Thread: Why are slabs so popular?

Post some pics. Slider blocks were often used screwed to the slabs, these still let the timber move generally, but not sure if that is what you are describing. Even some of those only allow movement in one direction, not both, so could still cause issues.

Yes, they are slider blocks Neil, but because the warping had started I put some screws straight through (some of the sliders were useless by this point and being dragged out). This was when I knew even less than now, remarkably.

Hi all

Just throwing my 2 cents worth in on the discussion. I have been milling slabs for the past 15 years or so, as well as cutting boards with the aim of matched continuous sets. I try to specialise only in premium slabs milled from huge salvaged redgum logs. They vary from 1.0- 1.8m wide and up to 7m long, but generally sit around the 1.2m x 3.6m size x 60-65 mm thick. (There are a few photo's on the Small Timber Milling Forum if you're interested, "Milling the Mother Log").

I air dry my slabs for a minimum of five years on a dead flat base, timber sealed correctly and racked carefully. After 5 years they generally sit steady at around 10-13% moisture, depending on the season. Over the years I have supplied many slabs for tables, never to have one bow or cup once machined flat and made into a table. I reply on this quality as I do not advertise and reply on word of mouth to generate a return for my small business/hobby.

So I have concluded over the years (still acknowledging different rates of shrinkage in different dimensions) that you can produce a good quality slab if it is milled, racked, dried and machined correctly. But most importantly, I feel it must be milled from the right log. All too often I have seen slabs milled from trees that are simply not mature enough for the purpose and should have been cut into boards, or were milled too close to the heart.

But hey, I'm not throwing too much science into it, even though I understand it, because I think the best slabs are cut by placing the utmost care and effort into achieving the best result with a good quality large log. A general understanding of the science is very helpful, but does not influence the outcome too much. I rely on my experience for this, which like everyone else who is into milling, has been forged by trial and error through piles of sawdust!

On the other hand, I do agree that as a furniture maker, if you are not set up to handle slabs, they are a back-breaking difficult thing to work with. I get mine machined through a massive 1500mm wide industrial thicknesser, which gives a perfect finish requiring minimal sanding. They get dropped off at the cabinet maker who has a forklift and the entire process is relatively easy.

Just my thoughts anyway.


Cheers

James

When I look at a slab all I can see (if it is thick enough of course) is how many very nice bowls it would make when I cut it up! I have not actually bought one yet as I have quite a lot of small blanks that I need to convert before I acquire any more timber.

Steve the bowl turner

Grain structure has a big influence.

Here in the West, Red Gum and Karri are usually sent to chip - as low grade pulp for cardboard manufacture...and a only about $2 bucks a m^3 stumpage.

Not that they don't make nice furniture - because they do... lots of marri & karri slab tables around now days.

In the old days there werent used much for furniture - because of their interlocking long grain structure (hard to machine and sand / finish) - the very reason they made good paper pulp - th elong grain recombines to make a strong cardboard - the color costs too much to bleach white for glossy magazine paper use which is why tas Globulous is used principally for high end paper... and why the darker redder & keno pockets timbers like Marri & Karri - are sent to chip/pulp for low grade corrugated cardboard use.

I would suggest to you - that its the long interlocked grain structure that allows Red Gum to be slabbed with far less splitting - than we get here with the short grained Jarrah - which works well on machines and sands - takes a finish well without the grain sticking up....requiring high build rate finishes.

These Jarrah slabs - "split like billie oh"... I used to put large quantities thru the kiln every 3 months or so... and they all split in from the ends - all our logs were end sealed when delivered and the slabs ends also sealed before being placed into the kiln.

Marri slab never gave me anywhere near the trouble that Jarrah does - its all about the physics of grain structure and relative differences in shrinkage / expansion rates in the respective species.

The same links I posted for Jarrah rates - if you search the main directory have Marri rates as well...for Radial and Tangential - and combined with the grain length and intertwined nature - splitting is far less of a problem in Marri.

Same with WA Sheoke - a softwood (Gymnosperm and distinct from Angiosperm) or reproduced via cones and spores/corms - instead of hardwood that reproduces bye flowers nuts and seeds. Sheoke slabs have minimal shrinkage rates - & 2 different grain directions - thus no splitting at all.

You just need to know what your doing when slabbing and treat each log as it's size age and species / grain properties etc dictates.

The timber even varys depending on it's growth site - some Jarrah logs that came from down on our south coast where the wind blows like 10 batsurds from Antarctica so hard you can smell the penguin shyte on it... and the one side of the log - was in such compression - that it would warp a few inches end to end, just coming off the log when milled, as the internal stresses were relieved by the action of the saw blade.

BUT that same timber had some beautiful curly grain patterns.... from the effects of wind compression over it's growth life of quite a few hundreds of years...

Big Jarraah paddock logs - that had the benefit of standing for ~200 years in a paddock where fertilizer is regularly applied annually...(and all the cow crap) as well as no competition from neighboring trees - would produce jarrah much less dense than normal forest logs - and often a pale salmon pink color, with large amounts of distance between annual growth rings... it would work like butter...

So there are marked differences even in same species logs depending where they were grown and how - when milling and drying.

To me at least - that's half the fascination in working timber - being able to work it all out, understand it and adapt the design and joints etc to complement the individual boards in a sympathetic way for the lifetime of the piece of furniture.

Others mileage may vary of course - experience teaches all of us different things.

IMG_0173.jpgslab it and kiln dry or slab it stack it and air dry

Red Cedar is an angiosperm (Reproduces by flowers fruits/nuts and seeds) ad thus by definition a hardwood (albeit a deciduous one).

If it's 50 mil thick slabs - strip stack it & air dry it under cover with good air circulation for 3 years!

That will pull it down to ~ 18% EMC roughly, dependent how dry the relative humidity of where you store it.

Then put it in a kiln to pull it down to ~ 12% EMC if you intend to make it into furniture to be used around the coastal zone of Australia.

If it's to go into a snow prone area (very dry relative humidity) or a 24 hour refrigerated air conditioned climate controlled building skyscraper (again very dry relative humidity) then probably you'll want to dry it down to an even lower EMC

Only kiln drying will get you down to 10 or 11% EMC then re stack under cover and allow to re-absorb up to 12% EMC.

The air drying takes about 1 year per inch thru the thinnest dimension + 1 year - so 2 inch thick slab will take 3 years to air dry as a rough rule of thumb to around 17% - 18% EMC.

The air drying gets rid of the free moisture (sap) from between the cellulose cells of the timber SLOWLY.

It's important to pull this free moisture out slowly with air drying - so you don't create a pressure differential, where the moisture inside the cell walls bursts thru the cell wall to even out the pressure gradient differential between the cells and inside the cells and causes structural collapse.

Once it's air dried - the kiln drying will heat the timber up to around 50C eventually to evaporate the moisture contained in the cells into a gas (steam) so that it can diffuse out thru the lumens (microscopic pores) in the cell wall without collapsing the cell walls.

That's how you get the timber down to a stable EMC of around 12% to be able to work it into a finished product without destroying it in the process and end up with stable timber to work with for furniture. If it was for joinery, air dried to around ~ 17% - 18% emc would suffice at a pinch

That's a brief summary of the timber drying process.

Kiln drying hardwood in an evaporative kiln - from ~18% EMC down to 12% EMC - will take around 3 months.

Nice looking log....

Here in NSW it is not difficult to get cedar down to 12% by air drying only. Good cedar can be ruined by a poorly managed kiln. As most kilns are set up for more difficult species, cedar dries too quickly in these units. Cedar would have to be one of the easiest timbers to air dry. I have been drying cedar for over 40yrs and have never used a kiln. Whereas, other species, eucalypts, I air dry then kiln dry.

Originally Posted by Timless Timber

...The air drying takes about 1 year per inch thru the thinnest dimension + 1 year - so 2 inch thick slab will take 3 years to air dry as a rough rule of thumb to around 17% - 18% EMC....

Certainly the longer it can dry the better, but I have always used 1 year per 1 inch, so as drying from 2 sides 50mm takes only 1 year. I know some of my slabs of RC are air dried within 6 months due to its low density but I never use them that fast.

Yes indeed there are a couple/few different styles of kilns now.

Mine was an ebac evaporative (essentially a reverse cycle refrigerated air conditioner).

Softwood kilns will go to 100C and dry pine in a matter of days... but would destroy hardwoods thru drying way too quick.

Max temp setting on the ebacs heater thermostat was 50C - which you reach at the end of 3 months working thru your drying schedule and measuring your water extraction daily (Typically the 13M^3 charge when full would yield ~ 20 - 25 liters of water a day) and as the water production drops, you increase the ambient temp...to bring it back up...

Locations away from the coast and the influence of moisture laden afternoon sea breezes (i.e. desert areas) will pull timbers down to below 17 - 18% EMC with air drying only.

The only way to really know your emc's factually is with a moisture meter.

I liked the Tramex brand , conductive impedance (non destructive) wood moisture encounter, and compared it several times with the older probe types results ...and found it to be very accurate.

That in essence takes out all the guess work.

Originally Posted by Timless Timber

Same with WA Sheoke - a softwood (Gymnosperm and distinct from Angiosperm) or reproduced via cones and spores/corms - instead of hardwood that reproduces bye flowers nuts and seeds. Sheoke slabs have minimal shrinkage rates - & 2 different grain directions - thus no splitting at all.

You just need to know what your doing when slabbing and treat each log as it's size age and species / grain properties etc dictates.

That is sage advice but difficult to apply if you haven't milled the timber yourself, know it's provenance or worked with that species before. This is an discussion of interest to me as I have two slabs waiting for my own use but have no idea what the average properties are for that timber as it is not a commercial eucalypt species so, apart from some basic timber paramaters, there is no info on grain properties or workability readily available. All I know from first inspection is that it is pretty hard and heavy.

By the way, sorry to appear as a pedant but sheoaks (Casuarinas and Allocasuarinas) are angiosperms and therefore hardwoods. Their 'cones' superficially resemble gymnosperm cones but are woody fruits. They also flower but the flowers are greatly modified for wind pollination with the sexes are presented seperately on the same or different individual plants. They do have very distinctive timber properties but I had thought from anecdotal information (from this forum mostly) that Casuarinas had high tangential shrinkage rates and split very rapidly if not milled quickly after felling. IS the WA species an exception?

Edit: It occurred to me after posting that you may have been referring to movement post reconditioning in slabs rather than prior to in sheoak. Forgive my error if that is the case. The WA forest product commmision figures would suggest that it is very stable when dry but splitting/and movement may be encountered during the drying process. As you say though shrinkage rates are only part of the story.

I too have a Tramex, has given many years of good service

I stand well corrected pamplemuse, you are 100% correct about WA she-oak being a hardwood, Angiosperm.
That has been a misconception of mine for a VERY long time.... and I should know better... just shows you, looks can be deceiving.
Well picked up.
I will now go self flagellate until I remember not to type off the top of my head without checking the facts.