Shellac problem

I'm finishing the top of a marquetry box with hard shellac. I did 3 coats of 50%, then lightly rubbed with 600 grit. I have then put on 3 coats of 75%, and sanded lightly with 600, then a further 3 coats of 75% followed by 600 grit and 900 grit. After this, I rubbed withh EEE and got a really nice deep gloss. Looks bloody lovely. But in one part I have a dull white blemish, about the size of a pea.

I'm happy to strip back with metho, and rework the finish. But I would really like to know what is causing the problem mark, so that I don't just repeat whatever is causing it.

I should also mention, that my metho is 100% and that I used white spirits with the wet and dry.

Any thoughts please?

Hi Chris,

the wood in area in question may have suffered some sort of bleaching prior to the application of your finish, or in the early stages of your application there may have been an introduction of a foreign substance like a drop of Bats pee which is a bit waxy and will slightly discolour wood fibres or not even allow the true wood colour to come through. A bit like glue size! We have the little critters here and you have to be careful to tarp your work last thing at night before the Bats come out. (spoken in a Dracula kind of accent if you like). In either case at the very least the area where the blemish is you need to remove the finish in order to either stain the raw fibres to match the surrounding wood or haul out the offending spot. With shellac being very easy to apply and remove it's really a matter of finding out exactly what the spot is then go from there.

Hope this helps...Oddjob1

A drop of sweat from your brow Chris?
Cheers,
Jim

G'day Chris - When did the white spot appear, was it early in the piece or after the final coat?

Definitely a contamination of some sort, sounds like a spot of water or as Jim said maybe a drop of sweat.

Quote:

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Originally Posted by ubeaut

G'day Chris - When did the white spot appear, was it early in the piece or after the final coat?

Definitely a contamination of some sort, sounds like a spot of water or as Jim said maybe a drop of sweat.

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It was late in the finish process, but I thought it had gone in the sand before the last coat.

You worry me when you mentiom white spirit.
I always thought white spirit was a dry cleaning fluid and is petrolum based, If you did use this solution it does not mix with shellack. Shellack only likes metho. My method has always been use a thick solution first cut this back and slowly break down the concentration. A realy good job will need up to 50 coats.

Rowley.

Hi all,
Can relate to the Bats urine big time !!!!!!! Little suckers always seem to roost/rest/urinate/defecate above the work bench or your tools. Nothing rusts a cast iron table faster than that.
I found if you hang a Bug Zapper in the workshop, they keep out, I don't know if it is the frequency of the sound emitted by the light or the electronic zapper thingy they don't like but - hell I don't care just so long as the little buggers go elsewhere.
Bushy

Could be you are moving too fast.
I would recommend that you simply wait. A dehumidifier may help too.
I tend to get some white when I recoat too soon when I use varnish.
Could be there is moisure trapped between coats. If you have enough build, hit it with a little denatured alcohol (on a rag) to pull out the moisture, or just wait about three days before you think of stripping away all your hard work.
G'luck!

Yep sounds like a bit of moisture trapped under the final coat. Try a quick light rub over with metho and if it disappears then a final coat of shellac should fix it. You will need to wash the surface well with mineral turpentine (white spirits) to get rid of any residual wax from EEE and sand lightly with (probably) 1200 grit first. Make sure the surface is completely dry before the final coat and whatever you do, don't sweat.

That should fix it for you. No guarantee as not really sure what the contamination is but should do the trick for you.

Cheers - Neil :fingerscrossed:

Thanks for all the advice. I stripped it back completely, then refinished it. The end result is magical. I am now an absolute convert to hard shellac, and strongly commend it to everyone. If is so simple to put on, and the result is stunning. Getting to the final stages for the box now, and will post pics when I get it complete.

Ahhhh... another convert.
I really like shellack too - 'cept when I try and move too fast for it.
Ya, make with the pics.