How To Repair A Water Stain On Wood Table

Posted Baronial xviii, 2021

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Work miracles on wood with oxalic acid.

Watering a potted plant can be disastrous if the found lives on superlative of something made out of woods. We've all seen the white spots and blackness rings that can effect when water seeps through the pot. And if you lot've ever tried to sand out these marks, you know it's a tough job that can exit telltale depressions on the surface. Fortunately, in many cases, this type of damage tin be most magically undone by treating the wood'due south surface with oxalic acid.

Oxalic acid removes the grayness color from oxidized wood, without changing the wood'due south natural color. That's why it'due south unremarkably used as the active ingredient in deck cleaners, and why restorers use it to remove gray or black water stains on furniture (see "Oxalic Acid Undoes Rust," below). Oxalic acid is also used in some household cleaning products for removing hard h2o stains, and it has many industrial uses as well. Although it is found as a natural ingredient in some vegetables (spinach and rhubarb), oxalic acrid is quite toxic if ingested in concentrated grade.

Place the stains

Every finish repair chore is unique, of course, so the outset step is to thoroughly examine the problem. The chest lid shown here has both whitish marks (also called blushing or blossom), and night gray and black discolorations. White marks are normally in the terminate; dark discolorations from water indicate more meaning damage, because they're down in the wood.

To assist formulate a plan to repair this finish, I dampened the entire lid with mineral spirits [Amazon] (paint thinner). This testing method is useful someday y'all desire to await closely at either erstwhile dry finish or blank wood. The look of the paint thinner-dampened surface is similar to how it would look if shellac or a clear oil based finish were applied. In this case, dampening the surface makes the whitish marks temporarily disappear (they reappear when the mineral spirits evaporates). That means a coat or two of finish is all that's needed to accept care of the white marks. (This is a stroke of luck; if the white marks hadn't disappeared, boosted repair steps would be necessary to remove them, and that'southward a topic for another story.)

Now I tin focus on the black rings. The mineral spirits test shows that they get darker, and that makes them good candidates for handling with oxalic acid. If the oxalic acid works, I won't have to aggressively sand the entire lid. Not simply would sanding remove the remaining intact finish (80%, in this instance), it would too lighten the chapeau's aged red color, so it would no longer match the balance of the chest that it belongs to.

Treat the stains

one. Start past thoroughly cleaning the surface. First, wipe it down with mineral spirits, to remove smooth and other crud that'south greasy or waxy. Mineral spirits also shows what the damaged areas will look like with a clear finish applied.

Every step of this handling should exist done consistently to the entire surface, not just the damaged expanse. The procedure involves flooding the surface with water. Fortunately, the harm shown here is on solid woods—using this treatment on a veneered surface can be risky.

2. When the mineral spirits has evaporated, consummate the cleaning process by wiping the surface with lather and water, using a soft cloth, to remove water-soluble residue. Let the surface to dry completely.

The commencement footstep is a thorough cleaning, using two different cleaners. Mineral spirits removes greasy residual, such as quondam wax or polish (Photo one). Mild dish soap and h2o removes any water-soluble crud (Photo two). Neither of these processes will harm an intact finish.

3. Sand lightly, using fine paper, a soft block and very little pressure. Although the goal is to remove the raised grain from the damaged expanse, information technology's important to sand the entire surface to maintain consistency.

The grain is raised very slightly in the h2o-damaged surface area, so a little sanding with 400 dust paper is necessary (Photograph 3). This stride should have about one minute.

4. Mix a saturated solution of oxalic acid in a non-metallic container. Add a spoonful at a time to the water and stir, until a layer of non-dissolved oxalic acid remains at the lesser.

Mix up a saturated solution of oxalic acid [Amazon] by adding the crystals to a jar of warm water with a plastic spoon (Photo four). Practise not use whatever metal containers or utensils—the acid could react with the metal. Add crystals a spoonful at a time and stir until no more volition dissolve into the water. I always use a saturated solution, so that I have a maximum-forcefulness problem solver.

five. Wipe on the oxalic acrid solution. Leave it on the surface for nigh five minutes to achieve the maximum consequence. And then wipe off the excess and let the surface dry thoroughly. The issue tin be almost instantaneous.

Wearing gloves and heart protection, use a rag or sponge to saturate the entire surface being treated, not merely the dark spots (Photo 5). Keep the surface wet for nearly 5 minutes to allow for the maximum result. Then wipe off the excess and let the surface dry completely. You may see the result immediately as you use the acid, or the spots may disappear gradually, as the acid dries. If a second awarding of acid is necessary, await to employ it until the start awarding has thoroughly stale, or it won't work. If two or three applications exercise non remove the stain completely, more acrid is not likely to help. You'll have to live with the remaining discoloration or resort to sanding to remove it. Withal, do not sand until you have thoroughly rinsed the surface—breathing dust that contains oxalic acid is extremely unpleasant and potentially hazardous.

vi. Alluvion the surface with water repeatedly, to remove whatsoever remaining oxalic acrid crystals.

When y'all've completed the oxalic applications, it'due south imperative to thoroughly rinse the treated surface with lots of make clean water, to flush away any acrid that remains on the woods (Photo 6). Flood the surface several times and dry information technology with a clean cloth or paper towel each time. Let the surface dry between each flooding.

Attempting to "neutralize" the acid that remains on the surface with a mild alkali such as baking soda, borax or ammonia is a cleansing option that is oft mentioned every bit an culling to rinsing. Even so, I accept never seen any authentic formulas that would make this chemic balancing act a applied possibility. Besides, I know that thorough rinsing works.

Dampen the sur- face up with mineral spirits to test the results. Here, the whitish blush areas well-nigh disappear and the blackness marks are 99.ix% gone. The repair is consummate; it'southward time to rebuild the terminate.

After the hat has thoroughly stale, don a respirator and lightly sand the unabridged surface with 400 grit paper, to cutting back whatever grain raised by the oxalic treatments. Exam the surface again with mineral spirits, to gauge the results (Photo 7). The test on this lid indicates that the surface is ready for finishing (Photo eight).

In this case, the end is blonde shellac, the aforementioned stop as the original. Adding a waterproof terminate over the shellac could help to forbid futurity damage. Moving the institute may be a better choice.

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