Cleaning a Wooden Deck or Fence

When it comes to cleaning wooden decks and privacy fences, the approach differs significantly from cleaning most other exterior surfaces, such as concrete or vinyl siding. Wood is a porous, organic material with some unique properties – some familiar, while others are more subtle. Unlike concrete or vinyl, wood requires gentler cleaning agents to remove contaminants without causing damage to the relatively soft organic fibers.

Instead of relying on a sodium hypochlorite-based cleaning solution, superior results can be obtained by using a multi-stage cleaning process which leverages the power of sodium percarbonate (an “oxygen bleach” commonly used in products like OxiClean) and oxalic acid. This is a deep dive into why this method is superior, and how these chemicals work synergistically to clean wood while not stripping years off its useable lifespan.

Sodium Hypochlorite is too Harsh for Wood

Sodium hypochlorite (commonly known as bleach) is highly effective for removing organic stains such as mold and mildew. In house washing, responsible use of this powerful cleaning agent can produce amazing results; however, this chemical’s high pH (typically around 12 – 13) makes it extremely alkaline, which can be detrimental to wood.

Wood is (mostly) composed of long cellulose fibers bound together by lignin. While cellulose is responsible for the tensile strength (e.g., why you cannot rip a 2x4 end-from-end) while lignin provided rigidity (e.g., why a baseball bat doesn’t bend) and compression strength (e.g., why wooden fences act as barriers). Together, cellulose and lignin form the highly versatile wood material so commonly used in construction of decks and fences.

Sodium hypochlorite is highly effective at breaking down organic materials, and lignin is no exception. Prolonged contact with sodium hypochlorite will significantly weaken and discolor lignin, while cellulose fibers swell and lift, leaving the surface rough and uneven. In short, sodium hypochlorite may clean wood, but that clean comes with a shortened wood lifespan.

Sodium Percarbonate is Gentle on Wood

Sodium percarbonate is a highly stable source of hydrogen peroxide, commonly used in a range of industrial applications. Hydrogen peroxide itself is relatively unstable in aqueous solutions, especially when exposed to heat or light, as it spontaneously decomposes into water and oxygen gas. For this reason, hydrogen peroxide is often generated on-demand by dissolving sodium percarbonate in water.

When solid sodium percarbonate dissolves in water, it produces an aqueous solution containing sodium carbonate and hydrogen peroxide. The sodium carbonate further dissolves into sodium ions and carbonate ions, creating an alkaline solution, typically with a pH between 10 and 11. Alkalinity is beneficial for breaking down oils, grease, and organic residues, as well as disrupting the bonds between dirt particles and wood fibers. Additionally, many organic stains become water-soluble in alkaline conditions. While the carbonate ions contribute to the alkalinity, sodium ions readily bind to hard water minerals like calcium, preventing the formation of deposits when the solution dries.

The real power of this cleaning compound lies in the hydrogen peroxide. As a versatile chemical, hydrogen peroxide can act either as an oxidizing agent or a reducing agent, depending on the conditions (which are beyond the scope of this blog post). It typically participates in oxidation-reduction (redox) reactions by producing reactive oxygen species, which are highly reactive molecules that can break down organic stains, biofilms, and other microorganisms.

What makes hydrogen peroxide (derived from sodium percarbonate) especially remarkable is that its breakdown products are simply water and oxygen – both environmentally benign. This makes sodium percarbonate an exceptionally effective and eco-friendly cleaning solution, particularly for delicate surfaces like wood, where more aggressive chlorine-based oxidizers would be inappropriate.

Oxalic Acid Neutralizes Alkalinity

After cleaning wood with sodium percarbonate, it’s essential to neutralize the surface pH, which is done with oxalic acid. This organic compound restores the wood’s natural pH and enhances its appearance. While the alkaline solution from sodium percarbonate can be rinsed away, the wood’s pH may remain elevated. Oxalic acid, with a pH around 1 or 2, counteracts the elevated pH of the sodium percarbonate cleaning solution. If the wood surface is to be stained or painted, then missing this step can easily spell disaster.

Oxalic Acid Brightens Wood

In addition to neutralizing the pH of the wood, oxalic acid is particularly effective at removing tannin stains – those dark discolorations often seen in cedar or other highly colorful wood species. These tannins are naturally present in the wood, and stains occur when these tannins react with iron. Oxalic acid is particularly suited for undoing this reaction between iron and the naturally occurring tannins, visibly brightening wood before your very eyes.

Synergy Between Sodium Percarbonate and Oxalic Acid

The multi-step process that combines sodium percarbonate and oxalic acid, provides a comprehensive solution for cleaning wooden surfaces. Sodium percarbonate removes debris and organic stains without damaging the lignin or cellulose fibers, while oxalic acid neutralizes the wood’s pH and restores natural color by reversing tannin stains. This eco-friendly, biodegradable approach minimizes risks to surrounding vegetation and soil, making it an ideal method for preserving the health of both wood and the environment.

Conclusion

Cleaning wooden decks and privacy fences requires a thoughtful approach that respects the material’s unique properties. While many exterior building materials are durable, with strong resistance to chemical reactivity, wood is not. The combination of sodium percarbonate and oxalic acid offers an effective, safe and eco-friendly solution. By avoiding inappropriate chemicals like sodium hypochlorite, we preserve the wood’s beauty and durability, ensuring it remains a valued part of any outdoor space for years to come. This method exemplifies the balance of science and craftsmanship needed to achieve professional results in wood care.

Surface Work Loves Cleaning Wood

While this blog post discusses the cleaning solutions used for wooden surfaces, it does not address the pressure side of the Cleaning Triangle. Simply put, this post is already too long, but using the wrong nozzle or pressure settings could produce unexpected results. Like I said, wood is not a forgiving material, and experience really matters here.

Whether it’s a wooden deck or fence, Surface Work wants to wash your wooden surfaces in Virginia Beach. From Kempsville to Sandbridge, Surface Work is committed to providing exceptional power washing results – every time. Since wood can exist in a wide range of conditions, it is one of the few surfaces that we cannot quote without first inspecting in person. If you have a deck or fence project, contact Surface Work today, and we can develop a cost-effective plan to clean (and perhaps stain) your wood.

Fizzy bubbles from sodium percarbonate cleaning solution.