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I'm finishing a double O with jatoba back and sides and a mahogany neck. My plan is to do a sealer coat or two of shellac and then fill the pores with some dark Mcfadden's pore filler I have (wanting the contrast), then put a couple more coats of shellac, then move forward with KTM 9.   I'm doing this on the premise that most things stick to shellac and shellac sticks to most things. I know shellac works well as an undercoat with KTM 9, but I've never used it with the Mcfadden's pore filler, which is sold for use with lacquer. Has anyone tried this?

It is a bit of a risk. We all know that oil and water don't mix and I am assuming your pore filler is oil based. If you want to continue in this direction, you will have to make sure your filler is completely cured before you seal with shellac. If any oil happens to migrate to the KTM, you are in a world of hurt, so to speak. Oil based fillers seem to be very slow drying so how long to leave the filler to dry is a matter of speculation. Behlen's water based filler is an excellent product. It is not as dark as an oil based filler, however.

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Stay with the happy people.
--Reynolds Large

Good thoughts TRein. How about using liquid stains to tint Z-poxy? I was just reading about stewmac's clear waterbased pore filler and how you could use the colortone liquid stain to tint that, I wonder if this would work with Z-poxy. Anyone tried that?

Sounds like a nightmare to me. I don't relish the thought of having to cut back Z-poxy to bare wood, although many here do just that. As I mentioned, the Behlen's waterbased filler is excellent, but cures to a light brown, not deep brown like an oil based filler. You could try tinting the Behlen's waterbased filler with Trans tint dyes (I will be experimenting with this shortly). Or, you could mix up some of John Gilbert's Durham Water Putty filler, which works very well. He mixes up a solution of 3 parts water to 1 part vinegar. Then he mixes 6 grams of Durham's Water Putty (available at nearly any hardware store) with 1/2 gram black aniline dye. Add 2.7 grams of the water/vinegar mixture to make a paste. Apply with a squeegee, burlap cloth, credit card, or whatever works for you. It has minimal shrinkage, is quite dark, and easy to sand. I am not a huge fan of it since it contains aniline, a known carcinogen. Is there enough aniline to worry about? I don't know.
There are other techniques you could use to make a dark filler under waterbase. Dry color with your topcoat as a binder would work, but it may be difficult to scrape clean. If you are willing to forego the dark filler aspect, then I can recommend the Behlen's brown filler as it comes from the can.

_________________
Stay with the happy people.
--Reynolds Large