Blue mould staining???

[agg221]

Hi Pete, interesting post.

 

I've got some current professional involvement with one of the major wood preservative manufacturers - we're trying to develop a non-biocidal alternative on their behalf, so are also working with TRADA and some of the major end users.

 

The fundamental issue is that the very factors which make timber an attractive option at the same time make its use a direct competition with nature - as trees have evolved, so have agents of decay as a fundamental lifecycle and you're trying to stop the process for as long as possible.

 

The factors which generate decomposition/degradation are environmental, and as you highlight relate to temperature and moisture content. The options for preventing it are therefore either to control the environment or to use chemical inhibition (biocides). Environmental approaches are ideal where possible, but they do require extremely tight control to be exercised when crossing from conditions which promote decay (usually the high moisture content when first milled for example) to conditions which inhibit it. In the commercial environment, kiln drying is a highly successful approach - the operation at a mill somewhere like BSW Timber in Carlisle for example is staggering in its efficiency, and facilitates transfer to a kiln kept at optimum conditions (which are sufficiently high in temperature to kill latent fungal infections) within less than an hour of a log entering the saw line. They achieve this through economy of scale - there's a log going in about every 30 seconds, 18hrs a day.

 

For the hobby miller, a different approach is required!

 

The use of a biocide is an effective approach to controlling the 'difficult' stage. It's also useful in controlling any other issues that may arise during the drying process, due to inability to control the conditions to closely.

 

Considering types of biocide - the highly persistent ones are inorganic while the organic ones tend to degrade over time. The other choice is fixed or mobile biocides. The fixed inorganic type are ideal for permanent exposure to environments where there is a risk of decay (class 5 would be the technical definition). The best of these was copper chrome arsenate (CCA) which is now banned. Other copper-based treatments, and some zinc-based have previously been used successfully, and are chemically fixed, but they have virtually been withdrawn. One issue with fixed type preservatives is that they are only operational within the region of the timber which they penetrate during initial treatment. Results suggest that subsequent development of surface checks requires that a minimum of 5mm penetration is achieved, which requires pressure treatment unless repeat applications are to be made at regular intervals throughout the life of the structure and often difficult to access the critical region which is usually concealed, which is why it remains sufficiently wet to promote decay.

 

The advantage of the non-fixed biocides, such as those based on boron, is that they remain water soluble so are taken further into the structure in the presence of water, which makes them long-term active in the event of irregular exposure to decay conditions. The down-side is that they leach under permanent exposure, so they aren't useful for class 5, more class 3 or 4. Practically speaking, OK for bits of house or shed, no good for fence posts!

 

As you point out, the big issue is end of life disposal. One of the biggest problems with CCA is that when the timber is eventually broken down (decay or combustion usually) it results in leaching of arsenic and chromium compounds. Copper and zinc based products are less severe in their effect, but the presence of copper results in highly toxic dioxin formation during combustion under the wrong conditions.

 

Fixed organic biocides are usually rather chemically reactive, usually through radical formation, which means they tend to have relatively short lifetimes. The advantage is that they do not usually have the same problems in terms of end-of-life disposal of the timber structure as they tend to break down either in service or through combustion, but the down side in terms of the lifetime of a structure is that they tend to require re-treatment, which is often not possible in the critical regions. The durability of modern softwood fence posts is highly questionable for this reason - I have spoken to some manufacturers who have significant concerns. Whilst this is unlikely to result major issues, childrens' play equipment is a very real problem.

 

In practical terms, a relatively short-lived fixed organic biocide would be the ideal choice for milled timber which is to be post-processed, since the biocide will chemically decompose (possibly accelerated by combustion) without leaching, and will last until the timber is sufficiently dry to inhibit decay. If it is to be used in an indoor (class 1 or 2) environment it will then be fine.

 

In an exterior environment, the ideal solution is to use naturally durable species such as oak, sweet chestnut or cedar.

 

However, the use of boron-based preservatives, with good understanding of their method of action, is probably one of the most effective approaches currently available in respect of its combination of effectiveness, aesthetics and toxicity.

 

Sorry for the very long post!

 

 

Alec

[Pete Bannister]

Alec

I think we agree on the matter. The object of my postings was to flag up the need for real awareness when embarking on the pesticide road. Just because you can buy it off-the-shelf somewhere can engender a sense that pesticides/biocides are 'safe' or are a universal panacea.

I was very interested to see Osmose make forays in the industrial heat treatment of softwoods some years. However, they took it down the oil impregnation path and came up with ‘Royale’. As you will know, Acetylation is now commercially viable (Accoya) and I hope this heralds a major positive step forward. I’ve yet to have a play with any acetylated timber though! Until Ive done that, I'll be a tad cagy about specifying it I guess

cheers

Pete

[Rob D]

Some serious heavyweight posting going on here!

 

 

But very informative thanks

[agg221]

Alec

I was very interested to see Osmose make forays in the industrial heat treatment of softwoods some years. However, they took it down the oil impregnation path and came up with ‘Royale’. As you will know, Acetylation is now commercially viable (Accoya) and I hope this heralds a major positive step forward. I’ve yet to have a play with any acetylated timber though! Until Ive done that, I'll be a tad cagy about specifying it I guess

cheers

Pete

 

The two approaches you mention above have thrown up some issues recently.

 

The first is the recent EU volatile organic content (VOC) legislation which came into force in 2010. This has, in effect, made the use of any organic compound with a boiling point below 250degC challenging to say the least. They're not banned, but the controls make it very difficult to apply them, particularly in volume. We were initially looking at systems based on a low toxicity organic solvent and had to change approach as feedback suggested that end users simply wouldn't introduce a new technology based on it, in part driven by the current legislation and in part by the fear that an extension to the legislation would make it rapidly obsolete. Essentially, anything fundamentally new now needs to be water based. A slight aside, but relevant, is that proper 'Cuprinol' (as in copper-oil, originally copper naphthanate in turpentine but latterly the octoylate in petroleum distillate) wasn't banned - it was withdrawn as the manufacturers couldn't justify the £40k annual fee for its registration as a biocide. This is another issue in introducing alternatives which work on a biocidal approach.

 

Acetylation has shown very good results with regard to durability - but has some adverse effects on the cell structure, most notably the timber becomes signficantly more brittle. It also changes both the appearance, which becomes muddy brown, and the smell, which becomes vinegary. It's also only effective on certain species, particularly radiata pine, so its uses are limited. This is very convenient for converting a low value, low durability species into something highly durable, but the cost of the process at present puts Accoya on a par with high durabilty hardwoods, so the benefits are mostly lost except for very high end painted joinery, mostly window frames, where the main benefits are easy machinability and high dimensional stability, the drawbacks being less signficant in these applications.

 

And yes, I think we agree, although the original poster may be beginning to wish he'd never asked! (hopefully he's got something useful to work with from the earlier posts)

 

 

Alec

[Pete Bannister]

Alec, I don’t want to derail Rowan's thread too much here, especially because its an interesting and worthy subject matter. However, your point regarding the withdrawal of (eg copper naphthanate) pesticides because of the cost UK registration is apt. Came across this recently when I was looking into the use of Armillatox. Its been withdrawn for the same reasons but is marketed instead as a cleaning agent, apparently thereby circumventing the legislation.

I take it you're in timber production?

 

cheers

Pete

[morten]

Hi Rowan, you're talking about conifers and so the blue stain (if its blue stain fungi and not iron stain) would be associated with the sapwood. In conifers, Ceratocystis spp. are the usual culprits.

Pete

 

The staining, that will only occur in the sapwood, can be vastly reduced by felling before the sugary nutrients are present in the wood (i.e. october - april, depending on climate).

That, and plenty of ventilation of the cut timber is the cheapest, easiest and most effective means of avoiding blue stain fungus.

[Pete Bannister]

some excellent additional advice from Morten.

cheers

[agg221]

Hi Pete, no I'm not in timber production, I'm in contract R&D - we're the ones currently developing the alternatives. I take it from your earlier comment that you're on the building surveying/remedial treatment side?

 

Alec

[Rowan the Bruce]

And yes, I think we agree, although the original poster may be beginning to wish he'd never asked! (hopefully he's got something useful to work with from the earlier posts)

Although it is a new subject for me to delve into, learning is the key to perfection. Some really useful tips and as the pine is to use as flooring for a kids playhouse I'm not too concerned with the asthetics of the wood this time. I am the type of person (bloody hippy) who uses chemicals, other than petrol/diesel in the kit, as little as possible so using a kiln and milling at favourable times is preferable. My lack of space is an issue and warm wet cornish summers too. Currently i have an entire trunk of Crytomeria stacked in my attic (hope the landlord doesn't read that!) seems like a good place to dry stuff, dark, air flow but warm. Thanks for the posts.

[Pete Bannister]

Hi Pete, no I'm not in timber production, I'm in contract R&D - we're the ones currently developing the alternatives. I take it from your earlier comment that you're on the building surveying/remedial treatment side?

 

Alec

 

Correct Alec. Bin over 25 yrs at it and its obviously showing! I’ve been with H+R E. I. for over 10 yrs doing building pathology. My interests in arboriculture is amateur and for someone who gravitates to timber (dead or alive) and its parasites there are some interesting observations on mycology to be had on this forum

cheers