Epoxy Pore Filling
It’s been said that whom ever decided that guitars need to be smooth and shiny should be dug up and shot...
Epoxy "finishing resins" and some epoxies do a very nice job of filling pores. Here is how I use epoxy to fill pores. This same method works very well with West Systems 105/205 epoxy, System III finishing resin, and Z-Poxy finishing resin. Please note that in the case of Z-Poxy and System III both companies make a number of epoxy offerings. For our purposes we want the finishing resin.
The primary difference is the viscosity where the finishing resins tend to be thinner and easier to work into pores.
As always be safe. Epoxy is a sensitizer and some folks do have allergic reactions to it. When working with epoxy protect your skin and eyes have ventilation, and a respirator is not a bad idea either.
For our test piece, since we have to look at it for a while, let's use Rosewood. On this particular piece the pores are pretty nasty.......
It looks like we have our work cut out for us with these pores.....
Z-Poxy is a very easy to use product and the mix ratio is 1:1.
Again be sure to use the "finishing resin" variety of Z-Poxy.
I used latex gloves being out of nitrile gloves when shooting this tutorial to keep the Z-Poxy off my skin but you should use nitrile gloves which are engineered for use with substances such as epoxy.
One of the benefits of using Z-Poxy is that the mix ratio at 1:1 is not critical. In my experience with System III the mix ratio is critical and they recommend that you use a gram scale to mix the two parts. Even though we are using Z-Poxy I like to use a gram scale anyway just to be sure.
For this demonstration I only need to mix up about 1 gram of Z-poxy for each of the two applications that I plan to do.
The Rosewood has been sanded first with 120 and then with 220. I used my random orbit sander because it is fast, dust free, and does not seem to leave any scratches.
One question that we repeatedly hear being asked is if shellac should be used prior to epoxy pore filling. The answer is no, epoxy does not adhere well to a shellac finish although shellac will adhere very well to an epoxy finish.
Once the Rosewood has been sanded and wiped clean of any dust the epoxy is applied. I like to work an approximately 6" X 6" area at once and then move on to another area.
I use a credit card type card as an applicator. This same card will later be used as a squeegee. When I was learning to pore fill with epoxy and other pore fillers the mistake that I made was using the card as a squeegee. Instead use the card to "mash" the epoxy downward into the pores. Do this from all directions with particular attention paid to 45 degrees to the grain of the wood.
Only after you have mashed the epoxy as best that you can into all of the pores in your working area then use the card as a squeegee to remove the excess epoxy from the surface of the wood. I usually dump my excess epoxy on the next area that I will be working.
Since you are removing the excess epoxy this filler goes a very long way and one package of Z-Poxy is probably enough to pore fill 4-5 guitars.
Here we see the epoxy being mashed into the pores from all directions.
And here is what our test piece looks like after one application of epoxy.
Typically it takes me two coats of Z-Poxy to fill the pores on most woods but your mileage may vary. The pore filling goes very fast and if it takes several or more coats to fill your pores just stay with it, observe full cure times, and also note the idea of mashing the epoxy into the pores as opposed to squeegeeing it off when the pores are not filled.
For clean up I use rubbing alcohol which also works very well on a lint free cloth to remove any build-up that you get around the bindings and edges of the guitar. Just smooth these areas out with the alcohol dampened cloth.
Let's let our test piece cure now - Z-Poxy recommends a 6 hour cure time and longer is better.
In the photo above the shiny streaks are the pores, not all the way filled yet but with epoxy building in the pores and reflecting the light.
Now that our test piece has cured we are ready to level sand and apply the second coat of epoxy.
For level sanding epoxy I like to use foam blocks that I cut out of foam that LMI offers. It is very dense and also conforms to curves well.
3M gold 240 paper works very well for this.
At this stage we are trying to build up the epoxy in the pores of the wood. So, with this objective in mind all we want to do is lightly sand the test piece just enough to take down any ridges that we have left from the application process. I lightly sand in the direction of the grain.
If the epoxy is being pulled out of the pores by sanding let it cure longer and/or sand with a lighter touch.
Now with our test piece lightly sanded we are ready to apply the second coat of epoxy.
Again a very little amount of epoxy goes a very long way.
And again we are using the card to mash the epoxy into the pores and once the entire area is filled we use the card as a squeegee to remove the excess.
Our second coat is now applied and needs to cure.
With the second coat now cured it's time to level sand again and check to see if our pores are completely filled. The same sanding process is once again used.
There are two schools of thought when using epoxy as a pore filler. Some folks like to leave a thin epoxy film on the entire surface of the wood for it's beauty and wetting properties. Other folks like to sand the epoxy back to the wood leaving it only in the pores.
Both methods work well so I am going to show you both of them.
I have sanded the epoxy off the surface and leveled the surface as well. In this picture the epoxy is only in the pores and the pores are now completely filled.
For the folks who want to leave a thin film of epoxy on the surface of the wood just sand back less and don't be concerned about sanding through the epoxy in places - it's bound to happen and easy to fix.
The fix for sanding through so that you can even out the color of the wood is to mix up a small batch of Z-Poxy and mix this with a 50:50 mix of denatured alcohol. This "thinned" epoxy mixture is then wiped onto the entire surface of the wood with a lint free rag.
Once the thinned epoxy is wiped onto the test piece you can see that the color has evened out and you can also see how well epoxy pops figure and wets the wood.
Our test piece is now completely filled. Remember what the wood looked like before we started?
The wood should be well sanded, free from scratches and dust. Do not apply a coat of shellac or any sealer prior to pore filling with epoxy. Shellac can be applied directly to cured epoxy but epoxy does not stick well if shellac has been applied to the wood first.
Necks - What works very well for me when pore filling necks is to paint the epoxy on with a finger in a nitrile glove. Again try to press the epoxy into the pores and then use your finger to squeegee the excess off. Clean-up with a lint free cloth dampened with rubbing or denatured alcohol. The gloved finger method usually results in a completely filled neck after only one application.
Silica filler can be mixed with epoxy pore filler and will help to fill larger pores faster in my experience. However... the first coat of epoxy that we apply usually does not fill the pores very well but what it does do is establish an epoxy base coat if you will not unlike primer and painting. As such do your first coat without fillers to establish that base coat which will help subsequent coat(s) with silica filler stick well.
Please also understand in advance that silica has it’s own safety issues and as always eye and skin protection and a decent respirator are a requirement when working with silica.
Most importantly - get comfortable, get a piece of scrap, and do a trial run. You will quickly learn what works best for you and hopefully find the process enjoyable.
And oh yes - let’s see our final results!