by Rick Hill
Q.
I have a general question regarding UV-cured finishes. Should the previous coat be totally cured before the next coat of topcoat is applied? Also, when using a water-based stain (high amount of pigment) with UV-cured topcoats, what interactions should one be concerned with?
We had a problem with stain adhesion when this combination was used. The stain seemed to pull apart, leaving some on the wood and pulling some off. The finishing supplier simply added more resin to the stain and an additive to the topcoat, which thinned it out. This obviously costs more. Are there any other options to try, such as higher-intensity UV lamps?
Finally, can you recommend any good reading on this subject?
A.
In response to your UV questions, we find that on 100 percent, solid roller-applied UV coatings, the first coat does not have to be fully cured to apply the second coat. (This is commonly called "B staging".)
In spray-applied UV coatings though, the UV first coat cannot be partially cured before applying the second coat. It either has to be fully cured or sprayed over an uncured first coat ("wet on wet").
These are general rules for UV coatings as discussed with Jim Bohanon, a specialist at the Valspar Corp. in High Point, NC. It may not apply to your exact coating from your current supplier.
Rick Hill is an independent representative and consultant for industrial wood finishes. He has been involved in the woodworking industry for 12 years, and has been known to actually hold, shoot, and clean a spray gun.
If you have an industry related question, visit WOODWEB's Finishing Forum to post your question.
