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TGIF stripping Sometimes, we’re faced with stripping and refinishing a piece of furniture. Finishes that are cracked severely or turned soft and gooey are beyond trying to save. Getting the old finish off Generally speaking, scraping or sanding is a poor way to remove an old finish. Unless you are taking off a significant amount of wood (like on a floor refinish), your removal of finish and stain will likely be uneven. And it will take a long, long time and lots of sandpaper to remove an old finish. Even if it looks good in the raw state, there may be some areas where finish remains in the surface of the wood. Likewise, removing with a heat gun is risky because of potential damage to the wood and glues. The way to go is with a chemical stripper. There are several types. With all types, be sure to wear eye and skin protection (including chemical-resistant gloves) and work in a ventilated area. While using a chemical stripper is messy and can be smelly, it’s usually over much faster than sanding and going through many sheets of gummed up sandpaper. Bite the bullet. Methylene Chloride (MC) This is the most common type and has been used for many years. It’s also one of the strongest and fastest working Be sure to use this in a well-ventilated area. This type is usually considered to work “from the bottom up” releasing the bond between the finish and the wood. It evaporates fairly quickly, so some types include a wax as a vapor sealer. For the same reason, put on a thick coat and don’t keep working it around. Another technique is to put on the stripper and cover it with a sheet of plastic (VisQueen). Let it work, usually longer than the can recommends, and scrape off with a putty knife and discard the gunk. A bucket of can of sawdust works well to hold the goo. MC is heavy so look for the can with the heaviest weight and it will have a better concentration of MC. Safety warning: MC is a suspected carcinogen. I have a friend who died from cancer that he attributed to his PhD lab work with MC. But tests have been somewhat inconclusive. Also it can affect the oxygen carrying capacity of your blood – don’t use this if you have a heart condition. N-methyl Pyrrolidone (NMP) Sometimes sold as “safe” or “citrus” strippers. It is a slower evaporating and slower working stripper. It is said to “work from the top down.” The recommended stripping dwell time is often optimistic, so let it work. Likewise, putting on a sheet of plastic will keep it wet longer. I’ve often put it on in the morning and let it work to mid-afternoon. Some people let it work overnight. NMP strippers also make an excellent brush cleaner. Put some in a jar and soak your brushes in it. The next day, they’ll clean up with soap and water. Safety warning: NMP is not “harmless” but evaporates so slowly that it will mostly dissipate. But ventilate where possible. With either of the above, especially in semi-paste format, use a stiff brush, cord, or angled scrapers to get all the residue out of the convex areas such as carvings, turnings, and moldings. You can also use coarse sawdust such as from a jointer or planer rubbed into the softened finish. Because of the potential for wax or residues, I recommend scrubbing with a strong solvent like acetone, lacquer thinner, or even mineral spirits. Acetone-Toluene-Methanol. (ATM) This is a mix of solvents commonly found in lacquer thinner. These are often labeled “Furniture Refinisher” and not stripper. Formsby’s Furniture Refinisher is one common type. This is flammable and needs to also be used in a well-ventilated area. To use this type, you scrub the finish with steel wool or Scotch-Brite soaked in the stripper, keep dipping it in and scrubbing and wipe with a cloth dampened in same. This is perhaps more laborious (you don’t just apply and wait). I’d recommend this for small objects only. ATM are effective on shellac, lacquer (the most common factory finish) and water based finishes, but not so much on varnishes. Lye (Sodium Hydroxide) This will remove some finishes, but has IMO, several disadvantages. It is very caustic and your skin and eyes need to be very protected. Vapors can also be noxious. It has become harder to obtain (you used to be able to find it grocery stores) since it’s used in meth labs. And it can alter the color of some woods via chemical reaction. Lye can also degrade some wood fibers. Residues , a strong alkali, may affect some finishes if not thoroughly rinsed. So scratch this one off your list. OK, so you don’t like stripping or don’t have a place to do it (especially in the winter time). You can “sub it out” (@stick) and have a furniture refinisher do the stripping for you They are likely to throw it in a tank of hot stripper for a while, so it may affect the joinery. Just a warning. After the stripping. Regardless of what stripper you use, make sure it’s thoroughly rinsed of and removed. Then let it dry well, for several days if possible (ATM is a little more forgiving if you are going back over with a shellac or lacquer). Sand to remove the fuzzies. Remember, it was once sanded before it was finished, you don’t need to do very strong sanding unless you are removing defects. Be especially careful on veneered or plywood surfaces. It’s easy to sand through these. I normally do a light sanding with 180 or 200 grit. Once that you are at this stage, continue with your staining and finishing just like you would with a new wood project. >>> OK >>>> I'm reaching the end of my list of topics that came to mind. I'm open to suggestions. What would you like to see / discuss? Further reading Refinishing considered bad? Not always. http://masterpiecefurniture.com/design_notes/flexner/antiques_roadshow.html
