Blushing happens because of many things; let’s take a look at some other reasons beside humidity becoming trapped under the film. We can experience a blush from an improper balance in our solvents either by choosing the wrong solvent or adding too much solvent. This causes the more true solvents to evaporate, leaving the diluents solvents and non solvent portion of the coating to evaporate later, thus trapping itself under the film. We also experience blushing when we have a condensation problem in our air lines, so be sure to invest in some good driers or inline filters. Another culprit is when the substrate is colder than the finish or the finish temperature is different than the ambient temperature. The two worst times to finish is in cold and/or damp conditions. A common occurrence…spraying finish over a stain that is not completely dried! This can cause a blush sometimes days later not to mention the possibility of experiencing adhesion issues! Did you know incompatible materials are another blushing villain? For best results, staying with one manufacturer from start to finish will ensure that your solvent blends will be consistent and compatible, lessening the chance of a blush even when humidity is not prevalent. If you’re mixing different manufacturers products, problems could exist further down the road, long after the job has left your site.

 

Last month I explained the “more on” theory. Here would be a good example of how that theory could cause you more grief than relief. If you add too much retarder into your coating, you can actually get the finish to blush more because it would stay open too long collecting the moisture and you could also experience too long of a dry time because you retarded the finish so much. When adding retarders to fight off the blushing, start with the smallest amount and add only as needed. Mornings tend to be more humid due to the morning dew, than later in the day. Once the sun comes out and the moisture dissipates into the air you may have no need to add retarders at all. Adding a ton of solvents to fix a blushing problem in the morning doesn’t mean you’ll need it later in the day.

 

Coatings with higher solid content tend to blush less than coatings with a lower solid content. This is because you have fewer solvents that can be trapped under the film. Solid content in a coating is important on a lot of different levels — more coverage, less applications, less likely to blush and better cost per square foot. Remember, it is the volume solids in a coating that is relevant not the weight. Weight solids would be like that SUPERSIZE drink you purchased at the fast food chain. Everything in the cup, all that ice and the cola. The Volume solids would be just the COLA (the product you’re really after).

 

Many times the blush will go away when left to dry, but in some cases the white haze will remain trapped under the coating. Depending on the type of coating you are working with, you may be able to fix the problem by misting some retarder over the surface to re-wet the coating enough to allow the trapped moisture to escape. This should be done fairly early in the drying process and caution should be used not to apply too heavily as you can experience sag or sheen problems. Let me give you a visual image on how a retarder can rewet a coating if needed to fix a problem. You have a rag heavily saturated in solvent that you placed on a table top, if you removed it quickly, nothing would happen to the finish. However if you allow the rag to remain there, the solvents in the rag would rewet or soften the finish and allow moisture to enter or release depending on the case. So use only what is needed. Oh and DON’T use a rag, but rather spray lightly.

 

If the blush is cured into the finish you will need to sand it out before re-applying another coat or you will just bury it deeper into the finish. Your supplier can help you choose the right retarders for your conditions.

 

Blushing is never fun, whether it’s the finish or an awkward moment, no one likes being stuck in a haze.