Recently, we have received multiple phone calls from customers on the subject of repairing damage that has been repaired before. First off, it should be stated that windshield repair is a permanent process. However, fixing a botched job is sometimes possible but it is important to weigh the benefits vs. the drawbacks of taking on such a challenge.
There are several different challenges you may encounter when presented with a repair that has been attempted previously. As unbelievable as it is to true professionals, there are windshield repair technicians who only use high viscosity pit resin to repair a rock chip. If you run across this type of attempted repair, the air pocket in the damage will not look filled and there will only be a layer of resin on the top that is cured, but if a previous technician has used a low viscosity resin, more than likely the air pocket of the damage will be partially filled. If the damage appears partially filled and you have ruled out the possibility of liquid being present in the damage, you can be reasonably sure a repair attempt has been made.
Yellowing in the pit area is a good indicator that either the previous repair is of considerable age or a low quality resin product was used. When you inspect the damage (a must before attempting any repair) use a probe or scribe to clean out the impact point. The best way to determine if a repair has been previously attempted is by noting the difference between the glass and the resin (resin will be softer). Assess the damage and determine if a re-repair is in the best interest of the customer, then before initializing the re-repair, inform your customer of your suspicions regarding a previous repair attempt and set realistic expectations for the outcome.
If resin has previously been cured inside some of the air spaces, the next step is to drill into the largest air pocket in the damage. The goal is to inject resin into the areas that were not filled in the previous repair attempt, which may require drilling in multiple areas if the air pockets are not connected. Before you start the repair you need to ask yourself if the completed re-repair will be cosmetically acceptable to the customer or if it would be better to explain to the customer why you must decline the job.
In summary: Properly evaluating the damage to determine the likelihood of success prior to starting a re-repair is essential. If it is possible to access the unfilled air space without creating too much additional cosmetic damage, the chances of a successful re-repair are quite high. By contrast, if it is necessary to drill multiple holes to get the damage completely filled with resin, you are essentially creating additional cosmetic damage that may look unsatisfactory to your customer. Setting realistic expectations for the customer and knowing the limits of your skill set will determine how satisfied your customers will be with the quality of your work.