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Im preparing to finish a guitar with mahogany veneer. The stew mac site suggests a wash coat, grain filler and sanding sealer to be used before the lacquer. It seems that the first three products are repetative.

What are the purposes of each?

Would each be required if its not solid wood but veneer?

Thanks!turbo41139021.001099537

Depends on the magnitude of the pores and your level of expectation for a quality finish.

Another consideration is to use Z-Poxy to fill the pores, sand and then follow by a coat or 2 of shellac and then lacquer. If there are still open pores after sanding, then repeat with another application of Z-Poxy. This can generate some frustration...if so, then work on being patient...you'll be rewarded.

Take your time and do it right. If you follow the instructions of the experts you'll have a much higher probability of success.

Good luck!

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JJ
Napa, CA
http://www.DonohueGuitars.com

Turbo, the purpose of the grain filler is to fill in the pores of the wood so
that the finish in the end will be flat and glassy, and not dimpled all over
where the lacquer sank into the pores. Some wood, like spruce, does not
have big open pores and does not require grain/pore filling. I believe the
"wash coat" just makes the pore filler a bit easier to apply and remove the
excess.   Anyway, then the next coat of sealer, after the pores have been
filled, seals in the aforementioned filler. Hope that makes some sense


Mike

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Mike

"The Dude abides. I don't know about you but I take comfort in that. It's good knowin' he's out there. The Dude. Takin' 'er easy for all us sinners. Shoosh." The Stranger

Thanks for the replies. Can I seal the wood without the grain filler? I imagine the grain filler will alter the looks somewhat because the pores are filled

Wash Coat: protects light wood from staining and gives a base for the grain filler to adhere to

The process of pore filling or rag-on finish application method may drag color from one wood and deposit it on the lighter woods like purflings and tops. The wash coat prevents the color stain from impregnating the lighter wood


Grain Filler: fills pores to level with the surface.

Seal Coat: a base film to give the lacquer a consistent film to adhere to.
MichaelP39021.400150463

the issue is not whether it is solid wood or veneer. the pores of the veneer are the same as the solid wood of the same species.

as was pointed out above, there are reasons for the use of the various elements of a finishing schedule if you want to get a quality finish with a minimum of input.

yes, you could just seal and spray topcoat, and sand, and spray top coat, and sand, and spray top coat, ad infinitum until the pores were filled with top coat and a sufficiently heavy, thick slab of finish existed so that when it shrinks as it cures the surface at each pore will be above the wood and you will be able to sand it out smooth, for a little while at least.

the point is that the pores must be filled or you will be wasting finish (expensive) and effort (frustrating) to only end up with a second rate final product.

Just to add a bit to the good info that's already been given.

Z-poxy as a filler has the advantage of minimal to no shrinkage (unlike sanding sealer), and it acts as a sealer. If you decide to use it, skip the shellac wash coat, as you might have problems with the Z-poxy not adhering well to shellac, though with a true wash coat that may not be an issue.

By using z-poxy, you could accomplish the first three steps, seal, grain fill, sanding sealer, just using the Z-poxy. Plus, if you like a natural look, the appearance would change much less than with a grain filler.

You might also consider French polish over the Z-poxy, as the seal, fill, and much of the finish building is already done with Z-poxy. With FP, I've found that it involves many small steps which can be tweaked along the way over time, but with lacquer, each coat is a bigger step, with a greater risk of ruining previous steps. It's a better match for my slow, methodical way of working. FP requires a minimum of equipment and virtually no cleanup, though you won't get as durable a finish.

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now known around here as Pat Foster
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http://www.patfosterguitars.com

I prefer paste wood pore filler. It can be tinted many colors.BarryDaniels39021.637337963

Thanks all for the info. It is very helpful! More specific to the lacquer (probably ktm9) from what I understand I spray, let dry, sand, spray with DA and then spray the next level of lacquer. Is this correct?

What grade sandpaper do I sand with after each lacquer layer?

Thanks again all for the help. Do you usually thicken with silica powder the epoxy? This is for an electric guitar so the sides are narrow.

I don't I like the viscosity of Zpoxy as is. It allows the epoxy to flow into the pores well. On smaller pores I would worry about possible bridging if thickened.

Just to clarify, the viscosity of zpoxy is ok and I won't have a problem with run-offs etc sealing the narrow sides?turbo41139022.4208796296

I also apply Z-Poxy to bare wood and sand back...several times... until all the pores are filled.

I prepare the wood by sanding to at least 400 grit before I apply the epoxy and then sand out the epoxy with 400 or higher. By the time you get to the finish application stage, you will have "inspected" every square millimeter of the surface and corrected (drop filled) any gaps or dings.

One more thing...before applying the epoxy (or any pore filler), make sure you have meticulously cleaned the surface with naphtha on a rag...several times... to remove the sanding dust from the pores.

BTW...did I mention patience and taking your time with each step before moving on to the next?

Good luck Turbo!

_________________
JJ
Napa, CA
http://www.DonohueGuitars.com

This process is not needed for FP right?

The rottenstone slurry process fills the grain but what about the seal coat function?

If I use darker bindings than my Mahogany I want to make sure they don't bleed into the Mahogany B/S or the Spruce top.

[QUOTE=turbo411] Just to clarify, the viscosity of zpoxy is ok and I won't have a problem with run-offs etc sealing the narrow sides?[/QUOTE]

Yes it can run off if allowed but I immediately clean up any drips.

I consider the low flow of thickened epoxy to be a disadvantage due to the likelihood of bridging small pores then shrinking back as it cures

Some sort of pore filling is needed, be it slurry, Pumice or epoxy if you want a level film.

I use Zpoxy on my French polish jobs because it is the quickest and a near fool proof method and the zpoxy pops the grain nicely.MichaelP39022.4859143519

Interesting....

I had thought that besides easier touch ups the advantage of FP was better tone with a less "stiff or hard" finish like poly so that the wood was more free to vibrate and breath a little.

That's just what I had gathered from my readings but of course there are lots of opinions on what finish is best for tone and which ones may restrict resonances.

When I get through pore filling the epoxy is only in the pores with the exception of a very thinned down wash coat. And top is not filled so the impact is minimal at worst. Remember we are not talking any thickness of epoxy on the outer surface other than a wash of 60% DA 40% Zpoxy to evenly wet the color.MichaelP39022.6770833333

Can you even out the color with the DA/epoxy wash coat if you plan to use a waterbase finish or will the DA eat through anything you put on?

The DA will flash off long before you could load a brush or fill a spraygun. I do this on every finish I apply that gets pore filled

The Da is just a solvent thinner just like a lacquer thinner. It disapates (flashes off) long before the epoxy is cured.MichaelP39022.7298726852

Is this 50 epoxy 50 DA wash coat the same kind of pre-treatment I would use on wood like poplar before I stain it so that the stain absorbs evenly and not blochy?

[QUOTE=turbo411] Is this 50 epoxy 50 DA wash coat the same kind of pre-treatment I would use on wood like poplar before I stain it so that the stain absorbs evenly and not blochy?[/QUOTE]

I use a 60% DA/40% Zpoxy, but the simple answer is yes. The only intent of this is to even the color after sanding back the pore fill just to the wood surface (removing any film build up on the surface). When you do this you will expose the wood more in some areas than others. This just levels out the color and leaves virtually no film thickness.MichaelP39023.3822685185

Thanks for the reply. In a previous thread you mentioned that you spray shellac after the 60/40 wash coat but before the lacquer. What is the purpose of this intermediary and is it required?

[QUOTE=turbo411] Thanks for the reply. In a previous thread you mentioned that you spray shellac after the 60/40 wash coat but before the lacquer. What is the purpose of this intermediary and is it required?

[/QUOTE]

The shellac is a sealer gives the KTM9 or nito a better base to adhere to. Some have experiancesd issues with KTM9 over epoxy, Most have not. The seal coat is just an insurance policy. NEVER apply epoxy over shellac. Only apply shllac over epoxy. epoxy will not adhere to shellack well but shellac will adhere to epoxy well if given a tooth (light sanding with 400p or 600p)