Open pore finishing

Re: Open pore finishing

William Duffield, on the Cohansey

>back in the good old days, they used ground glass suspended in Shellac. They mixed pumice with the first coats of French polish.

We use Behlens Por-o-Pac, which is basically the same sort of stuff in a BLO and japan driers vehicle. The nice thing about it is that you can add an oil based stain to the filler and kill two birds with one stone. No need to sand after applying, just rub it off with coarse burlap before it has a chance to set up completely, followed by soft knit cotton rags, let it dry a day or so, depending on weather, and seal it in with shellac. Follow directions on the can regarding thinning with MS, and applying with a brush. Also follow Finishing Rule Number Zero: Try it first on scrap, all the way to the end, to make sure you like the color and other features.

An advantage of pumice is that it is transparent and its index of refraction is close enough to the linseed oil or the shellac that it fills the pores without killing the depth or chatoyance of the wood, as long as you get all the air bubbles out from under it. If you want it to be opaque, pigment stains will do that for you.

Re: Open pore finishing

Michael R

>Por-o-pac is a good filler. It is sometimes easier to use if you wash coat the wood first, especially when you are staining before filling. When you apply it to bare wood, it can be hard not to leave streaks and smuges without a light sanding before finishing. If you wipe hard enough to get all the filler off the surface, you can pull some of the filler out of the pores. I use vinyl sealer as a wash coat, but shellac sould do just as well, and I imagine (haven't tried it) that a thin coat of wipe-on varnish would do also.

Striking the filler off with a squeegee works very well and doesn't tend to pull the filler out of the pores. I use an old silk screener's squeegee, but rubber will do as long as it's in good condition with no nicks.

Universal Tinting Colors colors work well to tint filler when needed. Oil-base stains work fine, but UTC's are concentrated and don't add additional resins and solvents.

I've only tried their water based filler once, and didn't like it. Flashed off too fast for me, and workability wasn't as good.

A minor point, but the filler in Por-o-pac is about 15% each of Silex (superfinely ground quartz), calcium sulfate, and magnesium silicate hydrate. Pumice is indeed often used in the bodying-up stage of french polishing, but it's very abrasive and so isn't used in many commercial wood fillers, if any.

Some old school finishers use Plaster of Paris as a grain filler. "Sgian Dubh" has recommended that in the past, but I never got the hang of it.

For your consideration..

Michael R

Re: Open pore finishing

William Duffield, on the Cohansey

>Thanks for the additional advise and for the correction. I forgot to mention the squeegee. I have a small tip: If the filler is drying, and you cant lay your hands on a squeegee (maybe someone forgot to clean it after the last time they used it), you can make do with an unbreakable electrical switch plate. That's the flexible kind, that cost a few cents more than the hard plastic one, but that we should be using for all receptacles and switches in the shop.

Do you think the abrasive problem with the pumice is mostly due to larger particle size? A more important question: I haven't used the por-o-pac without a pigment stain. If you use it natural, does it dry transparent, like pumice?

Re: Open pore finishing

Michael R

>I'm not sure. I do know that pumice is very abrasive and that Silex is much less so, calcium sulfate even less because it is soft. It may be the particle size; I know that Silex is ultrafine, an the little I've seen definitely seems finer than even FFFF pumice. I think silex particles are rounded, while pumice is basically ground up glass foam with the expected sharp edges. Don't quote me on this I haven't verified it. Maybe I'll drag out the old microscope & have a look.

I almost always use colored filler, but from what I remember the natural disappears pretty well on medium to light finishes like "natural" oak. It's just that most of the filled finishes I have done were pretty formal and required some color in the pores (walnut & mahogany.) The big problem with filler on large pored wood is packing the filler into the pores so you don't have air under the filler, which does look bad under clear fillers. That's one of the reasons I like a squeegee.

Michael R

Re: Open pore finishing

R.J.Whelan

>Tom .... here's what I do with open grain material:

1. Plane and scrape as usual

2. Apply tung or BLO and "sand it in" with 220 at an angle to the grain - sanding will produce a slurry that fills in the grain. Wait about a half hour and wipe down across the grain with burlap or some other rough material - don't be too agressive with the wiping off.

3. Wait 24 hours and sand with 220 (with the grain). If the grain is filled (probably not with oak, but maybe with mahogany) you can go on to 3. If not repeat step 2 as many times as necessary to get a smooth surface (twice usually does it for me).

3. Apply a coat of 2# shellac. Don't sand after this coat.

4. Apply another coat of shellac (I use 2# for both coats).

5. Sand with 320-360

6. Apply whatever topcoat(s) you want and sand with whatever grit you're used to.

This will give you a very smooth surface and the filled grain will match the rest of the timber. You can control sheen with final topcoat or by rubbing out with fine grit paper, synthetic pads or bronze wool (I don't like steel wool because of the possibility of tiny spots of rust if you don't remove every last spec.

Good luck ... rj