About timber treatment at Caerfagu

The majority of our timber is treated in our own pressure plant using the vacuum pressure process - currently the most permanent method in preserving timber life by reducing the risk of insect attack, fungal decay (rot) and other biological decay hazards. For impregnation we use Wolmanit® CX8-WB from BASF - one of the world‘s most successful chrome & arsenic free wood preservatives.

Freshly treated timber has a green finish, which, after few weeks of being exposed to natural elements, fades to a warm light straw colour.


Vacuum Pressure Treatment Process

Before we start the process we make sure that timber’s moisture content is no higher than 28%.  The timber is then loaded onto special tram cars similar to railway carriages . The 15 metre train of loaded timber is pushed into the pressure vessel and the door sealed awaiting the process to begin.

  • Initial vacuum
    First a vacuum is created in treatment plant - it needs to get as high as possible (around 90%) and be held for 10 – 15 mins.  This removes the air from the timber cells allowing the liquid to enter when the plant is flooded.
  • Fill period
    It is essential that the vacuum is maintained during this period. If it dropped, it would let some air back in the plant, so the tops of the packs would have more air in them and stop a full cell treatment. Consequently the lower half of the pack would be better treated than the top.
  • Pressure period
    The length of this period depends on the hazard class that timber is to be used for.
    Ground contact timber requires hazard class 4 (see table below). All timber at Caerfagu is treated to this standard.
  • Final vacuum
    This is the final cycle period after the pressure period has finished and the fluid has been drained from the treatment plant;  ensures that excess  fluid is taken out from the packs.

Vacuum Pressure Treatment


Following the treatment, timber is left outside the plant in dry conditions for a couple of days to let the chemicals physically fix in the intercellular spaces as the water evaporates.



All in all the pressure treatment process takes approx. 3 hrs and, at Caerfagu, we’re able to process around 20m³ of timber a day.

Timber before and after vacuum pressure treatment


Use classes for timber


Type of Use

End Use

1 & 2

Internal - wood is undercover, fully protected from the weather or where high environmental humidity can lead to occasional but not persistent wetting; insect risk

upper floor joist,   timber frames, tile battens


External - wood not covered and not in contact with the ground-either continually exposed to the weather-or if protected from the weather - subject to frequent wetting

 fence rails, decking boards, garden timbers, external joinery, cladding and sole plates above damp-proof course


External - wood in contact with the ground or fresh water and permanently exposed to wetting

 fence and gate posts, also all timber in ground contact e.g. decking joists & sleepers

Caerfagu opening times:

Mon - Fri
8.00am - 1.00pm
1.30pm - 5.00pm


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