Joist treatment

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Timber joists supporting wood flooring and timber decking


Joists are small (85x8mm) pieces of timber fixed perpendicularly to beams to support wood flooring and fixed to posts to support patio decking.  Depending on the wood used and whether the joists are indoors or outside, a targeted and appropriate treatment should be applied to the timber so that the joists have sufficient properties to durably withstand xylophagous insects (xylophagous insect larvae and termites) and xylophagous fungi.

Treating joists for internal use

Indoors, the treatment of woods with a conferred durability is through surface application.  Considering their location (sheltered, little or no exposure to damp), joists must have a performance level equivalent to class 2 use.

The treatment is usually applied by soaking or sprinkling. Most often, this is a treatment that will form an effective barrier inside the timber to prevent termite attacks and the laying of xylophagous larvae or the growth of xylophagous fungi.

Treating joists for outdoor use

Outdoor timber joists are either continuously exposed to the elements, or protected from the elements but subject to humidity. Normally placed on posts they are not in contact with the ground, timber joists must have a performance level corresponding to use class 3B/4. To allow the use of not naturally durable species, the timber is given an insecticide and fungicide treatment by impregnation so that it can withstand xylophagous insects (Capricorn, lyctus beetle larvae, woodworm and termites) and so-called dry and fibrous rot fungi.  It is applied in an autoclave (double vacuum or vacuum plus pressure)