Introduction: Repairing Split Wood

Picture of Repairing Split Wood

In an otherwise attractive piece of wood, an unsightly split or crack can run deep like family turmoil.  Most wood fillers are intended to be little more than aesthetic solutions.  Even the hardiest fillers are intended to withstand compressive forces but not sheer stress.  Here I will demonstrate my solution for when I don't want to give-up on a piece of wood.  This block was salvaged from a eucalyptus tree that fell on my grandmother's house (don't worry, I'm fine).  I want to be able to work on it without risk of further splittage.  
  I do all my wood repair at TechShop.

Step 1: Supplies

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I have found polyester resin to the be ideal for this kind of repair.  It is very strong in it's cured state, it seeps into fibers and produces a strong bond (it's intended use is laminating wood and resining fiberglass) and it is slightly flexible, so it will move with wood as it bends and expands with humidity.  

  *Not pictured: the necessary plastic bag

Step 2: Prep

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I prefer jet black for most wood replair work.  I have given-up trying to match wood colors when disguising a crack.  In dark wood a black fill won't stand-out much, and in light wood it can look like the figuring of white ebony or cappuccino gelato.  It's my piece, don't judge me.  Specialized pigments are available for resin, though I have found almost any black coloring works.  Here I am using black airbrush paint.  A little bit of it goes a long way.
  Tape-up the sides and bottom of the piece to keep the resin inside.  Cracks run deep, so it is sometimes wise to tape the entire piece inside a plastic bag.  Do the repair work before making any cuts or planing on the wood and don't worry about the resin puddling on the outside.  

Step 3: Pour

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Pour it in the cracks until it overflows.  

Step 4: And Use the Bag

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Just to keep everything within the confines of the wood, I taped a bag around it. 

Step 5: The Unveiling

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You got resin everywhere.  It's a good thing we used the plastic bag.  

Step 6: Finished

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Polyester resin can be worked with most woodworking tools.  Be careful if you choose to go at it with a chisel, the excess resin will throw-off glass-like shards when impacted.  A bandsaw will cut easily and safely, then the resin can be planed, routed, or sanded.  This is a structural repair, so the block is now fit for any purpose as a solid piece.


timsmith90 (author)2017-09-26

I don't think the resin would increase the structural strength of the timber. Clamping the timber with a wood glue is a better solution as it will be stronger and not split the same way again. The resin is just a filler not a form of strengthening which was required in your above posting.

DavidF559 (author)2017-04-15

Hi Folks.
I'm hoping somebody can advise me on the best approach for a project I wish to complete this summer. After reading through the comments I have discovered some answers to several questions but I'm still not sure of the best approach.

The project is a large outdoor table. It will be bar height and constructed of a large beech stump acting as the table base and the top will be a very large ring of beech roughly 10 inches thick. I need some advise as how to treat it to stop splitting and how to finish.
I had the idea to coat the top after flattening with a router jig with an outdoor epoxy to achieve a glass like finish and possibly fill the surface cracks with a glow powder/epoxy mix. Will this work? Should I soak with an oil first before applying the epoxy like in previous comments?
As for the base I was thinking of sealing the bottom/root section after flattening with an epoxy to prevent rot and stop any moisture being soaked up through the base. As for the rest of the base I plan on carving with various tools to depict a historical science from Irish folklore.
I know this sounds like a crazy project but I really think it would look amazing if I can pull it off.
All advise and comments welcome
Thanks in advance

Jimichan (author)2016-12-16

You should try clear resin with a glow-in-the-dark powdered pigment. It's fairly inexpensive on Amazon.

Hayilabc (author)2016-04-22

Will this work for surface "cracks"? We bought a table with a checkered wood detail but there are areas where the wood is missing. They are about 1/8 of an inch deep. Any advice on whether this process might work?

KellyCraig (author)Hayilabc2016-10-21

For those dealing with cracked beams and such, the ideal is to address the problem before it starts.

Sealing the wood doesn't work. Eventually, the wood will still lose moisture, which causes it to shrink, resulting in splits and cracks. I purchased a maple cutting board with this problem, then restored it using the approach noted below.

For the butcher block, I flooded the top with mineral oil. The first bottle disappeared almost as soon as I put it on. The second went in slower, so I just added more to the spots that soaked in each time I walked past to another project. Finally, it began taking the oil in rather slowly. At that point, I slathered on a generous layer and just walked way.

I ignored the top for a couple weeks. When I checked on it again, the oil had all soaked in. Too, it swelled the wood, just as water would, causing ALL the cracks and separations to close.

The same approach can be taken with exterior wood surfaces. If you applied a generous first application, the obviousness of your efforts would disappear shortly. A second application would fare only a bit better. However, the third or additional coats would remain evident for years.

The oil applications do not evaporate. They disappear because the oil wicks to the next dry area, deeper in the wood, until there is too little oil to wick further or the saturation has equalized throughout the wood.

The main things, when using oils to replace lost moisture are:

1) Use a non-hardening oil. That could be something like Chevron Shingle Oil (about ten dollars a gallon, in quantity), cheap motor oil (your mileage may vary) or mineral oil.

2) To increase penetration, I'd thin it about ten or fifteen percent. You can use paint thinner, naphtha, mineral spirits or turpentine. I'd opt for the cheapest, unless I was working on a specialty project.

3) The more aggressive and patient you are in your applications, the better your results will be. You can keep adding oil without doing anything to the surface, whether a day after an application or years after. The applications will build on each other .

HINT: Buy the cheapest mineral oil you can for food grade items. That would be around a buck or so a pint.

NOTES: Cedar shingles that are saturated with oil, in addition to not shrinking and splitting or cracking, will remain more resilient. Normally, walking on them in the middle of the summer would cause them to break. However, if they were saturated with oil, the would remain more flexible and less prone to breakage.

crf2720 (author)KellyCraig2016-11-21

After I saturate the wood with mineral oil and it swells, is it possible for me to stain and seal on top of that? Relatively new to finishing wood/woodworking and wanted to try this method before messing with the epoxy and everything. I am re-purposing some old 2" thick pine boards that are about 5.5" wide sections that are joined together to form a big butcher block almost. Ive attached a couple pictures of what I did with the board the first time, and what I am making this go around. The boards that I have left have been exposed to the weather for a while and have started cracking even though they are reinforced with 1/2" all thread trough both ends.

KellyCraig (author)crf27202016-12-03

Sorry for being so slow to get back to you.

Keep in mind, stain is, for the most part, a surface coat. Of course, much of it can get into cracks, grooves and open cells below the surface.

If the wood isn't oozing oil, it shouldn't be any problem staining it. As they say, do a small test sample. Let it set the appropriate amount of time to see if it hardens. If it does, you're good to go.

Water based stains aside, stains are made with linseed oil, a hardening oil. If you apply them to wood after the fact, they will act to seal the wood, at least to some degree. That will help seal moisture out and reduce moisture loss, in addition to what the oil does.

Anyway, I would slather oil on the top, sides and, if practical, the bottom. Let it soak in, and let it set for a few weeks before applying the stain. Monitor some small cracks or splits to see if they are starting to close. If they are, you might want to drag the process out.

When you think you've done all you can, go to the stain. If you are ready to bag it and move on, you can wash the excess off with a good oil busting dish soap. Just let it dry for a day or two before moving ahead.

Again, remember oil is a surface coat and not the most durable/wearing finish, to say the least.

KellyCraig (author)2016-10-21

I buy my epoxy in the gallon and a half containers (2-1 mix) and use it for cracks. The two to one mix seems much thinner than the fifty-fifty mixes I use, so it soaks in well.For
light woods, I don't color the mix. No one has yet to notice the clear
fill on in large cracks on a few butternut and other light wood
ornaments I've made

Painters' putty works good for sealing the
end of the cracks. The portion with the putty can be cut off with a
miter or other means.

PaulE61 (author)2016-02-23

@jimofoz, I am testing the epoxy method on scraps of wood before I work on my "live wood" table top that has several holes (some going right through the slab) but I have been having problems with the epoxy leaking through the tape. First I tried clear cellophane packing tape. No good. Then I tried hot glueing a cardboard to the bottom. Epoxy still leaked out. I haven't tried gaffer (duct) tape yet. Is that what you are using? Do you have some tips?

artobot (author)PaulE612016-02-23

Looks like he's using gorilla tape, thick, durable, and holds strong. Little bit more $ than a roll of duct tape, but it's worth it.

PaulE61 (author)artobot2016-02-24

Thanks, will try that.

ChrisFosterling (author)PaulE612016-09-15

I'm a little late to the party but after you apply the gorilla tape, I've had great luck in applying a little heat in the form of an iron on a low setting over a piece of cloth to soften the adhesive. Especially on wood grains.

headstack (author)PaulE612016-02-24

If you are hot gluing a patch over the through holes and getting "weep" it most likely means the patch does not have a perfect seal against an undulating/striated surface.

Using something with better sealing capabilities like Phenoseal should work.

I learned to use it as a "dam" around the top edges of cracks, so you can overfill and fair the filler down to grade after curing.

Squirt a healthy bead well outside the perimiter of the hole, slap your patch in place, plastic wrap and then a slice of Masonite works well, and jam that sucker tightly in place to create a liquid tight seal.

you'll want to make sure the caulk stays out of the hole so as not to blob up into the repair.

Have fun!

PaulE61 (author)headstack2016-02-24

Good idea about the "damming" to top edges.. and I guess any caulking (bathroom, exterior etc) should be equivalent to Phenoseal right?

max3dlee (author)2016-02-23

i just built a table for a buddy. there are several paper-width seams that he doesnt care about, but i do. i have seen some tutorials on using sawdust (actually powder from sanding) as a filler when mixed with glue. however, if I'm going to stain the table, the glue will prevent the putty from staining like the rest. my plan is to stain some scrap, sand that, then used the "pre-stained" powder with modgepodge as that dries clear, not yellow like woodglue.

my question is could I use the wood powder in this epoxy resin mix you've shown here instead of paint?

pskvorc (author)max3dlee2016-02-23

Repeated attempts to "match" face-grain with sawdust or "powder" have proven fruitless for me. After some thought and observation, I think I know why. Sawdust or "powder" is predominantly "end grain". As such, it absorbs colorants like end-grain does. Namely, 'darkly'. While I'm sure some extensive experimentation might result in an 'invisible' color match, I have yet to come to a point where I appreciate the effort relative to the outcome. Therefore, more often than not I do what the author (Scotttland) does and make the repair high contrast and therefore a "feature". Like ALL 'fixes' of this sort, they don't really fool experienced woodworkers. They're just a reasonable solution to salvaging a piece of wood or work that one really wants, or needs, to.

BrianJewett (author)pskvorc2016-02-23

There is a Japanese term for this that escapes me. They will take a broken piece of pottery and use gold to make an obvious repair. The idea is to embrace and even feature the repair as a values part of the history or life story of the piece. I think black filler is perfect. I'd even be tempted to try something really intense like red for the right piece.

That's almost beautiful. Great idea. And thx for the info

overst33r (author)BrianJewett2016-02-23

I believe that's called wabi-sabi.

BrianJewett (author)overst33r2016-02-23

No, it's related but not the same. Kintsugi is the word I was looking for. Wabi-sabi is simply embracing imperfection.

overst33r (author)BrianJewett2016-02-23

Oh that is cool. Every time I am on this website I learn something new (even in the comments)!

schabanow (author)BrianJewett2016-02-23

Interesting view (concerning gold-framed crackings)...

schabanow (author)BrianJewett2016-02-23

Interesting view (concerning gold-framed crackings)...

jvandeyacht (author)pskvorc2016-02-24

Thats a lesson i learned years ago. Now if i fill cracks or gouges etc. I intentionally use a contrasting color. Nothing looks worse than a almost matched match especially on floors.

EthanL22 (author)pskvorc2016-02-23

Do you have to stain it? This is like staining cherry or other blotchy wood that doesn't absorb consistently. Rather than using a penetrating stain why not try some kind of tinted lacquer that will put a coloured surface on the wood without actually changing the colour of the wood.

max3dlee (author)EthanL222016-02-23

Ive seen several tutorials on using tinted laquer, but at this point that is beyond my skill level and immediate resources.

I intend to use a sealant / pre-stain before staining as samples from the same pieces do blotch considerably.

As for the saw"powder", the seams are no more than maybe 1/64", probably less. I would not try this approach if they were wider and probably just cut another board.

GregF34 (author)2016-06-02

Can I use this technique to shore up the cracks in 4x4's on my children's playset ? I am interested mainly in structural integrity, and secondarily appearance...

Should I use epoxy or polyester resin ?

What is the best method to apply the epoxy/polyester resin on these vertical faces ?

I was waiting until the PTW was dry to stain and seal it... I waited a little too long... It was only 3 weeks old !

Thanks !!

HC1904 (author)GregF342016-07-19

I have exactly the same issue at the moment, I just started researching a solution and came across this post, it'd be great if someone could advise. Thanks.

KellyCraig (author)2016-04-19

I buy the two to one epoxy mix for my shop (gallon and half gallon). Recently, I picked up a small jar of turquoise powder folks use to embellish embossed cards they make. I mixed this will the epoxy and liked the effect.

On a whim, I took some of the oyster shells I'd picked up for inlay and crushed them down to about 1/8" to 1/4" chunks. Then I added it to the turquoise powder, in epoxy, then applied it to carvings I'd made on a turned rattle.

When hard, the end product would have made a good finger nail file (providing you were willing to lose hide too), but it sanded easily enough (remember, breathing the shell dust is VERY nasty). I only used 150 grit. After that, I ran it on my buffer and the oyster shell polished to a pearl like finish. Of course, the epoxy smoothed too.

When done, it could pass for a turquoise inlay for detail work.

Other turnings had cracks and I just filled them, called it a day, then turned them. The cracks are obvious, and not. People see them, but just accept them as part of the wood's character.

You can get a rough idea of what it looks like at the following Lumberjocks page:

Drod13 (author)2016-04-02

great tutorial. I have an antique single piece of wood carved into a pachyderm rocker for a child. Weighs close to 50lbs. The entire piece is 30"x22"x181/2". The crack is 1/4"and runs from the center of one side-back to front. It is a pretty straight crack. The piece is currently painted. I want to fill this and make any other repairs as well. Afterwards re-paint and gift away. Would I use the epoxy for this, as there are carved details I will have to match up. Use the filler with no color added? I am quite a perfectionist and have given myself ample time to educate before I attempt this.

Thanks and Cheers!

HasanN1 (author)2016-03-30

Would fiberglass resin work? And if so, could i still be able to dye it?

Zekeness (author)2016-03-20

Outstanding! I have some cracked billets of wood that I was going to turn into bowls, but when the wood split, checked, and warped; I gave up. This would make for an interesting design in the wood!

L230 (author)2016-03-13

Great tip!! Thanks for sharing!!!!!!! :)

KevinW118 (author)2016-03-04

Hi Scott, great article. You mentioned you now use Epoxy. I have two questions:

Is epoxy as strong and flexible as the polyester resin?( I have some large knots that have come out in my fir floor that need filling and sanding. I'd rather not get any cracks when the wood shrinks and expands).

And what stain would you now use to colour the epoxy?

Thanks in advance!!

joeofloath (author)2016-02-25

This is really cool, but be aware that polyester resin is hygroscopic, so if the piece is for outdoor use, use epoxy resin instead. Epoxy is superior in most ways but also costs about four times as much.

Scotttland (author)joeofloath2016-02-26

That's great advice, I've actually switched to using epoxy.

HTMF Metal Pizza (author)2016-02-25

Just wanted to add my appreciation for the tutorial. Very nicely done. Thank you.

GarrettW1 (author)2015-07-12

Where do you buy the polyester resin and stuff?

bgunville (author)GarrettW12016-02-24

try one of the box stores HD or Lowes, Or your local hardware store.

Poppyburner (author)GarrettW12016-02-23

Here in the UK, Halfords sell an opaque type for fibreglass:

Or there's Alec Tiranti (Sculptors' Tools, Materials & Studio Equipment):

headstack (author)2016-02-24

I don't see your reply here, but Phenoseal has some interesting properties.

It's quite soft and therefore finds its way into fairly complex surface textures making a good seal, yet after it has cured a bit is still very pliable and pares away from the wood with even a moderately sharp chisel.

I would steer away from products containing any Silicones as these will wreak havoc with finishing processes.

Other than Silicone causing fisheye hell, anything that seems to form a good seal and is viscous not to run or flatten out could be worth a try.

Mashed potato flakes, here we come! :-D

jacobz_20 (author)2016-02-23

If you used some sort of mold around it, would this work to replace the shaved-off corner, too? Or would the fact that it only has a single surface to cling to stop it from working effectively?

rallen71366 (author)jacobz_202016-02-23

If you're trying to replace a corner, the epoxy alone probably isn't going to have the durability you're looking for. You might try building a mold for the corner, then filling it with wood splints before you add the resin. Just an idea.

namora (author)rallen713662016-02-24

A paste of sawdust from the same wood will give an excellent match and sometimes the lack of grain is unnoticable,

jacobz_20 (author)rallen713662016-02-24

I was figuring the same thing.

I wasn't really planning on anything; I just noticed that the example block of wood is missing its corners and was wondering if this could take care of that too.

DewiH1 (author)2016-02-24

Thanks for sharing. I'm a retired cabinet maker/antique restorer, and I have used this method to repair prized heirlooms. Your use of polythene and adhesive tape makes for a tidy operation.

Jackn7 (author)2016-02-23

Heh... I posted a reply to someone here 3 years ago... and all of a sudden I am getting emails about comments on it.

I think the original post and my reply and others has been removed, which is fine. :)
Really not interested in carrying on a 3 year old argument. :D

I still have this Instructable as a Favorite... ;)

The really fun thing to do in a situation like this is to use glow in the dark epoxy or Ultra Violet stuff. :)

snodman (author)2016-02-23

I can think of a few places I can use this already. Thanks. I wish the trolls would stay off this site.

marcintosh (author)snodman2016-02-23

Trolls, why I rarely contribute projects any more

dkcoles (author)2016-02-23

Neat result. I like the fusion of wood and plastic and being able to see the imperfections of the wood without the downsides. Has anyone used a piece of repaired wood like this with some lights behind for a cool effect?

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