Old Shellac leaching problem


Hello,
My question pertains to stains, primers, sealers, etc.
I "rescue" old pieces of furniture, spice racks, coat racks etc. and give them new life as painted works of art with acrylic artists paints. These are not antique pieces and most of them are discards from flea markets, etc. I have an old coffee table which I need to prime before painting it.
It appears that this piece has a brownish shellac finish and through it's lifetime has had the top sanded down and subsequently pen and marker graffiti written on it. The sides and legs are not sanded. Since I am not attempting to preserve a quality piece of furniture, priming over all manner of nastiness is the preferred method.
As a primer I applied a coat of Zinssers Primer Sealer Stain-Killer Bulls Eye 1-2-3 to the entire table. It has worked wonders on past projects - metal or wood. The sides and legs - which have not been previously sanded - turned out fine. The previously sanded top started to leach through brown stains in several places. I applied a second coat of Zinssers and when dry, the leaching continued. I applied methyl hydrate (denature alcohol) to the dry, painted surface and sure enough the brown stains started to run through again. The primer was fine. After wiping off the brown drips and reapplying the methyl hydrate several times, it seems evident that there is no end to the amount of brown leaching coming through.
As I will be undoubtedly coming across other similar old pieces, is there a way to seal, deactivate, prime or in some way neutralize the old shellac before starting to prime? Is there something I can do to this already primed piece which will eliminate the brown leaching? Would a coat or 3 of varethane be an effective sealer - after which I can put more primer on top of the varethane?
Thank you for any insite.
Magda
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Shellac is dissolved by alcohol. Even old shellac is vulnerable. Putting shellac on shellac just makes a mix of old and new. If that's not what you want - old dirt in fresh shellac, get the old stuff cleaned off with alcohol before you try again.
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One of the beauties of shellac is that almost everyting adheres to it. That's why it's often used as a sealer before overcoating. Overcoat it with something (varnish, poly, even latex paint, whatever) that your acrylics adhere to well, then paint on! One or two overcoats at most should do it.
Regards.
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That's exactly what I did with the Zinsser's Bulls Eye Primer. After the first coat had dried brown areas leached up through it. They look like bad tea or tobacco stains. The same thing happened after the second coat. When I put methyl hydrate on the stains, they became wet and I was able to wipe off some brown, wet stain off the surface.... but the main stain stayed.
The legs of the table - which were not sanded originally - did not leach brown through and are ready to be painted with acrylic.
Maybe it's not shellac? If not, what else could it be?
Magda
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Try using shellac to cover one of the areas where the stain came through. After the shellac dries, try repriming that area and see if the stain comes back. I have always used shellac to prevent bleed-through and had good experience with it.
Bruce
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Have read suggestion to lightly spray dewaxed shellac and allow to dry. Seems a thin coat doesn't dissolve the previous enough to let the stain migrate up into the topcoat. Care in applying subsequent coats is needed also. Worth a try.
On Mon, 21 Nov 2005 12:21:23 -0500, "Bruce Boyd"

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After listening to various opinions on this topic....both here and elsewhere, it would appear that shellac is my friend :rolleyes: - go figure. It would also appear that the staining coming up through the (non-shellac) Bulls Eye primer may in fact NOT be shellac, since shellac is not dissolved by waterbased products. argh.
Sooooo..... live and learn and experiment. Short of going backwards a number of steps and sanding :( - would a couple of coats of varathane form enough of a barrier against the alien leaching? I could then prime on top of the varathane. (waterbased varathane in fact is very acrylic paint friendly).
(thinking of switching to origami)
Thanks
M.
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