In this treatment tip from our Senior Technical Advisor Gareth Jantjies, we would like to share some insight on a routine matter that can nevertheless create difficulties if not properly understood.
It relates to the under-treatment of timber.
Most of our customers understand the vacuum process and how to apply it, but some operators do not fully understand the reason why it is applied. The reason is that without a vacuum, the air pressure within the treatment vessel will expel the preservative chemical from within the wood after the pressure cycle. The result will be poorly treated timber.
“To ensure the longevity of our industry, we all need to produce top-quality treated timber.”
Gareth Jantjies, Dolphin Bay Senior Technical Advisor
Operators might find that they achieve penetration of the timber, but during a final vacuum the preservative is returned to the tank, resulting in under-treatment.
While the vacuum is being applied properly at most treatment plants, in some instances it has been observed that operators are trying to speed up the process by cutting the vacuum time, Gareth said. This is understandable because plants are often placed under enormous pressure to supply urgent orders, but it is not correct.
Cutting corners in the vacuum process is likely to prove painful in the long run as the product might not meet the specifications, resulting in possible product failures which, in turn, will play a role in tarnishing the reputation of our industry.
“To ensure the longevity of our industry, we all need to produce top-quality treated timber,” Gareth observed.
Water-based wood preservatives such as CCA cannot penetrate into the cells of the timber unless the air is removed first. This is why the Bethel, or full cell pressure treatment process, in which a vacuum is applied, must be used. The vacuum removes all the air and free moisture from the wood, including around and within the cells of the timber.
In the old Bethel (full cell) process, a 100% vacuum was first applied within the chamber, then the chamber was flooded with preservatives. The newer, modified Bethel (full cell) process is better because it saves time, enabling treaters to increase their output, explains Gareth.
In this new process, the treatment chamber is 90% flooded with chemical under pressure and, simultaneously, a vacuum of only 10% is created for between 10 and 15 minutes. The effect of the vacuum is that preservatives are pulled into the void created. Thereafter, the pressure process is initiated. Time is saved because it is much quicker to apply a partial vacuum, than a vacuum of 100%.
The duration of the vacuum is calculated according to the type of timber, the moisture levels within it, the desired solution strength and the desired retention levels, Gareth explains. The South African National Standards on wood treatment require certain levels of penetration and retention, depending on the type of timber being treated.
The basic equipment needed to apply a full vacuum includes adequate, working vacuum pumps and working seals on the treatment chamber.
“Dolphin Bay is committed to helping you to overcome any challenge you may face in the treatment process,” said Bertus. “Please do not hesitate to call us if you need advice or technical assistance of any kind.”