" " wisno wood furniture finishing: How to strip the old finish in the wood finishing

Monday, July 12, 2010

How to strip the old finish in the wood finishing

Strip the finish is a tough work, but sometimes it has to be done since many reasons. Finishing failure or the mistakes in the unfinished product are some reasons why we need to strip the finish. We also need to strip the finish when we want to refinish the old finish, especially when we want to finish with new color. According to the stripping method, a dry finishing layer can be classified into two kinds of finishing film layers: the finishing layer that can be resolved with solvent and the finishing layer than cannot be resolved with solvent. There are two different way to strip the finish according to the finishing type, strip the finish using thinner and strip the finish using chemical remover..

Strip the finishing layer with paint thinner.

There are some finishing type which are easily to be washed off and striped off with a thinner. They are the finishing which are dry by evaporation of their thinner without any chemical reaction in there. The lacquer or nitrocellulose finish is the most easiest finishing materials to be washed off with thinner. Other finishing materials such as: oil varnish, wax, shellac and water based finish are also be able to washed off with thinner but more difficult then the nitrocellulose. A simple test can be done to
determine whether a finishing layer can be resolved or not. Take a rag soaked in acetone or paint thinner and then use it to wipe on the finishing layer. If the finishing layer is rubbed off, it means that the finishing can be resolved and can be washed off with thinner. If the finish layer was not erased by this way then we have to remove the finish with chemical remover.

Wash off the finish with thinner is easier to do then chemically stripping, but it is still a big work. 
 
It is a step by step in stripping the finish with thinner (washed off the finish).
  • Take some cloth dampened with thinner and put on the surface of the finish until the surface becomes wet and soft. The thinner that is used to remove the finishing layer is thinner that has high solvability to dissolve the coating. Acetone is a best choice because it has very high solvability, but it is very quick to dry. To reduce its drying speed, acetone can be mixed with other solvents such as buthyl acetate, or lacquer thinner.
    • After finishing layer is wet and soft and then take other wet rag and wipe off the finishing layer. Do it until all the layers of finish removed from the surfaces. The objects with small size could be directly immersed in a thinner until the finishing layers become soft, and then cleaned again with a new thinner.
      • Use a stiff brush to clean the finishing materials that are still left in the cracks, pores, grain or other inside parts. Toothbrush can be used for this purpose with quite good results. To open the pores and grains sometimes we need to do with wire brush. Dampen the surface of paint thinner and then brush the surface carefully until all he finishing materials clean off.
        • Do a sanding to clean the rest of the finishing materials on the surfaces. The wash off process usually still leaves a light color from the stain that is absorbed and left in the wood. To clean it and make a clean surface such as white wood color, a good sanding is needed. A scuff sanding with # 180 sandpaper, then continued with # 240 sandpaper usually is enough to clear up the stain and produce a white wood surface. 
          Strip the finish chemically.
           
          The finish that are dry with a chemical reaction such as: polyurethane, acid curing, precatalyzed coating, UV coating, polyester, and other catalyzed coating can not be resolved with solvents. The water based coating sometimes is also take too long time to be washed off with thinner. The finishing removal for that finish requires a special chemical that is used to break the paint. The chemical for this purpose is called a paint remover. Paint remover will ruin the finish layer so that a finish layer can be removed and cleaned from the surface to produce a new surface. 

          It is the step to strip the finish by chemical remover
          • Apply paint remover to the surface, evenly. Then let it stay for several minutes. After a few minutes then the finish coat will shrink and apart from his underneath surface.
          •  Remove and clean the finish layer that is already contracted  with use a spatula or knife. Separate the finish layer from its underneath surface, until all the layers of paint  is lifted.
          • Use a cloth dampened with paint thinner to clean the surface from the remaining layers. To clean the finishing materials that are left inside the pores, cracks of wood grain we may need to do with wire brush or stiff brush.
          • Do the sanding on the surface until we got a smooth and white surface. A sanding  with a # 180 sandpaper, followed by # 240 sandpaper is a necessary to produce a white surface for a new finishing process.

          This thing must be considered in the finish stripped off
          • Paint remover is a reactive chemical it can caused an injury. Avoid getting the chemical into the skin or other body part when dealing with this chemical. Use safety equipment like gloves and masks.
          • Be careful when using paint thinner. The thinner may solve the glue in the wood. Too much paint thinner could resolve the glue and damage the wood construction or even in the veneer attachment.
          • The sanding process on the cleaned surfaces needs to be done correctly. The new finishing process always needs a clean, smooth and even surface. The surface which is still not clear or uneven will make problems to the next finishing process. So, although a bit difficult, the sanding should be done correctly to produce a smooth, even and clean surface. 

          1 comment:

          1. I have just installed iStripper, so I can have the sexiest virtual strippers on my taskbar.

            ReplyDelete