Sanding back a pore-filling coat of shellac

[Basschair]

Hello all,

I've been debating whether or not to post this, but it's a nagging question and I can't get over it.

I've put down coats of shellac to pore-fill, and am in the process now of sanding back to "bare" wood so that the surface is only wood and pores that have been filled or mostly filled. The woods are maple burl, Af. mahogany, and curly maple.

My basic question is this: after sanding back to the wood, should the surface look like raw, unfinished wood again (like it did before putting on the shellac) but smoother and perhaps with the little shiny freckles of shellac that are now in the pores? Once it looks that way should I stop sanding that area to avoid sanding too deep and opening new pores?

I've got spots on the mahogany that are pretty stubborn: they are much darker post-shellac, and initial sanding isn't changing that. There are other spots on the mahogany that have sanded into a much lighter shade (close to the original color) which indicates the bare wood, right? Is this normal with mahogany? I'm a little concerned that once I'm done sanding and the varnish goes on, it's going to end up blotchy because of these random dark spots.

[OHSPyro89]

Well if you used a clear shellac and are going to use a clear varnish, I don't think there will be color issues. If anything, test it on a test piece. Test pieces are god's gift to wood finishing.

I once saw a video, which is now buried somewhere in the internet, of a guy pore filling with drywall compound on an acoustic back. After he filled, he lightly sanded the surface. He sanded enough so the wood would show through the drywall compound, but was careful not to sand through the pore filler.

I'd say just take a little precaution and try not to sand very much at a time, it won't take much to sand through the filler.

[Basschair]

Originally Posted by OHSPyro89

I'd say just take a little precaution and try not to sand very much at a time, it won't take much to sand through the filler.

Yup, pale blonde, dewaxed shellac and clear varnish.

I guess my concerns could be boiled down to this: how do I know if I've sanded enough without sanding through?

[62bass]

Originally Posted by OHSPyro89

Well if you used a clear shellac and are going to use a clear varnish, I don't think there will be color issues. If anything, test it on a test piece. Test pieces are god's gift to wood finishing.

I once saw a video, which is now buried somewhere in the internet, of a guy pore filling with drywall compound on an acoustic back. After he filled, he lightly sanded the surface. He sanded enough so the wood would show through the drywall compound, but was careful not to sand through the pore filler.

I'd say just take a little precaution and try not to sand very much at a time, it won't take much to sand through the filler.

I agree with this. And it always helps to do a teat on scrap wood well ahead of time.

Dewaxed shellac and clear varnish should not be a problem. Once you apply the first clear top coat of varnish you'll see if you have a problem. If you do, just wipe it off with varnish thinner before it dries. Then do another coat of shellac.

Talcum powder is sometimes used as a pore filler with shellac and works well. Also rottenstone and pumice. Usually though these are mixed with an oil like boiled linseed and take on a darker colour. You can easily tint the shellac with alcohol soluble dyes too so that the filler isn't so white.

[Basschair]

Well, then I've most likely sanded too much. Or maybe not enough. Arghh!

I'm still wondering how to know when you've sanded just enough on mahogany...? I'm getting such a variety of results on this one. In fact, let me grab my camera and take a few shots to show what I mean.

Yeah!!! Another learning experience!

[Basschair]

Okay, here's the results I'm getting in different spots. What I was going for was this: coat with shellac and sand back to bare wood so that just the pores had shellac in them to create a more even surface...not perfectly flat, just more even. To me, that means I should see a wood color very close to what I started with before the shellac went on (such as the color of the core wood in the lower horn in the second-to-last pic). Agree? Disagree?

[62bass]

If you're talking about the little pin holes in the core wood that bothers you, try another coat of shellac. Don't sand as much and use a finer grit of sandpaper. The finish coat will also fill any pores. But any finish applied to wood, even something as clear as lacquer does colour the wood darker and pores will stand out a little more. Personally, I wouldn't be concerned. It will look good when finished.

Another option which is a step backwards and a lot of extra work--remove all the shellac and sand back to bare wood. Apply a heavy coat of boiled linseed oil or tung oil and wet sand with 600 grit paper. Wipe off the residue across the grain. The fine sanding dust will create a slurry with the oil and fill in the pores. When dry sand very, very lightly with 600 grit. Then finish with the clear coat. However, besides being such a lot of extra work for you, the oil will darken the wood a couple shades. Personally I think it would look good with that wood.

[Basschair]

Originally Posted by 62bass

If you're talking about the little pin holes in the core wood that bothers you, try another coat of shellac. Don't sand as much and use a finer grit of sandpaper. The finish coat will also fill any pores. But any finish applied to wood, even something as clear as lacquer does colour the wood darker and pores will stand out a little more. Personally, I wouldn't be concerned. It will look good when finished.

Another option which is a step backwards and a lot of extra work--remove all the shellac and sand back to bare wood. Apply a heavy coat of boiled linseed oil or tung oil and wet sand with 600 grit paper. Wipe off the residue across the grain. The fine sanding dust will create a slurry with the oil and fill in the pores. When dry sand very, very lightly with 600 grit. Then finish with the clear coat. However, besides being such a lot of extra work for you, the oil will darken the wood a couple shades. Personally I think it would look good with that wood.

Actually, I'm cool with the pin holes. I'm more concerned with the larger areas of darker wood. For example, in the first picture running down the center of the core wood is a darker area of mahogany that I probably didn't sand as much as the area to the right and left of it (where the mahogany looks much more pale, although the far right of the core wood is dark again).

Since this process is new to me, I'm not sure what to expect during the sanding process. Is it normal to have these areas of lighter wood? Is that something to be avoided as (I'm assuming here) it will show up lighter and/or darker after varnish goes on? Or, is this normal and the varnish will soak in to those lighter areas and darken them?

Ultimately, I'd like to do it right, or at least as right as someone who's doing it for the first time can get. I don't mind more sanding to even out the color, nor removing as much of the shellac as I can through sanding and lots of wiping with den. alcohol.

[62bass]

There will always be variations in the grain of the wood that will show up a different colour once a finish is applied. It might be because you didn't sand it evenly. I don't know from the picture. Try sanding everything evenly with a fine grit. Then apply another coat of shellac and see how it looks. If that doesn't help then sanding isn't the problem. Some guys go overboard trying to get an even colour to the whole body or piece of furniture--whatever. They apply a stain to the light areas to blend in better with the dark. When the differences were dramatic this can look good. But too much of this makes the wood look very bland and you almost are as well off painting it a solid colour, which is a shame with such a nice piece of mahogany.

Anyhow, to even it out more colourwise you would apply a glazing stain on the lighter areas to blend them in to the colour of the darker wood. I use a gelled oil based stain for this. Other guys use other types of stains. I find the gelled stains easiest to work with. I wipe a small amount on the desired area, wait a few minutes then start rubbing it off with a clean cloth until it's close match. It takes a bit of fiddling to get it right. If it's too dark wipe some stain off with a cloth wetted with paint thinner (for an oil based stain) You might have to do the whole process a couple times adjusting the colour each time to get it right. Obviously you need a few different colours of stain to mix together to get your final colour.

I've gotten fairly good at this from a lot of work restoring the finish on wood work in old houses and just did a big job with all the trim in my dining room at home. You just have to be able to look at a colour and determine what factory colour is closest and what other colours of stain would need to be added to it to make it a match to the original. It's not a science-just a skill you develop with practice. I've had a lot of practice.

Actually, this whole subject is covered in great detail complete with instructions and photos in the book I always recommend-"Hand Applied Finishes" by Jeff Jewitt and available from Taunton Press. It's worth picking up a copy just for that data alone, but the rest of the book covers many other types of finishes that can be applied by hand without spray equipment so it's a valuable resource for anyone who wants to do this type of work.

So give the sanding a try first. If that doesn't help consider the other option I've covered.

I know I could do the job if I had the bass in front of me and could study what's going on. You might be able to do it too with a bit of study, practice and patience.

It's going to be a nice looking bass when you get finished.

[Lonnybass]

Paul-

Slightly unrelated question but I'm curious from your photos - what's the roundover radius for the body? Did you do it on a router bit or with a spokeshave? I dig the contours you achieved...very MTD or KenSmith-like.

Lonnybass

[Jazzdogg]

Set up a work light so it shines parallel to the surface of your bass and wipe the wood with mineral spirits. Move the light around to assure you are able to see every square inch while wet. If you like the appearance while it's wet, you're usually good to go with finishing. If you don't like what you see, the mineral spirits will enable you to clearly see exactly which areas need more work before finish is applied.

Good luck!

[Mikey R]

Ive never used shellac so Im quite interested in this too.

So, question for the experts - successive coats of shellac burn in to the previous, so would it be possible to sand down till most of the wood is bare, maybe with a few blotches, then add one more very thin coat to even up the surface, sanding back but not all the way to bare wood? This way, all the pores are filled, and also the surface will have a thin and probably fairly even base coat, ready for the laquer? To me, this seems like a fair way to reduce the risk of blotchiness, but I may have misunderstood?

[Jazzdogg]

Originally Posted by Mikey R

Ive never used shellac so Im quite interested in this too.

So, question for the experts - successive coats of shellac burn in to the previous, so would it be possible to sand down till most of the wood is bare, maybe with a few blotches, then add one more very thin coat to even up the surface, sanding back but not all the way to bare wood? This way, all the pores are filled, and also the surface will have a thin and probably fairly even base coat, ready for the laquer? To me, this seems like a fair way to reduce the risk of blotchiness, but I may have misunderstood?

Blotchiness is usually a function or characteristic of the wood species, although I've seen botching as the result of really poor prep. I've also seen perfectly prepared cherry become blotchy with nothing but a clear coat. To mitigate against blotching, a barrier coat between the wood and the artificial colorant is generally effective; my favorite comprises two coats of 1.5-pound-cut dewaxed shellac, burnished into the surface using a French polishing applicator.

[62bass]

Originally Posted by Mikey R

Ive never used shellac so Im quite interested in this too.

So, question for the experts - successive coats of shellac burn in to the previous, so would it be possible to sand down till most of the wood is bare, maybe with a few blotches, then add one more very thin coat to even up the surface, sanding back but not all the way to bare wood? This way, all the pores are filled, and also the surface will have a thin and probably fairly even base coat, ready for the laquer? To me, this seems like a fair way to reduce the risk of blotchiness, but I may have misunderstood?

That's how I use it on furniture to get a very flat and flawless surface to top coat with alkyd varnish which I rub out to gloss. I use the Zinnsers Bulls Eye Seal Coat which is dewaxed and is a 2 lb cut. I usually thin the first coat a bit with shellac thinner. Successive coats go on full strength. I wouldn't try to fill the grain on oak or ash with it if I wanted a dead level surface for a top coat, but most other woods are okay.

Good sandpaper is important. I like the open coat stuff from 3M. Norton's also has it and I use that too. I keep knocking the dust off the sanding block too to make sure I don't get a clogged spot that could ruin my work.

Sometimes I use a very thin sealer coat on woods prone to blotching before applying a dye stain. Others use a thinned out hide glue. Or you can buy the prestain conditioner that Minwax sells. I've found that the thinned shellac is as good as anything.

[Mikey R]

Originally Posted by 62bass

That's how I use it on furniture to get a very flat and flawless surface to top coat with alkyd varnish which I rub out to gloss. I use the Zinnsers Bulls Eye Seal Coat which is dewaxed and is a 2 lb cut. I usually thin the first coat a bit with shellac thinner. Successive coats go on full strength. I wouldn't try to fill the grain on oak or ash with it if I wanted a dead level surface for a top coat, but most other woods are okay.

Good sandpaper is important. I like the open coat stuff from 3M. Norton's also has it and I use that too. I keep knocking the dust off the sanding block too to make sure I don't get a clogged spot that could ruin my work.

Sometimes I use a very thin sealer coat on woods prone to blotching before applying a dye stain. Others use a thinned out hide glue. Or you can buy the prestain conditioner that Minwax sells. I've found that the thinned shellac is as good as anything.

Thanks for all the info! Ive been considdering experimenting with tinted laquer rather than staining the wood directly, as this seems safer to avoid blotchiness. Obviously, alcohol based stains wont work over a shellac base coat, maybe I could try tinting the shellac coat over the base coat with dye, then finish up with a top coat of clear...? Lots to think about and experiment with.

Sorry, dragging the conversation off topic.

[Basschair]

Thanks for the advice guys. I'm going to continue sanding tomorrow to see about evening out the look of the mahogany and will follow that up with a wipe-down/cleanup using mineral spirits and good lighting. If it looks good, I'll stop being so anal about it and just get on with the finishing. If not, I'll try another thin coat of shellac and some very, VERY light sanding.

Lonny: for some reason, on this bass I didn't use a roundover bit at all, but did it solely with rasps, standard and microplane. I like a kind of thin centerline that runs through the upper waist and into the horn of this body style, but a flat edge for the edge behind the bridge and below the electronics. Unfortunately, I left the core wood too thick on this one so I can't thin it as much as I'd like. Of course, perhaps I can take this possible finishing debacle as a chance to revise (thin out) the scroll.

[Basschair]

Success!!! (I think)


So I spent a few more hours sanding...back to 220 over everything, then a smooth, even 320. Wiped down, then compressed air, then a few wipes with mineral spirits. The spots that were lighter in color were/are (my interpretation) areas where I did sand through the shellac to the bare wood, some of them to the point where new pores were opened. Still, the surface looks great. So, I'm going to go ahead with the first round of General Arm-r-Seal, thinned a smidge further with mineral spirits tomorrow. I've used it before, I like it a lot, and I'm thinning it a bit more (even though the label says it's not necessary) to keep the wiping nice and clean.

[Jazzdogg]

I'm happy for your success.

FWIW, because Arm-R-Seal is formulated as a wiping varnish, it's been pre-thinned at the factory.

Thinning the first coat of "normal" varnish will reduce its solids content and make it easier to sand flat and level before applying another coat. But, it can actually be disadvantageous to thin Arm-R-Seal; it's already thin enough.

[Basschair]

Originally Posted by Jazzdogg

I'm happy for your success.

FWIW, because Arm-R-Seal is formulated as a wiping varnish, it's been pre-thinned at the factory.

Thinning the first coat of "normal" varnish will reduce its solids content and make it easier to sand flat and level before applying another coat. But, it can actually be disadvantageous to thin Arm-R-Seal; it's already thin enough.

You think so? (absolutely no sarcasm intended there).
I used it on the last bass and it just seemed a little thick for wiping. Just the slightest bit. So I figured maybe about 5% addition of mineral spirits. It could definitely be my technique though. Well, when in doubt, test on scrap wood, yes?

[Jazzdogg]

Originally Posted by Basschair

You think so? (absolutely no sarcasm intended there).
I used it on the last bass and it just seemed a little thick for wiping. Just the slightest bit. So I figured maybe about 5% addition of mineral spirits. It could definitely be my technique though. Well, when in doubt, test on scrap wood, yes?

Test pieces are invaluable! And you're right; successful results are always a blend of tool & technique or finishing product(s) and technique(s). IME, wiping varnishes produce the best results with the least effort when several thin coats are applied. I've seen numerous problems when people tried to treat wiping varnish as though it were brushing varnish.

Edit to add: 5% mineral spirits isn't likely to hurt anything; with brushing varnish, I usually thin the first coat by 40-50%, and successive coats by about 20%.