Woodworking questions Oak, swelling and warping

[lw395]

Not exactly boaty this one, but I know there's some woodwork knowledge around here.
I have acquired a 'solid oak' table that's clearly got quite wet at some point.
Some parts of it are badly warped. It is a bit stained in places
The staining seems to be repsonding to oxalic acid.
My plan is to attack the staining with oxalic acid. Rinse and leave to dry.
Then I will need to cut out a few badly warped bits of the top and replace.
The main area of the top has swollen across the grain by about 10mm in 600mm. This is oak boards glued edge to edge.

How long do I need to leave it to 'dry out' assuming it's in a normal modern dry house? I can leave the bits in a spare bedroom.
How much of the swelling across the grain will shrink back as it dries? I think it's fairly dry right now having taken the varnish off by hot air. But the 'growth' seems permanent.
Obviously the oxalic acid will get it wet again.
Any suggestions of where to buy suitable oak to replace a few bits which are warped/split beyond hope?

What glue should I use?
I think I will be gluing in some strips about 30mm deep to the edges of the top where I will cut out hopelessly warped bits.

Should I have a plan B for xmas dinner? If it's not going to be done by then I need to look for something else....
I was thinking of polyurethane varnish as a finish, several coats of gloss and a final satin.
Any thoughts welcome.

 

[sarabande]

you don't want the table to adopt a "set" when it dries out, so ideally you should try to get all the flat bits in a heap and add some weight on top. Then let it dry out for 3 months inside the house.

However, the chances are that the oak was kiln dried when used to make the table, and having got wet it will refuse to go back to a 100% original shape. Sorry but I don't hold out much hope, short of planing off the mountainous bits.

 

[oldbilbo]

No idea of the size of table, but guessing about 8' x 4', you could try steel flooring cramps transversely with steel 'U' or RHS beam-tubes longitudinally/under, and steel 'F' cramps every 6" or so onto the long. beam-tubes. All should be 'borrowable'.

Spray lightly with a garden/domestic water-mist sprayer every 48 hours, both sides, while leaving in the room suggested. You may still need to plane down, but this is worth a try.

 

[lw395]

Thanks.
I think I'm resigned to planing bits and even replacing badly warped bits.
It's about 7' by 3'.
Cost wise, I'm ahead even if I make a whole new top for it. Unless I buy lots of tools of course!
Any thoughts on modern glues?
I mostly use epoxy for boat work and pva for odd jobs, I know these are not the best!

 

[sarabande]

you need one that does not stain the wood, is acid resistant, can be removed easily from non-contact areas. The fitters use Wakol adhesives

https://youtu.be/sr8WKhM5CBg also Amazon.


If the main carcase of the table is OK, why not go for a completely new top ? It will save you enormous time and faffing around, and will look much better. Kiln dried oak is readily available in the lengths you need, and if you finish the top with breadboard joints it will look splendid and be a heritage piece.

 

[reeac]

How was the top attached to the frame? The correct way is to have a number of small oak blocks, each featuring a tenon, which are attached by a single screw each to the underside of the top with the tenons protruding into a groove which runs all around the inner surfaces of the rectangular frame of the table. This method permits slight movement or warping of the top without affecting the frame. My brother in law made us a superb oak kitchen table using this technique (he was a mechanical engineer) and we've had it over 20 years now. I suggest that you get the top flat first, though.

 

[sarabande]

you certainly need to accommodate the natural movement of oak (and indeed all woods), even in a house. A rough guide is a movement of up to 3% of the length. That means clever thinking about the tenons at the breadboard joints, rather than fastening everything together immovably with a modern adhesive.

 

[Len Ingalls]

https://www.youtube.com/watch?v=L6t2AZubF8U

 

[PuffTheMagicDragon]

https://www.youtube.com/watch?v=L6t2AZubF8U

That's an impressive demonstration of porosity but, IMHO, don't take any notice of the chemical technobabble at the end when he tries to explain how the salt breaks up into "hydrochloric acid" and "household lye".

Plenty of good advice on his channel "Tips From a Shipwright" though.

 

[peter bush]

Mdf.Tablecloth.Done.

 

[lw395]

Mdf.Tablecloth.Done.

That's plan B.
Not sure MDF is strong enough for our cooking though!

I did the oxalic acid scrub today. Starting to look better already.

 

[Len Ingalls]

By cutting multiple 6mm dados with a router in the hidden surface (bottom of table top), stress warps can sometimes be prevented/eliminated.
A hot steam iron will sometimes help to flatten a cupped/warped board.
Using the clothes iron dry on the convex surface will speed drying & shrinking of the convex surface.
Using steam on the concave will expand & flatten the concave surface.

If the boards were wider than 4" originally,they may be prone to cupping. Re-rip the whole surface into 4" strips & re join ?
Hardwood cross battens on the underside could help.

Ensure the bottom surface is "sealed/varnished" well to balance humidity intake.

Google is your friend.

 

[TamT]

Dont use epoxy with oak. The tannins in the wood will eventually cause failure. If you have good fits and suitable clamps, cascamite is a better choice.

 

[Amulet]

Dismantle the planks. At 900ish wide I expect it's not one piece. Store them in the environment the table will live in. Thickness determines drying rate (if they are wet) - maybe 1 month for 18mm thick, 3-4 months for 25 mm or 9 months for 32 mm. This depends on how near they are to the equilibrium moisture content they are at present. I'd probe a bit of wood indoors with a cheap moisture meter (a few quid). Probe the table periodically, and wait til my table approached the same percentage moisture as other wood in the room - might be today. Join planks with loose tongues - strips of ply in grooves. (I'd biscuit them - but I guess you don't want to buy a biscuit jointer.) Plane the edges to be joined a tiny bit concave to avoid end splitting. You'll need some method of clamping the whole lot together as the glue dries. I have panel clamps. Bodge some system of clamps or straps. You need to squeeze it together edgeways and flatten it. At the same time as squeezing it, clamp it between bits of wood across-ways to flatten it - use g-clamps, weights or whatever. Stick brown sticky packing tape to the laths you use to clamp it - good tip for any clamping. The shiny side will prevent it sticking to any glue that oozes out. Cascamite is good.

If you must bodge it flat using crosswise battens underneath, the screws that fix them MUST be in slots on the battens to allow lateral movement. Otherwise it will split. This is not normal table making behaviour.

Traditionally tops are fixed with wooden "buttons" underneath that cutely mate with slots in the frame. After a few tables I couldn't be arsed with this and now opt for steel "shrinkage plates" (sometimes called "stretcher plates" - misleadingly) ugly, but a lot easier, and to see them you have to crawl under the table. Google them - they cost about 10p each.

At 900mm wide I'd not expect more than 5 mm movement crosswise in oak in varying humidity - probably actually less, I'm playing safe. A 1000 mm wide pine table recently settled about 7 mm narrower than I made it. Lengthwise shrinking should be negligible.

 

[Daydreamer]

@Amulet. Largely agree but it does rather depend on just how much the boards themselves have warped.

Plan C

Buy a solid oak kitchen work top. Plenty of online suppliers on Google, The best ones for a table top are the full stave prime oak type but they are of course the most expensive. I am just about to do that on a base I have made and I did make a rough estimate of the cost of buying European prime oak, cheaper but not by so very much.

Please don't use gloss polyurethane varnish It looks ghastly in my not very humble opinion. Use an oil finish. Its quick easy and repairable. I am happy with Liberon Finishing Oil but a tougher work surface can be achieved using one of the Osmo range of finishes