Pore filling over a shellac sealer coat

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Brian McCombs
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Pore filling over a shellac sealer coat

Postby Brian McCombs » Thu Jan 03, 2013 1:31 am

I performed a search but didn't really get the hits I was looking for.

I sprayed a shellac sealer coat on Mahogany back and sides. Lot's of deep pores....first time using mahogany, surprising how deep and numerous these pores are.
I've used a few different things in the past. Drywall compound (which works surprisingly well) and some type of stuff I got years ago from SMac.

The DWcompound is OK but it is difficult to dye..the last one I used it on, I tried to dye it real dark almost to a black but it dried to a funky purple. The stuff I got from SMac I do not like it, keeping it IN the pores is silly hard.....the remainder of it has turned rock hard in the can. Not sorry to see it go. Looking for something different and hopefully easier.

I ordered some Z=poxy which is in route - but after i bought it I see that it isn't recommended over shellac.....too late.

I plan to spray it with laquer when done...but I got a lot of pores to fill first. What to use?

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Waddy Thomson
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Re: Pore filling over a shellac sealer coat

Postby Waddy Thomson » Thu Jan 03, 2013 2:40 am

There's always the old standby - pumice!
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Harald Lane
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Re: Pore filling over a shellac sealer coat

Postby Harald Lane » Thu Jan 03, 2013 7:43 am

Depending on your top coat:
1) as Waddy said - pumice as you go with a shellac finish
2) using a sanding sealer , sometimes refered as Vinyl selaer if you want to go with anitro or 2k finish.
3) pumice with a little shellac over it, then go with a traditional varnish.

I´m sure, you can find some threads in the olf forum about using sanding sealer.

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Michael.N.
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Re: Pore filling over a shellac sealer coat

Postby Michael.N. » Thu Jan 03, 2013 9:16 am

I'm a little surprised that Z-poxy cannot go over shellac. If that is the case what do they use to protect the lighter coloured inlays?
You could try indian Ink to dye your Drywall compound, which shouldn't be that much different to my concoction:

viewtopic.php?f=11&t=70075&hilit=egg+white

or as others have stated, the Pumice method. Practice on scrap first. The last thing you need is the white of the Pumice showing through.
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Patrick delBosque
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Re: Pore filling over a shellac sealer coat

Postby Patrick delBosque » Fri Jan 04, 2013 8:04 pm

In the product description for Zpoxy on the LMI website, they say that Robbie Obrien recommends a shellac coat between the Zpoxy and the topcoat, so why wouldn't it work underneath the Zpoxy just as well?
Where did you read that caution, Brian?
BTW I have just finished two guitars using Zpoxy porefill and really like it, but did not use a scratch coat of shellac underneath, as I did not mind the "amber" look it gave to the light colored woods.
Patrick

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Brian McCombs
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Re: Pore filling over a shellac sealer coat

Postby Brian McCombs » Fri Jan 04, 2013 8:37 pm

Well I get conflicting info depending on where I look.....imagine that!.

If you type: Z-poxy over shellac . into a search engine you will find some that say it doesn't adhere well to shellac BUT shellac sticks onto Z-poxy ok...??? I try a test portion.

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Re: Pore filling over a shellac sealer coat

Postby jaujau » Fri Jan 04, 2013 9:37 pm

I always struggle when it comes to pore filling. I've probably french polished 10 guitars by now, and the pumice and shelllac fill the pores but leave some smudge on the surface, or never fills the pores quite through and it forces me to build more thick coats of shellac that end up being the filling coat, instead of the pumice.

I've read (in an article with Eugene Clarke) that the biggest mistake that beginners have is using too much shellac on the sealing wash coats, and i guess that next time I will give a lighter wash coat and try my luck with pumice filling.
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Brian McCombs
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Re: Pore filling over a shellac sealer coat

Postby Brian McCombs » Sat Jan 05, 2013 10:14 pm

[quote ]the biggest mistake that beginners have is using too much shellac on the sealing wash coats[/quote]

uh...yeah...he's right I'd say.....my sealer coat is very thick. I sprayed it with a new paint gun I bought. I orange peeled it pretty good - I have a lot of sanding to do....Top is ok. But the back and sides have too much without a doubt. I tried to practice on some other surfaces first but all I had was some plywood and it did not help much. Live and learn....I LOVE sanding stuff over and over and over. Maybe some of these pores will get smaller once I level it off...hoping.

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Re: Pore filling over a shellac sealer coat

Postby Scot Tremblay » Sat Jan 05, 2013 10:43 pm

Brian McCombs wrote:Well I get conflicting info depending on where I look.....imagine that!.

If you type: Z-poxy over shellac . into a search engine you will find some that say it doesn't adhere well to shellac BUT shellac sticks onto Z-poxy ok...??? I try a test portion.


I would imagine the reason for this advice is that the Z-poxy is harder than shellac and a harder finish really should not go over a softer. The softer moves more than the hard and can lead to checking, seperation etc. The other way around is usually fine (softer over harder) as long as the two are compatible (and most things are with shellac).
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Robert Webster
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Re: Pore filling over a shellac sealer coat

Postby Robert Webster » Sun Jan 06, 2013 7:46 pm

The Zpoxy and shellac thing might be a tempest in a teapot. After all, once you seal with shellac, apply the epoxy, and then allow it to cure, you're going to sand it all back to the bare wood. At this point the epoxy should only be in the pores. You can then seal and finish with whatever you like (except, perhaps, for varnish).

I've gone through that routine and have gotten results that we're initially excellent for a French polished surface. Unfortunately, epoxy fills all eventually shrink back a bit after 6 months to a year so that pores are once again evident. Same goes for the wishful thinking of using enough shellac to fill the pores. Shellac dries down extremely slowly over rosewoods and will sink back with time.

Bob

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Chris.Conery
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Re: Pore filling over a shellac sealer coat

Postby Chris.Conery » Mon Jan 07, 2013 4:55 pm

I have been zpoxying over a thin wash coat of shellac, sanding back to wood, usually two coats, sometimes more. It works fine, doesn't seem to shrink back. YMMV.
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Jim Kirby
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Re: Pore filling over a shellac sealer coat

Postby Jim Kirby » Tue Jan 08, 2013 1:12 pm

Robert Webster wrote:The Zpoxy and shellac thing might be a tempest in a teapot. After all, once you seal with shellac, apply the epoxy, and then allow it to cure, you're going to sand it all back to the bare wood. At this point the epoxy should only be in the pores. You can then seal and finish with whatever you like (except, perhaps, for varnish).

I've gone through that routine and have gotten results that we're initially excellent for a French polished surface. Unfortunately, epoxy fills all eventually shrink back a bit after 6 months to a year so that pores are once again evident. Same goes for the wishful thinking of using enough shellac to fill the pores. Shellac dries down extremely slowly over rosewoods and will sink back with time.

Bob


Not everyone sands back to bare wood, though - some people like the amber colored coat and leave a full Z-poxy layer, even using a 50/50 zpoxy/alcohol wash coat at the end to insure full coverage after level sanding. The warning may be more appropriate in these cases?

I've tested french polish shellac over a full Z-poxy coat on a test board, and it sticks fine and looks great, but I've never done this on a finished guitar - I usually sand back to wood.
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Re: Pore filling over a shellac sealer coat

Postby Robert Webster » Tue Jan 08, 2013 5:53 pm

Yes, practices with epoxy do vary. I know that Cyndy Burton uses 5min Devcon epoxy for pore filling over a shellac seal and manages to get a very fair surface and she doesn't sand back to the wood afterwards. She then French polishes without oil and after a short cure time, rubs out the surface to level it and then applies glaze coats. It's a marvelous looking finish for Jeff's guitars. However, I have seen a couple of her guitars that were 2-3 years old and pores are evident and I can only assume that it was shrink back in the epoxy that caused that.

Bob


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