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Forum topic by DrTebi posted 11-07-2015 04:30 AM 856 views 0 times favorited 12 replies Add to Favorites Watch
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DrTebi

256 posts in 2733 days


11-07-2015 04:30 AM

Topic tags/keywords: finishing

I have been wiping on shellac on dozens of pieces in the past years, always successfully, except for a couple of very rare occasions: After the fourth layer or so of shellac, the shellac just comes off! And once that happened, that blank patch just won’t take on any new shellac!

What’s going on here?

My procedure:
- hand-sand to down to 320
- raise grain with warm water, let dry, sand again with 320
- apply linseed oil, let dry 1-2 days
- wipe on freshly made shellac, 1/4 pound cut
- wet-sand after 2-4 layers
- wipe on shellac…


12 replies so far

View Rick M's profile

Rick M

7933 posts in 1846 days


#1 posted 11-07-2015 05:38 AM

I follow a similar regimen except I sand to 120, don’t wait for the oil to dry, and sand after the first coat. Could it be some issue peculiar to the brand of shellac?

-- http://thewoodknack.blogspot.com/

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AZWoody

697 posts in 690 days


#2 posted 11-07-2015 05:53 AM

In my opinion, many people over sand with fine grits. I will go 220, but a lot of times I just sand to 150.
The finer you go, the higher the chance you can seal the pores and the wood will not bond well with whatever finish you will try to apply.
I mainly use the 220 for the sanding in between the finishes. That’s where I’m trying to worry about making the finish smooth. The wood only needs so much sanding to get rid of machining and rough sanding marks. Once those are gone, the finishing agent is what makes the piece smooth to the touch.

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DrTebi

256 posts in 2733 days


#3 posted 11-07-2015 06:01 PM

Overdone sanding sounds very reasonable. That blank patch is very smooth.

I suppose I can try to roughen it up with some 120 or 100 paper, and try to finish it again then? Would it be advisable to sand the entire piece down, or just that spot?

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conifur

955 posts in 618 days


#4 posted 11-07-2015 07:30 PM

With 320 you may have burnished the wood and sealed it up.

-- Knowledge and experience equals Wisdom, Michael Frankowski

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DrTebi

256 posts in 2733 days


#5 posted 11-07-2015 10:06 PM



With 320 you may have burnished the wood and sealed it up.

- conifur

Yes. I will start reworking it today, and post results here later.

View soob's profile

soob

223 posts in 675 days


#6 posted 11-07-2015 11:00 PM

I’m no expert on shellac, but it gets wiped on woodturnings that have been sanded to 2000 grit and it sticks just fine.

I had similar issues with matte patches when I tried to make my own friction polishing using BLO. I believe uncured oil was causing the shellac adhesion issue. Let it dry for a week and try again.

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ClammyBallz

309 posts in 603 days


#7 posted 11-07-2015 11:17 PM

I always thought you were supposed to let BLO dry for a week.

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DrTebi

256 posts in 2733 days


#8 posted 11-08-2015 01:20 AM

I am starting to believe that it is indeed the oil. It’s just weird that shellac went on fine for four layers, and then it decided to wipe off and not accept any new shellac.

So I sanded it down with 100, oiled it again, waited an hour or so and tried some shellac. It still wouldn’t take on any. This may very well be because the oil is not dry enough.

Anyway, I decided to cheat on this piece. I started to put on some “Oil Based Arm-R-Seal Urethane Topcoat”, which seems to stick. Will do a couple more layers.

After all, this piece is a header for a door frame, that will be 10 feet up. So if it will have some slight imperfections, I can live with it.

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soob

223 posts in 675 days


#9 posted 11-08-2015 02:32 AM

With my abortive attempt at friction polish, it would look shiny until it started to dry, then it would turn matte.

View conifur's profile

conifur

955 posts in 618 days


#10 posted 11-08-2015 02:37 AM

Did you use Linseed Oil or Boiled Linseed Oil? BLO has a drying agent in it, LO does not, I still think you burnisherdpolished the wood to the point it wont take a finish, even though Shellac is one of the thinness.

-- Knowledge and experience equals Wisdom, Michael Frankowski

View Rick M's profile

Rick M

7933 posts in 1846 days


#11 posted 11-08-2015 03:21 AM

Oil will make no difference. Oil is used in French polishing to lubricate the applicator and turners mix oil and shellac to make friction polish. Shellac will even cover silicone contamination. If your shellac is falling off, my guess it either has something to do with wet sanding or your batch of shellac is bad.

-- http://thewoodknack.blogspot.com/

View DrTebi's profile

DrTebi

256 posts in 2733 days


#12 posted 11-08-2015 04:46 AM

I used BLO.

Well, that the shellac was bad is an idea, but the question remains, why did it work perfectly well on all the other pieces that I did with the same shellac?

That’s what drives me nuts… I cannot figure out what the problem was. It happened before on a door I finished. Everything went perfectly well, looks shiny (I do up to 8 layers of shellac after BLO), and then suddenly, on one corner, the shellac came off completely, down to the BLO finish!

Anyway, it won’t stop me from going on with shellac. I am restoring our late 19th century house/apartment, and have done all doors and trim work in that fashion so far. It looks wonderful, feels great, and is a lot more robust that I thought (e.g. no problems with the bathroom door, which gets a lot of handling and where lots of moisture gets stuck).

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