Treating hairline cracks

[SteveS]

I have at present an ebony-ended (raised ends) TT on my bench.

The ends are solid wood ebony.

There are many hairline cracks evident on the outside, and on inspection appear to go right through the wood.

There are many more hairline cracks on the inside than outside.

 

Any tips on how to handle this to stablise the cracks?

 

My current thinking is to open up the worst cracks slightly both sides with a knife (especially those that go right through) and force in some hot hide glue from both sides.

May be make a filler using hide glue and stained sawdust.

Then use a veneer with the grain going in the opposite direction to the grain of the ends, and glue this to the inside.

 

I will need to fill, stain, and refinish the ends.

 

Edited July 20, 2023 by SteveS

[SteveS]

Doing a bit of research, super thin CA glue might work.  Hopefully, it should run into the cracks.

 

(I've seen luthiers using this for cracks in guitars)

[Don Taylor]

There is a product called 'Captain Tolley's Creeping Crack Cure' that was developed specifically for fixing hairline cracks on boats, this might be useful for this application - caveat emptor!

https://captaintolley.com/

 

Available from most Chandleries and Amazon:

https://www.amazon.co.uk/Captain-Tolleys-Creeping-Crack-sealer/dp/B003T6EJ9A/ref=sr_1_4?crid=1XMIGUE19IEX1&keywords=captain+tolley's+creeping+crack+cure+8oz&qid=1689597635&sprefix=captain+tolley's%2Caps%2C310&sr=8-4 

[wunks]

For an applicator, cut a pointed piece of very thin plastic packaging material dip it in your glue of choice and work it edgewise into the crack.

[Theo]

3 hours ago, SteveS said:

Doing a bit of research, super thin CA glue might work.  Hopefully, it should run into the cracks.

 

(I've seen luthiers using this for cracks in guitars)

 

I've successfully used thin CA to repair hairline cracks in wooden ends, and in action boards, where the cracks are too small or too inaccessible to fill.  If the edges of the cracks are displaced it takes some care to get them held on the correct position before applying the glue.  On end frets I usually apply the glue from the inside, but it can bleed out onto the face surface.  

[Wally Carroll]

Thin CA for hairline cracks. Medium to thick CA for cracks you can see all the way through (the thin will run right through and get all over the other side of the instrument if the crack goes all the way through).  CA Accelerator is very useful in this application.  

Edited July 17, 2023 by Wally Carroll

[d.elliott]

The trouble with repairs that result in having to re-finish ends is not just the polishing with multiple coats, or even the choice of finish to avoid reactions with the original polish, its the sanding down, and wire-wooling to avoid loosing end details and the removal and re- bushing, masking metal labels etc. I try to preserve the original patina as well as all of the above by working from the fretting inside. I open the first third or so of the crack depth using a scalpel, I use a good grade of wood glue. when that is set I cap it with thin wood. If the face of the repair is springing, then I tack it inside with a dab of UV activated resin, which I can then remove  later. A bit like tacking a welded joint, then grinding off the tacks after the initial root run.

 

I assume that CA is Cyanoacrylate , AKA Super Glue? AKA SSFG, or seriously stuck finger glue

[SteveS]

Thanks everyone for the replies.

 

The problem is there are so many hairline cracks on the inside and fewer on the outside.

Opening the cracks on the inside isn't a viable option.

My thinking right now is to use super thin CA glue from the inside - cautiously at first to see how things go.

There aren't any cracks that run all the way through.

I'd like to keep the original patina, but if I have to refinish then I'll have to do that.  Sure it's a pain, but satisfying to have newly finished ends.

[Alex West]

I use an aliphatic resin glue called Chair Doctor, made (if I recall) by Veritas.  I'd suggest it's a bit more user-friendly than CA.  It's quite thin and works by capillary action to get into the very tiniest cracks.  I tend to flood the cracks with the glue using a small syringe applicator (or similar), then "pump" the cracks gently to make sure the glue is getting to all the hidden parts, then clamp (as necessary) to make sure the wood sets in the correct conformation.  It goes off in about an hour and is very strong but you can wipe off the excess after 5 or 10 minutes.  Depending on the application, there may not be any need to refresh the surface finish (French polish or otherwise.

 

If you do use a syringe, make sure you clean it out afterwards otherwise the glue sets in it and it can't be used again! (DAHIKT)

 

Alex West

[Richard Mellish]

7 hours ago, Don Taylor said:

There is a product called 'Captain Tolley's Creeping Crack Cure' that was developed specifically for fixing hairline cracks on boats, this might be useful for this application - caveat emptor!

https://captaintolley.com/

 

Available from most Chandleries and Amazon:

https://www.amazon.co.uk/Captain-Tolleys-Creeping-Crack-sealer/dp/B003T6EJ9A/ref=sr_1_4?crid=1XMIGUE19IEX1&keywords=captain+tolley's+creeping+crack+cure+8oz&qid=1689597635&sprefix=captain+tolley's%2Caps%2C310&sr=8-4 

I discovered Captain Tolley's through a post on an internet forum. I don't remember whether it was this forum or some other one. It gets into cracks by capillary action and works well for sealing them to stop water (or whatever) getting through, but I don't know how effective it would be for preventing relative movement.

[Alex West]

I settled on Chair Doctor when I did a comparative test of a few glues when I was sticking ebony veneer to sycamore for a bellows end repair.  Chair Doctor was the strongest and I've used it on hairline crack repairs since.  I've not tried Captain Tolley's on wood (though I have a tube of it on my fibreglass boat🙂).

 

Alex West

[SteveS]

Thanks all for your contributions.

I've ordered some Chair Doctor and super thin CA - I'll try both on some scrap to get a feel for how effective they are and their characteristics.

[Eddy]

Hi. A liuther recommended me for structural work this glue that You can find in Italy

 

https://www.saratoga.it/it/prodotto/1/58-colle-per-legno/174-mastro-d-ascia-colla-per-legno/

 

it’s very strong and It fills very well, with its expansion, also for hairline cracks

I used with wooden flutes and some works on concertina with ends damaged and It works fine

You can put It with a toothpick 

 

Eddy

[Alex West]

On 7/20/2023 at 3:20 PM, Eddy said:

Hi. A liuther recommended me for structural work this glue that You can find in Italy

 

https://www.saratoga.it/it/prodotto/1/58-colle-per-legno/174-mastro-d-ascia-colla-per-legno/

 

it’s very strong and It fills very well, with its expansion, also for hairline cracks

I used with wooden flutes and some works on concertina with ends damaged and It works fine

You can put It with a toothpick 

 

Eddy

It's a polyurethane glue (Gorilla Glue is a UK trademarked equivalent I'd guess) which has some advantages and disadvantages compared to PVA and aliphatic resins.  I'm not saying it's bad or being at all critical, and I don't claim to be an expert but it might not be so good (for example) with very fine or hairline cracks.  I would think that it wouldn't flow into the cracks in the way that Captain Tolleys or Chair Doctor would and it might start to expand a bit too quickly

 

Alex West

[Wally Carroll]

I wouldn't get polyurethane glue anywhere near a concertina.  It's great for larger scale structural work like repairing chair legs that have come loose and similar projects but it's very messy as it foams up when it dries and it is very difficult to remove any excess that may get on the surface (or on you).  If you've ever used a product called Great Stuff (a foaming insulation product), it behaves similar in how it expands when it dries. 

[alex_holden]

I'm not really a fan of PU glue either and probably wouldn't use it in instrument repair. It tends to get everywhere and if any gets on your skin or clothing it is very difficult to remove afterwards. Although it will foam up and expand to fill gaps, the dried foam has very little strength compared to a well-fitting joint.

[SteveS]