Thread: Green blackbutt question.

Originally Posted by 2sheds

Hi all,
Am using 250x75 bearers for my deck rebuild. Timber will be Blackbutt or Stringy Bark from a local and very reputable sawmill. Maximum length is 4200mm. Timber will obviously be green.

Questions:
1) Apart from sealing the end grain to prevent rot etc. should I treat the timber in any way to slow down shrinkage?
2) Should I leave the timber in a cool airy place for 6mths or so to partially season or
3) Should I just fix it in position and let it do whatever it will do?

Many thanks for any advice, Peter.

For a deck, I would just use it.

I agree with BobL, just use it. Dry hardwood becomes very much harder to work the dryer it gets. If you have the choice between blackbutt and stringy, take the blackbutt as it is more stable/durable and fire resistant.

I am not familiar with the east coast Blackbutt species shrinkage rate width wise.

Here in the west - ours (Eucalyptus patens) is quite a large rate.... (Tangential and radial shrinkage before reconditioning are 10.0 and 5.0 per cent respectively, and after reconditioning 7.0 and 3.5 per cent respectively) which means that depending how the bearers / joists are sawn (radial or tangential grain) you get variations in shrinkage rate between individual boards. (e.g. 250mm green sawn COULD end up 225 when dry or 237.5mm wide... so a difference of 12.5 mm of half an inch depending on how the bearer was sawn and the joist... if both are radial sawn or both are tangential sawn and you got that max shrinkage on each - then a possible 1 inch (25mm) difference in height between adjacent joists when green + whatever the decking board does on top of that.

Thus when you set out your bearers and joists on their supports, which are all run to a level (or string line) the varying thicknesses as they dry results in a floor that's POSSIBLY up and down like a fiddlers elbow once it shrinks to dry.

What I'd be tempted to do (if a flat floor is important to you - e.g. if you have elderly folk who might trip on a single high board, break a hip & die from their injuries), then let it dry for as long as you can - and skip dress it thru a thicknesser to gauge it all for just "height".

This way when you lay everything it SHOULD come up nice and flat.

Outdoor decks typically aren't as crucial for dead flat as internal T & G floors etc where furniture is expected to sit flat on it.

But if you have the ability to let them do their shrinking (or at least a goodly portion of it first) then skip dress them thru the thicknesser to rough gauge them to the height of the smallest one.... you will end up with a pretty acceptable result.

Maybe that's not necessary with your eastern states blackbutt - but I sawed and dried and ran a LOT of WA Blackbutt T & G Flooring over the years, and the shrinkage rates are just scary once your dealing in widths of 250mm. Just running 5 inch (125mm) cover (130mm with tongue) flooring out of boards sawn 150 green was about impossible. (150 - 10% shrinkage = 135mm then allow for straightening and you have tongues that are missing an edge etc... Admittedly we didn't have a self straightening 4 sider... it was an old 9 head Wadkin from the UK at the turn of the LAST century (1800's) that came out of the Donnelly Mill.... so we had to straighten every board by hand before running flooring.

Eventually we worked out that by sawing the boards ourselves with a portable lewisaw - that allows 10mm for kerf but the blade only removed 7mm - we gained 3 mm on sawn width on every board and after drying - that extra 3 mm (i.e 153 green) was often the difference between ending up with a tongue on a 125mm cover (130mm wide) floor board and not.

After a while at this sort of folly, you get used to allowing for shrinkage - when cutting your boards in blackbutt.

You become all too familar with the rates of shrinkage very quickly.

My 2c

East coast Blackbutt works well green. Ive used a lot over the years for scantling and never had a problem with excessive shrinkage. It does shrink, as all green timber will, but if installed at the same time it should all shrink evenly. Its much easier to skew nail green joists to bearers and also decking to green joists with the added bonus that as the green timber dries, it shrinks onto the nail shanks, giving a much tighter grip.

Makes sense Rusty.

According to this

Timber Floor Installation, Blackbutt, Recycled and Green Tree Flooring, Overlay: Nashtimbers.com.au

the shrinkage rate is only 6% from green off the saw for your eastern states blackbutt.

You wouldn't want to get West Oz variety when ordering... (It's that hard to come bye and thus expensive that it normally goes into high end value products like flooring etc... rather than construction lumber - so pretty unlikely).

Just shows you whats in a name - eh... "Blackbutt's ain't blackbutt's, Sol!" (Although I've had my butt kicked till it were a good shade of blue a few times growing up).

Thank you for your advice, it is very much appreciated. It's nice to get info from people who have been there done that.

Just by way of comment, I have two pieces of stringy bark (250x75x3500) which I bought 'green'. They have been seasoning off the ground in a shady spot for 2 years.
Both have shrunk to 240x70x3480. Blackbutt and Stringy Bark have roughly the same shrinkage rates so may have to do a bit of joist packing at some time in the future. Time will tell.

Thanks again, Peter.

Yes that's just 4% - you should be good with a packer here or there as time progresses.

Your very welcome - the smart bloke is the one who asks first before he's already done it!

Cheers