Green spotted gum - does it rot quickly?

[Coastal Settler]

Hello all,

Can anyone advise if I can use green poles of Spotted Gum as joists on an old dam jetty that I am restoring? I am asking because a friend visited recently, saw my work and told me that they will rot very quickly due to the sap crystalising in them.

The other thing my friend said was that although I thought I had stripped the bark and sapwood off (I did it with a hammer and chisel and there was a distinct difference between the sapwood and the heartwood IMO), that the whole trunk was basically sapwood apart from a very small core in the centre. He said they would rot out in a couple of months.

The reason I am using spotted gum is that it is free and I am allowed to harvest it on my land. I have Ironbark too, but I am not allowed to harvest it.

I have searched high and low on the internet to verify if what he said is correct and I have found nothing apart from articles about how strong Spotted Gum is. And in January I cut down, stripped and used a green pole for an H brace on a fence. I checked that pole, and do not see any sign of the rot he mentioned.

If he is right I need to start again, so I would like a second opinion. The last thing I want is an unsafe jetty with rotting joists.

Many thanks

PS: The joists sit about 1 metre above the waterline, they will not normally touch the water. The old structure appears to be made from Ironbark, it is still very sound except for the planks and one of the joists which I am replacing.

[BobL]

Hello all,

Can anyone advise if I can use green poles of Spotted Gum as joists on an old dam jetty that I am restoring? I am asking because a friend visited recently, saw my work and told me that they will rot very quickly due to the sap crystalising in them.

CSIRO durability classification fo SG in ground is class 2 (out of a scale of 1-5, 5 being the worst)

The Forest Products commission gives common uses for SG as
. . . . . heavy engineering construction and mining timbers, where shock resistance is important, house framing, flooring, tool handles, piles and poles, shipbuilding, agricultural machinery and
plywood.

I doubt they would use SG in these situations if there was a problem with it,

[Coastal Settler]

Hi Bob thanks for this, that is the kind of information I found too. All the info points to Spotted Gum being a good strong hardwood. The point my friend was making was that green spotted gum wood rots due to sap crystalising. I think the data on Green Gum is based on kiln dried/processed wood. I can't find anything though to back up what he said though about using it green.

[GraemeCook]

Good Morning Coastal Settler

Firstly, welcome to the Forum.

Spotted gum used to be known as Eucalyptus maculata until they changed its name to Corymbia maculata. Google on its latin name and you should get heaps of strikes.

When ocean going ships were made of wood, Tasmania had a major ship building industry producing both blue gum clippers (ocean traders) and barges (ketches designed for coastal trade). The prefered timbers for these vessels were:

Framing - spotted gum - Eucalyptus maculata,
Planking - Tasmanian blue gum - Eucalyptus globulus,
Decking and spars - celery top pine - Phyllocladus aspleniifolius.


Here is a photo of the oldest remaining coastal traders, locally known as barges, the May Queen, built at Franklin in 1867 from the above timbers. Her spotted gum framing is now 153 years old. How is that for longevity!

475165

[rustynail]

The heart wood of SG is far more durable than the sap wood. Unfortunately, your timber is predominantly sap wood and your friend is right, it will rot quickly. The trick to turning sap wood into durable timber is impregnation of a preservative (think CCA). Obviously you can't go down that route without the necessary equipment but there is a way of doing a home grown treatment. A drum is placed over a fire or large gas ring, creosote is poured into the drum to about a foot deep. The fresh cut logs are stripped of bark and stood in the drum, The creosote is brought to the boil and the sap is driven out the vertical end of the log causing the creosote to be drawn up behind. Once the top end of the log has blackened with creosote the logs are removed from the drum and another batch dropped in. The greener the logs the better it works.

[GraemeCook]

Rustynail

Are you still allowed to use creosote? I thought it had been banned as carcinogenic.

[AlexS]

Pretty sure it has, and even if you can lay hands on some I wouldn't want to be around it with fumes coming off it while it was boiling.

NSW EPA Creosote (https://www.epa.nsw.gov.au/your-environment/household-building-and-renovation/treated-timber/timber-treatments/creosote-treated-timber)

[rustynail]

Creosote oil is still available (Sceneys). It is not sold domestically but is available in 20ltr drums for industrial purposes.
There are a lot of products that are carcinogenic, including many timber species. We never stood around while it was boiling. Just let the fire go out and cool down. Used a respirator and handled with gloves. An old mate I used to work with has been treating timber this way for more than 60 years. He is now 94 and still able bodied. It is nasty stuff though.

[BobL]

It's actually not so bad for humans (from the MSDS)

- Causes eye irritation.
- May cause cancer.
- May cause respiratory irritation.
However its is devastating for things that live in water.
- Very toxic to aquatic life.
- Toxic to aquatic life with long lasting effects.

Whole houses were painted with the stuff in Pemberton where I lived as a kid - might explain a few thing?

Back to the OP. cI didn't realise most of the timber was sapwood which is I believe S5 rated (ie worst possible scale).

The grubs that love the sapwood develop some amazing patterns - some would be good enough to hang on a wall.
Look at at the patterns on the side of this log.
475203

[Coastal Settler]

Thanks all, I really appreciate your input. I'm going to ditch the spotted gum and go back to the drawing board.

[verawood]

Plenty of creosote replacements available, inc Bunnings.
Good luck at the drawing board. :)