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I make small items (coasters) that, after finishing them, they sick together. I have tried many finishes and have the same problem with all of them. io have had this same problem with: Lacquer, Polyerathane, Shellac, and Tung oil. I have also waxed them. I have tried placing all kinds of paper between them but they then stick to the paper. I have tried tissue paper, paper towels, waxed paper, printer paper and plastic. Any suggetions on how to avoid this? I have let them dry for about a month!
It's called blocking. A film finish when covered by something or especially another freshly finished part builds up solvent fumes and it softens the finish enough to stick. With most finishes it takes a full month before the finish is cured enough that this isn't an issue. If you used a finish with a hardener such as a fully catalyzed lacquer you would have less problems with blocking but it's still going to be an issue for about a week.
That definitely should not happen with most clearcoat finishes, especially shellac, nor with a penetrating oil like tung oil. Since you are having problems with every finish you try I'm guessing the problem is either in how you applying the finish or the environmental conditions. In general, you want to apply thin coats of finish and allow plenty of time between coats so that each coat can dry before the next is applied. If you are rushing that process a month might not be long enough for the solvents trapped in the lower coatings to outgas. Similarly, many finishes don't dry or cure well if the RH is really high.
What wood are you using? Some woods cause problems with the curing of finishes applied to them.
John
Thanks for this info. I have avoided lacquer because these are coasters and Laquer will not hold up to the water invloved when a glass condenstes onto its surface.
This sounds like the cause of my problem. Thanks for the input. I am using eastern red cedar but have also had this issue when using oak.
I have made hundreds of coasters with my CNC router and I always use Minwax semi-gloss rattle can polyurethane. If applied thick enough, it provides an excellent barrier to water from sweating of iced drinks. I haven't had any problems with them sticking together and I have shipped them all over the place. I pay attention to the instruction that says to either re-coat in less than 2 hours or wait at least 72 hours between coats. I use mostly walnut, soft maple and cherry woods. Here is a picture of one of the patterns.
Attachment 417179
A catalyzed lacquer will hold up a lot better to water but a conversion varnish would be waterproof as well as resistant to blocking. It would work much like lacquer however either a catalyzed lacquer or conversion varnish you would have to be careful how much you mixed at one time. After a certain amount of hours they would harden up in the container they were in. Because of this you would have to wash the sprayer out immediately after use.Quote:
Originally Posted by Jim Finn