Surface Finishing November 3, 2012 Reference: Understanding Wood Finishing by Bob Flexner American Woodturner, Summer 2005 CLEAN SURFACE A. Tack rag B. Compressed air C. Clean with mineral spirits SEALING-must be compatible with the finish A. Any finish will seal B. Sanding sealer 1. Contains mineral soap (zinc stearate) to make sanding easier, doesn t clog sandpaper 2. Will weaken the finish 3. Vinyl sealer for lacquer-hard to sand, but no soap 4. Sealers may raise the grain C. Surface quality-gloss, semi-gloss, satin, flat and dead flat-add flatting to scatter the light THE WAY FINISHES CURE-goes from a liquid to a solid A. Evaporative-shellac, lacquer 1. Solvent-alcohol for shellac and lacquer thinner for lacquer 2. Solvent evaporates leaving long strands that interlock-solvent will turn finish to a liquid B. Reactive-Varnish and curing oils 1. Chemical reaction after solvent evaporates.
-2-2. Chemical reactiom-crosslinking or polymerization-solvent won t break the bonds. Must sand to create a mechanical bond C. Conversion-needs catalyst to cure (varnish and Lacquer) 1. Can bond to lower coat before the finish cures, otherwise use mechanical bond 2. Expensive and not practical for woodturning D. Coalescing-water base 1. Droplets of a cured finish in water and glycol ether. 2. The water evaporates and the glycol ether softens the droplets so they intertwine but do not crosslink. 3. Can soften with alcohol or lacquer thinner 4. Same system in white and yellow glue-doesn t dissolve in water, but will in acetone or lacquer thinner. TYPES OF FINISHES A. Oil 1. Straight Oil-cures by absorbing oxygen or driers added a. Linseed oil-slow cure, driers added b. Tung oil-slow cure, very thin finish 2. Polymerized oil-fast cure,expensive-varnish better 3. Wiping varnish
-3- a. Thinned so it can be wiped with a cloth b. Some called an oil finish, but not oil c. Can be built to a thick layer d. Usually 2 parts mineral spirits to 1 part varnish e. Varnish made by cooking oil with resinsphenolic, polyurethane, etc. B. Oil/varnish blends 1. Slow cure, soft finish 2. Watco Oil C. Myth-Products with Tung Oil may not have any Tung Oil. Example: Tung Oil Varnish is wiping varnish D. Wax-Cures soft with little protection against heat, water, water-vapor exchange. Doesn t change the color of the wood. 1. Types a. Beeswax-soft with medium gloss sheen b. Carnauba wax-hard with high gloss sheen c. Paste wax-contains a solvent, may remove a finish if not completely cured. The solvent evaporates to form a solid E. Sanding Sealer 1. Any finish is a sealer 2. Sanding sealer makes the first coat easier to sand 3. Contains soap (zinc sterate) F. Shellac-natural resin secreted by the Lac Bug 1. Good sealer
-4-2. Good barrier to stain 3. Good rubbing properties 4. Dries fast-little dust problem 5. Easy to repair 6. Thinner-methanol, ethanol, or isopropyl alcohol G. Lacquer 1. Fast cure, little dust problem 2. Good resistance to wear and heat 3. Developed in the 1920 s from gun cotton and resins (nitrocellulose) H. Varnish 1. Excellent heat, wear, solvent, acid and alkali resistance. 2. Excellent water and water-vapor resistance 3. Slow cure, dust problem 4. Made by cooking a curing oil with a resin 5. Cures by absorbing oxygen as the thinner (mineral spirits) evaporates FINISHING THE FINISH A. Need to level the surface-use sandpaper, steel wool, 3M pads, rubbing compounds, and polishing compounds B. The shine is controlled by the findness of the scratches. C. The finish should be cured-know the hardness before sanding or rubbing, may go through the finish D. Rubbing compound
-5-1. Pumice-lava rock and lubricant 2. Rottenstone-limestone and lubricant 3. Lubricants a. Mineral spirits or naphtha b. Wax c. Soapy water 4. Commercial compounds a. Behlen s Rubbing Compound b. Mirror Glaze c. Automotive compounds E. Caring for the finish 1. Causes of deterioration a. Strong light b. Oxidation c. Contact with heat, water, solvents, acids and alkalis 2. Wax only protects from wear-adds to the shine a. Beeswax, carnauba wax b. Commercial wax-briwax, Minwax, Trewax, Johnson Paste Wax, etc. c. Little benefit from expensive waxes d. Caution-some waxes contain solvents that will damage finishes (tolulene in Briwax) TYPES OF DEMONSTRATED FINISHES CELLULOSE SANDING SEALER A. Contains soap (zinc state) for ease of sanding B. Wipe on two or more coats C. Run lathe slow with a wet paper towel to level the
-6- finish. If the towel grabs, rewet and continue. D. Smooth between coats with a Scotch Brit pad (purchase white floor finish pad at Home Depot or floor finishing supplier-very cheap) E. Final buff with a blue paper shop towel. F. May buff & wax for a higher shine or G. Proceed to a padding lacquer finish PADDING LACQUER FINISH A. Shellac, oil and additives B. Cover area in a circular, over lapping motion, while turning the lathe by hand. C. Wet blue towel with finish and run the lathe slow to level the finish D. Smooth with steel wool, sandpaper, or Scotch Brit E. Repeat for two to six coats F. Buff last coat (700-800 RPM) 1. White Diamond 2. White Rouge 3. Carnauba wax (hard wax) 4. Polish with a soft wheel SPRAY LACQUER A. Spray can (rattle can) B. Spray gun-air compressor (Presented by Ron Phillips) Wipe on Poly (Presented by Tom Cour) C A glue (Presented by Allen Becker) SUPPLIES A. Mylands Cellulose Sanding Sealer
B. Master s Magic Padding Lacquer C. Hud Crystal Coat D. Various friction polishes, Deft (lacquer) E. Waterlox-Tung Oil? (wiping varnish) F. Buffing supplies-indian Supply House (San Mateo, 1 block south of I-40) -7-1. 8 buffing wheels-one each for white diamond, white rough, carnauba wax, and polish 2. Remove sewing to make the wheels more flexible and soft. Particularly the final polish wheel MENTOR PROGRAM A SEMINAR CAN BE ARRANGED TO HAVE A HANDS ON WORK SHOP WITH SEVERAL INSTRUCTORS FOR DEMONSTRATIONS AND HANDS ON INSTRUCTION.