Grain filler - Am I using the wrong stuff?

[Boston Joe]

Hey all.

While I wait for my parts to arrive, I've been experimenting. The woods I'm using for my guitar are mahogany and koa - both very open grain woods. I've been trying to get the hang of filling the grain, but no matter what I do, I end up with a noticeable amount of open pores.

I've been using "Elmer's Wood Filler" which comes in a tube and has the consistency of a stiff toothpaste. I've had the best luck thinning it with a little water and trying to work it into the wood with my fingers, but I've done this 3 or 4 times on my test piece. and when the stuff dries and I sand it back, I can see open pores. I'm not sanding past the filler. The majority of the pores are filled, but there are always a fair number of missed ones.

So I'm wondering if maybe I'm not actually using the right product. The directions on the filler make it sound like it's more intended for filling cracks or gouges.

Am I right? If so, what product(s) should I be using? If not, what am I doing wrong?

 

[Cagey]

You guessed it - that's the wrong product. Wood filler is for cracks, screw holes, gouges, dents, etc. Think of it like "Bondo". Thinning it won't help much, because the solids are too coarse. Basically, you'll just be thinning the "carrier", which typically either evaporates or cures anyway, leading to shrinkage.

What you want is "Grain Filler", which is a little more difficult to find outside of woodworking specialty shops or online. The solids are much finer. It actually behaves more like a high-viscosity paint than anything else.

Most luthier supply shops carry it, if you can shop online. Here are some links to products at StewMac, Luthier's Mercantile. Locally, you if you have a Woodcraft Supply store, they have several offerings. Or, if you have one of those old-timey hardwares that carry all sorts of obscure stuff, they might have it.

Typically, you use a squeegee to kinda press the stuff into the grain of the wood, wait some recommended period of time, then scrub it off before it turns to rock. Wait for it to cure completely, then sand it back and check your results. You may have to do a second pass. In rare circumstances, you may need to do a third.

 

[Boston Joe]

Thank you. This was really vexing me. Will order some grain filler pronto!

 

[Cagey]

I should mention that when you read the instructions on the label for the grain filler and it says "Mix thoroughly", they're not kidding. Most of the solids will have dropped out of solution and turned into a thick muck at the bottom of the can. It's important that they be mixed back into the carrier or you'll just be covering your body with carrier rather than filling any grain. Lotta work, no progress. Also, be sure you have something under the can to catch spillage, because the carrier is fairly thin and you'll splash it around trying to mix the stuff until it thickens up. Good idea to wear latex or nitrile gloves, too.

 

[dmraco]

I like this stuff.  Works very well

http://myoldmasters.com/product/woodgrain-filler/

 

[Boston Joe]

I ordered some Aqua Coat. It looks like it's pretty easy to work with.

 

[Cagey]

I haven't used that stuff yet, but it sounds good. Be sure to follow their recommendations, step-wise. For instance, seal first, or the water will raise your grain. Also, since it's water-based, even though the wood will be sealed first, you'll still experience some minimal shrinkage. But, after a couple/three coats you'll reach a point of diminishing returns so it's time for a couple/few coats of sanding sealer sanded between coats. It'll do the final leveling before you start with color coats.

Fine finishes are all about surface prep.

 

[Boston Joe]

"Seal first" meaning what, exactly? I'm using poly for my finish, so does that mean it gets a coat of poly first?

 

[Cagey]

Usually manufacturers have a "system" consisting of several products designed to work together, with sealer being the first step. There's usually a designated thinner, tints, color coats, etc. But, in general, a "wash" coat of whatever you're going to finish with is fine.

A "wash" coat is just a thinned-down mixture of your finish coat that seals the wood and gives you a base to build on. In this case, since you're using polyurethane, you would thin with mineral spirits. If the manufacturer has a recommended product, use that if possible to keep the chemistry compatible. I'm not sure how important that is, but I'd stay away from anything "natural" or "green" or "odorless". Too often in their zeal to pacify the environmentalists and paranoiacs, critical components are removed that make the material less effective or prevent it from becoming as durable as it could be. You're not gonna bathe your kid in it for 5 years until the little rascal learns to shower, you're just gonna use enough to do a guitar body once, so try not to worry about it.

edit: If you're using a water-based poly, you would thin with water, not mineral spirits. And good luck with that.

 

[Boston Joe]

I'm using wipe-on poly, which I believe is already thinned with mineral spirits. Should I thin it more, or can I use it as-is?

 

[Cagey]

More. Make it like water. Needs to get in the grain.

 

[Boston Joe]

More. Make it like water. Needs to get in the grain.

OK. I can do that.

 

[stratamania]

Finishing takes patience, and even in Boston, you need some rags around.

Here is some music to keep you going...

When you have Boston Rags,
Finishing ain't no drag

:glasses9:

[youtube]https://www.youtube.com/watch?v=aJ3OZEiM9OQ[/youtube]

 

[Boston Joe]

Got the Aqua Coat. Been testing it. Initial reaction:  :icon_thumright: