How do I prevent stain from being removed during sanding?

Question

I am refinishing an old Remington 870 stock birch stock. I stained it with a dark cherry colored stain, and then began to apply Hope's 100% tung oil. I had read to wait at least a day before sanding and applying the next coat, though that seems to be a short period of time. However, when I sanded the stock, much of the stain I had applied was removed along with the tung oil (if I recall correctly, I was using 340 grit paper, and I had cut the first application of oil about 50% with mineral spirits).

I decided to restain the whole stock, and ended up staining it several times, letting it dry and wiping down with mineral spirits to remove the tackiness between each coat (I know that multiple coats are generally advised against, but the birch wasn't accepting the stain evenly and this helped me get a fairly even, nice stain). The stock is now fully dry (wiped the access stain off a day or two later with the help of mineral spirits, and then let dry for a week).

My question is: is there a way to properly apply tung oil to the stained wood without removing the stain during the sanding process? Do I simply need to wait longer for it to dry, not sand between the first couple of coats, use a finer grit sandpaper, or what?

Bonus question: This being my first woodworking project, my sanding left something to be desired. There are very minor sanding marks in the wood that I didn't notice before staining. They are mostly in the same direction of the grain of the wood, but a few of the swirls I didn't match perfectly. Is there anything I can do to fix this without removing the stain and starting over? It doesn't bother me very much, but I would feel unacceptably lazy if I didn't even make an effort to fix it.

Answer 1

My question is: is there a way to properly apply tung oil to the stained wood without removing the stain during the sanding process?

Yup: don't sand.

Drying oils are not a surface coating, they're a penetrating finish, so basically there's nearly no difference between sanding oiled wood and directly sanding the surface of the stained wood, which many guides specifically warn not to do.

Even when sanding a film-building finish (shellac, varnish, lacquer) great care must be exercised not to sand too much as if you break through the finish you can almost immediately reveal bare wood because stain penetration is extremely shallow.

Drying oils don't need to have the previous application sanded if they're applied appropriately. While it's become common advice to sand or scuff the surface when applying subsequent coats of tung oil in particular, but BLO as well, this is by no means the only way to do it.

The traditional method for applying drying oils specified that the surface should be wiped extremely thoroughly after application and in fact buffed hard with the wiping cloth, which ensures removal of all excess oil from the surface, and simultaneously burnishes the surface of the wood. Both of which were considered vital to the development of a good oiled finish.

There are very minor sanding marks in the wood that I didn't notice before staining. ... Is there anything I can do to fix this without removing the stain and starting over?

Basically your options are scraping or sanding to remove the marks, unless you switch to a film finish which can hide minor surface defects.

An oiled finish magnifies flaws, doesn't hide them, which is why surface prep for an oiled finish must be done more conscientiously than if using varnish, e.g. sanding to a higher grit. FYI when varnishing there's no benefit to sanding beyond about 220 grit and in fact you can often get away with stopping at 150, while if you're doing an oil finish it can be advisable to sand beyond 400.

Bonus answer to a point in one of your comments above:

I've read that with tung oil the first couple coats will get fully sanded away and the pulp mixture will fill in all of the imperfections in the surface

That's true to a degree but actually not the ideal way to go about doing this.

If you want to fill pores in the wood it's far preferable to use a grain filler, either homemade or commercial. Preferable because the results can be superior, and you get there faster and more reliably.

Since you might ask, homemade grain filler can be made from fine sanding dust (220 grit or higher) mixed with varnish; some people use oil as the binder but varnish sets harder and faster so it's preferable. You could also experiment with using wood glue.

Answer 2

The sanding between coats is entirely for the keeping a smooth finish. Any bubbles or raised grain are knocked back. When I sand, I rarely pass the sand paper more than a couple light passes. then check for visual and touch cues to see if anything more needs some extra sanding, say a drip that dried. If you are sanding away the stain you are sanding too much. It is also possible, especially with cutting the finish down, that you might not need to sand between each coat.

Answer 3

Something that nobody's mentioned so far is that if your stain isn't penetrating, you've got another problem.

If there's a previous finish still on top of the wood, forming a seal, stain won't penetrate, and the least bit of sanding will remove it.

'Sticky stain' is a very common symptom for this.

If that's the case, you might want to try to strip it again, and try a wash with something like acetone, lacquer thinner, mineral spirits, and / or turpentine. One of those should cut the finish and allow the stain to penetrate.