glue-chip problems

[Catharine C. Kennedy]

I've been working on a version of the Chapman & Smith glass sign. I used asphalum & sand-blasted as usual, then used the squirt bottle to apply the glue. When the glue came off (after drying), it came off pretty much in sheets with very little chipping done at all? How come?
I've been finding that I have consistantly had to double-chip to get decent results... Why?

[Mike Jackson]

Catharine,
You might want to go back and dig around for posts on the old Forum dealing with Glue-Chipping. Seems like we had a similar discussion there not long before the board crashed.

Grease or oil on the surface of the glass can cause problems. That can happen if you handle or touch the sandblasted surface, wash it with something oily, or even possibly happen as a result of oil introduced during sandblasting (depending on the kind of compressor and filtering system you have). If you sandblast the piece and let it set for a few days prior to pouring the glue, it might be possible for the surface to pick up airborn residue and contaminants.

You mentioned that you sandblasted the glass before pouring the glue, so that shouldn't be an issue. It usually doesn't take much depth or texture for the glue to have something to grip to on the glass surface.

Other than those suggestions, I would just get some 6" scrap glass and tape off the outside 1/2" and chip a BUNCH of test pieces. No design, just a chipped panel. Frost some longer, shorter, etc. Pour more glue on a few and so forth. After a while, you should start seeing a pattern of what works and what doesn't. I wouldn't go through all the hassle of doing a decorative design until I figured out how to get a good chip.

Good luck,
Mike Jackson

[Robare M. Novou]

I recall reading or hearing something about damping/wetting the surface of the blasted glass with water, prior to the application of the glue.

Seems to me, that in doing this, you're washing away the sandblasting dust, which might be the reason for the glue's inability to adhere to the glass.

Or...you might be sandblasting with too fine a grit?
Or, like me, your going blind, and cant tell if the glass you just blasted is blasted...it looks frosted, but that just might be the masking on the other side that is causing that frosted look. Just cause the asphaltum blasted away doesnt mean the glass is blasted/etched enough.

Dust off those blasted areas and look at the glass at an angle in a well lit area.

Or....not enough glue in your water to glue ratio.

Like Mike said...experiment first.

RMN

[Chris Welker]

I've done a few that came off in sheets like that. I think part of my problem was the glue layer was too thin.

[Larry White]

The above picture shows a test piece I did. This was done by creating a masking tape wall around the edge of the glass and the correct amount of glue (1:1.5 mix @ 3oz. glue/sq.ft.) flowed over the entire piece. What has happened is the glass was not precisely level and the glue flowed out thinner in the upper left hand corner and heavier in the lower right hand corner. After the glue had dried (all the water evaporated off) there was a thinner deposit of glue in the upper left hand corner. The glue, being thinner, and weaker, chipped first. The thinner glue gives a "shattering" type of pattern. The glue over the rest of the glass was the appropriate thickness to give a good chip. ...I don't know if this relates to your question or problem... just another piece of the puzzle.

...as for the peeling off in big sheets problem, to me that would indicate the glue isn't suficiently grabbing the glass. After sandblasting the glass, hold it flat and look down the blasted surface (like you check the straightness of a board) with some light to reflect off the surface. The glass should have a full matte finish, any shinny places would indicate glass that hasn't been blasted. Dust off the surface good and make sure your glue is the right strength and it is good and hot. ...and keep trying....