Surface Preparation for Painting Wood

PART 1–GENERAL

1.01 SUMMARY

1. This specification provides guidance on preparing wood surfaces for painting.

2. Wood surfaces scheduled to be refinished with a transparent finish shall have existing coating stripped and sanded prior to application of new coatings.

3. Wood surfaces scheduled to be finished with an opaque finish shall either be stripped or sanded as required to produce a smooth substrate for application of the new coatings.

4. See also:

   1. “Primers and Paints for Wood”

   2. “General Guidelines for Painting Exterior and Interior Surfaces”

   3. “Supplemental Guidelines for Removing Paint from Interior and Exterior Wood Surfaces”

   4. “Chemically Removing Paint from Wood Features”

   5. “Removing Paint from Wood Features Using Thermal Methods”

PART 2–PRODUCTS

2.01 MANUFACTURERS

1. American International Tool

Cranston, RI

1-800-932-5872

2. Benjamin Moore

Montvale, NJ

855-724-6802

3. PPG Architectural Coatings

1-800-441-9695

2.02 MATERIALS

NOTE: Chemical products are sometimes sold under a common name. This usually means that the substance is not as pure as the same chemical sold under its chemical name. The grade of purity of common name substances, however, is usually adequate for stain removal work, and these products should be purchased when available, as they tend to be less expensive. Common names are indicated below by an asterisk (*).

1. Paste Wood Filler: Solvent-based, air-drying, paste-type wood filler for use on open-grain wood on interior wood surfaces such as “Benwood Wood Grain Filler 238” (Benjamin Moore) or approved equal.

2. Trisodium Phosphate (TSP):

CAUTION: TSP IS BANNED IN SOME STATES. REGULATORY INFORMATION AND INFORMATION ON ALTERNATIVE OR EQUIVALENT CHEMICALS MAY BE REQUESTED FROM THE ENVIRONMENTAL PROTECTION AGENCY (EPA) REGIONAL OFFICE AND/OR THE STATE OFFICE OF ENVIRONMENTAL QUALITY.

1. 1. TSP is a strong base-type powdered cleaning chemical sold under several brand names.

   2. Other chemical or common names include Sodium Orthophosphate; Tribasic sodium phosphate; Trisodium orthophosphate; TSP*; Phosphate of soda. Available from chemical supply house, grocery store, supermarket or hardware store.

   3. Products sold as substitutes for TSP may contain soda ash (sodium carbonate) and/or zeolites.

      1. However, sodium carbonate is not as strongly basic as trisodium phosphate, making it less effective in demanding applications.

      2. Zeolites are used in laundry detergents and rapidly break down in water, claiming to be essentially nonpolluting.

   4. Potential Hazards: CAUSTIC TO FLESH, DAMAGING TO THROAT IF INHALED.

   5. Safety Precautions: Wear proper personal protective equipment, and avoid inhalation, contact with skin and eyes, and do not ingest.

-OR-

3. Non-ammoniated detergent such as “Tide”

-OR-

4. Liquid bleach containing 5% sodium hypochlorite (common household bleach)

5. Boiled linseed oil

6. Pure steam-distilled turpentine (must be clean and clear so that it will not adversely affect the texture or durability of the paint)

7. Caulking Compound (listed in order of recommended usage):

   1. Polyurethanes

      1. Easily workable

      2. Paintable

      3. 15-20 year life span

      4. Limited availability

   2. Polysulfides

      1. Slow-drying

      2. Can be sanded and painted

      3. Highly elastic

      4. Limited availability (most frequently used for marine repairs)

   3. Butyls

      1. Paintable

      2. Cannot be sanded

      3. 7-10 year life span

   4. Silicones

      1. Some can be painted

      2. Generally cannot be sanded

   5. Acrylic Latex:

      1. Paintable

      2. 5-10 year lifespan

8. Clean, potable water

2.02 EQUIPMENT

1. Sanding blocks, sanding sponges, orbital sander, all with a variety of grits.

2. HEPA-rated sanding vacuum.

3. Stiff, natural and nylon bristle brushes

PART 3–EXECUTION

3.01 PREPARATION

1. Protection: Spot-prime exposed ferrous metals such as exposed nails heads that could come in contact with surfaces that are to be painted over with water-based paints. Use a suitable corrosion-inhibiting primer capable of preventing flash rusting and compatible with the coating being used.

2. Lead paint hazards

   1. NOTE: SANDING DUST MAY CONTAIN LEAD; REGULATIONS PROVIDED BY THE EPA REGIONAL OFFICE AND/OR THE STATE OFFICE OF ENVIRONMENTAL QUALITY CONCERNING THE HANDLING OF LEAD-BASE PAINT MUST BE FOLLOWED.

   2. NOTE: SURFACES SHOULD BE TESTED FOR LEAD CONTENT IN ADVANCE OF WORK. IF THE TEST IS POSITIVE AND YOU ARE NOT CERTIFIED TO HANDLE LEAD-ABATEMENT TASKS, IT IS ILLEGAL FOR YOU TO PERFORM FURTHER WORK.

      1. As of 2010, those who perform indoor or outdoor renovation, repair, and painting projects that disturb lead-based paint in various facilities that were built before 1978 must be certified through the EPA, trained, and follow specific work practices to prevent lead contamination.

      2. Violators can be fined up to $37,500 per occurrence, per day.

   3. For further lead paint abatement information, consult resources produced by leading experts, including the EPA, HUD, NCPTT and the Building Research Council.

3. Surface Preparation:

   1. Lightly sand all surfaces, either by hand or with a sheet orbital sander, using fine grade sandpaper.

      1. Chemical paint removers often raise the wood grain. Any rough fibers of raised grain will need to be sanded smooth as they will otherwise weaken the paint film causing premature paint failure.

      2. Thermal methods of paint removal often leave behind hard particles of paint residue. These will also need to be removed prior to repainting to ensure a smooth paint finish.

      3. Other paint removal technologies include steam generators (like those used for wallpaper removal) and infrared paint stripping.

   2. If only limited paint removal is required, feather edges of sound paint to provide a smooth transition between the old and the new paint. Use either hand methods or a sheet orbital sander.

NOTE: BELT SANDERS SHOULD ONLY BE USED BY EXPERIENCED PERSONNEL. THEY WORK VERY QUICKLY AND IT IS EASY TO DAMAGE THE WOOD SUBSTRATE IF THEY ARE NOT USED CAREFULLY.

4. Scrape and clean small, dry, seasoned knots and apply a thin coat of white shellac or other recommended knot sealer before application of putty or plastic wood filler to finish surface imperfections. Sand smooth when dried.

5. Fill all nail holes, voids, surface defects, etc. prior to refinishing.

   1. Putty stop holes where nails are set and screws countersunk on all finished woodwork.

   2. Use putty or spackle to repair voids, cracks, minor splits, and similar surface defects in finished woodwork that is to be painted or stain-varnish finished.

6. Recondition wood to ensure a tight bond between the new paint and the wood. Wood that is not reconditioned after paint removal may absorb too much of the binder in the paint, resulting in poor binding of the prime coat.

   1. Mix 2 parts boiled linseed oil with 1 part pure steam-distilled turpentine.

   2. Apply liberally with a brush and allow to dry.

   3. Repeat as necessary until dry surface has a slight sheen.

7. If all paint has not been removed, wash the painted surfaces to remove all grease, dirt and mildew, and to ensure adequate adhesion of the prime coat.

   1. Traditionally, a solution of 3 quarts warm water mixed with 2/3 cup trisodium phosphate (TSP) and 1/2 cup NON-AMMONIATED detergent has been used for this cleaning process. Before attempting this, be sure to read the TSP cautions in 2.02 B. above, and consider alternatives to TSP use.

   2. To combat a mildew problem, add 1 quart of liquid bleach to solution. For stubborn mildew, straight bleach may be necessary.

   3. Scrub surfaces with a medium bristle brush and rinse with clean, clear water. Make sure the surface is completely rinsed before painting.

   4. NOTE: WHEN TSP IS MIXED WITH WATER, IT FORMS FREE ALKALI. THIS FREE ALKALI WILL CAUSE OIL-BASED PAINTS TO BECOME SOAPY SO THAT THEY WILL NOT STICK TO THE SUBSTRATE. RINSE SUBSTRATE THOROUGHLY WITH CLEAN WATER BEFORE PROCEEDING.

   5. NOTE: DETERGENTS THAT CONTAIN SODIUM CARBONATES WILL ALSO PREVENT OIL-BASED PAINTS FROM STICKING TO SUBSTRATE AND SHOULD THEREFORE BE AVOIDED OR THOROUGHLY RINSED. CHECK LABELS FOR INGREDIENTS.

   6. CAUTION: DO NOT MIX AMMONIA WITH CHLORINE BLEACH. A POISONOUS GAS WILL RESULT! For the same reason, do not utilize bleach on bird droppings.

8. Apply a water repellent or water repellant preservative (WRP) to all exterior items that are subject to extreme weather conditions, that are especially dry or that may have been consolidated.

   1. These exterior items include windows, cornices, or other severely peeling or exposed wood features.

   2. See “Preparing a Non-Toxic Water-Repellent Preservative” and “Applying a Water-Repellent Preservative to Wood” for guidance on preparation and application.

   3. It is generally beneficial to apply a water repellent or a water repellent preservative to any unpainted wood that is to be repainted, but especially to exposed exterior wood.

9. Caulk any end grain wood that will be subject to water infiltration and any places where wood trim pieces or door and window frames meet wall surfaces.

10. Wood trim which has been removed, or new pieces to be installed, may be “back-primed,” i.e. painted along the end grain for additional moisture-proofing. When transparent finish is required, backprime with spar varnish.