Why has my table cupped?

[Ozi]

What was it? Recently tanalised, wet rough sawn and not kilned intended for exterior use, greater than 100 mm thick so wouldn't have been kiln dried anyway. 26% MC is two percentage points greater than is allowable for dry grading of kiln dried construction timber.

How did you check the moisture content - moisture meter or oven drying methodology?

26% MC is a bit high even for stuff that's been kilned to a target of 20% MC and subsequently stored in an open sided shed, whether winter or summer and all seasons in between. I suspect there's a detail of some sort missing in your post that could put that reported 26% MC into context. Slainte.

I now have a 2m length with 45° of twist along it's length at around 10% MC. The rest is part of a bench I sold, no complaint yet but didn't dare ask. I did ask if by seasoned TP mean someone runs around the yard with a salt and pepper pot.

 

[Sgian Dubh]

View attachment 156559 I now have a 2m length with 45° of twist along it's length at around 10% MC. The rest is part of a bench I sold, no complaint yet but didn't dare ask. I did ask if by seasoned TP mean someone runs around the yard with a salt and pepper pot.

It's not unusual for such material to warp after it's been purchased, sometimes a little and sometimes quite dramatically as you describe. Rightly or wrongly the practice in the construction trade seems to be to pick out the best bits for elements of the construction needing close adherence to allowable tolerances, and use techniques to utilise the less than ideal stuff, e.g., employ enough fixings, cross-bracing, etc to force the warped stuff into something approximating acceptably true enough. The worst pieces, badly warped, full of knots, and other big faults is/was either burnt or, more likely nowadays, sent off for recycling. The construction sector is not my world and I make my comments above entirely from observation and from working with or talking to site joiners about their work environment.

Still, you didn't indicate how you established that 26% moisture content you reported in an earlier post. I'm interested to know because your reported MC is significantly higher than would be allowed for kiln dried dry graded construction material, and even air dried wood here in the UK will dry to about 18 - 20 MC, plus construction grade kiln dried wood stored in an open sided shed will naturally settle out at about 18 - 20% MC.

Anyway, all of what I've said above is just discussion about the nature of timber and its preparation and use in different professions and for different purposes (construction, joinery, furniture, for e.g.). I would certainly never consider buying construction grade material to turn into work or seating benches, tables, or any other kind of furniture or half decent show joinery such as panelling or internal trim (architrave, skirting), architectural doors, windows, and so on. Slainte.

 

[Jorny]

That's not quite so. The target for kilned construction grade timber in Europe is 20% MC ±2%. European furniture grade timber has a kilning target of 11% MC ±2%. In North America the kilning target for furniture grade wood is 7% MC ±2%.

As others have already said, Parbynat's problem was caused by construction grade material continuing to dry after making up the panel, with the panel presumably made up in lower relative humidity conditions than those in which the wood was stored at the time of purchase. Slainte.

I picked the number out of my head, and it refers to Swedish sawmills for their standardized dimensions for construction wood. Then the target is 16%, of course there are other standards and I do not know what is typical in the UK. The lower number I mentioned does not refer to the target from the kiln, I was perhaps unclear. I refered to the recommendet MC when the timber is used. In Sweden furniture grade timber is often delivered with a MC of 8% to 12%.

 

[Stevekane]

If I was to rewind the clock and start again which timber should I have chosen to make the table.
The options were-
c16
c24
spruce rough sawn
redwood rough sawn (more expensive)
PAR softwood (Most expensive)

I made a garden table from C24 timber and it worked well enough, but I spent some time picking lengths where the end grain was running between the two faces rather than being able to see the curving growth rings arching across from side to side, I think the ideal is called quarter sawn where the timber has been cut to creat these characteristics but of course construction timber is just sliced up, but if your lucky you can find lenghts where the tree has been sliced up giving this effect. My understanding is that as wood dries the rings want to flatten out, and if you look at your timber end on you get a some idea of how its going to behave.
BTW Im no expert on this, its just my understanding based on stuff from the internet,,,
Steve.

 

[Sgian Dubh]

I picked the number out of my head, and it refers to Swedish sawmills for their standardized dimensions for construction wood. Then the target is 16%, of course there are other standards and I do not know what is typical in the UK. The lower number I mentioned does not refer to the target from the kiln, I was perhaps unclear. I refered to the recommendet MC when the timber is used. In Sweden furniture grade timber is often delivered with a MC of 8% to 12%.

I think I know what you're referring to now. I suspect the kiln drying target for construction grade timber is likely to be the same as for the rest of Europe, i.e., 20% MC as I said before, but that in use the preferred MC is ~16% MC. In reality, making structural parts of houses such as joists and studwork with wood that is dried to that 20% MC means that over time it will continue to dry out as part of the fabric of a dry and climate controlled building (house, for example) to settle down to somewhere between 12 - 16% MC. Naturally wood continues to shrink and possibly warp as it continues to dry within the building's fabric, but by installing material as close to the likely final range of moisture content helps mitigate against excessive distortion. Additionally, after the long lengths of purchased and dimensioned wood has been cut to shorter lengths and is interlocked with other wooden parts of the structure with nails, screws, and possibly some joints, plus any cladding (plasterboard, floor boards, man-made panelling, etc) the whole assemblage will resist deforming.

As to the moisture content of furniture grade material destined for indoor use, that 8 - 12% MC you mention fits closely to the sort of moisture content range wooden furniture experiences in decently climate controlled habitable buildings. Slainte.

 

[stigg]

A friend brought some of the same c24 200x50 round and asked me to make some shelves. Just plane it up and cut to size. You could tell it had a high moisture when planing it. My advice was to take it home and put it in his house for a bit. preferably with something heavy on top.
'Not a chance the wife want's it done.'
The next week he was back asking me to plane it again as it had warped. Apparently he had put it on a heated floor for a week!
Told him it would warp again and not stay flat. Planed it flat and he went off happy.
Not seen him since.

 

[Parbynat]

A lot of good info for me to mull over.

Doug71- My MC reader is due to be delivered in the next 2 hours, I'm gonna be like a kid with a new toy when it arrives.

 

[Parbynat]

After checking several items in my house made from timber I seem to be averaging 9.5% when it comes to MC.
The timber planks I still have in the house range from 11.5% all the way upto 19%. I was surprised to still get such a high number on 1 of the lengths.
I will keep checking them for another week to try and gauge what kind of drying I am getting in my house at this time of year.
What a nice bit of kit they are tho.

 

[aet1]

Going back to your particular problem if it's for use in a garage the humidity will change a lot during the year so it is unlikely to stay flat, I use alternating direction of growth rings and have found a rolled to is more useful than a prominently curved one.
I've never used scaffold boards, but I do wonder if it would be better to slice them in two so the planks are narrower and alternate them so the ripples are smaller.

 

[Ozi]

What was it? Recently tanalised, wet rough sawn and not kilned intended for exterior use, greater than 100 mm thick so wouldn't have been kiln dried anyway. 26% MC is two percentage points greater than is allowable for dry grading of kiln dried construction timber.

How did you check the moisture content - moisture meter or oven drying methodology?

26% MC is a bit high even for stuff that's been kilned to a target of 20% MC and subsequently stored in an open sided shed, whether winter or summer and all seasons in between. I suspect there's a detail of some sort missing in your post that could put that reported 26% MC into context. Slainte.

Checked with a moisture meter. The detail is according to their driver and the evident mud splatters it's all stored outside not in a shed and mine came from near the bottom of the stack.

 

[Sgian Dubh]

Checked with a moisture meter. The detail is according to their driver and the evident mud splatters it's all stored outside not in a shed and mine came from near the bottom of the stack.

I suspect that probably contains the missing context I mentioned: that is, external storage and the stack might have experienced repeated wetting with rain, and even perhaps snow. Depending on how often and for how long the wood was exposed to repeated wetting it could be that the core of the wood you tested out with a moisture meter was much drier at, for example, close to 20% MC.

Moisture meters can only provide a reading within a narrow band of wood dependent upon the length of the pins, or the length of the projection of the frequency field with pinless meters. So, for example, a moisture meter with 7 mm long pins can give a pretty good median reading of the average moisture content of a 25 mm thick board, but wouldn't be able to give an equally reliable reading in a 100 mm thick board. For a 100 mm thick board you'd get a more reliable reading with a meter fitted with 25 mm long pins, and some of the more expensive meters are supplied with a connecting cord and plug attached to set of extra long pins mounted to a sliding hammer device to drive the pins deep into the wood. Slainte.

 

[Ozi]

I suspect that probably contains the missing context I mentioned: that is, external storage and the stack might have experienced repeated wetting with rain, and even perhaps snow. Depending on how often and for how long the wood was exposed to repeated wetting it could be that the core of the wood you tested out with a moisture meter was much drier at, for example, close to 20% MC.

Moisture meters can only provide a reading within a narrow band of wood dependent upon the length of the pins, or the length of the projection of the frequency field with pinless meters. So, for example, a moisture meter with 7 mm long pins can give a pretty good median reading of the average moisture content of a 25 mm thick board, but wouldn't be able to give an equally reliable reading in a 100 mm thick board. For a 100 mm thick board you'd get a more reliable reading with a meter fitted with 25 mm long pins, and some of the more expensive meters are supplied with a connecting cord and plug attached to set of extra long pins mounted to a sliding hammer device to drive the pins deep into the wood. Slainte.

It did vary a bit but I cut about 2" off the worst end as it was damaged and that was just as wet in the middle, Ok the end will have soaked up more than the middle but it still twisted Like a cork screw which is not what I'd expect from Kiln dried regularized timber. It was the last straw after many other issues.

 

[Sgian Dubh]

It did vary a bit but I cut about 2" off the worst end as it was damaged and that was just as wet in the middle, Ok the end will have soaked up more than the middle but it still twisted Like a cork screw which is not what I'd expect from Kiln dried regularized timber. It was the last straw after many other issues.

I also wouldn't expect kiln dried regularized material to be as wet as you described, and the warping you experienced is a likely result of the large amount of water you reported in the wood leaving the wood fibres. Given the description of the material by the seller you mentioned in your quotation above I suspect you'd have had good reason to reject what was delivered. Obviously I can only speculate about what happened and why, and whatever I might speculate could be wildly wrong so I'm not going to offer any theories. Slainte.

 

[HOJ]

I now have a 2m length with 45° of twist along it's length at around 10% MC. The rest is part of a bench I sold, no complaint yet but didn't dare ask. I did ask if by seasoned TP mean someone runs around the yard with a salt and pepper pot.

The timber you have bought, C16 (low grade structural timber), is conditioned in the way the description states, as in, it is graded to C16, kiln dried then regularised & then treated, generally with a water based preservative, which in effects makes it as wet as if it were fresh sawn, if not wetter, then the builders merchants leave it out in all weathers, which is why I said earlier on don't buy wood from them for anything but construction uses, having said that if it's as twisted as much as you say, its not fit for any purpose.

I did ask if by seasoned

Can't see them telling you it was seasoned, sawn from the log and processed as quick as possible.

 

[Sgian Dubh]

The timber you have bought, C16 (low grade structural timber), is conditioned in the way the description states, as in, it is graded to C16, kiln dried then regularised & then treated, generally with a water based preservative, which in effects makes it as wet as if it were fresh sawn, if not wetter, then the builders merchants leave it out in all weathers, which is why I said earlier on don't buy wood from them for anything but construction uses, having said that if it's as twisted as much as you say, its not fit for any purpose.


Can't see them telling you it was seasoned, sawn from the log and processed as quick as possible.

I'm an *****, and it took your post to realise my idiocy! I can't work out how I completely missed the fact that this 'problem' wood was not just kiln dried and regularised, but treated - I guess I just wasn't properly paying attention. As you point out treating the wood under pressure with water based Tanalith E results in adding significant water to the wood fibres.

As a result of you making me realise my basic error, I'd say much of what I said to Ozi can be ignored. On the other hand, I thank you for making me realise my stupidity, daftness, inattention, or whatever else you might call it. Slainte.

 

[HOJ]

I guess I just wasn't properly paying attention

Best just leave it there Richard, with huge respect, your knowledge on these matters is far greater than mine, i was just observing the fact it was treated timber, which I know from experience of regular use, is in some cases sopping wet, In my opinion this is the only use for this type of timber:

In all the timber I bought for this job, there weren't any lengths that couldn't be used, it wasn't from TP mind

 

[Sgian Dubh]

Best just leave it there Richard,

Good tip. I'm leaving it, ha, ha. Thanks for the wake up call though. I suspect I was running on autopilot, or something. Slainte.

 

[Doug71]

Bit of a thread hijack but kind of relevant.

This was among a delivery from Lavers a couple of weeks ago, some redwood 5ths (not treated), I don't normally use 5ths but it was only for some trestles and I didn't expect it would be this bad

The rest of the pieces were fine, guess this one was under a rip in the cover sheet or something. I left it outside and it soon dried out (windy day). @Sgian Dubh I just wondered how long it takes for the blue stain to develop, are we talking a few weeks? Has the wood as I suggested maybe got wet through a tear in the cover sheet and never really dried out? It was only that centre section that was wet, the ends were fine.

 

[Sgian Dubh]

Bit of a thread hijack but kind of relevant.

This was among a delivery from Lavers a couple of weeks ago, some redwood 5ths (not treated), I don't normally use 5ths but it was only for some trestles and I didn't expect it would be this bad

I just wondered how long it takes for the blue stain to develop, are we talking a few weeks? Has the wood as I suggested maybe got wet through a tear in the cover sheet and never really dried out? It was only that centre section that was wet, the ends were fine.

It looks like sap stain, but I could be wrong, it being hard to see exactly what you've got there in the photograph. Assuming I'm right, sap stain is visually unattractive but insignificant in terms of strength loss. Sap staining fungi, there are several, don't have the chemical armoury to break down cellulose and other strength providing structures in the timber, and have a strong preference for gymnosperms (softwoods). They live on sugars readily available in the wood's parenchyma so mostly restrict themselves to colonising sapwood, hence the name.

As to how long it takes for the stain to develop I really can't say with any certainty, but I suggest that an abundance of water (nearly 30% in your image, I think, so plenty I'd say) as well as substantial available sugars, plus warmth might lead to blue staining showing up in just a few days. Less water, warmth and sugars would delay blue staining progression but by how much is a bit of a guessing game. So, I suspect your guess about the wood getting wet, possibly rained on, after processing (boarding up, kilning, stacking, storage, transport, etc) is the cause in your case. Get the wood dry again, 20% MC, or below being an oft quoted number, and the fungal activity ceases, although the 20% figure relates primarily to dry rot which has the ability to thrive at lower moisture content than many other species of fungi.

Hope all the above helps, and just don't use the now presumably dried but discoloured piece(s) of wood where they're on show if you don't like the appearance, or if it is on show, er, well, paint it. Slainte.

 

[Adam W.]

Bit of a thread hijack but kind of relevant.

This was among a delivery from Lavers a couple of weeks ago, some redwood 5ths (not treated), I don't normally use 5ths but it was only for some trestles and I didn't expect it would be this bad

View attachment 156816

View attachment 156817

The rest of the pieces were fine, guess this one was under a rip in the cover sheet or something. I left it outside and it soon dried out (windy day). @Sgian Dubh I just wondered how long it takes for the blue stain to develop, are we talking a few weeks? Has the wood as I suggested maybe got wet through a tear in the cover sheet and never really dried out? It was only that centre section that was wet, the ends were fine.

The black stuff is mould and the blue stuff on the lower edge of the bottom picture under the meter is blue stain in the sapwood, you've also got it on the bearer at the front.