Preservatives & wood deck sealers

Written by greg jackson
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Preservatives & wood deck sealers
(wood texture image by Daniel Gillies from

A wood deck is a valuable improvement on a property. It provides an enjoyable enhancement to the outdoor environment of the home, and it also adds value to the property. It is important to retain the integrity of the wood deck, which requires regular refinishing. Wood preservatives that contain sealers are the best choice for this job.

Why Wood Decks Need Preservatives and Sealers

The enemies of wood are moisture, sunlight and biological entities. Living trees protect themselves naturally by producing certain chemicals through photosynthesis and other internal processes. Protecting sawn wood requires the use of preservatives and sealers to take the place of these biological elements. These products must contain some type of compound that not only permeates the fibres of the wood members, but also creates a barrier against water, ultraviolet light and natural enemies such as termites and fungi.

Types of Finishes for a Wood Deck

The U.S. Department of Agriculture and the Forest Service jointly sponsor the Forest Products Laboratory (FPL), an entity that tests and rates products related to the use and care of wood. An FPL fact sheet provides information about finishes for wood decks. It recommends three types of products categorised as preservatives and stains. Each of these types contains sealers that help to keep moisture from damaging the integrity of a wood deck. The three types of finishes are water-repellent preservatives, coloured water-repellent preservatives and semitransparent stains.

Water Repellents and Preservatives

Traditional water repellents contain organic solvents (turpentine, white spirit), a water repellent (paraffin wax) and some kind of sealer such as varnish or linseed oil. Solvents have been added to newer products to help the water-repellent elements penetrate the grain of the wood. These newer water-repellent preservatives also add a fungicide to protect the wood deck from mildew and mould. Many of these preservatives contain non-drying oils that further protect wood from degradation and fungi. Pressure-treated wood that is designed to prevent insect and fungus damage can also benefit from a water-repellent preservative.

Epoxy Sealers

Newer types of wood deck sealers use epoxy as the main preservative and sealing agent. The theory behind these sealers is the ability of epoxy to deflect and absorb the ultraviolet light that is so damaging to unprotected wood. Many of these epoxy-based sealers contain synthetic resins that replace the natural oils of traditional preservatives. These oils are a target for fungus growth, acting as a food source after the sealers they are mixed with are degraded by time and weathering. Epoxy resins are resistant to fungus, and are effective preservatives and sealers for a wood deck.

Pressure-Treated Wood Decks

Traditionally, pressure-treated wood contained chromated copper arsenate as the protective agent against fungus and pests. Controversy over the safety of this ingredient led to replacement compounds, such as amine copper quat and copper azone. Although pressure-treating wood will prevent rot and mildew, it will not protect wood against weathering. A preservative is still required, but it must be labelled as being appropriate to use on pressure-treated wood.

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