Trade Secrets!

Mixing red epoxy for cherry-finish repairs

Issue 11 January 04, 2007

KRUNCHED finish!
An experiment, and it worked!
To correct a bad repair on these nasty cracks, I mixed up some red-tinted epoxy

Boy, this 1960 Les Paul looked like trouble when it came in the door: deep cracks through the body that somebody had already tried and failed to fix.
It took two glues to set things right...

Dan Erlewine signature Dan Erlewine, January 4, 2007
Fixing somebody else’s fix:

Drawing: old superglue repair
What went wrong before?
The previous repair was done with superglue, which would have worked if it had really gotten down into the cracks. Fresh water-thin superglue will wick its way into a glue joint, but this glue had been too thick (maybe too old): it just sat on the surface and left the deep cracks untouched.
Photo: scraping away old superglue
I had to chip away a lot of dried superglue before I could start the repair. A fresh single-edged razor blade, held almost flat, slid under the edge of the glue — lifting it from the bare wood and finish beneath it. Superglue removes easily from dirty or oily surfaces, which this guitar had plenty of.

Two glues: One down deep, one to match the cherry red
Drawing: new two-glue repair
For gluing the deep splits through the mahogany body, I used hot hide glue. For repairing the finish, I tried something new: slow-setting epoxy tinted with ColorTone stain.
Image: Test On Scrap!
This technique is new to me, so I tried it out on some scrap a few days ago. If you’re taking a leap of faith on a new idea, don’t do it first on a customer’s guitar!
Photo: shop-made turnbuckle
Hot hide glue into the cracks
To push open the cracks in the control cavity wall, I made a turnbuckle from a bit of threaded rod in a hex connector. A scrap of wood and a half of a dowel protected the body while I cranked it open just enough to flood the cracks with hot hide glue. I used some thinned-down glue first, so it penetrated deep, then followed that immediately with normal viscosity.
Photo: suction cup idea
Here’s a neat trick:
I pumped glue into some cracks by pressing on it with a small suction cup like the one holding the thermometer on my kitchen window (which I promise to replace before Joan gets home). I let the hide glue dry overnight.
Photo: epoxy drop fill

Photo: cherry red epoxy
Clear red epoxy drop-fills
The next morning, I scrubbed away any hide glue residue using a rag dampened with hot water, then left the guitar to dry again for several hours. For smaller finish repairs, I often use what I call a superglue drop-fill technique. This situation was different: for these large chips and deep cracks, I used slow-set epoxy. The slower working time and thicker viscosity were suited to this job. And I tried something new: by adding red/brown stain, I had a gap-filling repair that blended right into that Gibson red finish.
Photo: stopwatch
Even slow-set epoxy sets pretty fast for this kind of work!
Slow-set epoxy takes some time to cure, but you’ll start to notice it thickening within 5-10 minutes of mixing parts A and B. This is a consideration when using it for a drop-fill. You need to work quickly even with the slow-set stuff.
Don’t mix up more than you can use in a few minutes.
Photo: mixing the color
I placed a drop of ColorTone cherry red stain on a yogurt cup lid and mixed a tiny bit of medium brown into it. With a pipette, I laid out a small pool of acetone as a vehicle to blend the stain into the epoxy.

I used very little color and very little acetone, lifting the glue off the lid with an angled drop-fill toothpick and adding it to my already-mixed epoxy. With the toothpick, you can pick up and move the epoxy, even level it a little while it flows into position. Burst any air bubbles (they look like tiny sharp points deep down in the glue), and let it dry for a minimum of two hours. I try to fill a crack with a single application, but some of these canyons required a second coat. That worked fine, and it didn’t leave a visible line between the two applications of glue.
Photo: filing the dried fills
After the fills dried overnight, I leveled them with nut and saddle files — using each grit in order, and stopping before hitting the surrounding finish with a file. I followed up the filing with 320-grit gold sandpaper held on a rubber sanding block with double-stick tape. I also used the 320-grit on a flat board when needed to knock down particular high spots.
Photo: scratching with a knifepoint
Last step: crack it up again!
After fine-sanding the work area up to 2000-grit, I buffed it smooth with medium buffing compound, and then swirl-mark remover. My new finish fixes weren’t quite done: all the old finish around them was checked with age — filled with a spider web pattern of cracks. By scratching with a sharp X-ACTO point, I added checkmarks to make my new work fit in with the old. A quick polish (without silicone) and I'm done!
Dan Erlewine signature

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