how to repair crack in soundboard of harp?

[kurth]

Small 26 string dusty strings about 40 yrs old with I'm pretty sure what's a laminated soundboard with a horizontal crack near low c that is half way across and apparently growing, visible on half the width on both sides. the other side it's only visible inside and hasn't reached the surface. It appears threatening so I loosened a few strings. Needless to say it's all the weathers fault !

so is wood the best patching material... glued cross grain'd , or does that matter on a lam top? what about alternative patching materials that might be available? thanks for any suggestions.

[Howard Klepper]

It's hard to give useful crack repair advice without photos. Even more so when the cracked panel is made from laminated hardwood. Both sides, please. And close up.

Did the crack appear during your ownership of the harp?

[kurth]

Originally Posted by Howard Klepper

It's hard to give useful crack repair advice without photos. Even more so when the cracked panel is made from laminated hardwood. Both sides, please. And close up.

Did the crack appear during your ownership of the harp?

thanks Howard....I'll work on the photos . Yes , recently...this year, maybe this week? Obviously I just noticed it. We're in a serious dry spell in my neck of the woods.

[kurth]

Originally Posted by Howard Klepper

It's hard to give useful crack repair advice without photos. Even more so when the cracked panel is made from laminated hardwood. Both sides, please. And close up.

Did the crack appear during your ownership of the harp?

https://postimg.cc/wR701DKG
https://postimg.cc/8JyZktYv

like I said...ugly & possibly structurally compromising
thanks for all suggestions
my thoughts...maybe carbonfiber sheet & epoxy. If it cools down the bass strings alittle it wouldn't be the end of the world.

[printer2]

Maybe a picture zoomed out a little to see where the crack is in relation with the rest of the instrument?

[kurth]

Originally Posted by printer2

Maybe a picture zoomed out a little to see where the crack is in relation with the rest of the instrument?

Fred ok, but for reference, the soundboard is about 33 1/2inches long and the crack is about 7 1/2 inches from the base , between the 4 & 5th bass strings. On the exterior, you can see it propagated almost 1/2 way across the whole width of the harp. I think the interior strip laid vertically where the strings tie off is what stopped it. Also, on the interior, the crack appears to be continuing onto the other side of the tie-off strip, but hasn't shown on the surface.
I'll take another 'context' photo tomorrow. It's obviously in need of structural repair. cosmetics are unimportant ...as long as it works.thanks

[kurth]

https://postimg.cc/hfWy9PFf

looking at the photo, it magnifies the 'slight bulge along the crack , that to me appears the lamination has separated some....just guessing....maybe first, a watered down glue to penetrate and a hard press, then interior reinforcement....
....how about vertical bracing, as well as a patch ?
or a awkwardly placed soundhole ?

...are epoxy's too brittle for the vibration?
thanks for any suggestions...

[Howard Klepper]

Are there just two layers, front and back?

I was expecting plywood, which always has at least three layers, and an odd number of layers so the outside laminates' grain runs in the same direction. What I think (correct me if not) I'm seeing here is that the main, thicker lamination is the inside, running at 90º to the thin veneer on the outside face. And what cracked from low humidity is the thicker inside lam, with the outside veneer not being thick and strong enough to resist tearing along with the inner lam when it opened.

That would make the inside damage structural, while the outside damage is cosmetic.

As with a guitar, you want to humidify to get the crack to close up, but not to make it so humid that the crack will open again (or open somewhere nearby) when the humidity is down in the normal range again. I'd suggest removing the strings adjacent to the crack and loosening the strings a little ways further out from the crack. Then give it a week at an elevated (like ~60%) room humidity. I suspect the crack will not close all the way. And if that's so, then there is little to be gained by splinting the crack as you would on a guitar, since it's on the inside where it won't be seen, and you are going to put cleats or a patch over it.

Do you have or can you borrow a deep sliding bar ("F") clamp, that can reach around to near the middle of the crack [this type: ]?

It looks like you need about a 4" reach. For a backup patch (which will be doing almost all the work of keeping the crack from reopening), I'd use something like a strip of maple (or other hardwood) about 3/32" thick, and about 2" wide and a little more than the length of the crack (narrowed at one end so it can fit between the string holes). It can have its grain running across the crack, or even better on a bias so it's at a little less than 90º from the way the crack runs. Bevel its edges to reduce the stress riser crossing the soundboard grain. Make an inside and an outside caul from hardwood or good plywood about 3/4" thick and use wax paper on both sides so the cauls don't get glue to the soundboard. You can place the cauls with adhesive tape when you glue.

I think epoxy would be best for this, especially if the crack is not fully closed. A hardware store brand would be fine, but not the 5 minute. Epoxies are not so rigid that they will crack if the soundboard flexes a little. Lightly sand the inside soundboard and the glue side of the patch wood to give the glue a fresh surface to adhere to. Don't apply any glue to the outside veneer.

It's important with epoxy to mix very thoroughly, which is one reason not to use the 5 minute (it's also not as strong as the slow stuff). Apply the glue liberally, clamp it tight, clean up epoxy squeeze out with small rags wet with alcohol (denatured from the hardware store), let it set for 24 hours.

If the crack is tight on the other side and looks closed after humidifying, you can just work in some Titebond with your fingers. A few diamond shaped cleats across it would be insurance.

[kurth]

Originally Posted by Howard Klepper

that looks to be correct.

I've got it inside a large plastic trash bag trying that now....

I've got lots of clamps...I can rig something that holds

the patch won't be able to go between the strings because the strip where the strings are tied is about 1/8" thk, or I'd have to make the patch thick enough to make it by-level and glue it to the top of the strip. so the patch would have to just butt up against the strip

ok thought epoxy would be best but it's good to get confirmation. My initial thought was apply a thin coating of clear silicone to the soundboard surface to totally seal the crack....let it set up for just a couple of hours and then the epoxy won't seep thru, but fills the crack, and the silicone can be pealed off w/o damaging. Now to find a couple of nice pieces of wood to make patches. I guess wood is probably the best patch mat'l due to thermal expansion....which obviously can cause problems.
...thanks Howard I appreciate your feedback

[mirwa]

I repair these,

The soundboard on that looks to be a laminate, the issue for me is the crack is too staright and indented inwards rather than pulled out like a tension crack would haplen, i almost suspect just looking at the crack and location that maybe the harp is folding itself under tension, any chance of a side view of the chamber

Steve

[kurth]

Originally Posted by mirwa

I repair these,

The soundboard on that looks to be a laminate, the issue for me is the crack is too staright and indented inwards rather than pulled out like a tension crack would haplen, i almost suspect just looking at the crack and location that maybe the harp is folding itself under tension, any chance of a side view of the chamber

Steve

yes....
https://postimg.cc/phT4qgZd

...oops...I shoulda thought of trying a straight edge. think you're absolutely right. But....wouldn't the string force fold it inward, instead of outward ? I'm confused and I don't get confused often. thank u
...also to factor in ...when I discovered it 3 or 4 days ago, I loosened all the bass strings up to about the 7th or 8th string. weird. but hopefully it makes sense to you.

[mirwa]

Inisde the chamber we have small square sections of reinforcement with large holes in the middle of them to allow the sound to port between chambers, have you got an open back or closed back, i would look i side and see where the nearest reinforcement is to that damage.

[kurth]

Originally Posted by mirwa

Inisde the chamber we have small square sections of reinforcement with large holes in the middle of them to allow the sound to port between chambers, have you got an open back or closed back, i would look i side and see where the nearest reinforcement is to that damage.

the harp has oblong soundports on the back side but "the small saquare sections of reinforcement" stumps me. the soundboard has a strip glued in the center that runs top to bottom and is used to tie off the strings. There's only one chamber. there's no reinforcement ie bracing. I'll take some more photos manana. gracias thanks

[mirwa]

Cool, sometimes we have multiple chambers up the back to balance the volume, each chamber in this scenario is seperated by a reinforcment as i described (it ties front back and sides), yours as per your description is one large chamber.

Since the crack is near the column pillar attachement point, can we see the structure inside the chamber behind this area and above the foot attachment

On the photos you supllied i can also see a small ripple in the side wall where it appears to have started the buckle under tension.

[Henning]

I am not very fond of the idea with silicone. Instead I would try to stick to superglue or titebond. Try to somehow fill the crack with superglue/titebond and glue a laminate on the crack, from the "inside". Is this the inside https://postimg.cc/wR701DKG ?
Superglue, a laminate, or perhaps a piece of wood then some strong super magnets. The wood or laminate cleet needs to be thick enough to straighten the part of the crack (that now is dented), when set under pressure. Otherwise there will be a not wished for dent in the soundboard. If any glue gets out of the crack I'd scrape it off gently. A kind of simple straight forward solution. Try to get the crack as even as possible. If some work needs to be done to the finish after crack repair. I would stick to cellulose lacquer. Because that's what the harp already is applied with, isn't? Supposedly, the soundboard being laminate, this a'int a top of the line quality harp, is it? Or at least not the most valuable instrument?
Supposedly, the work will be more easy to succeed with if the string tension is loosened for all the strings. Then you have a better control of "the arc" of the soundboard. I don't think it is a very difficult task.

Please, take my words for what they´re worth, I have no personal experience in repairing harps.