The first distinction to make when selecting an exterior timber coating is whether or not the look of the timber needs to change or whether a natural look is preferred. If the end result needs to look different to the natural appearance of the timber, then a stain is recommended. Containing more pigment than oils, stains are semi-transparent so they alter the colour while still allowing the grain pattern and knots to show through. Stains are an excellent choice for restoring the colour of aged timber or making a certain species look like one entirely different (e.g. Merbau stain on treated pine, to look like Merbau timber species).
Due to the extra pigment contained in stains, they generally offer greater durability when compared to oil-based coatings. The pigment helps absorb UV light, protecting the timber against exposure and degradation. Stains are available in water based options such as Intergrain® NaturalStain or oil based with similar distinguishing features as oil based vs water based oils.
Water based oils such as Intergrain® UltraDeck are in fact more durable and longer lasting than traditional oil based coatings and can last up to 3 times longer. This is because water based oils form a thin invisible film on the surface of the timber that seals the timber and acts as a protective barrier. Oil based products tend to penetrate the surface of the timber more than water based products but do not form a protective film.
Where odour or access to ventilation is a concern, water based oils are generally recommended as they are less odorous and emit lower VOCs (Volatile Organic Compounds) and are therefore also kinder to the environment. The convenience of a water cleanup for water based products is also considered an advantage by some compared to cleaning up with turpentine.
With respect to dry times, water based oils dry much faster than oil based however the longer ‘open time’ with oil based products is definitely an advantage for large surfaces. Appearance wise, an oil based coating such as Intergrain® Nature’s Timber Oil will provide a traditional, ‘oiled timber’ look and water based products will provide a slightly higher sheen.
Unlike stains and oils which have varying degrees of pigmentation, exterior clear finishes don’t contain pigment and are generally not as long lasting in comparison. They are typically suited to doors, window frames and trim and are not suitable for heavy wear surfaces such as decking and walkways.
Slip resistance is an important consideration for walkways and ramps or where a standard is required. Additives such as Intergrain® UltraGrip provide a textured surface finish and can be stirred into a coating to meet the required slip rating. ‘R ratings’ are the standard measure of slip resistance and R10 - R12 ratings are generally the most common requirement. It is important to note that a slip resistance additive will cause the appearance of a coating to change, particularly for high gloss products that change to a satin type finish.