Trade Secrets!

Adding color to hide glue for an invisible repair

Issue 64 June 26, 2008

Here’s a neat trick

Adding color to hide glue
for an invisible repair

If you’re not familiar with hot hide glue, here’s a technique that might surprise you. And if you’re not already a hide glue user, I want to talk you into joining the club!

Dan Erlewine signature Dan Erlewine, June 26, 2008
Dan Erlewine
The finish on this old Gibson A-50 mandolin shows its age, and that’s fine with me. But at the neck joint there’s some damage and a gap where the binding has pulled away from the side.

Behlen Ground Hide Glue
Behlen Ground Hide Glue
Damaged neck joint
Damaged neck joint closeup
To repair this tiny area, I mixed hot hide glue and ColorTone stain to create a colored glue to match the surrounding finish. This way, the glue filled the gap and touched up the finish at the same time. That's handy!

I didn't used to think of hide glue as handy. Before I started using an electric glue pot, I would heat a jar of glue in a pan of water on the kitchen stove. It was a hassle, so I didn’t use hide glue much. That was a mistake. I was missing out on the best glue for about half of the work I do. Now that it’s right here by my bench, warmed up and ready to go, I use hide glue every day.
A glue pot can hold way more glue than I need for instrument work, so instead of filling it with glue I fill it with water. The glue goes in a small jar sitting in the heated water, with plenty of room for my gluing tools:
Gluing tools
1. Long-handled glue brush
2. Glue jar (with the green cap, almost submerged)
3. Mixing cup (In the cup is a Q-tip, clean hot water, and a small brush I use to clean the glue brush.
4. Pipette filled with hot water
5. Thermometer
6. Hot wet rag

Electric Glue Pot
7. Next to the pot is a plastic cup, bottom-side up, with a smaller plastic cap on it. On the cup is tobacco brown Colortone Stain, and the little cap contains extra-thick hot hide glue mixed with a little of the stain.
Mixing cup for hide glue
A repair magnet in the bottom of the mixing cup holds it to the glue jar. This anchors the lightweight cup, and it’s a convenient way to lift the glue from the hot water.

Mixing Cups
Mixing Cups

I’m not painting with the glue, I’m just touching the glue-filled brush to the mandolin, using the drop-fill technique.

I love being able to clean hide glue with hot water and a Q-tip. Even though it’s already started to set, I’m still able to clean it off the binding. In the morning it’ll be really hardened; then I’ll use sandpaper and an X-Acto blade to smooth away any rough spots.

If more glue is needed, no problem: I’ll just warm up the leftover stained glue, melting it so it’s ready to use again. As a last step, I’ll brush a little fresh-mixed shellac over this repair.

Colortone Stain 
Colortone Concentrated Liquid Stain 

ColorTone Shellac Flakes
ColorTone Shellac Flakes
I predict you'll become a card-carrying member of the Hide Glue Club!

What’s so hot about hide glue?
Hide glue dries crystal-hard, unlike plastic resin glues, so it doesn’t dampen tone.
Hide glue joints don’t creep. Maybe you didn’t know this, but over time under string tension aliphatic resin glues (like Titebond) will stretch a little. This is called “creeping.” It’s not a problem with hide glue, which isn’t plastic-like in its makeup.
It’s really strong, similar to epoxy.
Joints can be heated/steamed back apart. Just like vintage!
Water-based, for easy cleanup.
It was used on the instruments we want to work on most. It’s what was used on those vintage guitars/mandolins/fiddles that we like to see come across our workbenches.

What about bottled hide glue?
If that’s the way for you to give hide glue a try, go for it. But use it before the expiration date on the bottle: hide glue has to be fresh in order to cure properly. (I learned this the hard way on a Martin repair years ago!) Mixing your own in a glue pot’s the best way to go.

Hotter glue means
more time to work

Here are a couple of ideas from Don MacRostie, head of StewMac’s R&D team.
When Don wants some extra working time before his glue sets, he gets it extra hot (about 180°). This combined with warming the parts gives him that extra edge on getting successful glue joints.

With the glue in a Grey Poupon mustard jar, he made a tripod to hold it above his heat gun. This is for a quick start to the day. Rather than waiting for the electric pot to get the glue hot, this rig gets the glue to working temperature in 5 minutes.

I made a miniature version of Don’s heater-upper: a small jar held over an alcohol lamp. A repair magnet holds the jar to a bent piece of steel in a vise.

This gizmo brings the little bit of glue I'm working with up to speed in a jiffy! Then it goes into the glue pot and stays ready all day.

Dan Erlewine signature

Nut and Saddle Vise
Nut and Saddle Vise

Don't miss an issue!

Get Trade Secrets delivered to your inbox. Only from StewMac.