Question about wet sanding w/ finish mixture and filling grain

[Fitzhugh Freeman]

I have some purpleheart that I'm finishing. I read so many conflicting posts about what to use that I just went with what I know best (doesn't mean I know it well - please keep that in mind). I'd read people who seemed to know what they were talking about say not to use water-based finishes, not to use oil-based finishes - both gave logical sounding reasons why doing so would mess with the natural pigments - one said not to use BLO, another said use BLO. I decided I would just let the chips fall where they may regarding the color retention and try to get a nice finish otherwise.

I sanded to 320, let it sit and get nice deep color, then mixed BLO, wipe on varnish (Formby's Tung Oil Finish - apparently contains a lot more Formby and Finish than Tung Oil!) and Naphtha, say a few big glugs of BLO, a few smaller glugs of Formby's and a bit less Naphtha. I wet sanded with 320, 400, will do another coat or two with 600, maybe higher if I'm bored. It went on nicely and brought out wonderful depth. I'm at the stage of wiping off the specks that rise to the surface after the first coat.

I wasn't working in good light (lesson learned) and walked out into the sun to admire my results. Oops. I hadn't properly filled the grain. I've read that this approach fills small grain features with muck made from the finish and wood dust. There was plenty of that around on the surface as I sanded but I think I wiped it all off. Note that most of the surface is very very smooth but there are what I think are medullary rays - running mostly along the grain - and these are the areas that need sealing. I've worked mostly with hard maple and not encountered this, and with oak, which I filled with CA and ran a card scraper over to get a glass-smooth finish, but not good color.

Any suggestions? How do you wipe down the surface after wet sanding and not wipe off all the muck? I assume any filler product would need to match the color of the wood.

[Harvey Pascoe]

Grain filling using oil or varnish and then wet sanding it is pretty much the same as using a filler stain. It takes a bit of experience and skill otherwise you get blotchiness. I wipe across the grain but a one time application rarely completely fills. I prefer to use homemade filler stains with inexpensive natural earth pigments that I mix with varnish. I first do the wet sanding without the pigment to see what the final color will be, then mix up my filler stain to match. This does NOT enhance the natural color of the wood but rather hides it. The result is artificial and muddy looking as all stains tend to be and only rarely do I use this method anymore. Either grain fill with shellac or go to rubbed out varnish if you want a glassy smooth finish. Making a slurry by means of sanding is a poor way to accomplish this IMHO.

[Prashun Patel]

I've finished several pieces this way.

I think a picture might say a lot.

There are two things you'll compete with when doing this type of finish: even sheen, and grain filling.

If you are experiencing sheen probs, then this will be solved by patiently applying a couple more coats.

While it is a slow way to fill the grain, it can be done. You can use 220, 320, or 400 grit sandpaper with the varnish. Don't be too aggressive in wiping it off. Move the slurry around, then buff most of it off; the rest can be sanded off/down before the next coat.

You might try just switching to a straight wiping varnish (no oil). That will allow the slurry to dry harder, which will make it easier to buff/sand off once dry.

A wiping varnish can be applied the same way as an oil varnish: rub on, rub in, rub off. You just start to build faster with straight varnish vis-a-vis OV.

[Harvey Pascoe]

Yep, going to straight varnish is what I did, I also let it set a bit and cure a little so as to avoid wiping too much off. This let me wipe harder and get a more even appearance and also seemed to aid in grain filling. I did this with Padauk which has very deep pores and it ended up looking like aged mahogany. Very aged. However, my final finish was a sprayed varnish and I did it only for grain filling. I think this method works a lot better on very dark woods than lighter woods. What do you think?

[Fitzhugh Freeman]

Thanks - I took the photos earlier but didn't have a chance to upload them until now. I just noticed there are a few areas that now look unfinished, two streaks about 1/8 to 1/4 inch wide and a few inches long. I don't have photos of those, need to charge the batteries again. I don't know of any silicone products around here - heard that can cause this. I haven't tried another coat yet.

I'm thinking another coat of the same mix, hoping it fixes the streaks before going to varnish as suggested.

Don't laugh - it is a small piece of wood, 4 1/2 by 11 inches, nothing but a piece of wood w/ lightly beveled edges. My girlfriend found it in the scrap bin at the McBeaths, wants to mount some art tiles she got on it and hang them on the wall - knows the color will likely change.


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I now know why it was in the scrap bin! I never imagined such a small piece of wood could need so much effort. The grain is going every which way in crazy waves. I think they change when I'm not looking. I don't know if all purpleheart has this much depth, but it is really beautiful. It looks worse in the photos - the dark/light spaces switch as angle changes - it's not all mottled like it looks.

[Harvey Pascoe]

I would not try sanding in another coat of whatever you used as you are likely to create a big mess with lots of blotchiness as you will sand through the existing in some ares and not others. At this point I'd suggest you continue on with whatever finish you planned on using. If you're looking for a mirror finish, you won't get it with wood that grainy and by that method. If you want a mirror finish it will take you another 5-6 coats of brush or spray on varnish with heavy sanding in between and then you can rub it out to whatever sheen you want.