glue chipping issue

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bob gamache
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glue chipping issue

Post by bob gamache » Tue Mar 13, 2012 4:55 pm

Hi Guys
Im in the process of glue chipping a piece of glass. The glue refuses to bond to 1/2 the sanblasted area, the other half chipped(currently chipping)just fine. The glue dried to a solid state perfectly, was trimmed and heat was applied as usual.

On one side the glue lifted in one solid piece without chipping the glass. I figured the glass was dirty the first time around so I washed it down with water to remove any residue. The second time i scratched up the surface to give it more bite then washed it first with water, then denatured alchohol. The 3rd time water, denatured then acetone.

This was my 4th attempt at chipping this sign.
Do you think it has something to do with the glass? Or am I missing something here??!! I never had this happen before.
What is your opinion?? I might mask it out and sandblast the unchipped areas lightly again.

thanks
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Bob Gamache

pat mackle
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Re: glue chipping issue

Post by pat mackle » Tue Mar 13, 2012 6:32 pm

"On one side the glue lifted in one solid piece without chipping the glass"
To me, this is a sign that this area of glue dried to fast. Was your glass level and pre warmed? It was probably just thousands thicker than the area that chipped. The fact that it rolled up instead of chipping suggests that the glue contacting the sandblasted surface was not well adhered to the glass when it began to dry and pull away. Glue that is drying well, and properly adhered to the glass before chipping, will begin to show the stress breaks that will become the fern chips. The glue is well locked onto the glass ready to chip off.
Also, the minute difference in the deposited thickness of glue is even more accentuated if the glass chipping process is sped up, either in the initial drying stage(ie: a fan), or the later drying stage(ie: heaters and or desiccant)
Unless you are set up to spread glue consistently for production chipping, I would err on "slow and steady..."
Keep in mind the there is a "wrenching" system that makes glue chip happen. The layer of applied glue must dry in such a way that the glue in contact with the glass reaches a state where it has dried sufficiantly to be well bonded to the glass at a one to one bonding size. In other words, the lower level of bonded glue can no longer stretch or shrink because it has set in place to the glass. At this point, the top surface of the glue is still drying and shrinking, far past the lower glue held in place by the glass. As the top surface dries further, and thus shrinking tighter, it exerts a contracting force on the lower bonded glue which causes it to curl and pull the bonded glass away from the glass surface.
Pat

Danny Baronian
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Re: glue chipping issue

Post by Danny Baronian » Tue Mar 13, 2012 6:56 pm

Hi Bob,

Someone at one of the Conclaves had a similar problem. Rick Glawson, or one of the many other smart alecks at the meet said to re blast with BB's. It was interesting to see the shocked / bewildered look, before said smart aleck cracked up, giving himself away as not being serious. That would surely eliminate your problem. For good.

How old is your glue, is the same as the last project you posted? With such a massive glue failure, I'd question the usefulness / age of the glue. Use a scrap of glass, preferably from the one shown, as well as a second piece from a different batch of glass, blast both, mix a fresh batch of glue, apply to the glass and see what you get. What grit is the blast media? I assume it's the same as your last project, which looked fine.

Years ago, I found a shop in a nearby town that did nothing but silver mirrors, politely invited myself over to learn as much as I could, which was good as he was in the process of closing shop. The reason he gave for getting out was that he was increasingly getting glass he couldn't silver, both new and old. His thought was that the glass had somehow been contaminated. The process he used was the same Dave Smith does, from cleaning to mixing and applying his own chemicals. While he didn't do glue chipping, could contamination be in play here, I don't know.

Just a thought.

Danny
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erik winkler
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Re: glue chipping issue

Post by erik winkler » Wed Mar 14, 2012 8:04 am

What do you guys think of this one?
If I look at the chipping pattern and the remains of the glue it self; the glue looks like it has been poored on rather thick (contains to little amount of water).
In combination with the process Pat explained I could guess that a rather thick glue sets more quickly then a more liquidy glue and therefore has no time enough to adhere to the blasted surface with its tiny molecular sticky fingers.

I would suggest some more testing:
1. Panel with the same thickness.
2. Panel with more water.
3. Panel which is preheated.
4. Panel which is preheated and heated to about 100 degrees fahrenheit (37 celcius) for about an hour, then turn of the heat and next morning heat the panel and let the chipping begin.

Furthermore as Danny said, what is your grid size, did it work the last time you chipped, did you use the grit for something else so it is contaminated etc.?

Erik
Last edited by erik winkler on Wed Mar 14, 2012 2:36 pm, edited 1 time in total.
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bob gamache
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Re: glue chipping issue

Post by bob gamache » Wed Mar 14, 2012 1:18 pm

Hi Guys
Thank you for the highly valued opinion and input!

Pat, The glass was level and warm before applying the glue. Today I applied a thinner more even coat of glue this time around hoping it does the trick! Its drying on its own now. I normally use a heater/fan (on low) for the duration of my projects. Its worked fine in the past, nice warm gentle air flow. However, This time I turned the heater off to let the glue dry on its own at a natural rate. My fingers are crossed!

Danny, the thought did cross my mind to break out my automatic bb gun after the fourth attempt and blast that sucker to smithereens!!! Instead I lit a cigar, had a little bourbon and called Roderick, got my thoughts together and posted here!

The blasting media and glue used were the same materials used for my other projects.
I was hoping the glass wasnt defective .....too expensive to start the project over.....its 22" x 44" - 3/4"bevel - 1/4" clear.

thanks
Bob Gamache

Robert Schwieger
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Re: glue chipping issue

Post by Robert Schwieger » Wed Mar 14, 2012 4:27 pm

Hello,
Glad to see the input on this matter as I had a similar problem on a large piece which was included in an earlier post. The glue curled off as stated in the above item. I had the blasting sub contracted originally by a reliable source. In my case I believe that the glue was not heated high enough but to make sure it wasn't something else I hand etched the blasted areas with an electric engraver. The end results were very good but I think that the culprit was the under heated glue. Although it may consume some time the engraver does work especially if you need to correct small areas that don't chip. Thanks for the input. Bob

bob gamache
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Re: glue chipping issue

Post by bob gamache » Wed Mar 14, 2012 9:13 pm

Hey Bob
I'm happy to hear I'm not alone! As far as heating the glue I use an electric glue pot that keeps the glue at 140 degrees. Ill let you know how my job ends up.
Bob Gamache

vance galliher
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Re: glue chipping issue

Post by vance galliher » Wed Mar 14, 2012 9:44 pm

hahaaaaa....no advise on this one bob, but know you're not alone in this glue/glass dance.
vance
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Lee Littlewood
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Re: glue chipping issue

Post by Lee Littlewood » Wed Mar 14, 2012 9:51 pm

Pat's comment made me think of something my friend who does production chipping mentioned once. He was talking about the trials & tribulations of setting up a "chipping room" in his (extensive) shop. He also does a lot of sandblasting, both mechanized and by hand, so he was (I think) spraying on a protective layer over the blasted panes (I forget the brand name, I think of it as like Rain-x).
So some of the fumes/overspray/whatever got into the ventilation system and thence onto a batch of blasted glass before the glue was poured. And one side of a pane would chip and the other wouldn't - he said that was the clue that got him looking at the ventilation system, 'cause the side closer to the vent was always the non-chip side. So he changed the ventilation somehow and all was purry purry puss puss.

So what things can have a gradient from one side to the other ? Glue thickness; temperature; draft (air movement); sunlight; magnetic north (I'm reaching here); maybe a deeper blast if it's closer to you... It's hard to see the glass itself being much different from side-to-side.
As Sherlock Holmes (an early Letterhead) once said, "If all the normal causes are eliminated, then the remaining possibilities, no matter how improbable, must be the answer."
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erik winkler
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Re: glue chipping issue

Post by erik winkler » Thu Mar 15, 2012 1:26 am

Lee Littlewood wrote:As Sherlock Holmes (an early Letterhead) once said, "If all the normal causes are eliminated, then the remaining possibilities, no matter how improbable, must be the answer."
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Erik
Realizing we are in the 2nd renaissance of the arts.
Learn, copy and trying to improve...
Still in the learning phase ;-)
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