yesterday.Dw1217.There was no rust on the pinchweld.It did not look like there was any primer on the old bead of urethane.It just pulled right up as if you were removing blue tape.As for primers,look at essex 5404sa.This is supposed to re-activate a PAAS system.By using this on pinchwelds also does it affect anything when it has also covered some of the old urethane?As for the urethane to urethane bond I was wondering if it had to do with cold weather installs.Guess not.It seems we are back to the contamination issue.Or some bad urethane.

Re: bad urethene adhesion

I've noticed that sometimes a new urethane bead will not stick to the old bead and I believe this has to do with how the bead is run. If you hold you gun verticle to the pinchweld it will cause the urethane to "wet out" and adhere better. I've seen a lot of techs that hold the gun off the body and let the urethane drop onto the old bead. It won't stick as well.

Re: bad urethene adhesion

i disagree with fubar, when you set the glass and push it in it gets just as good adhesion as anyway else.

Re: bad urethene adhesion

I also disagree,if we dont know pevious urethans how can dealers tell us it will match.I have seen way to many partials that we were told was fine 15 years ago that let loose in2-3 years.My reputation and future is in a job,I know from past why we dont have problems and I will challenge the man. who says his urethanr will work with all others.Also no matter how careful I feel the old gets contamination no matter what.

Re: bad urethene adhesion

I tested urethane to urethane & priming urethane & then sooting urethane over. noticed no real diffefence in bonding together, So now I prime whole pinch weld because then urethane is bound to adhere onto something

Re: bad urethene adhesion

urethene rep told me that if you prime over urethene bed the primer sets like a paint coating, and when there is stress on bond the primer cracks and can flake of urethene. did a 03 dodge caravan friday, factory set, and the urethene torn apart close to pinchweld. maybe its u400 thats doing this? hope not, for alot of reasons.

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