White rings — or even white shapes other than rings — usually result from moisture getting into the finish. That causes a spiderweb of minute cracks, which makes the area look white. Sometimes the cracks become almost invisible when the moisture evaporates. Bona, a company known for a line of floor finishing and cleaning products, suggests nudging the moisture out by gently warming the area with a hair dryer (set it to low and move it back and forth over the area for up to 10 minutes) or a dry iron. If you use an iron, use the lowest setting, place a cloth between the sole and the table and check your progress every 10 minutes. Do not use a steam setting — that would only compound the problem.
If heat doesn’t work, try working something oily into the finish to replace the moisture, which would then eliminate the white haze. Many people turn to mayonnaise because it’s oil in a paste form. “Whether you’re using mayo (full fat) or petroleum jelly, the idea is to apply a small portion to a cleaning cloth and buff out the water stain,” Bona suggests on its website. “If it doesn’t work after the buffing, you can try applying the mayo or petroleum jelly to the stain and let it sit overnight.”
If the white marks persist, a variety of products can help extract moisture and fill fine cracks to make them less noticeable. Liberon ring remover ($29.99 for a 125 milliliter can at Rockler), for example, works on most finishes, including varnishes, shellac, lacquer, French polish and polyurethane. Just rub it in with a cloth, allow it to dry and form a powder, then buff with a clean cloth. If your table is waxed, remove the wax first with mineral spirits and rub on new wax after using the ring remover. If the repaired area looks too shiny, take out some of the gloss by rubbing it with superfine steel wool (sold as 4/0 or 0000).
Not all water damage responds to these treatments, though. Sometimes the water leaves dark stains, not white ones. That’s a sign that the water has gotten through the finish and into the wood, where the moisture reacted with tannin and caused a stain. The only satisfactory solution then is to strip the finish, take out the stain with a wood bleach or by sanding, and refinish.
And there is the case you are asking about: where the moisture not only made the wood look white but also created a noticeable bump. Your table is almost certainly veneered, meaning that the top has a thin layer of beautiful wood glued to a base material, which could be plywood or particleboard. When veneer gets wet for too long — a likely scenario under a potted plant — the moisture cannot only cause cracks in the finish; it can also cause the glue to lose its grip, allowing the veneer to swell from the moisture and bubble up.
Carol Fiedler Kawaguchi, who repairs and refinishes furniture through her business, C-Saw, on Bainbridge Island in Washington, said she has sometimes been able to get bubbles on veneer flat again by slicing them, poking in a little hide glue on the side of a knife blade, and then clamping the veneer until the glue dries. If the patch is too far from an edge to secure clamps, she uses thick pieces of wood to span the table and clamps them near the edges. Wax paper can keep excess glue from also gluing down the boards.
But before you try to flatten the bubbles, Fiedler Kawaguchi suggests that you gently sand the raised area to see if you can expose veneer that’s its natural color. Some veneer is extremely thin. If the veneer on your table is white all the way through, don’t waste your time trying to glue it down.
A better solution would be to patch the veneer. Rockler.com sells mahogany veneer, which appears from your pictures to be the type of wood you’d need, at $11.99 for a hobby pack of 3 square feet, which should be more than enough. With a utility knife, outline a small square on the tabletop with the white bubble in the center. Make repeated cuts until you have sliced through the veneer. With a sharp chisel, clean out all the veneer and old glue within that area. Make a pattern of the opening by placing a piece of paper over it and pressing along all the edges. Then cut a matching square of veneer, taking care to align the grain lines to match the surrounding surface. Custom-fit the patch by sanding the veneer edges where necessary. Consider applying finish to the patch before you glue it in place using hide glue, or plan to refinish the tabletop.
Hide glue is an ideal choice for working with veneer. It’s what holds together most older pieces of furniture, so it’s plenty tenacious. One benefit is that it dries hard, so you can completely sand away any overflow. (Most wood glues become sticky because of the friction heat of sanding, so they leave a residue that interferes with refinishing.) Also, you can soften dried hide glue with heat or moisture, which means you can remove the patch and redo it if you don’t like your first attempt.
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