There seems to be several concurrent threads right now about pore filling and I seem to be the spokesman for a finishing resin called Zpoxy. I find myself repeating the same thing over and over, posting the same pictures and links. I thought it would be more efficient to just post one thread about this product and then I can point to it whenever the subject comes up.
Disclaimer: I am not a finishing expert or "professional" or anything like that. In fact I am about as amateur as you can get. That might have some advantage for you folks who are finishing your first or second guitar and considering which products and methods you might want to use. I will certainly say that a professional who makes her living finishing lots and lots of guitars probably won't use this method.
Second, there are lots and lots and lots of pore filling products on the market, and even more home brew methods. I've only tried a couple of them (which I'll talk about) but I'm not prepared to argue the merits of one over another. I'll try to show some photos of what works for me - if you have something your really like how about doing your own thread and showing your pictures.
Third, of course, your milage and results may vary. In fact, they will probably vary a lot. Practice on scrap.
Forth, always practice any finishing technique or product on scrap of the same wood that you will be finishing. Keep all the cutoffs from building your guitar for this purpose. Don't have any scrap? Get some.
Fifth, I have only worked with lacquer on top of the finishing resin. I've tried both solvent based (nitrocellulose) lacquer and so called water born lacquer. Both work fine - I have had no problems with adhering, witness lines, blushing, or anything else. I can't comment on any other finish - practice on scrap.
The product I use is a finishing resin called Zpoxy. I buy it from LMII but I think it is available elsewhere on the internet. It is a slow curing material, takes about 24 hours to completely cure. It has a slight amber tint to it that may or may not be desirable (practice on scrap). It is forgiving about mixing ratio - I don't weigh it but rather just squeeze about the same amount into a cup. A little seems to go a long ways - I have finished a dozen guitars with my first 12 oz bottles
https://www.lmii.com/glue/3050-z-poxy-finishing-resin-12-oz.html
Most epoxies are soluble in denatured alcohol (DA) - you can use that for clean up and to dilute the resin. When you first mix some DA in it it turns cloudy, but with some stirring it will clear. We'll talk about dilution later.
OK, lets get on with it. Why "pore fill"? Some woods used in lutherie have small surface pores - they show up as fine little lines in the surface of the wood. Rosewood, mahogany, koa, some other hardwoods are porous. If you put many of the popular finishes over these woods the pores are not filled and they leave little lines in the finish. Here is a piece of EIR with nitrocellulose lacquer. It had one application of a commercial paste pore filler which either was not enough or shrunk back. The white lines is polishing compound in the pores
Whatever product you are using for pore filling, the basic method is to apply it across the grain forcing it into the little pores. I do the same with Zpoxy.
This particular guitar is a basic mahogany back and sides, spruce top and rosewood trim. Soft woods like spruce and cedar, as well as maple are not porous and do not need to be filled. We'll talk more about maple in a minute. Sand the entire guitar to 320, scrape the binding and purfling to get every bit of dust out of it and tape off wood that you don't want to get the resin on. Remember that this is your last chance to get the little scratches out - make it perfect.
If you are going to do any staining, I think this is the best time. The wood is at its most absorbent and the resin will seal in the stain. Obviously this is very critical and definitely should be practices on scrap. This is a mahogany neck that I wanted to stain to match the cocobolo on the back. This isn't a good picture, sorry, but I've got a scrap of mahogany that I'm trying to color match to the scrap of coco, then I'll stain the neck in the background
Here is the stained neck with the coco, its ready for pore filling
For the pore filling itself I mix the resin 1:1 by approximate volume and simply work it onto the wood with some sort of squeegie - a plastic card works very nicely
Get it as smooth as possible but don't worry - let it cure over night. Curved surfaces like a neck are a bit harder, just keep working it across the surface of the wood
Sand it back level with the wood, you can start with 220 and go to 320
Now apply a second coat. This time I mix the resin, then dilute it maybe 5 or 10 to one with DA. I just put a good splash in and mix it in thoroughly. The diluted resin can be applied with a little foam brush.
Let that cure overnight
and sand this back again level with the wood.
(the forum software has told me I can't upload any more pictures so I'll post this and go on.
Disclaimer: I am not a finishing expert or "professional" or anything like that. In fact I am about as amateur as you can get. That might have some advantage for you folks who are finishing your first or second guitar and considering which products and methods you might want to use. I will certainly say that a professional who makes her living finishing lots and lots of guitars probably won't use this method.
Second, there are lots and lots and lots of pore filling products on the market, and even more home brew methods. I've only tried a couple of them (which I'll talk about) but I'm not prepared to argue the merits of one over another. I'll try to show some photos of what works for me - if you have something your really like how about doing your own thread and showing your pictures.
Third, of course, your milage and results may vary. In fact, they will probably vary a lot. Practice on scrap.
Forth, always practice any finishing technique or product on scrap of the same wood that you will be finishing. Keep all the cutoffs from building your guitar for this purpose. Don't have any scrap? Get some.
Fifth, I have only worked with lacquer on top of the finishing resin. I've tried both solvent based (nitrocellulose) lacquer and so called water born lacquer. Both work fine - I have had no problems with adhering, witness lines, blushing, or anything else. I can't comment on any other finish - practice on scrap.
The product I use is a finishing resin called Zpoxy. I buy it from LMII but I think it is available elsewhere on the internet. It is a slow curing material, takes about 24 hours to completely cure. It has a slight amber tint to it that may or may not be desirable (practice on scrap). It is forgiving about mixing ratio - I don't weigh it but rather just squeeze about the same amount into a cup. A little seems to go a long ways - I have finished a dozen guitars with my first 12 oz bottles
https://www.lmii.com/glue/3050-z-poxy-finishing-resin-12-oz.html
Most epoxies are soluble in denatured alcohol (DA) - you can use that for clean up and to dilute the resin. When you first mix some DA in it it turns cloudy, but with some stirring it will clear. We'll talk about dilution later.
OK, lets get on with it. Why "pore fill"? Some woods used in lutherie have small surface pores - they show up as fine little lines in the surface of the wood. Rosewood, mahogany, koa, some other hardwoods are porous. If you put many of the popular finishes over these woods the pores are not filled and they leave little lines in the finish. Here is a piece of EIR with nitrocellulose lacquer. It had one application of a commercial paste pore filler which either was not enough or shrunk back. The white lines is polishing compound in the pores
Whatever product you are using for pore filling, the basic method is to apply it across the grain forcing it into the little pores. I do the same with Zpoxy.
This particular guitar is a basic mahogany back and sides, spruce top and rosewood trim. Soft woods like spruce and cedar, as well as maple are not porous and do not need to be filled. We'll talk more about maple in a minute. Sand the entire guitar to 320, scrape the binding and purfling to get every bit of dust out of it and tape off wood that you don't want to get the resin on. Remember that this is your last chance to get the little scratches out - make it perfect.
If you are going to do any staining, I think this is the best time. The wood is at its most absorbent and the resin will seal in the stain. Obviously this is very critical and definitely should be practices on scrap. This is a mahogany neck that I wanted to stain to match the cocobolo on the back. This isn't a good picture, sorry, but I've got a scrap of mahogany that I'm trying to color match to the scrap of coco, then I'll stain the neck in the background
Here is the stained neck with the coco, its ready for pore filling
For the pore filling itself I mix the resin 1:1 by approximate volume and simply work it onto the wood with some sort of squeegie - a plastic card works very nicely
Get it as smooth as possible but don't worry - let it cure over night. Curved surfaces like a neck are a bit harder, just keep working it across the surface of the wood
Sand it back level with the wood, you can start with 220 and go to 320
Now apply a second coat. This time I mix the resin, then dilute it maybe 5 or 10 to one with DA. I just put a good splash in and mix it in thoroughly. The diluted resin can be applied with a little foam brush.
Let that cure overnight
and sand this back again level with the wood.
(the forum software has told me I can't upload any more pictures so I'll post this and go on.
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