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Ready to grain fill a new mahogany neck and have found my filler hard as a rock. I’ve used shellac and sandpaper to create a slurry for flat surfaces but don’t feel confident I can do this on a neck.
I looked up on my shelf and saw a 5 quart container of System Three micro balloons left over from a strip kayak project and decided to make my own. I mixed a small quantity with TruOil to the consistency of mayonnaise and applied it to a test piece of mahogany. Waited a few minutes and rubbed it clean across the grain. A few more minutes and applied a coat of TruOil and everything looked good.
Going to test it with shellac and then wipe on poly.
Anybody see any downsides?

You might run into problems with oil based finishes drying properly on oily woods like rosewood and ebony. Even though the neck shaft is mahogany what are the fingerboard (edges that get finish) and headplate made of?

Last thing you want is something that won't cure packed into wood pores.

Shellac seems like the safest bet.

It's a real day spoiler when finishes stay tacky.

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Brian R, Wood Mechanic
N8ZED

Yeah, right after posting I thought of that. The balloons are a phenolic resin material so you may be right.
I’m going to test it again using poly Instead of TruOil and see how well it dries. If it’s successful I’ll have a lifetime supply

shellac makes a good sealer for tru oil
as for finish you need to seal that is part of the prep process. Poly , oil base anything read the directions on the can they will tell you what you should use. In most cases shellac is fine but if you don't seal that makes the filling process that much more difficult
so this is my process
A sand to 180 finer than that you can loose tooth and you won't get good adhesion
B seal 1 to 2 coats no more
C fill I use aqua coat there are may methods Pore o Paq , even elmers water based wood filler it accepts stain well
I generally do 3 coats and pay attention at the end grain areas
D seal usually 1 coat
now your ready to apply finish no matter how you do it spray brush your good to go but think of the process as a
3 steps build coat apply about 4 to 6 coats level sand with 400 and 600 now do your drop in and touch up, then 2 to 3 coats of final finish allow good cure time and level sand 800 to 2000
then if your doing gloss you buff and polish satin I like 0000 steel wool or just 1 finish spray of satin

you end result is all about your prep and cure you cannot rush a perfect finish

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it