Fixing White Water Rings | Popular Woodworking Magazine
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Understanding of the causes and remedies of this typically superficial damage.
A a friend sent me a web link to a video and a short text recommending the use of mayonnaise to remove the white water rings on the tables thinking I would mock this remedy. I did not. I’ve actually seen mayonnaise work quite well.
But the removal of white watermarks is unpredictable. There is no foolproof procedure. The variables that affect the result include the type of finish, how old and porous it is, and how long the watermark has remained.
I wrote about methods for removing white watermarks in the April 2001 (# 121) issue of Popular magazine for woodworking. I don’t have much to add to these, but I can better explain why the signs are occurring – and knowing what’s going on ultimately helps to understand the remedies.
Watermarks and blush
White water-induced rings are similar in causes and remedies to varnish and shellac redness. When you spray one of these finishes on a humid day, the finish “blushes”. It becomes milky white. This discoloration can be removed in one of several ways: sand with steel wool or other abrasive; spray over a slow evaporating thinner, such as a paint retarder; or wait overnight. Sometimes it will disappear on its own.
Abrasion works because the redness is almost always very close to the surface. Spray paint retarder works by redissolving the finish onto the surface, then taking longer to evaporate to give the moisture time to dry before the finish dries. Waiting overnight works if there is still enough solvent in the finish to compress the molecules as the moisture evaporates. In the case of slower evaporating solvent-free shellac, you can wait for a drier day and sprinkle some denatured alcohol on the blush. You can do the same with paint by spraying paint thinner on a drier day.
Redness does not occur in slower drying finishes like paint and water-based finish, but watermarks can occur if the finish is old and cracked.
The same three tricks for removing redness usually work on watermarks: abrade, redissolve (with paint and shellac), or give the mark time to lighten on its own.
So what’s going on in the end to break the transparency, in both blush and watermarks? One of two things. Either tiny water molecules are binding to the finish causing the light to be interrupted, or the water molecules are evaporating through the finish and leaving voids that interrupt the light.
The second explanation makes more sense to me because it fits my experience better. It is best suited to fading redness after a short time and is best suited to a solvent which has the effect of completely removing redness or watermarks.
It also fits to better explain watermarks. The water enters a slightly deteriorated and therefore porous finish, dissolves impurities and leaves gaps when it dries.
Either explanation could explain why abrasion removes redness or watermark. The damage is almost always very close to the surface and you are simply removing that part of the finish.
The safest way to remove watermarks is to abrade them. Works with all finishes except ultra high performance finishes such as catalyzed (conversion) paint, which is too hard to be removed with fine abrasives. I even managed to remove the watermarks with a mildly abrasive toothpaste (this was at a relative’s home when no steel wool or sandpaper was available).
The problem with using an abrasive is that it changes the luster of the finish in the areas you rub. The abrasive makes shinier finishes flatter and flat finishes shinier. You can play around trying to get the abrasive you are using the right way, but still create the shine with the scratches rather than the flattened agents in the finish, and the scratches will look different in reflected light.
The solution to achieving an even shine is to rub the entire surface. Or you can apply another finishing coat after removing the watermarks.
Using a solvent to remove watermarks works on shellac and lacquer, which redissolve on contact with their solvent (shellac alcohol and paint thinner). I’ve even had success at times using denatured alcohol on a lacquer finish. Success varies depending on how the lacquer was made.
Just like with blush, the solvent dissolves the surface of the finish so that the molecules settle back to fill the voids. With the old paint and water-based finish, which can be watermarked because the finish is porous, a solvent cannot be used. You will need to abrade the finish.
I’ve also heard of using a heat gun to remove watermarks. Basically, you are heating the finish to put it back in solution so that the voids disappear. This only works with shellac and lacquer, but as you can imagine it is risky because if you heat the surface too much, you could cause the finish to bubble.
So why does mayonnaise sometimes work, at least to fade the watermark a bit? It is because mayonnaise enters the finish in the same way as water and fills the gaps. Furniture polish isn’t effective because it evaporates, but mayonnaise isn’t, at least for a long time.
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