damage returns

[TTGLASSMAN]

Can someone give me advice? Sometimes when I have a beeswing type crack or combo break I think it will turn out great cause it looks completely filled in when the bridge is on. I use a "glass medic" style bridge with the disposable plastic pistons(this may be the problem). After I take the bridge off, apply pit filler and then cure. I notice part of the break comes back as if the resin oosed out while curing. Did I not have adequate pressure to start? Is my resin too thin?(glass medic regular repair resin)? I understand sometimes it happens when I apply heat to get the cracks to fill and think the cooling of the glass may also cause the cracks to comeback while curing. If I don't use heat, they wont fill and if I do, I risk this problem. Can I win?

I'm thinking off getting a new bridge and/or try new resins if this is the case?
I have done a lot of repairs and it does nt happen all the time.

Thanks in advance for any advice.

Dave
Cincinnati, Ohio

[mafsu]

I know some will disagree with me but, I would only use heat as a way to get something to fill as a last resort. I would use pressure from a probe as close to the injector as possible to open the break up thus allowing the resin to flow. I haven't used Glass medic equipment or resin but I don't think that is the problem. After the break appears filled it is always a good idea to allow the repair to sit under pressure for 3-5 minutes before curing. You can also try pressure curing( a good thread was written on this topic a couple of weeks ago). I also always cure these for 5-10 minutes before adding pit resin. This allows trpped air to escape and prevents any gases from the curing process from being trapped inside.

[larry]

I can't remember the last time I used heat. You might try drilling just a little ways into the impact point. I use a very small drill bit, .025, Liquid Resins part #215, and Janvil's part # JA-184, .030. If it doesn't fill just lightly tap a small prob in the hole, not hard enough that you can tell anything happened. If you still can't get it to fill then redrill just a little deeper, and tap again. Hope this is of some help.

[GlassStarz]

Pressure Cure,pressure Cure,pressure Cure

[gold star wsr]

In agreement with mafsu and larry, I also use heat very sparingly, in fact, practically never. IMHO using heat should not even be taught as part of routine repairs...just as a last resort technique. Before you go and purchase new equipment, invest time in practice, practice, practice. It is probably not the equipment that is causing the difficulty. It is more likely that you need to extend your pressure and vacuum cycles and also apply pressure to the crack to facilitate the resin flow. If it looks good with the injector in place, try curing under pressure.

[chips1144]

Im no expert, but I would think heat would close up the repair legs, then when it cools down I would expect them to reappear, in essence the resin was never in the repair... just my thoughts...

[gold star wsr]

Yes, chips1144, that is often exactly the case. The glass expands, causing the crack to appear to be filled, but this actually blocks the flow of the resin. Once the glass is cooled, the crack seems to 're-appear' ... fact is, it never really was filled at all because of the applied heat. If anyone doubts this. try an experiment: on a practice glass, dont set up the equipment, just apply heat to a star break, and watch the legs close up, seeming to go away. Then see them open again as the glass cools.

[mafsu]

It's simply a matter of physics, matter when heated will expand in an effort to cool (or expend stored energy)to it's normal temperature. When cooled it will contract in an effort to heat itself(or retain stored energy).

[magicogar]

Pressure Cure!!

I worked on a batwing the other day and I thought everything filled. Low and behold, the darn thing had air pockets after curing. I would never thought resin would flow out of small cracks. From now on, I'll probably will pressure cure all my repairs.