Advice needed - cracks in dining table

[hellobadger]

Hi everyone,

I've recently completed a dining table. It's a large solid piece of Elm with epoxy resin filling any voids. I know that some people don't like epoxy tables but I do and I also believe it was the best use of this particular piece of wood. As you can see from the pictures, some cracks (currently about 1mm wide) have started to develop at one end of the table. They are on the top, the edge and the underside. The table was completed and finished with Rubio Monocoat approx 1 month ago.

The question is - what to do about it? Should I just wait and see how much these cracks develop and maybe just fill them if it 'stabilises'? Or, should I act now and add some butterfly joints to try and stop the cracks getting bigger?

I think I know why this has happened:
- I started with a very thick slab, approx 70mm and brought it down to 50mm. This fresh wood is probably the reason for the movement if it had trapped moisture in it?
- The steel framed table base and 'c-channel' steels allow no movement whatsoever.
- Perhaps the damn thing just wasn't dry enough. I did check it with a moisture meter and it seemed ok, but that was before I removed 20mm of thickness.

Any advice really appreciated.

Andy

 

[alex robinson]

Don't let other people's opinions make you feel bad - taste is personal and all that matters is you like it (though for what it is worth I also think it looks great).

Less good news regarding the cracks. The slab hadn't stabilized to the moisture content for being inside. They will continue to grow until the wood has acclimatized. You might stop them with bow ties, but you would probably just move the stress and cause cracks to happen elsewhere. I would leave it for several months and touch up with epoxy or super glue depending on the sizes. Unfortunately that will mean refinishing.

Woodworking is a cruel and space demanding game! Leaving stuff to acclimatize months is always a hassle, but generally good if you can.

 

[Phil Pascoe]

The steel framed table base and 'c-channel' steels allow no movement whatsoever ...

I suspect that is where your problem lies. Take the fixings out leaving one at each end, and leave the thing alone for a few months.

 

[Fitzroy]

It is due to movement of the slab, which will always occur. Some of this movement is due to initial conditioning of the wood, and some due to the seasonal movement due to relative humidity fluctuations summer to winter. Getting a thick slab to to be equalized with a house environment is really tough. Ideally you would want it kiln dried to 10-12% moisture content to limit issues.

The c-channel is designed to keep the slab flat, and should have elongated bolt holes so that it does not limit expansion/contraction across the width. I've not use metal c channel but I have used a wooden batten in a similar fashion. If this is not how it is installed then it could be causing or exacerbating the splits.

It's a great table, I'd leave it to acclimatize for 12months then fill the splits with epoxy and refinish the table.

Fitz

 

[Sgian Dubh]

- Perhaps the damn thing just wasn't dry enough.

That's your key problem almost certainly identified.

As to what you do about it I'd say Phil Pascoe and Fitzroy have got it mostly covered.

I'm one of those 'some people' that don't like epoxy slathered and void filled tables (horrible bloody things) but each to their own, and I don't suppose you plan to inflict the monstrosity on me where I live, which is great. Slainte.

 

[Ollie78]

Elm is known for moving. I agree with the comments about making the holes bigger to allow movement. And it could have been too wet.

I would take it off the base and let it sit a week or a few, then insert a couple of butterfly's accross the split, elongate holes I'm the base by quite a bit and re assemble it.

 

[Amplidyne]

How it looks is up to you. I like epoxy filled stuff.
However wood is a natural material, and it will always move even when properly seasoned. That's why traditional techniques all provide for movement. Basically you need slots for the screws in your steel frame. Then you can address the splits in any way you wish, and any further movement won't result in more splits. (Well hopefully at least!)

 

[Cabinetman]

Also I’m sorry to say the epoxy is also stopping the wood shrinking, and it’s just close to the end where the cracks are appearing, looks like you will have to fill the cracks with more of the stuff in a years? time.
Ian

 

[AJB Temple]

You have not understood how steel C channels are supposed to work. If you watch the early Blacktail vidoes, the C channels use bolt slots not holes. The bolts are fed into threaded studs let into the wood (in may case tapped and threaded wood) and tightened NOT TOO MUCH so that movement is allowed.
The C channels will stop cupping of the wood but will still allow lateral movement. You need ideally to use dome head bolts as they have a wide surface area that will slip across the slots (not holes!) in the C channel.

I have done this a few times now and it is crucial to understand the process. I do not use epoxy as this always makes things worse. If I did use epoxy it would not be until Iwas certain the wood had reached correct moisture content. I also do not cut the ends of the boards off until that point - it is one of the last things I do - I leave 4-5 mm of trim waste at each end so I can monitor what is happening at plank ends.

When I get the planks for a table, I machine them to thickness, usually a bit at a time on each side, and then leave them for 6 months in a dry place which is not too humid indoors (a barn in my case). I buy them dry in the first place and check the moisture. Elm is absolutely notorious for moving and I would never use it for a table having had experience of it for floors, unless I was 100% sure that it was at the moisture content I wanted and confident I could maintain that both in the workshop and the likely finished environment.

Rubio M is fine. Even better with a nanocoat on it. But now I fear you will have to strip it off with a ROS and let the elm stabilise and you MUST deal with the C channels as above.

 

[Phil Pascoe]

Elm notorious for moving? I remember nearly sixty years ago at school seeing a board of elm (about 12' long) kept purely because one end was at a near right angle to the other. A beautiful timber, though.

 

[hellobadger]

I really appreciate all of the replies.

I wasn't clear enough in my first message - I did use bolts into threaded inserts, and the c-channels allow for some lateral movement because they have slots not holes. However, all of this was probably irrelevant because the table base has only holes for the screws, and this is what doesn't allow movement in any direction. It felt wrong when I was bolting it together and........here we are. Sounds like I've got a hellish job ahead of me.

 

[AJB Temple]

- The steel framed table base and 'c-channel' steels allow no movement whatsoever.
Any advice really appreciated.

Andy

Hi Andy - this is what you said ^^ that led to my reply. Your big risk with elm (and many things) is lateral movement, so if your fixing allows "no movement whatsoever", then something has to give and it won't be the steel. The bolts need to be just a bit more than finger tight, and presumably you have threaded metal stud inserts (stainless steel) into the elm and glued this in with suitable adhesive. Just barely tight bolts will stop cupping if the C channels are routed in accurately but will allow lateral movement. On a largish table of say 2.4 metres by 1 metre, I use at least 3 C channels.

My personal opinion based on experience of making tables, is that you probably need to strip the table and check the C channels. I presume you also finished the underside of the table with Rubio M? If you didn't then that will not have helped - the table needs to be dry and both sides coated with whatever finish you are using. Rubio stabilises quite quickly after rub off and we tend to get top and bottom coat done the same day. We also finish inside the C channel route outs as well (and beneath and leg route outs if we used custom steel legs). This is very important - the more so if your C channels are close to the ends).

I don't think the epoxy should make a massive difference really as long as you have not applied it to wood that is not sufficiently dry. That said, I do not personally make tables with epoxy fillings so have no expertise with that.