Protecting your wooden building and outdoor product.
Introduction
Some woods have natural durability against decay (rot). Others can be made more durable through treatment with preservatives.
Water repellents (WR’s) and water-repellent preservatives (WRP’s) penetrate wood finishes and increase the durability of wood by enabling the wood to repel water. This ability to repel water is achieved by a wax, oil or a similar water-repelling substance.
By repelling water the wood is able to resist decay by stopping the wood-decay fungi which need moisture to live. The addition of a fungicide to the water repellent (which converts it to a WRP) further enhances the effectiveness of the finish by inhibiting the growth of mildew and the decaying fungi. They also decrease the swelling and shrinking that lead to cracking and warping, but it will not stop the natural process completely.
Wood is the material of choice for many structures. Problems such as mildew, cracking, splitting, and wood decay can be controlled with proper care and maintenance, These problems can be avoided with the knowledge about the factors that affect wood, particularly wood that is exposed is outdoors. If wooden structures are given proper care initially and are maintained periodically they can be functional, structurally sound and aesthetically pleasing for a long time.
Weathering
Regardless of the care taken in building a structure, wood ages when exposed outside. The aging process is called weathering. Weathering is a degradation of the wood’s surface caused by the combined effects of the ultraviolet (UV) radiation in sunlight, water and abrasion by wind-blown sand or other particles. This degradation should not be confused with decay.
Weathering is first manifested by a change in the colour of the wood. The colour of most timber is either light green or brown. Cedar has the freshly sawn natural colour and when weathered it tends to get lighter, whereas light wood tends to get darker.
A loosening of the wood fibres and gradual erosion of the wood surface follows the change in colour. Rain washes the degraded wood materials from the surface. Rain and changes in humidity also cause dimensional changes in the wood that accelerate the erosion process. This is a natural process and should be expected.
Treated Wood
Wood that has been pressure-treated with waterborne chemicals can easily be finished with a WRP if the wood is clean and reasonably dry. If the wood is still waterlogged from the preservative treatment, it should be allowed to dry for several days once the structure is built. It is very important to allow enough time for the wood to dry sufficiently.
New Wood
WR and WRP formulations as pre-treatments for paint have less wax or water repellents compared with those formulated for use without paint. When used as a pre-treatment a WRP can be applied in the same way as when used as a natural finish. Freshly treated wood must be allowed to dry. If the treatment is applied with a brush, allow 2 days of drying in warm weather before painting. If the wood is dipped for 10 seconds or more, 1 week for drying is necessary before painting. If enough time is not allowed for the solvent to dry, the paint applied over the treated wood may not cure or bond properly. Also joints much as in the fascia should be caulked after treatment with a WR or WRP.
Service Life
The service life of WR’s or WRP’s is about one year on exposed wood surfaces. WRP’s are extremely easy to reapply and absorb readily into the end grain of lumber and can stop water absorption for many years. It s recommended that a treatment is reapplied at least once a year.