Wood is a delicate organic material that requires frequent, periodic care.
Unlike concrete, bricks or stone, wood can be easily damaged by sharp and/or hard objects, but more generally, any applied pressure. So, can you use a pressure washer to wash wood and wooden surfaces?
The answer is a decisive yes, but with an asterisk.
Pressure washing wood requires you to follow a strict protocol and to know what you are doing if you are to not damage your patio, fence, or whatever you may be working on.
Follow along to find out how to wash wood with a pressure washer and what to look out for when doing so.
Let us start with a politically incorrect fact: Not all wood is equal. The first distinction should be made between hardwood and softwood (opens in a new tab).
Hardwood vs. Softwood
Ideally, fence pieces and floorboards should always be made from the denser hardwood, as it is more durable and fire resistant. These woods include alder, hickory, maple, oak, walnut, and in general, most common broad-leaved trees.
However, in some cases, softwood, from needle and cone trees may be used to save money, especially in decorative fencing. These woods include pine, redwood, or yew.
Whereas most hardwood is much more forgiving, softwood is quite prone to damage by pressure. Therefore, if you suspect that your fence is made from softwood, reconsider if pressure washing is necessary. If so, apply this tutorial in the mildest ranges described (e.g., pressure, tip choice).
Does that mean you are safe If you do have hardwood? Maybe. To get a grasp of just how delicate your wood is, refer to a table of Janka hardness (opens in a new tab).
If your wood is painted, pressure washers should not be used on it, period. Pressure washing is in fact one of the most effective ways to peel old paint off (opens in a new tab), albeit usually at pressure settings which are not compatible with wooden surfaces. You may get away with using the mildest possible setting on painted surfaces but unless you are a pro, paint is a no-go.
A plain wooden surface with applied stain—a conditioner that protects the wood—is the most beautiful building material on this planet. However, it requires special care.
No wood should be left unstained and must be re-stained periodically. In fact, most people clean their wooden surfaces to re-stain them (opens in a new tab), which may be exactly why you are reading this article. If not, do so anyway, as unstained wood is extremely prone to damage!
How to Go About Pressure Washing Wood?
With all of the above considered, pressure washing may be perfectly suitable for your wood. However, care must be taken when setting pressure and selecting the right tip for the job. Most detergents must be avoided, and only select few, which are compatible, may be used.
When the pressure washing job is done, wood requires aftercare, to give the wood a fresh shine, nourish it and prolong its life. This is typically done by applying stain, but you can find many more wood-care products on the market which will further improve your wood’s condition.
Remember that it is always safer not to use a pressure washer at all. Unless you feel confident in doing so and are prepared to take the task seriously, you should consider other cleaning methods.
When to Clean and Treat Wood?
Cleaning and retreating your wood is crucial to recover its shine and extend overall life. The general recommendation is to do so every 2-3 years. As a quick test, try dropping a few droplets of water on the surface. If the water beads up, you’re fine. If not, it’s time to clean and then treat the wood.
You want to do so when there is no rain forecasted for at least the following three days. However, extremely hot/sunny days should be avoided when applying detergents.
As covered in our nozzle guide, the choice of a tip (nozzle) is one of the most crucial aspects of pressure washing. Whereas 65° fan tips are somewhat safe to spray right onto the palm of your hand, a 0° tip may chip off your fingers (not joking, please do not ever try this at home). Naturally, the former choice is the more suitable for wood. Always go for a 65° fan tip if possible.
40° fan tips may be applicable to more durable wood as well. However, do not attempt to use them before thoroughly exhausting the possibilities of the 65° fan tip and testing the 40° fan tip on a small area, before proceeding to wash the rest of the surface.
As a rule of thumb, go for the lowest pressure possible. Most sources recommend a range of 500-600 psi, which I am personally comfortable with. Never exceed 1000 psi if you want to keep your wood safe.
Unlike most surfaces, wood requires a special kind of cleaner, a wood cleaner. Common detergents should never be applied to wood to avoid damage, discoloration, or degradation.
When choosing a wood cleaner, you must always make sure it is safe to use in pressure washers, to avoid damage to the washer itself. Many brands also make special cleaners for specific types of woods, which should be sought out if available.
Pressure Washing Techniques.
Pressure washing is a skill, to which certain techniques apply. Whereas hard, inorganic construction materials are forgiving and following these tips is in their case a matter of efficacy. In case of wood, they are mandatory. We cannot stress enough that the way you go about washing wooden surfaces is crucial to avoid damaging them.
Read the manual to all products you’ll be using and follow the safety guidelines strictly
Do not forget to follow all safety precautions, including wearing protective equipment such as gloves and safety goggles. Always know how to operate, turn on and turn off the pressure washer.
Clear your surroundings
Any obstacles should be cleared to avoid tangling up your hose in them, tripping over them, or damaging them by the water stream. If objects can’t be moved (e.g., plants), cover them with a sheet of plastic for at least a minimal protection from direct water stream impact. If cleaning a deck, its surface should also be swept thoroughly before you apply any liquids to it.
Test out your setting
Test the impact of your water stream at the setting you wish to use for cleaning on a small, hidden area before proceeding to wash it, to avoid potentially damaging the entire surface.
Keep the nozzle at a large, constant distance from the surface
I recommend starting with your gun 2 feet above the surface. If not effective, move closer, but no less than 6 inches from the surface. Once you select your preferred distance, stick to it throughout the cleaning process, unless you intend to spot clean.
Follow the grain
Spray along the grain of the wood rather than across it to minimize the risk of damage and even clean somewhat more effectively.
Keep it moving
Always keep your nozzle moving. Applying pressure to a single spot is sure to damage wood.
Apply cleaner as per manufacturers recommendations
Each cleaner comes with instructions on how to use it, including the type of washer it should be used in, surface it should be used on and for how long it must be left on the surface to thoroughly clean it. You may also be required to use a utility brush to scrub the cleaner into tight corners.
Never allow detergent to dry on the surface
You should make sure your detergent (cleaner) doesn’t dry on the surface you’re cleaning. For this exact reason, abstain from cleaning on sunny days, or at least under direct sunlight and at noon.
Proceed from bottom to top when applying cleaner and top to bottom when washing it off
If you’re applying a cleaner to a vertical surface (e.g., wall, fence), do so from bottom to top. Vice versa, cleaner should be removed from top to bottom. This is done do enhance cleaning efficacy and to avoid streaks.
Leave surface to dry for at least 48 hours before applying aftercare
Wood holds water much longer than most surfaces. Thoroughly drying the wood may take a surprisingly long time. Make sure to provide it that time before applying stains and other woodcare products.
Always apply woodcare products!
Pressure washing leaves wood naked, porous. Always apply stain after cleaning, regardless of if re-staining was the purpose of your washing. Check this guide (opens in a new tab) to learn how to do exactly that.
In summary, despite their delicate nature, unpainted wooden surfaces can be washed by a pressure washer if care is taken to prevent damage and proper cleaning techniques are followed. Always take safety precautions to protect you, your surroundings, your pressure washer and the surface you’re cleaning.
Pressure washer tips should be kept wide-angle and pump pressure to a minimum, to avoid damage to the surface by the impact of the water stream. Common detergents are unsuitable and specialized wood cleaners must be used to avoid chemical damage. Lastly, wood must be stained after each cleaning to keep it healthy and durable. Always follow the instruction on all products you’re using and don’t be shy to use customer hot lines if you find yourself struggling.