Parker's Cracked Martin

Do you remember the Martin soprano we brought home from camp last month? While at camp, it fell to the ground and landed on the strap button, causing the sides to crack. Parker and I agreed that I would glue all the cracks up carefully, but would not do a full refinish of the cracked sides. This means that in the right light you may still see some of the cracks or be able to barely trace them with your finger. The alternative would be scraping and sanding the sides and then staining and finishing to match. It would have tripled the price of the repair.

For old instruments, I like to use hide glue or another animal based glue. This is what would have been used in the Martin factory 100 years ago. It can easily be undone with heat or steam and new hide glue sticks to old. The hard part is that you have to use it hot. I buy a brand called Old Brown Glue, which is pre-mixed and can be heated again and again without spoiling. I have had this bottle for about 2 years. (I really wish I had a sink/bathroom/kitchen in the shop, it would make this a lot easier.) I heat some water in my electric kettle, then pour it into a little crock pot. I add some cool water and use a thermometer. The goal is around 135 degrees F. I then put the bottle in the hot water a let it sit till the consistency looks like this.

Before I got started, I looked in the sound hole and saw a lot of glue already in there. It looks like at least one of the cracks was old and had been repaired in the past. See the line of glue inside? Instead of adding wooden cleats to support the crack, they just left a thick mass of glue. Cleaning the whole thing out would be possible, but likely hours of work. I chose to leave it in there.

I decided to do the glue-up in two halves, which will make it easier. Hot hide glue starts to gel quickly, so you have to work fast. Old Brown Glue stays “open” longer, but it is still better to break the job up. First, I rub the glue into the crack from the outside. I know it looks messy, but this glue cleans up off with no residue.

The goal is to work it through the cracks until it seeps a little bit to the inside. See the glue work through a little bit above the old thick glue line?

Now I will use blue tape and clamps to push it all together, cleaning up any squeeze out.