Starting with basics, the type of wood used will provide a certain level of protection and if that timber has been pressure treated, an additional layer of defense will be provided. A coating of a good quality sealer will add to that protection, especially if it is applied within the first couple of months. As well as offering protection to the timber, against the likes of fungus and insects, sealer helps prevent cracking, splitting and warping.
There are three basic types of primers or sealers that can be used for wood fence protection. All contain some form of water repellent preservative, since moisture is the primary cause of outdoor wood degradation.
- Latex - Covers marks or black tannic acid stains and provides a base for later treatments
- Shellac - Offers a hard surface that will stand up to years of harsh treatment from rain and wind
- Alkyd - Soaks into the wood and creates a barrier to moisture and fungi that grow in it
If you intend staining the timber, using a wood sealer beforehand, especially on soft woods, will allow for a more even application of the stain. Even if you prefer the natural look of the wood, using a wood-toned or low pigment stain makes for a good choice.
If your garden fence has been up for a while, a sealer will only offer limited benefit unless you first treat the wood with something like oxalic acid which is often a component of many deck washes. Oxalic acid quite often goes by the name of wood cleaner, wood bleach or even wood brightener.
Wood used in fences, such as cedar, oak or pine, has a tendency to become gray as it ages. Although not a miracle cure, Oxalic acid can bring many older fences back from the brink and make them look nearly new and bare. It does this by reaching down into the top layers, fluffing them up as it goes and killing off any mold or fungus that may have taken up residence. Indeed, many a garden fence has gained several more years of life from a simple application of this wash, which can be painted, brushed or sprayed on.
Once the fence dries, the wood is ready for treatment to keep it looking good. That usually comes down to painting or staining. Sealers can help, but they will not be as effective as they would on new wood since even oxalic-acid washed wood fences that are several years old do not have the absorbency of new timber.
In these circumstances, your choices are either staining or painting. Strictly speaking, stains only color but do not offer wood fence protection. However, not all stains are created equal with many types combining compounds that provide both protection and color. On the other hand, all paints, whether latex or oil-based, will not only color but by their very nature also protect.