Using a wood preserver on decking helps to protect and preserve decking boards, posts, and supports, from mould, algae, fungi, wood rot and insect attack, all of which can degrade untreated wood over time.
Types of Wood Preservative
Wood preserver come in water-based and solvent-based formulas and are usually available in both clear and coloured variations. Solvent-based wood preservatives generally penetrate deeper into the timber and often dry quicker than water-based formulas. Water-based preservatives are far less smelly to work with and are less harmful to the environment.
Although solvent-based formulas have traditionally been used for exterior wood care, stricter legislation regarding high VOC’s (Volatile Organic Compounds) means that many solvent-based wood preservers are being slowly phased out and replaced with water-based alternatives.
Using a clear wood preserver on decking will retain the natural look of the wood whereas a coloured preservative will stain the wood, effectively acting as a decking stain. Although wood preservatives will protect decking from biological threats such as mould, algae, and wood rot, they are not sufficient, or durable enough, to use as a standalone decking treatment. For this reason, once preserved, decked areas must be treated with a suitable decking oil, decking stain or decking paint.
Which wood preservative should be used on decking?
Before buying a wood preservative to treat decking, it’s important to know what sort of decking treatment or finish you’ll be using. Some wood preservatives contain a small amount of wax to provide exterior wood with a degree of weather protection. Whilst this isn’t an issue with most solvent-based decking oils, it can be a problem with water-based decking paints, stains and oils as the wax within the preservative can repel the finish, and prevent it from adhering or bonding with the surface of the deck. This can result in the decking finish flaking and peeling from the surface of the deck.
Top 3 wax-free wood preservers for decking
These clear, wax-free wood preservers are ideal for use with water-based and solvent-based decking paints, decking stains and decking oils. Take care if you choose a coloured version of the same products as although the ‘clear’ variations do not contain wax, the coloured versions of the same products often do.
- Barrettine Premier Universal Preserver: A clear, wax-free, solvent-based, exterior wood preserver perfect for wooden decking and other exterior wood to prevent wood boring insects, wood rotting fungi and blue stain
- Sadolin Quick Drying Wood Preserver: A clear, water-based, wax-free wood preserver for new and bare timber. Perfect as a pre-treatment before applying a decking stain, paint or oil. Provides excellent protection against wood destroying fungi and blue stain
- Cuprinol Wood Preserver Clear: A clear, water-based, wax-free wood preservative treatment for interior and exterior timber that prevents insect attack, rot and decay
Wood preservers that contain wax
The following preservers contain a small amount of wax and although fine with solvent-based decking oils, should not be used with decking treatments that coat the decking such as water-based decking stains or paints.
- Barrettine Premier Wood Preservative: A solvent-based high-performance exterior wood preserver suitable for garden decking. available in clear and coloured
- Ronseal Total Wood Preservative: A highly penetrative, solvent-based wood preserver for exterior timbers including decking. The clear formula is wax-free whilst the coloured versions contain wax
How to preserve wooden decking
For the best protection, preserve all or as many of the timber components as possible with two coats of wood preservative. This should include all sides, edges and especially the end grain or ‘sawn ends’ as these are the most vulnerable parts of the timber. Once the preserver has fully dried, treat all sides again, where possible, with the chosen decking finish or treatment.
Before buying a wood preservative for decking, be sure to check that it will be compatible with your chosen top-coat. If unsure, most manufacturers of wood preservers and decking finishes have a technical help line that can be called for product advice and help.
Other essential decking treatments and finishes
Before applying a wood preserver to decking, it is important to think about the following.
New decking preservation
New softwood decking boards are often supplied having already been tanalised to protect and preserve them. Although these are ready to be used, there is no harm in applying a fresh coat of preservative for extra protection. New hardwood decking is very resilient to mould, algae and insect attack and will rarely need preserving. If unsure, check with the decking manufacturer or supplier.
Old decking preservation
If you are restoring a decking that hasn’t been treated for a number of years, there’s a good chance that it has already been affected by mould, algae, or other biological issues. Before applying a wood preservative to the decking, it is important to ensure that any dirt, mould, algae, or old decking finishes such as decking paints, oils or stains are fully removed.
An ideal way to do this is to sweep the decking with a stiff broom or use a jet or power washer. If it has been coated with a decking paint or stain and the pressure washer cannot remove it, a chemical decking stripper may be required. More information on pressure and power washers can be found on our patio care and maintenance page.
Once the decking has been cleaned, it is highly recommended that the wood is treated with a dedicated mould and algae treatment or decking cleaner. This will clean and remove any visible traces of mould and algae from the decking. It will also kill off any active or dormant mould or algae spores within the wood grain, that would otherwise soon regrow.
The next step is to apply the wood preservative to the decking, taking care to ensure that it is the right type of preservative for the decking finish that you intend to use. The preserver will help to protect the decking boards from mould, algae, lichens, insect attack, and wood rot. It is usually recommended that wood preservers are allowed to dry for several days prior to over-coating. This varies from product to product but will be detailed on the tin or container.
Once the preserver has fully dried, the final decking finish can be applied. The most popular option is usually a clear or coloured decking oil. These are less fussy with the type of preservative used and are very easy to maintain and restore when the decking finish starts to look tired or worn.
decking stains come in two different forms. There are the pigmented or coloured decking oils that are often labelled as decking stains and then the coating, or varnish type stains that form a tough, durable skin or coating over the surface of decking boards. Oil-based stains are again less fussy about the type of preservative used but the ‘coating’ type stains should not be applied over a wood preservative that contains wax, silicon or any other type of water-repellent.
decking paints are very similar to the coating type of decking stains. Decking paints dry to an opaque finish and are often available in a wide range of shades and modern colours including popular greys and blues. Many decking paints are water-based so again care should be taken with the type of wood preservative used prior to painting the deck.
Not sure what you need to clean, maintain or restore your garden decking? Read our decking care, maintenance and treatment guide to find out what you need to restore your wooden decking.