Spruce lumber bench split; repair suggestions request

[Jim Clendon]

Hi all,

So, this is my first post (ever, anywhere). I have become obsessed with hand tool wood work and have been at it now for about 3 years. I, like many others, cruise the web and read articles or watch videos, however, it seems to me that becoming involved in an internet 'community' of like minded folks may add a dimension to the inter-web. I.e. subject specific response targeting the topic of interest to the level which one is wiling to dive into... For me, hand-tool woodworking is a journey onto it's own and is far from my experiences as a framing carpenter and an Engineer, yet transferable as well... Anyhow, my query:

I built a 10' Roubo-ish bench last summer; mortised the legs into the top complete with top stretchers which which were mortised into the legs. Material was lumber yard 2x6 (in Canada, SPF #2 or better, hand picked); moisture tested at time of construction (~ 15%). Top Geometry: 24"W x ~5-1/8"th x ~10'L. Inside clear space along each leg frame (between mortise cheeks): ~16". Finish: nil. Location: single family home garage with electric space heater during winters to maintain temp above freezing.

I knew shrinkage cracking would occur, and to my satisfaction, until about 4 weeks ago; I would see a few cracks open and close but never more than maybe 1/64". About 4weeks ago we got hit with an arctic front and here in Western Canada the ambient air temp in my garage environment circulating between about 1 deg C and 15 deg C and the air is dry, freeze dry. Today is 40below (C or F) so there is just no moisture.

My bench is presenting a 3/32" max crack. Not surprising.

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The one next to my tail-vise is the most severe.

As would be expected, where the legs mortise into the top, the cross-grain direction is restrained and the radial/tangential movement of the material is experiencing its minimum volume condition due to weather conditions.

I was waiting for this, now I want to pack the cracks and and post-stress the top. My plan is to re-flatten and finally seal the bench this early spring. I was going to apply sanding sealer (3 coats at end grain locations) and a couple of coats of spar urethane to all surfaces except the top. For the top only, I was going to flood with a few coats of BLO.

SO what I want to know is, does anyone have experience, with doing similar to what I have explained?

As well, thinking about packing epoxy putty (like Quickwood) from below, filling with flowable epoxy, then packing the epoxy putt from above?
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Thanks,

Jim C.

[Once I can afford the Maple wood, benchcrafted vises, and hand-tool work time; I dream of a bench similar to what I have seen built by others]

[Lee Schierer]

15% wood moisture is considerably higher than I would have recommended for your project. I wouldn't recommend any type of filler. With some care and a shop vac you can pull PVA glue down into those cracks one at a time and then clamp the crack tightly together. To prevent future cracks you first need to remove the base so the top can be repaired. Once you have the top completely repaired, seal all the surfaces with a good quality finish. This will moderate seasonal moisture changes. Then alter the mortises on the bottom of the top so they fit on the tenons. Most likely you will need to remove some material to account for the shrunken top. You may also need to add a shim to the inside face of the tendons to fill the gap.

[Jim Koepke]

Howdy Jim and welcome to the Creek.

You may want to google > bow tie wood repair < it is also sometimes called a dutchman.

This helps to keep cracks from expanding with moisture changes in the wood.

jtk

[William Fretwell]

Welcome to the Creek, dry here in Ontario as well, my heated shop dial in the red all winter!
Perhaps add a rough location to your profile it helps people understand your wood!

As for cracking, it may not have been dry to start and if not free to move will crack. Wood will move across the grain every year and must be free to do so, wet wood just makes this worse. Filling the crack is just driving a wedge in the crack, when it swells in the summer the crack will just get deeper. My advice, re-attach the top so it’s free to move and leave the crack alone. Give it some years to settle down.

Applying an oil finish will help moderate moisture movement, especially to end grain but not solve your problem.

[Kris Cook]

15% is pretty high. Not sure if you are near the coast or not but I am in western Montana and I would expect wood to equilibrate in the 6%-8% range. At this point you may want to let it finish doing its thing before you deal with the cracks.

I would probably use epoxy and a heat gun or hair dryer to flow it all the way down the cracks with tape or something on the bottom to back it up.

[Andrew Seemann]

Note, before you read this post, which may bum you out, please note that it is meant to be helpful, even though it may sound a little harsh. Wood movement and reading grain is part of learning woodworking, and when you are in extreme climates like you and I are in, it becomes even more important. I have a large body of work with cracks and warps proving beyond a doubt that it took me a while to master wood movement and grain patterns myself:)

The biggest issue is that you have joints in the top where the grain is fighting each other pretty badly (and the bench is losing the battle). The big crack is where two pieces of grain are going in the opposite direction, and there appear to be vertical and horizontal grain glued together, along with pith wood (center of the tree) in the laminations. If you do benches out of construction lumber, taking a 2x8 or 2x10 and ripping down the middle and gluing them up is probably a better way to go (now you tell me, he says!) because you end up with a little more friendly grain pattern to glue together. Actually given the lumber used and the climatic extremes, it isn't in that bad of shape. The moisture content may have been a little high at the time, but that cracking was probably going to occur in winter due to the mismatch in the grain glue up.

I wouldn't recommend filling the cracks, when the humidity goes back up, the wood is going to expand, and the fill will be in the way, which could cause new cracks or warpage or pushing the filler out of the joint. Putting a finish on will help some as it will slow, but not eliminate, the moisture problem; the goal is to slow the transfer of moisture in the extremes of summer and winter.

the If the bench is usable, I'd say use it until you can afford to make another bench out of some kind of hardwood dried closer to 6-9% and without any pith. Or it may work well enough to not need replacement anytime soon.

[Kris Cook]

Jim - It looks like you got three other answers during the time I was typing mine.:rolleyes:

[Andrew Seemann]

Looking at the pictures more, does the attachment of the top allow for movement across the width or is the top stretcher trying to keep the top the same width? If it is, that will make your cracking problem worse. I don't know much about the Roubo design (I don't care for it myself) but I think the legs are usually morticed in to the top without a stretcher to allow for movement in the width of the top. For a Scandinavian bench, the top is held to the stretcher by pins or lag screws, which are put in in away that allows for movement.

Again, don't get too bummed out, these are the growing pains that we all went through.

[Jim Clendon]

One major factor at the time of build. My wife and daughter were out of town for 4days and climatization could not be achieved. Considering kiln dried spruce is 19% when it enters the market, 15% was terrific for my last minute procurement.
I have considered this approach and it is not my preferred approach.

[Jim Clendon]

Thanks Jim
familiar with this feature, considered it and ruled it out

[Jim Clendon]

Thanks Andrew
Your input is appreciated. I had mentioned earlier that circumstances did not allow me to properly allow my material to Acclimatize. I had four days to build my bench without my wife or daughter around. I’ve built a bench previously, but shorter which did not exhibit the transverse cracking. Though shorter, it was wider. For that bench, I had ripped 2 x 8 for the top material. No pith. You are correct, the one I am having problems with, built of 2 x 6 has a lot of pith material. To be completely honest, I thought this would occur but just not to the severity. Even though it is my second bench, it is still intended to be a bridge until I figure out exactly what I want in a bench design Find the money and time to build a hardwood version.
I think I will use the epoxy putty only from the top, reflatten and seal it.
I didn’t feel comfortable with the top being unsupported in the short direction over the legs, with hardwood I would certainly feel okay with omitting the top stretcher.
Currently, my bench is less than 6%mc.

[Jason Dean]

Jim,

My phone isn't the best picture viewer. That said, all those cracks look like failures along the glue line. Does that jive with what you are seeing?

If they are glue line failures, What glue did you use and how hard did you have to clamp your laminations?

[Jim Clendon]

Pva glue; white then yellow. Clamped well over night.
Most cracking is the glue line, not all.

[Scott Winners]

Agree, from Fairbanks, with what you have already heard. One thing I will do different for my next bench is bring the stock in as soon as I decide what I really want, and keep it in the shop for a year after it is stable before I do the build. Year round average MC for me, my EMC, is 11%.

I too would not put any filler in any of the cracks. The wood will need (and will find) a place to go when it swells back up in spring.

Nice bench.

[Christopher Charles]

Welcome to the Creek! And I thought it was cold here in N. Idaho...

Nice bench with some new 'beauty marks'. I agree with others that filling is not desirable. A bowtie patch would be important if the integrity of the bench is in question. Otherwise, I would recommend simply flattening as needed and carrying on :)

Best,
Chris

[Warren Mickley]

The problem is not the moisture content at time of building. The problem is the top stretcher keeping the top from shrinking and swelling with the seasons. If you had the top quite dry when built the stretchers prevent swelling. So instead of expanding the wood gets compressed. Then when the humidity falls the top is narrower than originally. I would rip the top where it is cracked and reglue. Then enlarge the holes in the top where there are leg tenons (at the back) so that movement can occur.

[William Fretwell]

Bill Howes did a thread on “Spruce workbench, lessons learned” back in December, it may be of some use to read it.

[Rob Luter]

.... I would rip the top where it is cracked and reglue. Then enlarge the holes in the top where there are leg tenons (at the back) so that movement can occur.

This. I have first hand experience. :o It hasn't happened to me since.

[Jim Clendon]

Hi William,

I have searched "Bill Howes" as well as "Spruce workbench, lessons learned" in the search bar without success... Perhaps I am approaching the search incorrectly...
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[William Fretwell]

Look on page 13 of Neanderthal that is where it is today.

[Pat Barry]

The cracks all seem to be what I would term delamination, not cracks in the wood itself. My take is that more of these may develop over time. I would attempt to fix by injecting glue and clamping - if that works, great.

[Robert Engel]

The cracks all seem to be what I would term delamination, not cracks in the wood itself. My take is that more of these may develop over time. I would attempt to fix by injecting glue and clamping - if that works, great.

Yes!! + what Rob said. I think what has happened is as the wood continued to dry, the top shrunk width wise and the weakest point gave. I think its most likely due to the base attachment not allowing for movement rather than MC.

Further inspection would be needed to confirm this. But I would say remove the top from the trestles, fill the cracks with epoxy and see if you can clamp it out. Or even better, rip the top down like Rob said.

If you can't clamp it, the epoxy will stabilize the gap.

Re-evaluate how the top is attached and be sure to re-attach to allow for movement.

[James Pallas]

Don’t forget about those legs. If the mortises are tight legs that size can generate considerable pressure along the line of the mortise cut.
Jim

[Pat Barry]

Some have suggested the crossrails, which are not going to shrink lengthwise, as compared to the top aceoos its width may be a cause. Maybe, but that explanation doesn't obviously account for all the delaminations I see. The root cause was likely either insufficient glue, not enough clamp pressure, or surfaces that were no amenable to glue adhesion. This may be as bad as it ever gets. If so, I would not discount simply filling the gaps with epoxy because I think this outweighs having large gaps which will continually catch dirt, shavings, sawdust, etc.

[Matthew Springer]

>My wife and daughter were out of town for 4days and climatization could not be achieved. Considering kiln dried spruce is 19% when it enters the market, 15% was terrific for my last minute procurement.
A word of encouragement: We've all been there. Or at least I have. It's better to do the work when you can and hope for the best than to not do it at all.

I just grabbed a bunch of 4x4 and 4x6 from my local big box store for a pair of Japanese style sawhorses. Planed em all down by planer then hand planed smooth. Then had the kids come back to town and let everything sit for 3 weeks until I could get back to it. I had rhombuses out by almost 1/4 inch at the corners and everything had twisted. But that's the only thing I could have done. They are still awesome and were a lot of fun to build.