Thanks for reading.
I usually repair mandolins and like using hide glue. However I have a small problem:
I'm repairing a nyckelhapa (Swedish bowed fiddle), made in 2006. It has a 2 piece front (3-4mm thick, soundboard) and the centre joint has just failed. I was bringing the last of 16 strings up to tension when there was a loud snapping sound and a six inch hairline crack appeared on the glue line, under the bridge (the total seam length is about 20 inches.. The nyckelharpa is constructed like a violin or cello. It has a bassbar and a soundpost. The soundpost in this instrument is way too thin and now I've removed it I can see it was badly fitted and has compressed. Once the strings were loosened it's was a very loose fit- probably why it failed..
For some reason best known to themselves, most Swedish nyckelhapa makers use PVA wood glue. Unfortunately PVA has been used on this instrument.
So I'm after some advice. I don't want to strip the instrument down. The (arched) top hasn't sunk, the crack is clean along the glue line and the soundboard it 3-4mm thick. I can easily get glue into the joint and clamp it. The question is what glue to use.
My head tells me to use PVA, but all my instincts say it's the wrong glue for the job. So could I use Titebond (yellow)? Is titebond compatable with PVA, do you think and titebond would penetrate into the wood and would this give a stronger joint.
Give me you thoughts please.
Polyvinyl acetate is white or Elmers glue, Aliphatic Resin is yellow carpenters glue, both are PVA glues.
I'm guessing someone experienced in instrument building would have used Titebond (Aliphatic Resin) or the like. The way I see it is that you have nothing to lose by trying the re-glue. If it fails your right back where you are now, if not, you have just averted a lot of work.
Thanks for answering
I've been reading a bit more on the net and my guess is that Aliphatic resin would be compatable (would bond to) white (unmodified) PVA.
However I've decided to use white PVA as it's what has already been used. I think it will hold, so long as it's not unduely stressed or exposed to heat. The string tension pushing down on a nyckelharpa bridge is very high (about twice that of a mandola). I'm fairly certain that the faulty sound post caused the problem.
Mike, are you sure it's white? Can you see anywhere in the instrument where you have glue squeeze out? One usually won't find White glue used in higher quality instruments (never say never). The only place I'll use any white glue on an instrument might be a couple of small dots to glue a nut down, that's it. Because of the potential for glue creep and low temperature tolerance, I would leave the white glue on the shelf. I can tell you though that I have had good luck with Titebond used on dirty joints, I would recommend using that instead.
A few small cleats might not be a bad idea either, with the downward pressure you mention.
Thanks for the reply. I know that white PVA would never usually be used for instrument making. Like you I might use PVA or superglue for dots etc, otherwise I stick to hide glue.
The problem is in Sweden many nyckelharpa makers do use PVA. The reason for this that the nyckelharpa was revived in the 1970's and in order to do this "kits" of wood, instructions and blueprints were sent out to be made at adult evening education classes. They just used the glue that was available - white PVA. Some of these student became established makers and continued to use white PVA. Many of the makers are now in their 70's and 80's still use white PVA and won't change.
Earlier this year I replaced the top of a nyckelharpa (which had colapsed) because the bassbar had detached, due to glue creep (white PVA again). I made a new soundboard/bassbar and glued it on with hide glue. As you would expect it's the soundboards that seem to fail (usually takes a few years). The rest of the construction is fairly industrial and so PVA seems to hold it OK.
I managed to scrape off some excess glue (where it had squeezed out) from the one I'm repairing now and put it into some water. It dissolved instantly and gave a white colour - no water resistance at all. The maker was in his 80's and very sadly is now dead. Otherwise the instrument is well made but he used the wrong glue.
Thanks everyone for posting.
I now have a useful, bit of information. For many years I was a research scientist so I decided to set up a little experiment.
I took some small flat bits of pine (Clothes pegs) I coated the flat surface of a pair with Evo Stik white PVA wood glue (a British brand not sure if sold in US), and coated another pair with Titebond original. I left these to dry in a warm dry room (conservatory) for 3 hours.
1. Glued the Titebond coated together with white PVA
2. Glued the white PVA coated together with Titebond original (Yellow)
3. Glued 2 fresh bits of wood together with Titebond
Area glued was about 1 1/2 inch x 1/4
I clamped and let these dry over night.
I tested the joints by holding the wood firmly in a vice and pushing with a blunt chistle against the joint line. As expected the joints all held firm.
I then stressed the joints by hitting sideways with a sharp blow with the blunt chistle using a fairly light hammer.
Number one above sheared along the glue line and both of the glued surfaces were largely undamaged - In other words the joint failed.
With 2 and 3 (Titebond glued) above the wood gave way but the joint remained firm.
It's a one off experiment but it's what I thought might happen, and it does show that Titebond can glue wood coated with white PVA.
Decided to use Titebond for this repair
Mike from sunny London
Repaired and almost fully assembled