• It's time to cast your vote in the April 2025 Turning Challenge. (click here for details)
  • Congratulations to Steve Bonny for "A Book Holds What Time Lets Go" being selected as Turning of the Week for 28 April, 2025 (click here for details)
  • Welcome new registering member. Your username must be your real First and Last name (for example: John Doe). "Screen names" and "handles" are not allowed and your registration will be deleted if you don't use your real name. Also, do not use all caps nor all lower case.

Strengthening hairline cracks.....

Odie

Odie

Panning for Montana gold, with Betsy, the mule!
TOTW Team
Joined
Dec 22, 2006
Messages
7,364
Likes
12,163
Location
Missoula, MT
Usually, I attempt to eliminate any checking, or hairline cracks, just to be on the safe side......but, sometimes I take my chances with repairs. For large cracks and voids, I've been using epoxy for a filler. Epoxy tends to discolor in some cases, and requires masking off the edges to prevent any telltale residue that gets into the pores of the wood. With minutely small cracks, I've been using Titebond III simply pushed into the small hairline crack/check with only thump pressure......and, no masking. This seems to be a good solution.....and, pretty much remains undetectable.

My purpose is to prevent the hairline crack from separating over time. I'm not sure how long this kind of strengthening technique will last......hopefully forever.....or years, at least.

IMG_2344.JPG IMG_2345.JPG

Here are two examples of hairline cracks repaired with TB III in the manner described above. I'm pleased that I can't see the cracks in these photos, but they are there. They can be spotted with the eye, if the observer looks closely.

I'd like to hear from those who have used this technique, or other methods of dealing with those pesky little hairline checks/cracks and unavoidable voids. Detailed responses are appreciated.......thanx

ko
 
All I can see is a great looking piece of timber.

I have not used the titebond/thumb method but do like the idea. Titebond is perhaps the strongest glue for joining wood.

I have used CA for hair line repairs. To avoid the staining that CA causes, I will spray the area with rattle can lacquer first. The lacquer seals the surface against staining, yet allows the CA to wick into the hairline opening.

For voids, epoxy and a suitable filler do well for me.

Did I mention great looking piece of timber?
 
One more thing about the Titebond III......I'm not sure how much penetration I'm getting into the hairline crack. There's not much gap there, and using the thumb applies some pressure to force the TB into the gap......but, is it enough for much, or any penetration? I don't think there would have to be much penetration for the desired result. TB is pretty strong stuff......so, if the penetration is 1/16", that would probably be good enough......or not?......you think?

Over time, I'm sure some cracks will tend to shift, and others may not. It all may depend on the species, grain, climate, etc.......?

ko
 
That is the only thing I like about using CA for hairline cracks, you can use the thin grade and it draws right into the crack and
you can then follow up with a medium grade glue to fill a larger crack when needed. I just don't like what CA glue does to the
wood around the repair.

Keep us updated with the Titebond III crack repairs, I for one would like to use an alternative to CA glues if there is a better option.
 
odie said:
One more thing about the Titebond III......I'm not sure how much penetration I'm getting into the hairline crack. There's not much gap there, and using the thumb applies some pressure to force the TB into the gap......but, is it enough for much, or any penetration? I don't think there would have to be much penetration for the desired result. TB is pretty strong stuff......so, if the penetration is 1/16", that would probably be good enough......or not?......you think?

Over time, I'm sure some cracks will tend to shift, and others may not. It all may depend on the species, grain, climate, etc.......?

ko
Click to expand...
Kelly I have been woodworking for a long time and when you apply glue to 2 pieces of wood if you do not apply fully to both edges you will have joint failure. So in my opinion for hairline cracks what you are seeing is a cosmetic seal and not enough to hold the wood from movement. You could turn a bowl and try your idea and then cut it open and see where the TB is. I do not think it will penetrate a hairline even 1/32.
 
I have tried that method, and just never felt my thumb would work the glue down in far enough. I have tried pressure squirting the glue into the crack with the nozzle down on the wood, and didn't trust it either. I have flexed the crack to open and close it a bit to help wiggle it down, and didn't trust that either. Never tried the soak in 1/2 glue and 1/2 water which is supposed to penetrate all the way, and swells up the wood for a tight and almost invisible fix, which is supposed to stay after it dries back out again. 24 hour or so soak, but don't remember. If I am going to repair the crack, I do the thin, then thick or medium CA glue method. Pretty sure the thin will wick the thick all the way down into the smallest parts of the crack.

robo hippy
 
Jamie Straw said:
:D:D:D I love typos. That is a beautiful bowl, Odie. What kind of wood?
Click to expand...

Thanks, Jamie......It's Fiddleback Maple with some reddish mineral (?) staining. The other one is Goncalo Alves.......

Darn that auto correct feature.....does that all the time! :oops:

Mike Johnson said:
That is the only thing I like about using CA for hairline cracks, you can use the thin grade and it draws right into the crack and
you can then follow up with a medium grade glue to fill a larger crack when needed. I just don't like what CA glue does to the
wood around the repair.

Keep us updated with the Titebond III crack repairs, I for one would like to use an alternative to CA glues if there is a better option.
Click to expand...

That staining from CA is why I stopped using it.....epoxy sometimes does that too, but not as bad as the CA. Others are using CA.....maybe they have a secret I don't know! :confused:

Gerald Lawrence said:
Kelly I have been woodworking for a long time and when you apply glue to 2 pieces of wood if you do not apply fully to both edges you will have joint failure. So in my opinion for hairline cracks what you are seeing is a cosmetic seal and not enough to hold the wood from movement. You could turn a bowl and try your idea and then cut it open and see where the TB is. I do not think it will penetrate a hairline even 1/32.
Click to expand...

Gerald....that's what I'm afraid of. I'm wondering if using TB this way is not as good a repair as I'd hoped. Next time I ruin a bowl that has a TB repair like this, I'll take your suggestion, and cut it open to find out. I'm using TB to attach waste blocks to bowls, and I can see it does penetrate the bowl wood a little.....but, there's much more pressure behind the union.

robo hippy said:
I have tried that method, and just never felt my thumb would work the glue down in far enough. I have tried pressure squirting the glue into the crack with the nozzle down on the wood, and didn't trust it either. I have flexed the crack to open and close it a bit to help wiggle it down, and didn't trust that either. Never tried the soak in 1/2 glue and 1/2 water which is supposed to penetrate all the way, and swells up the wood for a tight and almost invisible fix, which is supposed to stay after it dries back out again. 24 hour or so soak, but don't remember. If I am going to repair the crack, I do the thin, then thick or medium CA glue method. Pretty sure the thin will wick the thick all the way down into the smallest parts of the crack.

robo hippy
Click to expand...

You know.....that's the thing, robo.....It doesn't seem like anyone has come up with a "sure-fire" method of repairing cracks that is 100% guaranteed.....with no staining. As you mentioned, if you can open up the crack, then it would seem that penetration is much more likely. Many cracks, you just can't do that, though......

As I said, I used CA at one time, but unsuccessfully, because of the staining, and inability to be compatible with Danish Oil. A few years ago, I tossed all I had out because it all hardened.......:mad:

I was up late in the shop, and gotta get up early........so, I'm outa here........:D
 
If you can form two clamping cauls for the interior and exterior shape of the bowl, then you could seal them to prevent migration of the glue and use a clamp to force a glue/wood mixture into the crack. A little sawdust or coloring or whatever you prefer,mixed with the glue.

Alternatively, you might consider a band clamp around the perimeter of the workpiece to tighten the crack. I don't know that either these methods will work well for a large object, but I've used both of them successfully smaller items.
 
Last edited:
If I can't get rid of the crack, I make some thing else out of it. It doesn't seem to be possible to make a crack invisible. I have heard that the soak method does though, but never tried it.

robo hippy
 
Mike, I'm very much a rookie at turning. Would you share what you did on the platter in the photo? Thanks.
 
Most of the videos on YouTube are limited in knowledge of what they are doing and the techniques used.
Number One, High Voltage and Higher Currents can quickly kill you if you don't take proper precautions.
I use a a high voltage neon transformer with (2) insulated electrodes to apply the voltage to the wood piece.
I wear high voltage rubber gloves when using the insulated electrodes applied to the wood piece.
The electrodes have 18" long plastic/wood/fiberglass handles to keep the voltage away from the user.
The wood is brushed with a solution of water and baking soda to provide a current path for the voltage.
When the probes are applied to the wood it takes several seconds for the voltage/current to create a carbon
track on the surface of the wood. The longer you apply the voltage/current the deeper and longer the lichtenburg
designs burn into the wood piece. You can move the probes to various locations to create a random pattern on the
wood piece. You also need to re-apply the water baking soda solution when it dries out to provide a path for the elctricity
to follow. The wiring used to power the insulated probes should be high voltage rated wires rated for the voltage/current
output of the transformer. The handles attached to the electrodes should also be rated for the voltage/current of the transformer.
You can apply the electrodes and watch the progression of the lichtenburg design and let it progress in different directions by
moving one of the probes in the ditrection you want the design to progress in. The longer you leave the electrodes in one spot
the deeper the lichtenburg design will burn in. It takes practice to control the direction of the designs and some people will use a
spray bottle to apply more wetting solution while the process is burning to guide the design. Much care is needed and a full
understanding of the potential danger involved with using this technique. Water and high voltage/currents are an accident waiting
to happen. You need to insulate yourself from any possibility of contacting the wood the electrodes and the wiring when working
around this equipment. When you are done appying the lichtenburg designs you shut off the power supply and make sure it is off.
Take your wood piece from the area and rinse it off with water and use a tooth brush to clean the carbon from the lichtenburg designs.
Let the wood piece dry or use a heat gun to dry the wood piece, remount the wood piece on the lathe and lightly sand the piece to
clean up and create clean detail lichtenburg designs, apply your finish as you would with other projects.
 
Odie,

Timely thread for me, too, as I have a beautiful bowl with a PITA crack...hairline, but too long. I've only tried TBIII on a few bowls, though I've used gallons of the stuff and never had a failure...though I've only been using it for 10, maybe 12 years...it was only TBII before that.

My approach for a bowl with a crack that was a bit more than a hairline was to finish turn my bowl, then apply glue with a finger then blast it with the airchuck. After repeating that a few times, I smeared fine sanding dust in the crack, blasted air, more glue...you get the picture. After drying 24 hours, I took one last light pass with gouge and then sanded.

I probably think too much. Another approach that might be worth considering is what Bob Hicks, the editor of Messing About in Boats, uses for getting maximum epoxy penetration for a topcoat on the boats that he builds. He lives in the South, and opens up his shop until it gets as hot as he can handle. Then he applies the epoxy, closes his shop doors, and hits his ultra powerful airconditioning. He wrote a bit of a treatise on it, maybe 20 years ago. He suggests that the wood sucks the epoxy in as it contracts and cools. Makes sense to me, and it would seem to for bowls, too. I'd add warming the bowl back to room temp before the glue sets.

Thanks, Mike, for the picture and info on Lichtenburg burning. Very cool.
 
Here is my experience with cracks.
  1. First my opinion is that using sanding dust or wood particles mixed with any kind of glue is very iffy and generally makes a crack more obvious than just plain gluing. This because the glue turns the wood dust much darker and even if you try to pack in dry dust, it just looks like a repair that didn't work.
  2. Unless the joint can be perfectly closed together the repair is going to stick out like a sore thumb. Sometimes it still shows even when the crack can be perfectly closed.
  3. PVA glue is bad about staining so that the wood doesn't take a finish evenly. So, trying to work it into a crack means that it is also being worked into the surrounding wood. Maybe if you apply a finish first things might work better. Also, PVA has a tendency to creep over time and create a ridge. Hide glue is usually better about creeping, but still has plenty of disadvantages.
  4. You can shoot a light coat of lacquer before using CA to reduce or eliminate staining. There are super thin tips available that help to get the CA down into a crack without getting it on the surface.
  5. If possible do the glue repair before turning to final thickness.
  6. Cross grain cracks are much harder to hide than cracks along growth rings.
  7. Sometimes coffee grounds can be used to make a faux bark inclusion.
  8. A complete break is usually a lost cause, but I always use these lost causes as a test bed. I dropped the bowl pictured below and the glue repair was too obvious so it became my first basket illusion piece. It was sort of crude, but it set me off on a new course.
index.php
 
Zach LaPerriere said:
Odie,

Timely thread for me, too, as I have a beautiful bowl with a PITA crack...hairline, but too long. I've only tried TBIII on a few bowls, though I've used gallons of the stuff and never had a failure...though I've only been using it for 10, maybe 12 years...it was only TBII before that.

My approach for a bowl with a crack that was a bit more than a hairline was to finish turn my bowl, then apply glue with a finger then blast it with the airchuck. After repeating that a few times, I smeared fine sanding dust in the crack, blasted air, more glue...you get the picture. After drying 24 hours, I took one last light pass with gouge and then sanded.


Thanks, Mike, for the picture and info on Lichtenburg burning. Very cool.
Click to expand...

This use of air reminded me of a post about filling glue into a crack in church pews. Apply glue to crack on one side and use the hose of shop vac to draw glue into the crack from the other side. In the case of a bowl glue could be applied to the inside and vacum to the outside.
 
Bill raises a good point regarding sanding dust making the crack darker. The other factor is that Titebond III doesn't dry clear. Titebond II dries clear, though it's only rated as water-resistant, not waterproof. I've never done a side-be-side test, but my feeling from using gallons on both in the woodworking world outside of bowls is that Titebond III is the superior product.

Now all I need to be semi-scientific is a bowl with hairline cracks on both sides—fix one side with TBII and the other side with TBIII....;)
 
You must log in or register to reply here.
Back
Top