I don't believe any of it slows the natural decay of wood (apart
possibly from creosote), it just presents a more acceptable appearance.
UV is the killer, and only opaque finishes offer any protection against
No idea. I have never used it. Generally, their products have a
better solids content than others which is supposed to be one of the
reasons for longevity. However, I would still only select a solvent
Re- own brands: All wood preservatives sold in the UK (and EC) are
subject to the COPRegulations 1986 and to efficacy testing
requirements. Such tests are pretty expensive and as a result many
"traditional" preservatives have fallen by the wayside. This has
meant that only larger organisations have survived in the production
of active ingredients and formulations of these. Thus, all
preservatives are and have to be "fit for purpose" and "safe to use
as directed" so what you are getting is the result of bulk purchase
and sale by a supermarked specialist.
What does not seem to have been addressed in the trail below is to ask
the following questions:
Against what organisms do you wish to treat this wood? THIS is the
key question when determining what preservative to use.
Also What species of wood? Hard or soft? durable or perisable?
permiable or impermiable? All questions which will result in an answer
which is needed to decide the preservative to be used.
Preservatives are used to protect against the following:
Precursor soft rot staining fungi
Fungal decay such as wet and dry rots
The active ingredients for these are different.
To protect against insect attack you need an insecticide such as
permethrin or cypermethrin
To protect against fungi you need a fungicide and there are about 10
or so "regular" ones on the market and consist of heavy metal ions
normally associated with complex organic molecules or simply boron
based active ingredients
To protect against UV you need a UV blocker
Most decent coatings have some form of water repellant as fungi cannot
survive in dry wood and if you keep the wood dry it will not rot,
So, if you want to PRESERVE the wood (as oppose to protect) then you
would best be advised to put on (in accordance with the instructions)
a preservative and there are combination ones (Insecticide /
fungicide) on sale. I would unhesitatingly go for an OS (organic
solvent) based one and apply it only on a late afternoon of a sunny
dry day when the wood is at as high a temp as possible. As it cools
down the air within will contract and bring in more of the
preservative to the inner parts of the wood. Lateral penetration into
the side grain could be as much as a mm or two if the right product is
used in the right way in a permeable softwood such as Scots pine. You
would get very little penetration to most hardwoods.
The application of more than one coat will increase the loading and
I suspect that what you are really after is a protecitve coating and
as far as I am concerned after more than 30 years in the business I
would go for Sikkens /Saddolins from AKZO Nobel. It will require re
treating every couple of years but this can be done very very easily
as no scraping or serious preparation is needed and it can be done
with brush or spray.
Having used shed water based wood preservatives as directed, then
watched little fungi sprouting from the wood whenever it rains, I can
safely say it was not fit for purpose.
There are ways to convince people somethig is fit for purpose when it
isnt. Playing with the definitions is one way. You are being rather
I have to say I agree with you entirely. I've just had about 500 yards of
post and rail wooden fencing creosoted - or so I thought. The first 200
yards or so was done and we ran out of product - it was then that I noticed
that the product was called 'Creotreat' (IIRC). Cross with myself I made
enquiries and found a fencing stockist who would sell me proper coal tar
creosote and finished the rest of the fence with it.
About 3 months later the 'Creotreated' fence has got the litchins and mosses
growing again on the wood and most of the product seems to have been washed
off. OTOH the creosoted fence still looks good with no crap growing on it.
Not suprised! :
Usually the MSDS tells what 'goodies' there are in there...
Something like this would be a fair comparison with creosote:
The best way to treat existing wood is to prevent it from being wet all the
New wood can be pressure treated.
If the fence is thin enough to dry out a few times a year it won't rot very
fast if at all.
The posts will as they don't dry out, even pressure treated ones.
Putting them in a concrete shell keeps them wet so they rot quicker than if
you dig a small diameter hole and pack it with gravel.
Sheds need a good overlap on the roof to keep them dry.
If you don't like the colour of the old wood just dye it, its quick and
Interesting thread. Anything as fine and penetrating as creosote has to
be a health risk I would have thought. I doubt there's a mask capable of
filtering the fumes, which linger in clothing etc.
The fact remains that wood rots at the base, whatever it is, and
whatever it's treated with. The gravel/cement mix should help in theory,
though I haven't tried it yet.
Fence posts for motorways treated to 8 kgs per cubic metre with CCA
(before it was banned) had a design life of 50 years. Evidence to date
supports a greater life expectancy.
Fence posts rot at the ground interface as a result of a variety of
Work was done by Ed Baines at Imperial College in the early 1970s that
showed nitrogen (from salts) being preferentially deposited in the
area just at ground level having wicked up the endgrain buried in the
ground and evaporated as the post became aerated. This increase in
richness of available nitrogen allowed the devolopment of precursor
moulds and stain fungi, then soft rots and eventually various
basidomycetes which rotted the wood. Wood that is anerobic (in the
mud) will only have the pit membranes and other minor parts of the
cell destroyed by bacteria and will remain largely intact - CV the
Wood that is open to ventilation and below 18% MC (the post) will not
The key to preserving fence posts is to protect the end grain from
wicking and water if possible.
The Romans used to char the ends in an attempt to do this (as well as
vinegar and other attempts at preservative!)
I have found that a good bitumastic paint, a dpm and IF the water
table is not high the previously suggested gravel below to be
effective but do use concrete at ground level. My hardwood poles of
non durable but treated timber have lasted 25 years to date. My CCA
treated soft wood (when I had to remove a post for other reasons)
showed only very minor surface softening.
I maintain paraffin wax is the best way to achieve this as it doesn't
form a film which might be compromised as the wood moves, but is about
as hydrophobic as you can get. I believe they use it in forestry to
prevent premature drying of logs
My hardwood poles of
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