re-appearing darkness

[PortMerc]

Intermittent problem: Sometimes, after about two or three cycles the crack/damage looks perfect. So I add the pit resin and cure it. Then after I cure and polish I find that there are dark spots in the repair that were not there while I was working on it.
I've tried several different techniques to stop this, heat, longer curing time, ect. How can I prevent this if it looks perfect while under the pressure cycle and doesn't re-appear till after I've cured it?

Thanks, Seth

[Brent Deines]

Maybe too much heat which can expand the glass, then as it cools and opens back up air space appears. Too much pressure against the glass can partially close the break giving the illusion of a filled break, but when the pressure is released the air will begin to reappear. In both cases the air may not appear immediately, but by the time the the curing is complete air can show up.

Have you tried removing the injector, placing the pit resin and curing tab, then waiting a couple of minutes to see if air appears before curing?

Also, what resin are you using?

[PortMerc]

That's a great idea, I will try that.
All of my supplies have com from Delta

[Clarity Glass]

as a delta user I use a 4x mirror, check for air in break when injector is in up position. When I see no air (black) in break, I'll usually do a couple 1 min. cycles then apply pit resin and cure. When I first started I did the exact same thing as you and had the same results. I was improperly trained that most chips could be repaired in 5 minutes/15 min tops. Now almost six years later most of my repairs take 45 minutes start to finish. Take your time,use fresh seals, and you will see a huge difference.

[Dave M]

Brent,
Not totally disagreeing with you, but if you read PortMerc' original post he says that AFTER the black spots appear did he try using heat. You're correct if he is using heat prior to curing or too much injector pressure.
PortMerc, keeping in mind that you use Delta Kits, follow what Brent says. I use GT and have always cured under pressure for about 2 minutes with great results. This was not a practice of GT, but something I picked up on this forum that has worked for years.

[Brent Deines]

I know those of you who like to cure under pressure will disagree with me on this and I don't mean to offend anyone, but since PortMerc is using a Delta Kits injector there is no reason he should "have" to cure under pressure. If you are using a Delta Kits injector and find you have to cure under pressure you are doing something wrong. Curing under pressure in this case may make the break "appear" to be filled, but that does not actually address the problem as I see it.

I understand what you are saying Dave, and since you are not using a Delta Kits injector I have no problem with your advice, but for Delta Kits users I don't recommend curing under pressure. Systems that use suction cups rather than vacuum cups to attach to the glass require more pressure to make a good seal, so often users of these types of systems will opt for curing under pressure. In my opinion however, you never know for sure if you have the break completely filled until you remove the pressure from the injector, as the pressure can partially and temporarily close the breaks, limiting the amount of resin that you can inject. If you cannot remove the injector without air appearing you have not completely removed the air, or you are using so much pressure against the glass that when you release the pressure air is being drawn in from the surface as the glass returns to it original un-flexed state.

I've gone round and round with other forum members on this issue before, so let say this again to make myself very clear. I try to restrict my advice to Delta Kits users, technicians who have not identified the equipment they are using, or technicians who ask about a generic problem that does not have a system specific answer, but when it comes to Delta Kits users I sure would like to have them use the manufacturer recommended procedures before trying things that are not recommended by Delta Kits. It just saves our tech support team a lot of time and headaches.

[Dave M]

Brent,
This may be a little off subject, so I'll understand if you change it to another topic.
I understand what you are saying about needing to apply more pressure to attach an injector using suction cups, opposed to a Delta injector with vacuum pumps. However, this is done prior to the repair process, so are you saying that the glass would be more "deformed' using suction cups? I use very little pressure to attach my injector.I don't understand the connection to pressure curing. OR, are you saying that the injector itself, no matter what manufacturer, could apply too much pressure so back it off a little.
This is the first time I have heard mention opting to cure under pressure because of an injector that uses regular suction cups. Again, this was not something that GT teaches but heard of it here. (from who I can't remember)

[Brent Deines]

When you use suction cups to attach the bridge there is flex in the suction cups, so naturally you need to apply more pressure against the glass with the injector to get a good seal. We still sell bridges with suction cups, although not very many these days, and even though we use the exact same injector more pressure against the glass is necessary to get the same seal. The vacuum cups have almost no flex so they are more stable and require less pressure on the injector seal to get a leak free seal against the glass.

That's my long winded way of saying I'm talking about the injector against the glass, not the bridge against the glass. I'm sure you use as little pressure as possible which is good, but in my experience there is no way to get a suction cup mounted bridge to be as stable as a vacuum cup mounted bridge without applying a bit more pressure with the injector. Clear as mud?

[GlassStarz]

I like to pressure cure that said you shouldnt do it with the tripod style injectors you run the risk of curing the resin on the screw down piston and freezing up the injector with cured resin in the threads I agree with Brent unless you are using something like the Resinator you probably should pass on the pressure cure

[PortMerc]

Thank you both for the advise. I have been doing four to five repairs a day since class and am slowly getting my own groove.
I don't disagree with you Dave as you have more experience and are using a different system. But I'd like to cure without any pressure. I think that by applying pressure while I am curing the glass in an unnatural state creates sort of an illusion. I'd like to know that the damage has ZERO air in it before curing.
Today I tried letting the repair sit for a while. I found two things, #1 sometimes I need to drill down (just a tiny bit) to allow more resin to flow to those last tiny spots. And #2 using the evaporator on EVERY repair makes a significant difference. I was trying my rookie best to inspect for water, but the last six repairs I did I used the evaporator even if there was no sign of water and my work has come out perfectly. Even a six inch crack today with a 90 degree bend half way through. I think being in Portland and all our rain has something to do with it. I'll continue to practice different stuff on my practice windshields. Thank you all for the good advise.