Cracks from one edge to another

[keithmac]

I tried to find the answer to this using several searches, but could not.
Are there any special requirements in dealing with a cracked windshield where the crack is short hairline, but it travels from the right hand edge of the windshield to the top of the windshield, it is only about 4 inches long total.

[keithmac]

Online research suggests that this is a stress fracture (there is no obvious impact point), and is unrepairable. Is that correct?

Thanks for any info.

[screenman]

Many people say it should not be done, I have repaired quite a few that have not gone on to give problems. I find them very ease to fill as they are often very wide, and if not the applying a little pressure to the outside corner really opens them up. brent may give me a reason not too, but in the past I have even used pit fill to fill a couple up that have been very wide.

Often they are caused by a badly fitted windshield, or a poor quality one.

[Brent Deines]

We repair them as well. As long as you can get to both edges or anchor both edges by drilling and filling as close to the edge as you can there is no reason it won't hold. I also agree with screenman that a higher viscosity can be used for particularly wide cracks.

A lot of technicians shy away from anything out of the ordinary but if you are properly trained, using the right equipment and using a high quality resin there are far fewer limitations than some in this industry would lead you to believe. I high quality fill resin has exceptional bonding strength to to assure the bond between the glass and the resin does not fail. A high quality fill resin is also flexible so even if the windshield is fitted poorly as screenman mentioned is often the case, the resin will have enough elasticity to flex with the glass. This is extremely important to understand because there are a lot of resins on the market these days that are brittle and cannot flex enough to handle the stress a crack as you described is subjected to. You should also know that acid free resins do not have the same bonding strength that resins containing acid do. That is not to say they are bad for some applications, just that in something as volatile as a stress crack they may not hold as well as a high quality resin that contains acid.

I don't want to get too far off the subject but it is also important to understand that there are a number of different types of acids used in the formulation of windshield repair resins. Some are more expensive than others but the trade off is often safety. Harsh acids are not a substitute for other additives that also improve adhesion, elasticity, tensile strength, shore hardness, etc. and should never be used as a filler for the purpose of cost reduction. Some will tell you all resins are the same but that simply is not the case and I feel using a "safe" high quality resin is paramount to completing successful windshield repairs.