Friday, April 25, 2014

Shellac Problems

I'm running into some issues with French Polishing on the LP Junior. Everything seems to be working out fine on the top and back. The shellac is smoothing out nicely and I will be progressing to the alcohol only steps soon. 

But I'm running into two problems with the sides. 

The first is a dry spot, that just does not seem to be taking the shellac at all. I have been over it several times slowly rubbing the shellac in, but the dry spot only seems to grow.

The second problem is residual darkening from drips when I was working on the top and the back. I've tried sanding back and then reapplying shellac, but I can still make out some of the spots. This is worse in the area around the neck and next to the dry spot mentioned above.
So after a lot of internet searches with no luck, I ran up to Woodcraft for some advice. The clerk who has been an expert on finishes in the past made a few recommendations. The darks spots are actually caused by thinned out shellac from the drips that seeped deeper into the pores. Then when I tried to add more shellac while working on the sides, it was a heavier weight. The pores of the walnut was not able to absorb the thicker shellac as well.

I was worried I would have to sand the shellac all the way back. Instead the person at Woodcraft recommended using just pure denatured alcohol to remove the shellac instead of sanding. After a few minutes of rubbing the alcohol in it removed much of the shellac. Then I followed up with a quick light sanding using 400 grit paper coated in mineral oil. I was then able to start french polishing again, but this time I started with a heavily diluted coat of shellac. After that sealed the sides I started using the heavier 3 pound cut I was working with before to build the layers.

Now this just leaves the issue of the dry spots. For this the issue the internet did seem to help a little as did my friend at Woodcraft. Fixing this will be a slower issue. The online source recommended slowly working around the edges of the dry spots and building up there. I believe the quote was something along the lines, "you have to sneak up on the dry spots in order to fill them. My friend at Woodcraft reminded about using mineral oil to keep the polishing pad well lubricated. Without the lubrication the cotton rag will heat up while rubbing and cause friction on the wood, there by pulling the shellac up rather than applying it. This will cause the dry spot to grow. So this is where everything stands at this point. I am slowly building the shellac up on these dry edges.

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