Tacky!

[Matt P]

I thinned some MinWax Clear Gloss Polyurethane with 50% mineral spirits so I could wipe it on rather than brush it. It has not dried properly and is very tacky. Is this because of too much mineral spirits in the blend, or could the poly be old?
tx,
Matt

[Steve Schoene]

Just adding mineral spirits shouldn't have a large impact on curing speed, and if anything is likely to speed it up because you wipe on a thinner coat than if you had brushed it on. If it has reached the "tacky" point, then the thinner has likely almost all evaporated and it is now the chemical cure that is lagging.

You haven't indicated how long it has been drying. The cure time will depend mostly on temperature, but it could also be affected by humidity, the kind of wood, how much time was allowed between multiple coats, the type of stain or dye used under the top coat. If you can add to the description of what was done it will help figure out the problem. In the mean time, I'd advise patience.

As far as age goes, varnishes have a very long shelf life until opened. Then the clock starts clicking.

[Matt P]

Thank you Steve, the poly was about 3/4 full, opened about a year ago.. it's been drying about 4 hours, medium humidity, over a shellac wash coat on bocote wood. Being impatient, I wiped some of the stickiness off with mineral spirits. Maybe will buy some fresh poly.. !

[Steve Schoene]

Your problem may be the bocote, which is an oily hardwood. The shellac wash coat is the right idea, but it may take more than a thin wash coat of shellac to keep the oiliness separated from the poly. You do have to be sure that you are using dewaxed shellac under poly.

I would certainly give more than 4 hours drying time under the circumstance. Four hours is pretty much ideal, and with the bocote you can expect longer drying. If it doesn't dry enough to sand in 24 hours, then you may have a problem.

[Howard Acheson]

Matt, you have two strikes against you. As Steve has said, your wood is contains a high amount of natural oil which will inhibit the drying of the finish. However, as important is the age of your finish. Any finish that has been opened and then sat unused for a year is very likely to be bad. An indication of a out-of-date finish is that it dries very slowly and maybe never cures.

If it does not get hard within a few days, I would recommend stripping off the finish and starting over with a fresh can. You could also apply a coat of dewaxed shellac first to the wood. This will seal in the natural oils and your varnish top coat will readily adhere to it.