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Having raised grain issues with a German spruce top . I can't seem to sand down the raised grain between applications of shellac . ....Yes I'm a noob , but I've French polished quite a few types of wood . This is different . Maybe I'm expecting too much too quickly with the grain filling of this particular wood . It has improved after lots of application sessions but it's taking longer than I would have thought . Any suggestions would be greatly appreciated .

Howdy,

Just want to confirm something - are you pore filling on the top? I’m not sure you need to pore fill the spruce. Perhaps it’s not raising the grain but just pushing around the material you’re using to try to fill the pores?

Hopefully one of the French polish experts will chime in.

Brad


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Yeah , I'm not pore filling , I'm trying to get build up but the shellac doesn't seem to be building in between the hard raised portion of the grain . When I sand in an attempt to lower the grain to the same level as the soft portion I get raised grain all over again .

Oh, got it. Grain filling in this case meaning building up the shellac so it’s level between the hard and soft grain lines of the spruce.

What is being done to level it? Sanding can introduce that corduroy effect, if that’s what you’re seeing.


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If you are looking for smooth; put a very thin coat of shellac on, and sand smooth. Do that until even, and then use shellac with less alcohol. The soft wood absorbs the shellac MUCH more than the winter wood does. If you just wet it with water, you can't really smooth it, because the swelling will go down. When you use the thinned shellac, like sanding sealer, the wood stays plump, and you can sand it smooth.

Corduroy comes if you use a thin varnish, like shellac, that absorbs deeply, you don't sand smooth. until it stops swelling. It can work, but it is a completely different look.

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Why be normal?

Scraping gives corduroy (bumps of light wood between sunken dark grain lines). Sanding gives washboard (dips of light wood between raised dark grain lines). Use both to create a flat surface.

In my experience, grain raising is a one-time thing on the first application of shellac. The surface is rough, like the fuzzy texture you get when raising the grain with water, but hardened. A light scraping or sanding removes it, and further applications don't do it again. Or if French polishing, you can use pumice on the pad to grind up the raised fibers and use them to fill the grain texture more quickly. Maybe a good option if you're getting it repeatedly.

Wipe-on also works for softwood filling, especially if you pour a puddle and push it around so it has time to soak in rather than smearing a thin film that dries almost instantly. If you want to retain a more flat bare wood appearance or prevent darkening of woods like heel endgrain, wipe on the first coat with a fairly dry cloth to intentionally create a thin surface film to prevent deep penetration by heavier subsequent coats. But for soundboards I usually prefer to use the puddle method for the initial coat, to give the deepest appearance possible.

Shellac builds faster on the hard 'latewood', perhaps because the alcohol can't penetrate and dries off quicker, leaving more shellac there. I've found that when doing FP on softwoods it works well to wipe on a very thin 'spit coat' and give it plenty of time for the alcohol to dry out before you add more finish. Using a mix of 2/3 acetone and 1/3 alcohol as the solvent works better: the mix is said to be 'azeotropic' evaporating faster than either solvent alone, so it 'flashes off' very quickly (use good ventilation!). The mix doesn't have much time to penetrate the soft earlywood, which leaves more of the shellac on the surface to grab finish from the next pass of the pad. Whatever the reason, as usual, patience is the best way to solve the problem: you can't make FP do anything it doesn't want to do.

Wow. I thought for sure that the light wood swelled. Checked the ElectroLess Paul, and the light summer wood is way below the hard wood. I used a couple thick coats, mixed with other resins thinned in alcohol, and it was done. Very corduroy.

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Why be normal?

On a side note be sure and sand with barely any pressure. As soft tops can get the wavy look just from sanding with too much pressure as the soft part of tops sands quicker than the harder ridges.

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I've been doing FP for many years now and as I am reading this I'm thinking, why have I never had this problem before? I use a damp rag to raise grain and always use a stuff block when sanding. Not sure if that's why but give it a try on the next one maybe.

Given the problem, this suggestion about using a stiff block, as opposed to a flexible block, makes a lot of sense. A flexible pad is just going to cushion around the harder wood and sand the softer wood. You can't get anywhere that way.

Scraping softwoods tends to give a corduroy effect. The scraper cuts away the hard latewood and compresses the earlywood, which springs back later, leaving the latewood lines below the surface. This is a prized look in the violin world, since that's what Strad did, but guitar buyers see it as a 'defect'. You really need to finish up softwoods with a hard block on guitars.

Shellac always has some water in it, and that swells the grain at least a bit.

I once tried to build a guitar in the 'old world tradition.' I used edge tools only and that includes a scraper for finishing. The spruce top did exactly as Alan said, courderoy.

Other thing I have seen in other luthier built guitars that came into my shop was the braces ghosting through the top. I had mentioned that here and some of you wise folks sugges noted that when they glued the braces on some sort of swelling occured before the final sanding so it probably thinned the top over the swollen braces which later showed through the finish.

Another related issue is sanding too hard (even with a block) on the top after the box is completed. I once spilled some thinned epoxy porefill on a WRC top. I figured, I would just treat the whole top with epoxy to even out the color. When it turned into a blotchy mess, I decided I needed to sand it all off. When all was said and done, I learned that you have to be very light with block sanding your plates. Too much pressure ends up sanding the top thinner right over the braces where it is very stiff and less so on the more flexible areas. Good lesson to learn early on.

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Thanks guys , It was suggested that I use a stiff sanding block . I did that and it worked well . Cork was the culprit . Thanks everyone for all the info , which all goes into the great grey filing cabinet . All the mistakes you mentioned were all performed by me at least once .......

You get to be a Master when you've made all the mistakes, and stop making them again. By that measure, I guess I'm a journeyman.