“What is happening to my finish? I’m doing the same thing I’ve been doing for months now and all of a sudden I’m getting wrinkles in the finish that looks like someone put stripper or something on it”.

Welcome to a recoat window. If you are working with catalyzed finishes, you may experience a recoat window due to temperature change and the use of the solvents you are adding into the finish. Here is what is happening; the temperature is changing, it is getting cooler and the finish is taking longer to cure. Adding any retarders will just keep the coating open longer and cause it to cross link much slower.  When the next coat of finish is applied, it will want to connect, or cross link to the previous coat like two Lego pieces snapping together. However because the first coat is still curing, it is too soft and the solvents from the second coat you are now trying to apply rewets the surface film and allows the catalyst to penetrate underneath and cross link again or disturb the original linking and boom! You get a buckle, rise or Wrinkle.

 

This is like a kick in the pants. What was great in the summer is not great in the fall. Just because you have been adding a retarder all summer long due to the higher temperatures to keep your finish from curing too fast, blushing, having overspray or solvent pop issues doesn’t mean it is the course of action when the weather starts to cool down. If you continue to add the same solvent (retarder) in your finish during cooler temperatures we are slowing down our cure or cross linking time too much so now the cross linking process may take too long to cure, not at all or opens the door to the horror of finish gremlins “recoat windows”.

 

To help you get an idea of what a recoat window is, let’s use the analogy of making ice cubes in an ice tray. Understanding the hydrogen bonding forces that align the water molecules to freeze is kind of like understanding how the catalysts cross links.

 

Let’s say you fill an ice tray with water and place it in the freezer. Then, 20 minutes later, you add more water into the tray. No harm done. The water hadn’t started to freeze yet and so the new water is received in the beginning stages of bonding. Now let’s say you want to add water to the ice tray hours later after the ice cubes are formed and are now solid in the tray. The water you add on top will simply freeze itself to the current ice cube and will become a solid mass connected firmly on top making one cube. However if you add water to the ice tray once the ice started to form, say when it has a slight film forming in the tray, the water would rewet or break through the film already starting to cross link, thus disturbing the process and adding to the mix. Removing the ice now from the tray when the ice is solid will cause the ice to shatter when you twist the ice tray to pop the cubes out. Bam! You hit the recoat window of making ice.

 

Cross liking of the catalyst is similar. When the retarder is put in the finish it opens up the window of that in-between time when you don’t want to recoat, so be conscious of that. If you hit a recoat window the whole coat of finish will wrinkle or react. Sometimes however you may see some small wrinkles here and there. Not all over the surface, these can be caused by other cross linking villains.

Let’s say the table top you sprayed today looks great except for one tiny spot about 3 inches from the center and that is the same spot where you needed to sand that pesky dust bunny from the previous coat earlier in the day before putting your final coat on. The problem here could be a result of that film being sanded just a bit too thin in that one spot causing the solvents in the last coat to rewet or penetrate enough through the film and create the double cross (no pun intended) or Blister (Film defect which occurs when volatiles leaving a film are trapped and expand inside the film.) No recoat window here, just a vulnerable area. Had it been left to fully cure chances of that area reacting would have been minimized. It seems that many finishing villains stem once again from time tables and that is affected by the solvents we choose to use and the time we allow the coating to cure. To obtain consistent and reliable results, the key to success in our finishing process must be that we allow the proper time for the coating (chemistry) to react and cure. If you try to expedite this process we may find ourselves face to face with a scary situation.

 

Another form of wrinkle can happen when we try to apply a harder or hotter finish on a softer or weaker coating; the harder coating will cause the softer to give way or wrinkle from a mismatch or incompatibility. This is much like when Vinyl sealers sometimes cause wrinkles, applying two heavy coats of a vinyl sealer tend to be too soft and stretch when we put a catalyzed topcoat on. The catalyzed topcoat will shrink or grab the vinyl pulling and stretching it until the film gives way and voila… wrinkle!!

 

When glazing, wrinkles can happen many times if we topcoat before the glaze is dry or cured enough or we have the glaze applied to heavy this can tend to make the topcoat wrinkle. Many glazes have recoat windows that must be observed or failure is sure to follow. Always stay within the parameters of the glazes windows and all will be great, step outside of the time frames and the goblins will haunt you for life.

 

Till next time, may the only monsters you see this fall be the kids at your door on Halloween night.