Design & DIY

How to remove water stains from wood furniture

Perhaps the culprit is a cold gin and tonic that condensed on a hot summer day, or an overflowed plant pot, but water can leave your furniture with unsightly blemishes. The first step to solving this damage is to figure out just where the stain lies.

Is the damage in the finish or the wood below?

Unlike the spar varnish on a boat, furniture finishes are not impervious to water. But modern varnishes will give you greater protection than earlier-generation coatings like lacquer and shellac. The latter two have organic bases, and within the hour you can see the telltale white stain of water infiltration. Varnishes, on the other hand, may require that your wet glass sit there all weekend in order for the water to paint a white ring. That white stain tells you that the damage is just within the finish film.

If the stain you’re confronting is not white, but rather grayish-black, this is the signature of water that has made it through the finish and into the wood. What you have now is a fungal attack enabled by moisture that has been around long enough to create a mycological habitat in your table top. While moulds may be the cause here, the stain may also be from iron in the water reacting with tannins in the wood. Generally, these sorts of stains happen beneath plant pots with porous bases, hence they really get ‘established’.

Repairing white water marks

The first step to restoring water-damaged finish is to drive out the moisture. It’s possible to do this with an iron over a cloth, but too much heat, or too textured a cloth, and you may imprint the finish. And if the surface is veneer on an antique, chances are it’s glued on with hide glue. Dwell too long on the stain, and you might be regluing veneer next. My favourite way to dry this up is to use radiant heat from a heat lamp. The beauty of radiant heat is that it warms the object and not just the surface of the finish. Again though, exercise caution: keep the lamp about 50cm away so that you don’t bake the surface.

Keep checking the stain every few minutes, and when it has faded away, remove the heat. There may still be traces of the white mark, but the next step should set the surface right. Take a piece of cloth dipped in Danish oil, and rub it into the area of the stain. Let it soak in for half an hour before wiping it clean. If the surface is generally dull or lightly scratched, you may wish to oil the entire surface now. 

Dealing with black water marks

This process is more involved, as we need to remove all the finish from the damaged surface. Using stripper or sandpaper, you’ll need to get back to the bare wood before you tackle the damage. Pour half a litre of warm water into a non-ferrous container, and then begin adding oxalic acid crystals (the hardware store should have this stuff, as it also used to remove iron stains) until no more will dissolve—a saturated solution. After stirring, brush it onto the entire surface to avoid blotches. It shouldn’t be too long before the stain vanishes, and then you need to rinse the area well to be sure you leave no residue. Evidence of remaining chemical will appear as crystals on the dried surface. If this happens, wipe them off first, then just rinse some more. The water will likely cause the surface to be a tad furry upon drying. Sand lightly with 220 grit paper to knock down these fibres, and then you’re good to go with new finish.

Sean Ledoux is a designer/master fine craftsman working with wood and other found media to create unique furniture. Having diversified skills helps support studio life in North Bay, ON.