epoxy porefill/ nitro top coat methods ?

[Stu]

G'day all.

For my next one to be refinished, I want to try other sorts or porefill/grainfill methods than a shellac coat , timber grainfill slurry then shellac coat before shooting pre-cat nitro.
I want to make the jump to epoxy as the primary source of porefill.
Most of you guys use it, and rave about it, which is great to hear.

The only part I can't seem to find info on is on what methods ,if any are used for sealing off before hand. I know epoxy darkens up endgrain
on blackwoood big time and that is what I'm trying to avoid.

Does anyone seal off with something before epoxy porefill?
And what will work with nitro topcoat as a binder (if needed)

This is the guitar I'll epoxy grainfill.
http://www.bluestoneguitars.com.au./id74.html

Thanks, Stu

[Allen]

I'm using WEST Systems for pore filler and love it. I don't use shellac to seal anything. I've heard others say that epoxy doesn't work well over shellac, so I've not used shellac before hand. I didn't feel it was worth the risk of having a finish go bad.

I wouldn't say that the epoxy has darkened the wood any more than wetting the wood out with some other product. but if your building electrics with lots of end grain I can see how this would be and issue.

Most woods will fill with one application, but I've come across a few types that will require up to 3 applications (such as Australian Cedar). After sanding I always apply another coat thinned 1:1 with metho. It just wets out everything and guarantees that when you apply your finish there isn't going to be any nasty surprises of light and dark patches.

I'm using Mirotone precat. and all I do before spraying is giving the surface that should be pretty well perfect by now, just a little light rub with a foam sanding sponge, or P240 equivalent. The lacquer sticks like mad. I know this by how hard it is to get it off for the bridge glue up.

[Richard]

I swear by Z-Poxy for the pore fill.

Like the WEST Systems product it depends on the wood you're using but normally 1-2 coats. I've never tried WEST but will probably give it a shot after my current stock of Z-Poxy is gone. For me Blackwood is generally one coat of z-poxy.

I apply the epoxy with a credit card, working in small areas, cleaning each up as best I can as I go along. After it's dried (day/s later) I take a ROS with 320 grit to very quickly it to smooth it over, careful to not go down into the wood. Most of the time after one coat and sanding it's ready for finishing, but this is dictated by the look and feel of the wood - repeat as needed.

For the finishing I'm also using the Mirotone precat. Fantastic stuff that I also now swear by. Depending on the look I'm after (or the customer is after) I use either full gloss or satin which are both capable of stunning finishes in their own way.

[Hesh1956]

Stu what Allen said.

Epoxy will pop the figure and darken the wood some and this is more profound in my experience with blackwood and koa but very pleasing nonetheless.

You do have the option of just filling the pores with epoxy and sanding the surface back to the wood. However, depending on the epoxy the end grain could still remain slightly darkened.

First off though when I speak of epoxy know in advance that I am speaking of an epoxy finishing resin and/or West Systems. Epoxy finishing resins are produced by Z-Poxy and System III. Both Z-Poxy and SIII also make epoxy glue so be sure to get and use the finishing resin variety.

Finishing resins are specially formulated to be pretty thin and workable and sand very well.

In the case of West Systems, although it's a fantastic glue too it is thin enough to use as a pore filler.

Although any old cheap a** epoxy may work as a pore filler your experience will be better with the finishing resin variety IMHO and avoid anything with a working time of 30 minutes or less.

Epoxy will not stick well to shellac but shellac sticks great to cured epoxy. Trust me please and save yourself the headaches.......

Also Z-Poxy adds a very slight amber color and so does West Systems where as SIII is more clear but far more sensitive in the mix ratio that has to be dead nuts on or the stuff will not cure leaving you with a gummy mess.

Do small areas at a time like a 6" X 6" area and use a credit or gift type card to "mash" the epoxy into the pores. Work it back and forth in all directions with the final strokes at 45 degrees to the grain. Use the card as a squeegee for the final strokes and wipe the excess on the next area that you plan to do. A very little bit of epoxy goes a very long way with one teaspoon often being enough for an entire guitar back.

On the first coat you will be covering the entire surface including, hopefully, getting it in all of the pores. It usually takes me two coats to do a complete job. Now this is where you have the option of sanding it back to just be in the pores or leaving an epoxy film on the guitar. If you want to leave the film on the guitar and sand through in areas mix up epoxy with a 50/50 mix of denatured alcohol and wipe the entire guitar, not the top unless you want an aged look, with a lintless cloth and the mixture. This last, thinned layer will even out the color.

Now if you only want the epoxy in the pores sand it back and seal with shellac. It is fine to spray nitro directly on the epoxy if you leave the epoxy layer on the guitar and no seal coat or shellac is required.

When pore filling I use a rag with DA on it to smooth the epoxy on the edges of the bindings and take up the build-up.

Good luck.

[Stu]

Thanks for your detailed replies Allen, Richard and Hesh. Much appreciated.


Allen, I saw your tutorial on refinishing and that helped alot in understanding your processes.
(I was a Panel Beater for 17 yrs so have had generous booth time experience too but swapped to an apprenticeship in Carpentry a couple years back).

I'm currently using west systems with the 205 and 206 hardeners and
probably a good idea if I experiment a great deal more with this until I'm happy with the 'end grain dilemma'.

I guess the only true comparison with epoxy grainfill between acoustics and electrics would be the neck. That's really the only area on an acoustic which shows a generous amount of endgrain as the body is
pretty much endgrain free.

Which leads me to wonder if I'm biting off more than I can chew, considering the amount of carves and bevels on this build increasing the area of endgrain? (see link in opening post)

Happy to let this one roll a bit longer and experiment a bit .

Thanks gents,
Stu

[Allen]

I've epoxy filled all my necks and I haven't been disappointed with the end grain in the heel. There is a nice even transition from edge grain to end grain. Where I do see a noticeable difference is at the top of the head stock. Since it's a sharp change in grain orientation, it's certainly more pronounced.

I haven't tried not applying epoxy there to see if it would end up being less dark though. There's a little experiment for you to try.

[Stu]

I've done quite a few test pieces on Blackwood today and last night.

One on a 60 grit older endgrain. Very dark results. (60 grit ???? pfft)

one on fresh sanded endgrain to 240 grit = slight darkening and
quicker soak up into grain

another fresh sanded to 400 grit = slightly lighter colouring than above
and less soak up with smoother
cured finish. (as expected)


I'm happy with the levels of darkening on the end grain although I
will do another test to see if there is any darkening effect when cutting epoxy with mineral spirits 1:1 compard to straight uncut.

What have you guys experienced?

cheers, Stu

[Allen]

When I use the 1:1 mix with metho, the wood has already soaked up the epoxy and I only use this to even out any sand trough areas, so I don't notice it darkening it any more at all. What milage you get out of it as a first coat though would be interesting.

[Stu]

O.K. I've done a few tests and I'm sold on epoxy as a porefill.

I preferred to run it through its paces first to understand its merits
and limitations before I started on the real process, which I've done.

Thanks for the help on this one, all. Pics to follow when done.



cheers, Stu