Grain Filling

I'm thinking of filling the grain on the wenge sides and back on a uke I just built, and hoping I can get some advice on this issue. Ideally I'm looking for something clear, so it won't alter the appearance of the wood. My local woodcraft had System 3 Epoxy filler which I had seen recommended before, but it's a bit more expensive than I'd like. I've also heard recommendations for Z-Poxy before but I'm not sure if I'd be able to find it locally (though it does cost half as much as the smallest System3). I also see that Stewmac offers a clear waterbase grain filler from ColorTone, but haven't heard anything about that.

I'm planning on finishing the uke with KTM9 waterbased finish. It looks like LMII recommends System3 filler for this but I'm wondering if anyone has any advice or tips for working with these open grained woods?

Z-Poxy is used by many instrument makers and works very well. It's mixed half-and-half and does not have to be measured as accurately as System 3. If you use it, make sure it's the Finishing Resin you get and not one of the adhesives.There's a 3-part tutorial by Todd Stock on YouTube.

http://www.youtube.com/watch?v=YYHxMg7n9cI

I've used the System Three Clear Coat before with good results as long as you make sure it is thoroughly cured before applying your finish. Mixing the exact ratio however seems critical; I use a gram scale. A blow dryer is often used with System Three to really get it to work into the grain.
I don't like water based or even mineral based fillers as they seem to shrink back more than I'd like. Don't expect any grain filler to do a sufficient job with one coat, two coats seems minimal. Sand lightly between coats. When I'm applying lacquer I always like to use a vinyl sealer between my filler coats and my finish.

That's an excellent link Dave.

I've used epoxy quite a lot building some wood kayaks and other misc boat projects. I started out with System-3 and later switched to a local brand "Florida Fiberglass" (also a 2-1 by volume mix ratio). I've been using it as my grain filler on some ukes I'm working on. I also have Z-poxy but use it as a general adhesive in the shop when I want a strong or water proof bond. Z-poxy is definetly not as clear as System-3, but the amber tint it adds might be considered a feature in uke building.

From the Kayak building I learned or read the following:

- I used metered measuring cups for mixing and never had any issues of the epoxy not curing. With Z-poxy, I just eyeball it.

- It's best to put the first coat of epoxy on bare wood at a time of day where the temperature is falling, or pre-heating your wood with a blow drier or heat gun. The theory is heating the wood constricts the pores and as it cools the pores expand and suck the epoxy in. The opposite is said to possibly create air bubbles. I follow this rule more out of superstition than experience with doing the opposite. It doesn't matter for subsequent coats.

- You can recoat epoxy over epoxy without sanding providing you do it within 48 hours or so

- Epoxy continues to cure for a couple of weeks and as it does is creates what they call amine-blush that needs to be washed off before applying any sort of finish. They say it's best to wait 3 weeks before applying any finish - I was rarely that patient and never saw any problems applying varnish directly over the epoxy after 1 - 2 weeks. Going with Laquer I would follow Chuck's advice and use a sealer between.

- it's better to scrape epoxy than sand it. In the green state (first couple of days) it's pretty toxic stuff and sanding it gums up the sand paper.

- Some people have allegic reactions to epoxy from the start and others build up allergies to the stuff the more they use it, so even if you don't break out using it, it's best to avoid getting it on you.

- great information at www.westsystem.com

take care,
-darrel

I think it's important to mention that the edge of your scraper or squeegee be in pristine condition, unless you like to sand. If there are imperfections in it it will leave lines as you drag it across the surface. For the same reasons keep your work surfaces clean--no dust or dirt! If your applicator catches little bits of grit it'll create grooves as you fill. I like to sand the corners of my scrapers round to eliminate the overlap lines. Hard rubber scrapers, such as the kind used to apply auto body filler and credit cards work fine. I like to sand the edges with 600 grit W/D sandpaper often. The idea is to get the surface as finished as you can so you won't have to sand too much later. Anyone who's done good drywall or auto body work will know what I mean and should have no trouble with grain filling.

Watch those videos folks - they are very good and show a meticulous approach to grain filling that will turn your instrument into a Macafferi flamingo in no time! And where is the argument about what stuffing all those pores with plaster of Paris or plastic does to the final tone? Ah what the heck, I'll get back to my paste filler tomorrow...

The advice here is spot on. I use WEST Systems epoxy and follow all the above mentioned steps. The amine blush thing...wash it with water...oddly enough that's the solvent for it. And don't worry too much about wetting the wood because you've already sealed it pretty well with the epoxy.