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Preparing Exterior Wood for Paint on Your Historic Building | Wisconsin Historical Society

Guide or Instruction

Preparing Exterior Wood for Paint on Your Historic Building

Preparing Exterior Wood for Paint on Your Historic Building | Wisconsin Historical Society

Thorough preparation is the best way to ensure that the paint job on your historic house or building will last. You will get the best adhesion from your primer, caulk and paint by thoroughly preparing the surfaces to be painted. This preparation will take time, but you won't have to repaint every 3 to 5 years. With proper preparation, an exterior paint job can last 10 to 20 years.

You should also do yearly paint maintenance to stop any minor paint peeling problem from becoming a total paint loss in the affected area.

Gather Your Tools and Materials

To prepare exterior wood for painting, you will need the following tools and materials:

  • Hand house scrapers with carbide blades
  • Ladders and/or scaffolding
  • Ground tarps
  • Spray bottles with water to wet-scrape old paint
  • Scrub brush on an extension pole for scrubbing
  • Plastic bucket to contain the cleaning solution
  • Trisodium phosphate (TSP), regular or synthetic
  • HEPA filtered vacuum
  • Paint grinding tool hooked up to a HEPA vacuum and/or an Infrared paint removal device
  • Garden hose with a spray nozzle
  • Safety glasses and rubber gloves
  • Double cartridge respirator rated for lead paint
  • Siding or trim to match original (to replace bad pieces)
  • Architectural epoxy for wood rot repair
  • Moisture meter

Step 1: Remove Loose Paint

EnlargePaint prep

Step 1

Source: Bob Yapp

Your first step to prepare your house or building for paint is to remove the old paint. Your house or building might have many coats of paint on its exterior. The presence of many paint layers can lead to paint failure due to the incompatibility of the different paints. If your house or building has fewer than three complete paint jobs (fewer than nine coats of paint), you can wet scrape off all of the unstable paint. The best tool for this work is a hand scraper with a carbide blade.

If your house or building has three or more complete paint jobs, you should remove all the paint using one of these two tools:

  • A paint grinding tool hooked up to a HEPA vacuum
  • An infrared paint removal tool

Both of these tools are approved for safe lead paint removal by the Environmental Protection Agency.

Step 2: Clean the Surfaces to be Painted

EnlargePaint prep

Step 2

Source: Bob Yapp

The best way to clean a wood surface for painting is to hand scrub it with a mixture of TSP and water. A synthetic version of TSP is available that will not harm groundwater. Even if you use the synthetic version, you should tarp off the area where you're working to prevent the TSP from getting into the ground. Use ¼ cup of TSP for every gallon of water. Be sure to wear eye protection and gloves. Hand-wash all bare wood and solid paint that remains on the surface. Rinse the surfaces with clear water from your garden hose.

Never use high-pressure washing to clean a wood surface. High-pressure washing is a major cause of catastrophic paint failure. Pressure washing also damages the surface of the aged wood, causing it to get a “fuzzy” washboard appearance. Pressure washing blows out the softer spring and summer wood grain and makes it more difficult for paint to adhere to the wood.

Step 3: Repair or Replace Unusable Wood

EnlargePaint prep

Step 3

Source: Bob Yapp

Repair any rotted or cracked siding and trim with architectural epoxies. Replace damaged wood with replacement materials that closely match the original materials.

Step 4: Check Wood Moisture Content

EnlargePaint prep

Step 4

Note: While the photo shows a clapboard wall, the equipment and process is the same. Source: Bob Yapp

Before you apply any primer, paint, or caulk, use a moisture meter to test the moisture content of the wood. Paint will not adhere to any wood surface with a moisture content that exceeds 15%.  You can buy a moisture meter through woodworking supply companies and some lumberyards.







The information presented here is not intended to provide comprehensive technical advice or instructions on solving historic preservation issues. Any information contained or referenced is meant to provide a basic understanding of historic preservation practices. Read full disclaimer.