Official Luthiers Forum!

For those of you who pore fill with epoxy, and do 3 or so coats, what is your process? Do you sand between coats? (agressively, or lightly, just knock off ridges and nubs). I was thinking epoxy on epoxy might not be a good adhesion issue.

Thanks!

Mike

Not sure I understand your question… When I use epoxy to pore fill I usually do one application and sand back to the wood, that stuff is thick. Presuming it could be, adhesion is not an issue if the epoxy is only in the pores.
In any case sanding epoxy is not exactly fun or fast, so if you insist on 2 or 3 applications I would sand level between them.

_________________
Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

I've only done it once, but I did 2 coats, and probably only needed one. After the first coat, I waited for the epoxy to gel to an almost-solid state, then scraped it back with a razor blade, which removed all but a VERY thin coat. The second coat went on shortly after - no sanding of the first coat required since the epoxy has not fully cured so a chemical bond is achieved between the two coats (and Zpoxy doesn't blush). I scraped the second coat back with a razor as well, and sanding after cure was a breeze.

Next time I will put the first coat on thicker so a second coat won't be necessary, and since I'll be scraping it anyway, a thicker coat is not a problem for sanding. And, since I wait until the epoxy is fairly hard before scraping, I don't have to worry about "pulling" it out of the pores when I scrape. That's what has worked for me anyway.

This is probably all wrong, but has worked for me (twice, koa both times). Two applications with a rubber squeegie, close to full strength (maybe 5% alcohol). Sanded them both back to the wood (180 grit) trying for complete pore fill. Third coat thinned 30-40%, applied with a little foam paint "brush" and sanded just enought to level it and give it a tooth (220 - 320). This was the "grain popper". KTM over the top

viewtopic.php?f=10104&t=29796

On my last one, a koa topped Weissie, I masked the bridge area to keep the Zpoxy out of the wood, but I pulled the masking tape when I started shooting the KTM. My reasoning is that I can level and polish the KTM much better if I don't have the ridge of the masking tape. I then used paint stripper and a scraper to remove the finish under the bridge area. It is dramatic the difference in color of the koa where the Zpoxy was used - it really does make a big difference in the grain.

Well, the only reason I am doing 2 coats is because I recall Todd posting something about that some time ago (showed the "pop")

Also, after I sand back 24 hours later, and wipe with alcohol, I swear I am looking at unfilled pores. Bubinga, if it matters. I guess the only way to know for sure is to put some coating on.

Doing the sides tonight... Gonna try that scrape idea (once set is well under way)


Mike

Some VERY interesting news to report back. I tried CharlieT's idea of scraping while not fully cured. Voila! It worked! This makes sense to me. Once the epoxy has reached the "gummy" state, surface tension no longer plays a big role (if any at all). So, I finally have the "expoxy putty" material I have been seeking that cures clear (albiet with a bit of tonal color). I used a razor blade (with rounded corners) to "pull" the thickened, almost plastic, material around. I waited until the cure was about halfway set (about 2 hours after application in an environmentally controlled room). When I sanded today, no visible pores.

For me, I do not care about the sanding work. I just care about the pores being filled, and staying so after I sand.

Thanks CharlieT!

Mike

Nice to hear it worked for you Mike! I forgot to mention that I rounded the corners of my razors, so I'm glad you did that.

Charlie,

It just makes sense. Really helps with "packing" the epoxy into the pores. Doing it when the epoxy is thin and not cured means it can be easily defeated by surface tension. Really, if done right, there should be no need for multiple (or wash) coats.

Mike

Are you requesting clarification or focussing on linguistics?

I have never heard of Charlie's concept. This could be one of those accidental discoveries. I have searched the web high and low for a putty type epoxy that could be pressed into the pores without developing surface tension remnant pores. I tried it and worked. For me anyways.

Mike

I may not have done it right, but the squeegee didn't work well for me. I found it left more epoxy on the surface than I wanted and still left some of the pores unfilled after the epoxy cured. For me, having the epoxy very viscous, as it is when it has gelled for a while, so that it will hold whatever shape you put it in, was key to being able to press it down into the pores and have it stay there perfectly, which it does with little effort running a razor over it. And the razor leaves virtually nothing on the wood surface and results in a nice, smooth surface. Works for me.

Filippo,

I'm with Charlie on this. I actually have been searching for a putty epoxy that would cure clear. So far, no such beast. Most putties are filled with something. "Done right" refers to scraping it at about the right viscosity. It's like moving a putty around. Also, I sand back to wood (so far). Not sure I want and expoy finish.

Moke

I just delivered a coco BS with a redwood top classical and I used the Zpoxy and followed the tutorial found on OLF. I actually put four coats on because I kept sanding back to aggressively and opened up too many pores. I then did the 3rd coat with less of a sand back and then a wash coat of thinned zpoxy. It cured for a week or so, did the toothing with scotchbrite pad then I shot with nitro. It turned out great. But a big pain to photograph well. IMHO try the process that is on the tutorials. Worked well for me.

Karl Dahlman

I have finished three guitars with zpoxy with good results, I am no expert but as a newbe I made lots of mistakes and found some corrections. I did sand back each time and found open pores. I looked at this not so much as opening up new pores but finding pores I did not fill. I found that it is easy to bridge over the pores with the zpoxy instead of filling them. So I work the zpoxy for 15 minutes or more working to push or smush the zpoxy into the pores. While doing so I watch carefully for very tiny bubbles, when I am seeing the bubbles I know that I am starting or still filling the pores. When after seeing the bubbles and seeing them disappear I have more confidence that I have filled the pores in the area I am working. I do end up with sand throughs when sanding between applications. I apply a thinned layer of zpoxy with a rag as a last application to even out the color and only lightly sand this layer to get rid of any nits.

_________________
http://www.Harvestmoonguitars.com

I like to compare this problem to wood filler. Wood filler (eg Elmers) is a viscous material with no surface tension. It's a putty. When you apply it, and scrape off the excess, every pore and crack is filled. Most of the new wood fillers have minimal shrinkage. When moving a viscous epoxy around, surface tension can play havoc with the fills. I have pushed it around with a squeegee endlessly, and find open pores (especially on the curves of the sides) after sanding. Using Charlie's idea, I only had to do one application. I do not want a thin film of epoxy left on the wood. I want the finish material (EM6000) to adhere to wood.

Mike

That's a good way to put it, Mike.

Another benefit, I believe, is that the epoxy is applied at a low viscosity and allowed to sit for quite a while, giving it more time to seep into pores and displace the air in them, which mean no (or very few) air pockets that will open up upon sanding. The way I see it, however the epoxy is applied, it is going to quickly fill up most of the pores, but will continue to slowly find it's way into smaller pores, nooks, crannies, damaged wood fibers, etc., and that process will continue whether the excess epoxy is squeegeed off right away, or left to gel first. If squeegeed off quickly, there will likely be open pores after cure, especially if the "squeegeer" does a good job removing the excess epoxy, leaving little to displace any remaining air that find its way to the surface after squeegeeing. By waiting until the epoxy becomes semi-solid you're giving it a LOT more time to find those remaining air pockets and fill them. Also, I wouldn't be surprised if allowing the epoxy to sit until it gels reduces the likelihood of "splotchiness" after sanding since the epoxy has a chance to absorb a bit deeper into the wood.

In addition to all of that, I believe removing the semi-solid epoxy with a single-edge razor produces a thinner, smoother surface that requires less prep before applying finish. In the semi-solid state, the epoxy doesn't try to "pull out" of the pores when the razor runs over it...it just stays beautifully flat.

To be honest, I didn't really think about it. I knew I had left a really thin layer of epoxy when I scraped, so I wasn't too worried about leaving too much epoxy under the finish. Instead, I just focused on removing some tiny ridges left by the razor, and achieving a level surface. I don't recall seeing any color variation, and don't see any now under the finish. I did put down a coat of shellac between the epoxy and the lacquer.

I'll pay more attention next time.

We all want the same thing... Filled pores. Some like the color and "popping" effect that epoxy creates. Personally, I would prefer a clear epoxy with no color. Since all I wants is filled pores, a clear, colorless epoxy would be ideal.

Mike

Do you put the first (or only) coat of epoxy directly on to the bare wood or do you seal it first with a shellac coating?

I prefer to do it directly over the bare wood. No worries about delaminations caused by the sealer failing, epoxy sticks to stuff really well on it's own.

_________________
Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

I do one coat. I used to apply it with a squeegee but I found that I (or at least think) get better results if I just rub it on while wearing gloves. Then after I;ve rubbed the whole thing pretty well, I pull of what I can wearing the same pair of gloves. Next I sand back so there is bare wood again...as in I stop as soon as I start getting wood dust.

Just out of curiosity has anyone on here ever tried using knife grade epoxy? It's usually used for mending seems on granite countertops but after making some countertops for an architect about 6 years ago I tried using this stuff on wood. The material I was using at the time was some stuff called paperstone which is basically dimensionally thick high pressure laminate.

Anyways I used this stuff to bond some parts together to make an ADA counter section and it worked great so I decided to try it on wood. I've been using it ever since and I'd highly recommend it. It dries totally clear as long as your build layer is not too thick. For filling deep pits, say over an 8th of an inch it can start to get cloudy. It's a really nice consistency and mixes much like bondo. It can be applied and worked with a putty knife and gives off almost zero odor. The other nice thing is you can buy compatible pigments in a wide range of colors if that's what you're going for.

I've applied lacquer over it and haven't found any compatibility issues though like other epoxies it will alter the color of the wood slightly when compared to wood that's been sanded back down or didn't get epoxy in the first place. Under finish the difference becomes very slight. Anyways, I've gotten it from granite and stone suppliers in my area, it might be worth a look. The brand I've used is Akemi out of Germany.

Hmmm. Interesting. I have been asking for sometime if there was a high viscosity epoxy (almost like wood filler). I've seen those epoxy putty ads. But drying clear is crucial. 1/8" deep holes would let light inside the guitar, so I don't think that is an issue. Thanks for bringing this up. I may give this a whirl. BTW, you will hear the term "finish epoxy" versus other types. Z-Poxy, a type many of us use is a finish epoxy. Apprently, it's not so good as a glue. But somehow, it's ideal for surface finishing. It does work well... but a certain skill level is (and experience) are developed over time to achieve the desired result. Z-Poxy will change the color of the wood.

Mike

John,

Thanks for the info. I checked their site, but I'm not sure exactly what to look for. Can you specify exactly which product you are using? Are you getting it locally or ordering from Germany?

Thanks

If I remember tomorrow I'll try and grab a look at exactly which type I've used. It's possible that they've changed the label slightly since I bought it last. I've bought it twice from a local supplier who specializes in stone supplies.

I'm thinking it's this one though

http://www.akemina.com/en/products/stonerange/adhesive/polyesterbased/knife/list/679/

It's listed as milky but it really doesn't show until it gets pretty thick. The color tubes are here: http://www.akemina.com/en/products/stonerange/adhesive/polyesterbased/cs-bondings/list/2075/