[Brent Deines]

There are a number of reasons that might keep a leg from filling, but just because they are sub-surface is not one of them. Before I go any further I need to state that when talking procedure, I can only speak for Delta Kits windshield repair products, as we tend to buck many of the trends other manufacturers have adopted over the years. If using another system I always recommend contacting the manufacturer of that system if having difficulty filling breaks.

So with that in mind, the legs of a sub-surface star break should fill just fine with the right amount of pressure and the right resin, but air will be compressed and trapped at the end, or in rare instances against the edges of the crack. When the vacuum cycle is applied the air is pulled from it's resting place at the end of the crack and up though the injector. This is why Delta Kits is so adamant about using hydraulic pressure vs air pressure to inject the resin into the break. If air is used you are trying to push resin with air on one end, and against air on the other end. If too much pressure is used the air will push into or through the resin, but that cannot happen with a true hydraulic system.

Many systems claim to use hydraulics, but if you analyze the delivery system it is clear that the air is not completely removed from the system. With the Delta Kits system there really is not a lot of vacuum used. We use just enough vacuum to get the air to start flowing, and then let gravity take over, very much like the way a siphon hose works, except with air rather than fluid. I'm sorry, this is beginning to sound like a sales pitch, and that is not my intention, but this is a very important fact to consider and we have done a great deal of research on this matter. However I will refrain from going into more detail about what makes a system perform or fail to perform for now.

Some of the things that can keep a leg from filling are a blockage (glass particle) at the beginning of the leg that will not allow the resin to pass, too much pressure on the injector against the glass which flexes the glass down and tightens the crack, too much heat which expands the glass and can tighten a crack, or an ineffective delivery system (injector).

As for drilling, I agree that conversation should probably be another thread, or added on to an existing thread, but it is tied into the resin delivery method as well.

Once again I would like to make it very clear that nearly everything I write about methods is system specific. If you don't use a Delta Kits system it is quite likely that much of what I share will be of little value to you. I would also caution Delta Kits users that much of what you read on this forum is posted by technicians who do not use Delta Kits product, and therefore much of what they share will have little or no value to you. In fact, in many cases it can get you into trouble, so please be sure you differentiate between system specific procedures and generic procedures.

Darn it screenman, you beat me to it. Good points!