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What is the advantage of Zpoxy over regular old hardware store epoxy?

Zpoxy as well as other epoxy pore fillers, West, System 3 are finishing resins which allow spreadability, good working time and
they cure rock hard. Hardware store variety not so much.

Thanks. Never used epoxy filler and getting ready to fill craters.

Zpoxy has an amber tint to it as well, that might affect which wood species you want to use it on.


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A caution for the first-time user: Squeegee off as much as you can after each application, and there will be at least two applications involved, plus a final wipe coat to make sure the entire surface is sealed. And neatness is seriously necessary, very seriously necessary. Ain't like paint.

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Peter Havriluk

It dries clear. Others may not.

Peter,
How does your final wipe coat differ from the first two squeegee coats and do you sand down virtually to bare wood after it?
-d.

Final wipe coat is insurance against having inadvertently cut through the filler coats. Thin, padded on with a cloth. Light sanding to knock off the dust that might have gotten into it. I did all my leveling before applying the wipe coat.

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Peter Havriluk

Z-Poxy is a 50/50, non-critical mix finishing resin, but will blush if in higher humidity, as faster-curing epoxies like Z-Poxy tend to generate more blush. It's important to clean off any blush with liquid detergent, water, and a maroon ScotchBrite pad, as it will interfere with subsequent coats of sealer and finish, and will eventually react with anything that passes through the wood or finish. Some epoxy manufacturers suggest that water alone is the preferred solvent for blush, so worth checking with the maker of the system. Dry sanding the surface without first removing the blush will not clear the contamination and instead will work the blush into the sanding scratches.

A second caution is that the Z-Poxy hardener darkens with age, and a sand-through on a final coat can show a light spot on rosewoods. Another of the schools of epoxy practice used a heavy coat of epoxy and heat to level..with the issue that the thicker the coating, the more amber-appearing. Very thin coatings add the least film thickness and result in the most uniform color.

Finally, thinning beyond 10% or so with denatured alcohol can slow the cure a bit and introduce water into the uncured resin, which can result in a softer film. This thicker viscocity is one of the issues we've seen with Z-Poxy...while the material runs a bit less than low and low-to-medium viscosity systems, it also does not tend to penetrate as nicely into pores.

West, Maas, and System 3 all make low-blush or non-blushing formulations, but the one we've found we like the best is System 3 Silver Tip with their fast hardener...the viscosity is perfect - not too thick or too thin, clear, and not too critical on the mix in very small batches (we do 5 grams resin for normal work, but have mixed down to 2.5 grams resin using a sensitive scale). With the fast hardener, a second or third coat can be applied without sanding if done in 72 hours or less, but we lightly scrape with a razer blade scraper and tooth with maroon ScotchBrite anyway - if only to keep surface build down to a minimum.

FWIW, there are a couple videos on YouTube that cover pore filling with epoxy, including with Z-Poxy (search for 'guitar Z-Poxy pore filling') - with a well-engineered holder for the body and neck, back and sides can be done in one session.

The Etore or similar window squeegee is the real key to any epoxy pore filling. Unlike a Bondo squeegee or credit card, a thick-edged window washing squeegee can generate some real pressure to force the epoxy in the pores, as well as stripping off excess epoxy so as to leave the thinnest film. With Silver Tip being water-clear, we don't worry about a sand-through on the first two coats, but do leave a thin, continuous layer for the final coat, toothing it with ScotchBrite for a good mechanical bond with sealers or topcoat.

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For the times they are a changin'

- Bob Dylan

You will want an epoxy that bonds well with what you are pore filling (wood? oily wood, sealed wood?), is designed to be applied thin, as in finishing resin, won't turn green as it cures, and is user friendly. And you will want to choose an epoxy that has demonstrated compatibility with the finishing system you plan to use.

Typical choices are Zpoxy, or products from System Three and West Systems.

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Joe Beaver
Maker of Sawdust

If you go with the WEST System, be sure to use the 207 hardener to avoid any potential for blush problems.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Milburn uses the cheap hardware stuff in his French Polish tutorial. I have only used epoxy once and I just used Loctite 5-minute from the hardware store. But like Milburn I also use the epoxy like a traditional filler and sand back to wood leaving only the pores filled.

Trevor brings up a good point, blush. It happens with some epoxys in the right conditions. I currently use System Three Clear Coat, it doesn't blush, and as Trevor said West System with the right hardener won't either. Zpoxy will blush if the RH is up.

To reduce the chances of blush you can use humidity control in the work area. If you don't have that you can reduce the risk by warming the wood with a heat gun or hair dryer just before appling the epoxy. That seems to work when you have moderately high RH (say 45-55). I haven't tried with higher RH.

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Joe Beaver
Maker of Sawdust

The trouble with the non-specialist epoxies (used for laminating, gluing, filling rather than surface coating) is that they can go white on you way down the track, like a couple of years. So be sure you use an epoxy system especially formulated not to blush. The WEST 105 resin + 207 hardener is one of these systems. There are others, but I know the WEST system works for me and I don't fancy finding out in a couple of years that another system doesn't.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Has anyone here seen blush occur with System Three, West, or Z-poxy under finish on a guitar after a couple years (or more)? If so, under what conditions did it happen?

Along with humidity and temperature, how much of a factor is application thickness in blushing?

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Yes, WEST with 206 hardener (should have used 207). Guitar stored in a soft case at typ. 60% humidity, developed white patches after ~2 years. Coating thickness was full cover, but as thin as I could get it. I didn't measure it. I don't know if thickness is a factor, but a continuous film will likely give a more visible problem than a pore fill sanded back to the wood. The application temp. would have been above 25C and the RH close to 45%. I still have the guitar (it is the original falcate braced prototype) and the white area has grown and intensified over the years.

WEST with 206 won't always go white on you, but WEST with 207 never has for me.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

"WEST with 206 won't always go white on you, but WEST with 207 never has for me."

Do you think it was amine blush or the reaction to ultraviolet light that caused it to go cloudy? The 207 has UV protection added, which supposedly still works even after the hardener has turned dark amber (as it will after a couple of years - which gives a light amber tint to the mixed epoxy).

I doubt it was any reaction to UV as that guitar spent most of its time in a case. More likely some sort of reaction to humidity after initial cure, but whether it would be technically correct to call that amine blush or just "bloom" is a different matter.

It was finished in nitro and buffed out perfectly clear, so initially there was no apparent issue. That's the scary bit!

Here's some background on WEST 207 Hardener. Read between the lines for the implications regarding the other hardeners. For example, "206 Slow Hardener is not intended for clear coating" quoted from the WEST 206 page. I like it that WEST are very specific about the performance of 207. I've found it problematical getting other suppliers to match WEST's statements so emphatically.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

www.oneoceankayaks.com/Epoxresl.htm#blush

Kayak builders use clear epoxy coatings for some of their boats. Here is a test one of them did on various epoxies

We have seen separation of lacquer finish over time due at least partially to reaction of moisture passing through the lacquer (excessively acidic perspiration left on the instrument over an extended period of time) with the amine salts (carbomates) which were not fully removed. At first, we believed this was epoxy shrink-back in the pores causing mechanical separation, but have seen the same thing occur even where woods without significant pores (maple; cherry) were treated with Z-Poxy to add a layer of higher index-of-refraction material to the finish.

The finish separation appears to be confined to just a few guitars, and to owners who perspire heavily and have out-of-the norm body chemistry (very acidic...4.5-5.0, although some studies claim normal male perspiration is closer to 5.5 than the 7.0 for females). We suspect the alkaline carbomate residue is reacting with the lower pH perspiration which is passed through the lacquer film over time, with the reaction products creating a visible residue and forcing separation of the sealer from the epoxy.

The other factor is amine bloom, which is different from blush, and is the unreacted amine component of the epoxy migrating to the surface...this waxy-appearing haze on the surface is easier to detect than the blush, as at the RH we apply epoxy (45%-50% RH), the amount of blush may be undetectable by visual inspection and the pH test may be inconclusive (indicates conditions are conducive to blush and bloom, versus the presence of those compounds). Accurate mixing can help with bloom, and in any case, bloom may or may not react with atmospheric CO2 and water vapor and be converted to carbomate (blush).

Both blush and bloom can cause issues with subsequent finish operations, which - after using Z-Poxy (blush prone), West 105/207 (minimal blush/bloom and usually free of both at our shop temperature and RH), and Maas Low Viscosity (poor handling) - led us to System 3 SilverTip (as well as Mr. Greven's use) , which is essentially blush and bloom-free even in small quantity mixes, and has excellent handling characteristics. Even then, we do a water and detergent wash-down and a distilled water rinse with final naphtha wipe before sealing.

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For the times they are a changin'

- Bob Dylan

Woodie, good report, thank you for posting. One question, why has Silvertip been chosen as oposed to Clear Coat?

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Joe Beaver
Maker of Sawdust

Handling, mix sensitivity, cure time, and recoat time. The viscosity is just right out of the containers for pore filling, versus Clear Coat, which is just a bit thinner than we prefer. Pretty insensitive to mix ratio, which is an issue with some System 3 epoxies. With fast hardener, 2-3 coats a day are possible, depending on ambient temperature, and no-sand recoat up to 72 hours.

_________________
For the times they are a changin'

- Bob Dylan

Thanks Woodie,
Just curious why Silvertip was chosen since it is a lamenting epoxy, designed to bond fiberglass cloth to wood, whereas Clear Coat is designed as a finishing epoxy.

That doesn't mean one is inherently better than the other for our purpose.

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Joe Beaver
Maker of Sawdust

Both are billed as suitable for raw wood, so not an issue there. Really a case of a perfect viscosity, faster cure, and generally better handling characteristics without having to either bulk or thin. After the latest cycle of 10 new guitars and two refinishes (one full and one partial), plus a couple minor furniture projects, I really began to appreciate the 'not too thick/not too thin' characteristics. Comes down to preference, with the boss still preferring the higher viscosity of the Z-Poxy, but really disliking the blush issues.

_________________
For the times they are a changin'

- Bob Dylan

I haven't seen any blushing with Z-poxy, yet. The oldest guitar I've built that has Z-poxy on it is three years old and it's fine. I always apply Z-poxy with the room temperature at least 70 degrees F, RH = 45-50%, and let it sit overnight between applications. Maybe I've just been lucky so far. I like Z-poxy, but if Silver Tip is less susceptible to blushing, it might be wise for me to switch to it for the added insurance. I'll give it a try on the current guitar when I get to that point.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter