Why do I get air bubbles where I have already filled the crack with resin?

Question:

When repairing cracks, why do I get air bubbles where I have already filled the crack with resin?

Answer:

If you simply run resin along the crack, it will seep in at different places depending on the width of the crack. Always fill the crack from the impact point until it will travel no further into the crack, then add a drop at a time to the surface of the crack about 1/16” behind where it stopped flowing. The result will be that with each drop of resin added, the resin will flow another ¼” to ½”. Repeat until the crack is full. Sliding a bridge, using an injector at each end, or using a crack spreader will also often create air bubbles. It is best to fill the crack when it is in its natural state, rather than using a lot of pressure on the inside or outside the glass whenever possible. As you fill the crack cover with curing tape. This will help keep air from entering back into the crack where is already been filled.