Timber treatment

Timber is vulnerable to attack from insects, damp and fungi and needs protection from all of these to extend its working life. All Imprest products are treated using a vacuum-pressure-vacuum method and we also offer timber treatment as a separate service.


Preservatives and hazard classes

We have 2 treatment tanks and water-borne, chromiumfree wood preservative – Impralit®-KDS. Please click here to read more about Impralit®-KDS. Chemical is safe for the environment and give the necessary protection depending on the hazard class. For different products, markets & customers we are using different treatment processes but the majority of our timber is being treated according to European Standard EN 351-1 to meet the following hazard classes:
  • HC2 – for outside undercover usage
  • HC3 – for outside non ground contact usage
  • HC4 – for outside in ground usage.


During the summertime untreated products are being treated with anti-stain preservative by dipping in order to avoid bluestain & mould.


We are controlling our treatment quality by measuring the volume of the preservative that we pump into the timber and/or by using long pressure times. The actual service life of the timber depends on a proper treatment process, on the moisture content of the timber that should be under 28% and finally on the wood species. Pine is more easy to treat but spruce has better natural resistance.

Enclosed is a small overview about different treatment classes based on EN 351-1:

 Species   Hazard class   Analytical
 Tolerances1    Pre vacuum   Pressure   Final
Service life2
 Spruce  HC2 3 mm lateral  75 30 min 30-45 min      

15-20 min
 5-10 years
 Spruce  HC3 3 mm lateral  75 45 min 45-90 min  10-15 years
 Spruce  HC4 6 mm lateral  75 45 min 180-360 min  10-15 years
 Pine  HC2 3 mm lateral  90 20 min  30 min  10-15 years
 Pine  HC3 6 mm lateral  90 30 min 45 min  15-20 years
 Pine  HC4 Full sapwood  90 30 min 60 min  15-20 years

1 % of test specimen that must conform
2 Imprest guarantees service life only if the timber has been kiln dried prior to the treatment

       Wood is put into tank & pre-vacuum begins.
Air & moisture is pulled out from wood cells.
     Tank is filled up with impregnation liquid.
     With hydraulic pressure liquid is pressed into wood.
     Tank is emptied.
     Final vacuum pulls out unnecessary impregnation liquid.