# Fixing Cracks in Slabs



## Manitario (Jul 4, 2010)

I'm building a dining room table using several 2.5" thick slabs of elm. On one of the ends there are a couple of long cracks through the slabs. I've seen many tables like this with "butterflies" over the cracks; my questions for those of you that have done this:
-is this necessary to stop the cracks from progressing?
-do the "butterflies need to be the full thickness of the slab?
Thanks!


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## Bonka (Apr 13, 2012)

The butterflys should be about half the slab thickness. The cracks will probably progress. The butterflys will enhance the appearance. I was told by a man with lots of experience that a blemish can be enhanced by calling attention to it.


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## donwilwol (May 16, 2011)

I don't usually make my butterflys that think. I think 1/2" to 5/8" is enough. If the wood isn't completely dry the crack may continue. If its done moving it may not. Sometime you can glue the crack and clamp it shut before you add the butterfly, depending how far and how bad its cracked.


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## gfadvm (Jan 13, 2011)

I have filled cracks with epoxy and then inlayed 1/4-3/8" thick butterflies. So far, so good. Elm can be more difficult than the walnut I have done so your milage may vary.


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## Timberwerks (Sep 29, 2009)

I like to go 2/3 the thickness. I've used this method for many years and have never had issues with the cracks opening further.


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## renners (Apr 9, 2010)

Just a thought, but if you want to stop those splits getting bigger, could you drive a couple of long screws discretely at the end of the split to pin it together. You can still add glue and as many butterflies as you like.


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## Dennisgrosen (Nov 14, 2009)

if you want the table build without the cracks 
and want to avoid butterflyes 
then Charles Neil have a very interressting video on you-tube 
about using a bandsaw to ripsaw thrugh the cracks and glue the board together again 
several times until the crack is gone …. its a nearly invisble fix 
take a look at the video-clip before you deside what to do

good luck 
Dennis


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## Manitario (Jul 4, 2010)

Thanks for the replies guys. I like the cracks in the slabs; the table will have live edges so the cracks add character; I just don't want them to eventually destroy the table!


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## MNgary (Oct 13, 2011)

My understanding is that butterflies are used to strengthen a cracked panel. For example, if a tabletop has cracked, you need to strengthen the top so that if someone sits on it, for example, the panel doesn't flex to the extant that the crack extends further across the panel. In short, the butterfly prevents a downward force (90 degrees to the panel) from flexing a panel weakened by having a crack through it.

I suspect your cracks are the result of tensions from within the slab and, unless the wood is done moving (tensions are stabilized), I doubt butterflies will help. However, to prevent the cracks from extending as a result of heavy downward pressure, butterflies can be your solution. But make sure they are thick enough to add strength and not just decoration.


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## CharlesNeil (Oct 21, 2007)

done numerous of these, what I do is to use some of the pour on stuff either the epoxy or the polyester stuff 
( enviorlite , Lowes , craft stores), anyway, put tape on the bottom of the crack and pour the stuff into it, what I have found is that often the crack can be more severe inside the slab, the epoxy will dry slow and flow into it, its more expensive than regular epoxy, but because of the slow dry it fills well and throughly, just make sure the tape is well stuck to the underside, a quick spray with some spray shellac or lacquer will make sure the tape holds well, other wise, it takes alot of material to fill the crack, he he he, trust me I know, 
the Enviorlite is cheaper and does a good job, its polyester, then I have also done the butterflies, just for looks mostly, does nice


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## JonathanG (Jan 18, 2010)

Great advice on the slower curing epoxy to really fill the internal cracks and really stabilize and strengthen things, Charles. Also good advice on the quick coat of shellac to help the tape fully seal!


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## Manitario (Jul 4, 2010)

Thanks for the advice guys! I picked up some Envirolite tonight Charles; I'll give it a try, it certainly is a lot easier to use than chiseling out butterflies on areas people will never see.


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## CharlesNeil (Oct 21, 2007)

here is a little more on using the epoxy/enviorlite, it really does well on slabs, that could be prone to having issues, not to say this is the cheapest way or the only way, but it has never failed me, http://intheworkshop.wordpress.com/2010/10/19/clario-slab-finishing-and-stuff/


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## Manitario (Jul 4, 2010)

An update; I used the Envirolite; it was easy to use and has a long open time which was helpful because many of the cracks were quite deep and took a lot of epoxy to fill. Its other advantage is that it is relatively thin, so again, easy to pour into cracks. It also drys clear, compared to some 5 min epoxies that have a yellowish tinge. 
I also ended up using butterflies that were 2/3 the thickness of the top; not easy to do considering the top is 2 1/4" thick, but I hope this will prevent any further cracking in the long run.


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## donwilwol (May 16, 2011)

will we see pic's ? A link to a project ?


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## Manitario (Jul 4, 2010)

Hey Don, I'm just putting the final coats of finish on it…I'm hoping after Christmas I'll be able to recruit a couple of guys to help me wrestle it from the shop into the house (the top weighs in excess of 150lbs) and then post some pics.


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## CharlesNeil (Oct 21, 2007)

Rob, the 5 min epoxy even the clear ones will look cloudy, its because it dries too fast for the air to escape, so it is cloudy, if you use a slower setting epoxy some times you can get it to clear, if you flash over it with a butane tourch, its the heat that thins it a bit as well , also on the pour ons, the tourch works wonders for bubbles and so forth. Also exhaling on it breaks the bubbles, its the carbon dioxide, same with the tourch, just be carefule with the tourch, doesnt take but a quick flash


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## Manitario (Jul 4, 2010)

Table is finally done! The Envirolite worked well, it just was a pain to sand…looks good though and its long open time allowed it to flow into the cracks nicely. 
http://lumberjocks.com/projects/78137


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## SCOTSMAN (Aug 1, 2008)

Mix up some car body filler ideal also for holes in bowls anyway make it black by adding old printer toner and set it into the hole crack and leave it proud then trim back sand etc it looks stunning against the lighter wood better with a good strong contrast than a weak poor match. Alistair


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