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Help With Epoxy Grain Fill

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OK...someone please set me straight on this epoxy grain fill thing.

I'm using 5-minute 2-part epoxy (Loctite), cures nice & hard in about an hour. I am applying what I feel to be a medium-thick layer. When I level with 300 grit, I get the usual slight uneven-ness but the problem I'm having is that I cannot seem to level everything (eliminating every tiny shiny spot) without sanding through to the wood underneath.


You can see the dark lines that are the shiny low spots left in the epoxy; when I try to get these level, I always end up sanding through to the wood nearby (light spots on the lower bout).

So my question is....should I be levelling this so that I have a very thin layer of epoxy covering everything, without going down to wood? Or should I sand down to the wood everywhere, leaving the epoxy just in the pores?

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Yes, I would recommend finding -some- way to get 100% coverage with the epoxy.

Maybe cut it/thin it (you know you can cut epoxy with Acetone, right? ...slows down the drying time a little tho...and apply another thin coat.

When I was using it for spalts, I remember there was a spot that I sanded thru to raw wood.

I said Drak, not to worry old friend, it'll just fill in with all the lacquer coats, it wasn't a BIG spot after all...

Well, when I did that, I could see a little difference in the 'look', I could see -that- spot if I looked at it, it was very slightly different looking than the rest.

Of course, I sanded the whole thing off and did it again so there was complete coverage next time.

Just trying to save you some future pain. :D

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OK thanks! I think I will go back over and do both. Spot-fill the sand-throughs and the valleys both, then re-level and repeat as often as I need to. This is already my 2nd application, and I can see no evidence of witness lines or anything from the first application, so I think spot-filling will be the way to go.

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one of those littletubes when combined and mixed does one thin coat.if you cut it with a little acetone(which you need to do to not have air pockets.)

do not ever try to mix up part of the little tube...the 2 parts do not come out evenly,so you MUST mix the entire tube at once...if the mix is not right it will not cure...ever

empty the entire tube in a paper bowl...take a plastic spoon and mix it very,very well....then add the acetone until it is fairly thin(like spray paint)

then spread it on with a card of some sort...i use business cards because they are free from www.vistaprint.com and i have alot of them...

when you run out,make another tube..

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Yeah I wasn't using the syring-tubes, I was using the "professional grade" with the resin & hardener each in their own squeeze bottle, mixing by weight into a disposable paper bowl. And yeah I mix the living hell out of it. I've been using epoxy at my job for the past 12 years, but more like the 24-hour stuff and not the 5-minute.

The 5-min stuff is indeed pretty thick, I'll try cutting with acetone. I think my main problem is that I'm having to press too hard with the trowel to spread it out, so some parts end up being very thin. I also think I'm not applying enough.

Then again, I may just go with the 24-hour, it is already very runny so it will self-level to an extent that the 5-minute won't. That's where my problem is.

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OK...spot filling did not work for me worth beans. I'd try to level the filled area and blend it into the surroundings, and about half the time I'd sand through in a new spot. So I took it all down to wood; the 5-min epoxy did not fill the pores at all, just sat on top of them. So back to square 1.

Yesterday I used a 24-hr epoxy, very thin almost the consistency of water. Heated it up very gently to promote thorough mixing. This went on very easily, I could work deliberately and it flowed out quite nicely. However, this also meant that it went on thinner, so when I went to scuff it up and level it....you guessed it, more sand-throughs. So I gently took it down to wood again, but at least this time the grain is about 90% filled, as the epoxy was able to get into the pores better. But man, it took quite a while to sand it down.

I know I could get a uniform layer of epoxy everywhere if I wanted to, but this would mean putting on a rather thick layer and then levelling down to an unknown thickness. It would probably be fine for a solid body, but this goes against my "thinner is better" instincts for an acoustic, so I will just call it a day here and proceed with the clear coat.

I probably could have gotten the same result with my trusty Minwax sanding sealer and saved myself about ten 220-grit sanding discs.

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Sanding discs? That could be your problem right there. The ROS has it's place, but levelling or cutting back something you don't want to sand through on isn't it! You need a semihard block and a pair of hands. How are you applying the stuff? I'm able to get the epoxy squeegeed to almost dead flat, then a quick rough over with 400 grit to knock off any high spots and matte it all down. The only place I have trouble is on the endgrain sections - something you don't have to deal with on bent sides.

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The 5-minute stuff was rather stiff, I had two spare plastic credit cards to do the deed.

The 24-hr epoxy went on with a paper business card, and the transitions flowed out nicely.

Maybe it is my sanding, I was using a pretty light touch...but my god man, it took me an hour just to sand the sides back down to bare wood with 220...WITH the RO sander. I'm not sure I have a long-enough life span to level epoxy by hand with 400.

Unless maybe I use an even thinner coat...

Edited by erikbojerik
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Eric, when I finished a guitar in one color and grain filled in another, through trial and error I found out a good way to grain fill with epoxy. Keep in mind that I could not sand as it would damage the uniformity of the transparent purple clear coat that was sprayed before grainfilling. I sprayed my tinted clear(you could spray some sort of sealer I suppose), then I wiped some medium viscosity epoxy to grainfill. I just put acetone in thick epoxy until I got it to a workable consistency. I then used a rubber squeegee(like for wetting out FRP's) to move the epoxy over the finish. I tried to keep as much epoxy in the grain and as much off of the rest of the finish as possible. Then I waited for it to partially cure and lightly wiped the whole thing down with paint thinner. This left a very light glaze of epoxy over the finish, looked a bit foggy to me. So I waited for the epoxy to cure a bit longer, then repeated. I did this wait, then wipe procedure about 3 or 4 times. I had to repeat the entire process(grainfill, wait, wipe, etc) about 2 or 3 times. In the end, I did no sanding and the surface was as flat as I could ask for. The whole process took maybe 1 hour of labor and 1 cumulative day of waiting...took a week to figure out the technique though :D. If you want some added insurance, when you're done, maybe respray with sealer and lightly level sand.

Just my $.02, apply lightly with 1 to 2 grains of salt for best results(the advice, not the epoxy :D ).

EDIT: The whole idea behind spraying a sealer then filling and never sanding...well the advantage of it at least, is that more pores cannot appear. You have a set amount that will be open when you spray and that's it. Whereas when you grainfill then sand, you're potentially making matters worse.



Edited by thegarehanman
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Thanks Russ. I may give that a shot.

So now I've gone & applied some more 24-hr to the back only. This time, I tried to spread it as thin as a paper business card would allow (which is not much pressure, mind you). Well, it is actually possible to apply it too thin, with the pores still showing through the epoxy. So I went ever so slightly thicker, until the pores just disappeared, then stopped. When it comes time to sand, I'll give it a shot by hand with 400.

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like russ said...you need to thin it with acetone

I'm using 24-hr, it is already nearly water thin, basically the viscosity of Tru Oil. It is so thin I can squeege it across the body and the pores will drink it up and still show, that's why I had to go over it with a little more. Why thin it even more?

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  • 3 weeks later...

OK...I've finally reached the end of the marathon epoxy grain fill episode.

The final chaper....I used the 24-hour epoxy, ever so slightly warmed so it was thin as water, then spread it out over the entire instrument so that all the grain was filled, let it cure.

Then I went at it by hand with 320-grit with a foam sanding block. I had the same sand-through problems as last time...I'd try to level a spot that was slightly high, and sand through in a nearby area where the epoxy was thinner. This was probably my thinnest coat that still filled the grain.

So I sanded it all off. Again. Only this time, the epoxy stayed in the grain, probably because of how thin it was and the slow cure time allowed it to penetrate better. So now it looks very nice and matte all over, and when I wipe with naptha there are very few pores that show.

In retrospect, it appears I've more or less done what Russ recommened....except that I added about 10 hours of extra sanding time by letting the epoxy cure fully and sanding off, instead of wiping it off while still tacky.

But now my arms look like Popeye, and chicks dig me. :D Well, one chick at least.

Thanks for all the help!

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