09-03-2010 09:27 AM
A friend of mine is finishing a walnut gun stock. He's using "tung oil" and has applied approx. 18 coats. He said it looked great until he noticed dimples in the finish. He thinks it's the pores. So, is that possible and is there a way to fix it or does he need to sand it all back down and use a sealer? Any sealer better than others? Any help would be appreciated.
09-03-2010 12:01 PM
The first question is "what kind" of tung oil. Most brands of tung oil finish aren't tung oil, and some of them behave quite differently from tung oil. The dimples are likely to be the pores, but they have been their right from the beginning. Can'yt really answer the question without knowing the variety of finish. (Brand name and the name the label are both needed.)
09-04-2010 02:51 AM
…to the WOOD Magazine Forums, particularly to the Finishing & Refinishing Forum. I hope you will visit often. You will find a number of accomplished woodworkers and finishers here who stand ready to assist you with your finishing and refinishing questions.
Walnut is a semi-diffuse porous (or semi-ring porous, depending on your point of view) hardwood. It can indeed exhibit “dimples” when finish is applied, depending on how those dimples are described. If we are dealing with pores which are not yet filled they will appear as very small depressions in the finish that are quite small in diameter, typically smaller than the diameter of a mechanical pencil lead. They will also be more or less uniform in their distribution and will closely follow the growth rings of the walnut with the greatest concentration of them associated with the bands of earlywood. If they are larger and are random in their distribution they are almost certainly something else.
Beyond that, it is difficult to imagine that the pores in the walnut would not have been filled after the application of 18 coats of virtually any finish, even pure tung oil. At the very least the dimples should have been obvious after just a few coats of finish and become less prominent as more coats of finish were applied. To have noticed them only after 18 coats of finish suggests at least the possibility of something else. Certainly if one of the tung oil pretenders was used, whether actually an oil/varnish blend or a wiping varnish, the pores should by now have completely disappeared. So, while it will be helpful to know what finish your friend actually applied, it may also be useful to know the process he used in applying the finish. Specifically: 1) what preparations did he make to the gun stock before he began to apply the finish, i.e. was stripping of a previous finish involved and how was that accomplished, 2) did he sand between coats, 3) how long did he wait between coats? A somewhat different but related question is how will this gun be used? Is it a field gun that will be subject to the weather, or is it primarily a show piece?
Whatever finish was applied; if the only objective is to remove the “dimples” (and the dimples are indeed evidence of open pores in the walnut) it is unlikely that the finish will have to be removed. It will need to be leveled so that the finish in the pores is brought to the same level as the finish around the pores. This will require some cutting back of the finish by sanding or scraping. Knowing what is on the stock will determine the direction after that.
Finally, “sealer” is just another name for the first coat of finish. Sealing, in and of itself does little to fill pores and products marketed as “sealers” are generally to be avoided. The pores in wood like walnut can be filled with a paste wood-filler; but, it is almost certainly too late for that, if it would have been a good idea in the first place. Filling the pores with finish would probably be the direction I would take in finishing a gun stock; but again, that should have been largely accomplished already with 18 coats of finish, depending on technique. Of bigger concern to me is the use of tung oil (if that is what is on the stock). Oil finishes, whether tung or boiled linseed oil exhibit very poor properties with respect to moisture resistance and resistance to abrasion. Both also oxidize quickly resulting in a dull and lifeless finish. A more common and far more durable oil finish for working gun stocks is Tru-Oil which is polymerized linseed oil. The polymerization process significantly improves durability of the finish…