Tanalised wood--how deep does the preservative penetrate?

[blod]

I am putting up a tanalised shed but I want to make the roof a bit wider and longer, for more of an overhang, and put up a fascia board to support gutters, and I want to add wider decorative trim on the corners. I want to use tanalised woof for all these things but the choice of wood where I live is very limited. So I thought I might get, say, a 3 inch square length of tanalised and use the table saw to cut thinner lengths. Or I could plane down a 1" thick board....anyway, would that work? I don't know if the pressure-treatment goes all through the wood or if newly cut edges would be as prone to rotting as ordinary softwood.

The local timber yard sells feather edge boards that would be good (if cut narrower) to make the decorative trim for the corners of the shed. With that thinner wood (max about 1/2 inch) be pretty much sure to be treated all the way through?

[The Natural Philosopher]

Nope. I've sawn tanalised timber, and the color is at best a mm or so deep.

[Cash]

blod,

It would depend on how the timber was tanalised. If it was merely dipped or soaked, then it would fairly superficial - if it was pressure/vacuum treated, then it should 'right through'.

As a matter of interest, I have a fence made of tanalised timber that was erected some 10 years ago (all pressure treated) which is as good now as when it was done - and the 100mm square posts showed tanalising right to the core (as specified by me).

Cash

[Chris George]

Tanalith process is defined as a pressure impregnation anything else is immersion

Old CCA was good but the Eurocrappers have f****d up the process by taking out the A and as a result is it not so effective Chris

[The Natural Philosopher]

Well I dunno about all that. I bought a LOT of 'pressure treated' wood and no WAY did the greenish cast go more than 1mm into it.

Maybe a bit more at the corners. Oh it penetrates all right..its not just a surface treatment, but the price of it alone suggests that its not fully impregnated with copper salts. No way! It would be hugely expensive.

Its just a way of getting treatment beyond the immediate surface, it doesn't fully penetrate the wood by any means.

[Andy Dingley]

Just one of tanalised timber's several failings is that if you saw or drill into it, then you might as well not have bothered. It's a surface treatment and it's of limited depth. IMHO, you're better with _untreated_ timber, of a species that is inherently more rot- resistant. This needn't be expensive, decent larch isn't.

For more detail, try and find excerpts from BS 8417 (2003) (town library might help, as it's =A3100 ish from HMSO). In particular, look at the differences between "class 3" (what you can usually get) and "class 4" (what you need to use for contact with the ground) treatments.

Timber's expensive and variable in quality, it's worth hunting to find the best sources.

[Andy Dingley]

Tanalith is not pressure impregnation (which barely works) it's a vacuum process. Although it's also followed by an overpressure, it's the vacuum that makes the difference in penetration depth. Things that merely claim to be "pressure treated" are usually just that alone, and they're nowhere near as deeply penetrated.

Tanalith is a trademark, and protected. "Tanalised" is a derivation of this and less easy to protect. If I wanted to be sure that it really was what I thought, then I'd have more confidence if I saw the word Tanalith than just seeing "tanalised"

Tanalith C was the CCA-based process and Tanalith E is the new one (since 2002), without the chrome or the arsenic. Tanalith C is still (AFAIK) in production for export, and it's popular in Africa. Tanalith E is also showing good results at resisting rot in the UK climate, compared to Tanalith C and there's no reason at all to consider it as "ineffective". Can't say how it stands up against termites though, which is AFAIK why Africa still likes CCA.

[Chris George]

Fair comment Andy, but by pressure I really meant that it was an industrial process which involved both high and low pressures in a cycle and of course you are right that in order to get the pressure to work it involves a reduction of pressure first as with the VAC VAC but on the issue of the merits of CCA verus the stuff produced now, I can tell you from first hand experience that in 35 years of surveying I never found CCA affected by dry rot (unless the end had been cut) and just last week I came across timbers that were completely attacked in treated side grain by a normal attack of dry rot - unless I had seen it myself I would not have believed it so sadly we can no longer rely on Tanalised timber to be rot proof I am going to take samples and send them off for analysis probably by Hicksons or the like just to check it really was subjected to the proper process Chris

[The Natural Philosopher]

I think that's a BIT harsh. Sawing the ends of and plastering them with=20 something is not too bad.

Also remember that fascias et al are not generally subject to prolonged=20 damp: they tend to dry out periodically and that kills rot.

What kills wood in under a year if not treated is being pushed into the=20 ground. Perfect breeding ground for fungi.

The other big rotter is the flat topped post where rainwater soaks into=20 the end and most and algae accumulates.

[The Medway Handyman]

OMG I hope Dennis doesn't read that. He'll be down the timber yard with his fairly old plunger...

[The Medway Handyman]

Treat it with a decent wood treatment, should be fine.

[Kipper at sea]

p.- Hide quoted text -

Your right, its only skin deep. GPO as it was called now Telecom, tried it as against creosote for their telegraph poles but soon went back to creosote

[dmc]

Jacksons (local to me) claim their pressure treatment is better than most.

Their website boasts about it - and clearly shows it not being through the entire thickness (not even close).

Given they claim to be better than most I suspect most stuff is very limited penetration.

a few images. No idea what particular cocktail of nasty chemicals they use mind.

Darren

[Dave Liquorice]

But the bit in the ground will be OK and the bit 6" or so above ground level. It's the bit in air just above ground level that rots, plenty of oxygen and just the right amount of damp by capillary action up the timber.

Yeah, tends to rot the core out.

[The Medway Handyman]

Good question. I've e mail the Tanalised people

and asked them. I'll post back when they reply.

[Bill]

I asked here a bit back, but everyone was asleep, so.....

When adding some fascia boards to my shed, I treated them with the clear version of Barrettine Wood Preserver. It seemed powerful, and killed the grass where I spilt some, so looked good.

Her indoors now wants me to coat our tanalised front fence with something like

is advertised on the other tin, but seems not to be stocked anywhere locally. She wants the fence to end up a very light brown colour, and none of the creosotey things seem light enough. This stuff is in a sort of paraffiny type solvent.

What does anyone think of brushing quantities of this onto the fence? The front looks of the property depend a lot on my not making a complete mess of it. Would it be mad and hazardous to try to spray it? Would it be sensible to try to mix some dye into the clear and hope the colour is slightly consistent? I can buy the clear locally.

[The Natural Philosopher]

Shades of Eskimo Nell again.

[The Natural Philosopher]

I think not., if the mushrooms that spring up from bits of buried timber in the garden are anything to go by..sure, the spores strike above ground, but they rapidly expand below as mycelia. Fungi dont need light, or air..

Yup.

[Dave Plowman (News)]

Just what use could wood be put to without it being cut or penetrated in some way?

[Chris George]

The Natural Philosopher is right

Dr Ed Bains did the original work on this in the ICST lab back in the early seventies when we were both students together doing our theses It transpires (pun intended) that what happens when a stake is put in the ground that there is some wicking of the salts in the ground up the timber to the point at ground level where they can evaporate. These salts bring nitrogen to the substrate (wood) and make it really rather tasty for the precursor (generally stainers) fungi only to be followed by the rotting fungi The wood immediately adjacent to the ground rots preferentially. The wood above ground and the wood below ground at the point where it is anaerobic does not rot. Most of us who have replaced old fence posts will confirm this on looking at the posts on removal. Generally at the top there is much less decay (albeit some) as it gets to dry out and gets too hot in the sun

Chris