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Waterproofing wood treatments in the garden

A person applies wood stain to a garden table.

Picture this: It’s the first sunny Sunday of the year. Time to get out into the garden to soak up the sun. Or you would, if you could get out on the decking without slipping on the grimy layer of green algae that’s also taken over the chairs, shed and fence. Not exactly the tranquil place of relaxation you dreamt of during those dark and rainy days. We don’t think about waterproofing wood treatments when we come home from the garden centre with a fresh collection of beautiful new tables and chairs.

“It’s already been treated, surely?”

Probably not! Although oil stains look great and offer some protection against moisture ingress, they don’t seal wood fully.

Oil stains do not fully waterproof wood. Waterproofing wood treatments like Roxil Wood Protection Cream provide protection against water ingress. Combined with Roxil Coloured Wood Stain Preserver, it protects against most types of wood damage.

Let’s dig into where the moisture that ruins untreated wood comes from.

Wet wood is unsafe wood

Water-damaged, untreated wooden decking.

To understand why waterproofing wood is necessary, we have to look inside timber. 

Although living trees are made up mostly of water, dry timber generally contains less than 25% moisture. Living trees soak up moisture using capillary action. This aids in photosynthesis. Around 90% of this water is eventually released through its leaves.

When wood is freshly cut, its moisture content will usually mirror the relative humidity of the atmosphere it exists in. Very simply, wet environments make for wet timber. 

Here’s the problem:

When timber gets wet, it expands. When 30% of the wood’s composition is water, moisture binds itself to the cell walls. At over 30% moisture content, water fills timber’s internal cavities. This disrupts its internal structure.

Outwardly, this results in swelling, warping and cracking. Once damaged in this way, microorganisms like the fungi responsible for wood rot can penetrate more deeply into timber. 

When a saturated piece of wood becomes wetter in certain areas then dries, that saturated area will shrink at a different rate than the drier areas. This can cause the wood to become bent or bowed. 

When two pieces of wood are joined together to form a structure and then become deformed by moisture, it’s easy to see where real danger can manifest. Again, not good when you’re trying to relax in the garden shed. Waterproofing wood minimises the risk of warping. But some kinds of wood are more vulnerable than others.

Types of wood: Hardwood and Softwood  

Planks of softwood prior to treatment.
A designer looks over a selection of hardwood samples.

Timber used by buildings and furniture can be grouped into two broad types of wood: hardwood and softwood. Hardwoods and softwoods are distinguished by when they lose their leaves.

Softwood comes from evergreen trees, which keep their leaves throughout the year.

Hardwoods come from deciduous trees that lose their leaves each autumn. Due to their density, some waterproofing wood treatments are unsuitable for hardwoods.


Softwoods are universally lighter in colour than hardwood. They are absorbent, which makes them vulnerable to moisture ingress and woodworm infestation.

A Mother and Son build a wooden project in the garden.

Species of popular softwood include:

  • Larch
  • Pine
  • Cedar
  • Fir


Softwood tables and chairs out in the garden on a sunny day.

In the UK, softwoods are used in a wide variety of outside applications: 

      • Garden chairs and tables
      • Fencing
      • Potting sheds
      • Decking 
      • Doors and windows

      Due to its versatility, easy workability and light weight, most outside garden furniture and small structures are built using softwood. 

      Softwoods are more sustainable than hardwoods. They grow quickly, allowing for faster timber production and minimising the need for vast swathes of land. Some hardwoods also contain allergens and irritants. Softwoods are allergen-free.

      As an added bonus, softwood tends to be cheaper than hardwood. Waterproofing softwood structures like garden furniture is a must.


      Hardwood is generally more durable than softwood. It is usually denser, darker and much more expensive to source than softwood. These attributes make hardwood suited for large structural works or fine furniture.

      A lumberjack process a mighty oak tree.

      Types of popular hardwoods include:

      • Oak
      • Maple
      • Beech
      • Ash


      A carpenter in his workshop.

      Hardwood has a wide range of uses:

      • flooring
      • luxury cabinets, chests and wardrobes
      • building construction
      • boats

      Both types of wood are susceptible to wood rot and water damage. However, hardwood can withstand more damage than softwood because it is dense.

      Softwoods are easy to treat with biocidal and waterproofing protection due to their absorbent nature. However, not all hardwoods can be protected in this way. Some weathered hardwoods are suitable for wood protection liquids and creams.

      Tannins in wood


      In a forest, natural tannins leach out of trees into the river.

      Some weathered hardwoods like oak and chestnut contain high levels of tannin (or Quertannic Acid, if you want to get specific). Woods high in tannins take on a rich dark brown hue. 

      Tannins are soluble. When water saturates the surface of timber, the tannins wash out. This washes out of the wood and leaves behind a fine dust that absorbs back into the wood and adjoining porous surfaces as a light brown watermark. This is widely known as ‘tannin leaching’. In nature, tannins regularly wash out of trees near bodies of water. This can cause rivers to take on a tea-stained hue.

      Tannin leaching is most noticeable in hardwoods used for fencing, decking or cladding. Woods of all kinds contain a percentage of tannins.

      Waterproofing wood treatments create a barrier that reduces tannin leaching. This means wood will maintain its natural colour for longer.

      Sapwood and heartwood

      There are three main components to wood: bark, sapwood and heartwood. While the bark is discarded during timber production, sapwood and heartwood make up the main outer and inner parts of the wood. Timber can be processed from both types of wood. This is why both may be present in outdoor wood furniture and structures. 


      Sap wood drips out of a tree.

      Sapwood makes up the soft outer layer of a tree and is named because sap travels through the tree via this wood. Sap is the lifeblood of the tree. It contains water, minerals, hormones and sugars.

      Sapwood also tends to be light in colour. It is vulnerable to moisture damage, rot and insect attack. As a result, it tends not to be used for entire pieces of furniture.

      Sapwood can be used sparingly to add lighter accents to bigger pieces. 



      A detailed cross-section of heartwood.

      The inner part of the tree is made up of heartwood, which is much harder than sapwood. The richer and deeper colours of heartwood are usually preferred by carpenters and decorative woodworkers. As it is denser, heartwood makes up the strongest part of the tree. Most modern timber is processed from heartwood, especially for weight-bearing structures of any kind.

      In outdoor structures that use both types of wood, moisture protection is a must. Excess moisture impacts the natural look of wood. It can darken wood’s natural tone and accentuate contrasts. It can also magnify imperfections and make wood grain more pronounced.

      In incredibly controlled conditions, this can be desirable. However, even controlled exposure will make timber weak. Waterproofing wood treatments protect the vulnerable sapwood and hardier heartwood from moisture damage.


      A garden bench covered in algae.

      Algae thrives in wet conditions. Algae usually presents on wood as a thin film of dark or light green fur. Lichen tends to be dry and flaky, while moss is usually fibrous and thick.

      There are millions of types of algae, moss and lichen in the UK. Like living trees, they eat by using water to aid in photosynthesis. 

      Algae growth can turn patios and decks from safe spaces to slip hazards. They can stain the surface of untreated wood. Although moist conditions will always damage the durability of wood, moss growth does not directly damage wood in the same way that dry and wet rot does. They can stain clothes. 

      Even worse, when you introduce mould spores from outside into the home, they could lead to mould growth indoors as well. Waterproofing wood treatments do not remove the chances of algae growth. It does maintain an environment that algae does not like to grow on. Check out more on protecting wood against biological growth here.

      Waterproofing wood in the garden with Roxil

      Waterproofing wood is simple with RoxilSunny Sundays don’t last forever. Make sure you enjoy them. 

      For more information call
      01403 210204