Official Luthiers Forum!

It’s been a while since I’ve done a gloss coat. In the past, I have leveled the epoxy and scuffed, but left a thin layer on., Royal Lac instructions are to sand back to wood…

What do y’all do?

I sand back to wood. Then wipe on several coats of Seal-Lac followed by Royal Lac French polish.


Steve

_________________
Steve Smith
"Music is what feelings sound like"

Are you using regular or PostCat? For the life of me, I can’t get a pad to work, even at 50/50 dilution….

I thought I saw somewhere that Royal Lac can be sprayed.

If you have the setup. I don’t…

I do not do a hard sand back to wood. But sand throughs are unavoidable. I go by feel. If a sand through appears I avoid it. When done, I do a thinned wash coat of epoxy to even the color. When dry, scuff lightly with scotch brite. Does this answer ur question?

It does.

I use regular but would like to try post cat. I put 4 or 5 drops of RL on the fad and about the same of alcohol (everclear for me). A touch of walnut oil every once in a while keeps things moving smoothly. I occasionally will apply using small circles to build but mostly apply by going back and forth with the grain, what Robbie OBrian calls the fly on, fly off method.


Steve

_________________
Steve Smith
"Music is what feelings sound like"

Sorry, I forgot to mention I use Aquacoat filler with RL. When using epoxy I also tried to avoid sand throughs.


Steve

_________________
Steve Smith
"Music is what feelings sound like"

My problem with sanding back to bare wood is that, with some woods, that just opens up new pores. So, when following the epoxy pore fill then topcoat method, I try to leave a film of epoxy as the base coat for the topcoat.

After re-reading, I realized this was not about epoxy pore fill. So mileage may vary. If you stop and think about it, if you somehow manage to sand without reaching wood, a wash coat is essentially not needed. Won't hurt anything. But if I do get to wood, then the washcoat evens out the color. For me, the trick is to avoid those areas so as not to open the pores.

I sand back to wood leaving only the pores filled. Lately I have been using aquacoat filler and I like it quite a bit. I use Royal Lac just like I would do FP. Have not tried the post cat stuff.

You could try spraying a couple of coats with a cheap $15 HF jamb gun (al fresco), allow them to dry , and then sand them smooth. That may give you a base layer to finish with French polish. Chuck Tweedy used to do something similar, except I think he would use better equipment, build the finish, allow it to dry, sand smooth and then French polish a few top coats (IIRC).

Depends on the filler. When I used Z-poxy, I sanded back to wood, then put on another thin coat. Using Devcon now, doesn't seem to need the final thin coat. Z-poxy has a light amber color; Devcon is clear, which seems to be a factor.

_________________
formerly known around here as burbank
_________________

http://www.patfosterguitars.com

Thanks folks! I just envision a neverending cycle of porefilling, sanding, opening new pores etc…

I'm late to the game but I do sand Zpoxy back level with the wood and then apply one more very thinned coat which soaks in but also coats the surface. Scuff sand that and its ready for finish.

I've done pore filling on two guitars. On the Z poxy arch top, I did just what they say. sand smooth, and then a thinned coat to make an even color. With Aquacoat, I just filled. It goes on pretty even. I don't care for Aquacoat under colored varnish. It looks cold to me. Under the clear Osmo oil wax finish, it looks nice.

_________________
Why be normal?

Just to add to what I said above: I also do this with Royal Lac, which involves first coating the guitar with regular shellac, then using the proprietary topcoat. You can put the base coats of regular shellac on top of the film of epoxy. I know the instructions say to sand back, but I don't like that. It opens new pores when I do it.

That’s the worry…

I do "epoxy pore fill" on laminated construction because I use epoxy as a clear glue so any bleed through isn't noticeable. Pore filling with epoxy then fills the remaining pores to give a homogeneous surface on which to apply topcoats. Epoxy pore fill is a relatively recent way to fill pores and may not be the best in the long run. Some epoxy/hardener combinations turn cloudy over time. Also I haven't found epoxy to be an especially easy pore filler to apply.
For French polish work a traditional pore filling is pumice and shellac. Although a bit tedious to apply it may not be any worse than epoxy and will give you a surface compatible with your shellac based top coat.
Why do Humans love "Shiny" so much?

Different finishes tend to have different refractive indexes. If there is a layer of a different finish on the surface under the final coat some light will be reflected off the interface, producing a 'veiled' look. We see this very plainly when there is glue on the surface under finish, but almost any combination can do this. I've noticed it with oil-resin varnish over shellac, for example. It's particularly noticeable when you've sanded through the under layer in some places but not others as a splotchy look.

I seal the wood to be filled with a spit coat of shellac, and then fill it, normally these days with a French polish type of pumice fill, using the shellac as binder. No matter how level you get it, it will shrink back over time. I usually sand back and re-fill, which gets any pores that were opened up in the sanding. Then I sand back to wood again, and start in with my final finish, which is normally oil-resin varnish. The filler absorbs some of that, and shrinks back, so after about three coats of varnish I allow it to sit for a week or more, and once again, sand back to the wood. Now I'm ready to apply the final finish...

What oil varnish are you using? I've been wanting to try this finish for some time but can't seem to find one I like out of a can.

Alan, I'm interested in your oil varnish too.

Also -

Alan wrote - "Then I sand back to wood again, and start in with my final finish, which is normally oil-resin varnish. The filler absorbs some of that, and shrinks back, so after about three coats of varnish I allow it to sit for a week or more, and once again, sand back to the wood. Now I'm ready to apply the final finish..."

A problem I run into with oil based finishes is getting them to dry on oily woods (EIR, Ebony, Cocobolo...), sometimes they don't.

So, in the case of oily wood and sanding back a filler, are you starting with a wash coat or two of shellac as a sealer and then moving on to the oil finish? For me, the sealer coat of shellac has to be 100% or trouble is brewing.

I'd love to know there is a drying secret I'm missing.

_________________
Brian R, Wood Mechanic
N8ZED

Oily woods are generally a problem with oil-resin varnishes. Some are more sensitive than others to the presences of non-drying oils in the wood, and some woods are worse than others. Even in a normally 'good' species of wood you can run into problems from time to time. Usually UV light on the piece right after varnishing will help. My understanding is that the UV and volatile organics in the varnish react to produce ozone, which speeds up the normal oxidation reaction that cures the varnish. Often this can be enough to get the first coat to harden properly, after which you're usually OK. Don't re-coat until the first coat has cured enough to 'dust' when sanded lightly! The second coat might cure OK while the first is still soft, and that might never cure. The whole thing can peel up like bad sunburn.

These days I'm using 'Murdoch's Ure-Alkyd 500' floor varnish, made by Sutherland-Welles in Vermont, USA. They make the synthetic resin from waste left over from the Cabot cheese factory. It cures very hard and clear, with only a little yellowing. It also goes on very thin; I'm ending up with film thicknesses of around .0025"-.0035", similar to a good French polish, but this wears better and is more chemical resistant.

With this varnish I sometimes find it helpful when it has failed to cure in spots to wipe back with acetone to get the uncured varnish and what ever oil you can out of the surface. Sometimes another coat of varnish will then cure. If not, a thin layer of CA works better to stop the surface out than shellac, and it seems to be more compatible with the varnish in appearance.

Another varnish that I've seen recommended for guitars is Pratt & Lambert #38. I have less experience with that. It's not as hard, but may cure better on oily woods.

Alan would a seal coat of shellac perhaps help with the adhesion on oily wood problem?