Using an exterior wood varnish that is suitable for a garden sheds, log cabins, and summerhouses, is a great way to protect them from weathering and biological threats such as mould, algae, fungi, and insect attack.
What are shed varnishes?
Shed varnishes are coating systems that form a protective layer over the shed timbers to seal and protect them. Varnish or coating type systems are better suited to smooth planed and tongue & groove sheds, summer-houses, and log cabins whereas coloured shed paints and shed stains can be used on both smooth planed and rough sawn featherboard, or shiplap sheds
Which varnish is best for sheds?
There are a variety of exterior wood varnishes available that are perfect for use on garden structures like sheds. Many are clear so will simply enhance the natural colour and character of the timber, whilst others are colour tinted, allowing you to change the appearance of your shed or other exterior buildings. Some of the coloured products are simply varnishes that contain a wood stain whilst others work as a two part system where the wood is stained first, and then the stain is overcoated with a clear or same colour top-coat.
Top name brands that produce exterior coating systems that are suitable for sheds, summerhouses and other exterior buildings include Sadolin, Sikkens and Dulux Trade who are regarded by many as some of the best products on the market.
5 of the best shed varnish and coating systems
- Sadolin Classic Wood Protection: A high quality, solvent-based, protective wood stain for interior and exterior timber that can be used as a standalone product or as a base-stain for Sadolin Extra Durable. Ideal for exterior cladding, fascias, sheds, decking and other rough sawn timber. Available in a range of colours in 1L, 2.5L and 5L sizes
- Sikkens Cetol Filter 7 Plus: A medium build, solvent-borne durable woodstain for exterior joinery. This flexible coating is resistant cracking and flaking making it perfect for smooth softwood and hardwood surfaces. Provides up to 5 years protection from weathering and UV damage
- Sadolin Beautiflex: A solvent-based, opaque wood stain for all exterior wood, including decking and sheds. Highly durable and flexible, water and UV resistant. Available in Hickory, Black and White.
- Dulux Trade Ultimate Woostain: A high performance, solvent-based exterior wood stain suitable for smooth softwood and hardwood timbers. Provides up to 10 Year Weathershield Protection
- Dulux Trade Clear Yacht Varnish: A high-build, solvent-based, clear gloss yacht varnish for smooth planed exterior wood. Perfect for exterior doors, windows, joinery and more. Provides a highly durable and flexible finish to protect exterior wood. Contains UV filters to protect against the damaging effects of sunlight
How do exterior wood varnishes perform?
Many exterior wood varnishes and other coating systems are designed to erode with weathering over time. They are designed to be ‘topped-up’ before the coating fails, exposing the bare wood. Once bare wood is exposed, moisture can penetrate beneath the surrounding coating and will eventually start to lift the finish causing cracking and peeling. Exterior coating systems are generally designed to last for 3 to 5 years before requiring maintenance to top up the finish. This is usually done by cleaning, then lightly sanding the old finish to remove any surface dirt and debris prior to re-coating.
The main differences between an interior wood varnish and an exterior wood varnish is that exterior varnishes are more flexible and actually softer than interior formulations.
‘Softer?’ we hear you say. Exterior wood varnishes are formulated to flex and move with the wood so that they do not split, crack and peel. Using an exterior wood varnish on a floor wouldn’t last as long and will scuff and scratch easier. Likewise, using an interior floor varnish on an exterior structure such as a garden shed, log cabin or summerhouse will over-time crack, split and peel because of its inability to stretch and move with the expansion and contraction of the wood, which is far more extreme than with interior wood.
Varnishing or coating a new shed
Applying a varnish or coating system to a new shed, log cabin or summerhouse is pretty straight forward. If using a wood or shed preservative first, ensure that it does not contain wax, silicon or oil as these will prevent the varnish or coating from adhering to the shed. Find out about shed preservatives here.
Varnishing or coating an old shed
When coating an old shed with a varnish its important that the wood is in good condition.
- Old coatings of paint, varnish or stain that are peeling, cracking and flaking must be removed
- Sheds that have been previously oiled may not be suitable for varnishing unless they have not been oiled for a number of years. scrubbing the wood with methylated spirit and applying the varnish to a small test area is recommended to test adhesion and final finish
- All traces of mould, algae and other biological growth must be removed. Remove all build up with a paint scraper or stiff brush then treat the wood with a fungicidal wash or wood cleaner
- Treat the shed once it is clean and dry with a wax, silicon and oil free wood or shed preservative. Allow to fully dry for at least 24 hours before applying the shed varnish.
The main difference between a shed varnish and a paint is that varnishes, clear and coloured are translucent and allow the wood grain to show through the coating. garden paints for sheds are opaque and come in a wide range of colours including pastel shades and vibrant tones.
Using garden fence products to treat garden sheds
An alternative to using a shed varnish, shed paint or shed stain is the multitude of garden fence paint and garden fence stain products. These are also designed to colour and protect garden fences from the effects of weathering and are commonly used on wooden sheds to do the same.
Garden Shed FAQ’s
Can’t find the answer to your garden shed care or maintenance project above? See our frequently asked garden shed questions and answers page, where we try to answer some of the more commonly asked questions relating to garden shed care, maintenance, and shed treatments.