Wood is an excellent building material for the outdoors. Whether it is used for house siding, outdoor furniture, decks, fences, or sheds, wood holds up well against weathering, as long as it is maintained. But whenever water and wood mix, there is the possibility of water stains.
Water Stains: No Two Are the Same
Applying oil- and water-based wood sealers in advance and regularly sealing the wood is the best way to avoid water staining. Yet well-intentioned routines often fall by the wayside or the wood may not have been sealed in the first place.
Because water stains on wood come in different varieties, there is no single method of restoration. Removing water stains from wood is an imperfect science that requires patience, flexibility, and educated trial-and-error. You'll first need to assess the type of water stain that you have on the wood, then choose the method that works best.
Unpainted wood may have been previously treated with wood preservatives. Newer wood preservatives, while toxic, are far less toxic than older wood preservatives. As all are fungicides and pesticides that may be harmful to your health, care should be taken when working with wood that you suspect may contain wood preservatives. Household bleach is moderately caustic and oxalic acid is highly caustic, so always wear safety protection when working with these materials.
When to Remove Water Stains From Wood
Water-stained wood outdoors is best cleaned in the driest part of the year. Many of these stain removal methods require ample drying time, so further rain would only complicate your efforts. If any of the wood items can be moved into a garage, shop, or other dry, warm area, they can be cleaned at any time of the year and in any conditions.
- Working Time: 10 minutes
- Total Time: 25 minutes
- Skill Level: Beginner
- Material Cost: $5 to $15
What You’ll Need
All of the tools and materials, with the exception of the pressure washer, are inexpensive and easy to obtain. Depending on the cleaning method you choose for your situation, you may need only a select number of these tools and materials.
- Household clothes iron
- Clean, white, dry cotton cloth
- Garden hose and nozzle
- Pressure washer
- Stiff synthetic bristle brush
- Clean bucket
- Dense sponge
- Waterproof gloves
- Random orbital sander
- Fine grit (#220) sandpaper
- Eye protection
- Fine steel wool
- Deck cleaning solution
- Household bleach
- Concentrated oxalic acid wood bleach
- Cut lemon
Remove Milky-White Water Stains on Wood
White or light rings on outdoor tables are usually caused by wet glasses that discolor the top protective sealant. This type of stain is fairly easy to clean, with generally good results. First, try removing the stain with a dry iron and a clean cloth. If that does not work, try the abrasive method with fine steel wool and a lemon.
Drain all water from the iron. The iron must be absolutely dry before use. If the iron produces any steam, it may create stains on the wood.
Turn the iron to dry (or no steam) mode and let it heat up to its lowest level.
Lay a clean, dry, and white cotton cloth over the stained area. Dyed fabrics may transfer to the wood.
Pass the warm iron over the cloth a few times.
Periodically, lift the cloth to check on your progress. Use a new section of the cloth each time you put it back down.
Remove Water Stains on Wood Siding
Water stains on wood siding are often caused by dirt that has wicked up from dirty water puddles or wet soil. A frequent location for this type of staining is the bottom section of cedar or other wood house exterior siding that has come into contact with soil. Dirt-embedded wood siding may appear to be stained even when it isn't. Often, washing the wood clear of the embedded soil is enough to clean it.
With a spade or shovel, clear out about 12 inches of soil downward from the bottom lip of the siding.
With a garden hose and nozzle, spray one section of the stained wood siding from the top-down. If extra force is needed, gently spray the siding with a pressure washer.
If the cleaning is successful, continue with the rest of the siding.
Remove Dark Water Stains With a Bleach Solution
Dark water stains are difficult to remove from wood. However, by gently bleaching the wood with a diluted household bleach solution, you may be able to erase troublesome stains. Be sure to wear waterproof gloves for this method since bleach is caustic.
Create a solution of 50-percent cool water and 50-percent bleach.
Lightly apply the solution to the wood stains with a dense sponge. Do not drench the wood.
Allow the bleached wood to fully dry. This may take as long as a day or two, depending on the weather.
Assess the results. If a stronger solution is needed, change the mix to 25-percent water and 75-percent bleach and reapply.
Remove Stubborn Black Water Stains With Oxalic Acid
For extremely dark, stubborn black water stains and tannins, use a powerful bleaching concentrate called oxalic acid. Wear waterproof gloves and eye protection.
Dissolve the oxalic acid concentrate in hot water in a separate bucket or according to manufacturer's instructions.
Apply the hot solution to the stained wood with a scrub brush.
Since the solution must remain hot to be effective, reapply the solution as needed until the wood has bleached to the desired degree.
Rinse with clean water and allow to dry.
Remove Water Stains on Wood Decks
Water stains on wood decks may be accentuated by the dirt content in the water. When dirty water pools up and dries, dark-bordered stains are left behind. Wood decks require pressure washing and hand scrubbing.
Water down the deck by lightly spraying with the pressure washer on a wide spray.
Apply the deck cleaning solution to the deck stains.
Scrub the stained area and at least a couple of feet beyond with the synthetic brush.
Thoroughly wash off the cleaning solution and dirt with the pressure washer on a wide spray.
Remove Water Stains by Sanding
If the wood can be sanded and the stain has not penetrated too far, you may be able to sand it out. Sanding should usually be your last option because it scours off wood from the surface and can potentially damage it. Always start with finer-grit sandpaper, then work to coarser grit papers.
Fit the random orbital sander with a sanding disk.
Test sanding one side of the water stain to see if light sanding will remove it. If so, continue.
Move the random orbital sander in wide, sweeping passes. Do not press hard on the sander.
Occasionally sweep or vacuum off the wood dust to check on your progress.
Tips for Removing Water Stains From Wood
Since water itself is clear, it is usually other materials borne by the water that causes the staining:
- Wood tannins activated by the water can cause deep, dark stains.
- Water causes mold and mildew. Water, too, carries dirt into the pores of the wood and results in dark stains.
- Chalky-white water stains are often the result of alkaline-rich mineral deposits in hard water.
When to Call a Professional
Most of the methods for removing water stains from wood are basic and require no professional help. However, if you do decide to use a pressure washer, you may wish to hire a professional. Pressure washers are so powerful that they can deeply gouge the wood. Also, injection injuries can occur when water is forced under the skin at high pressure.