Using the damp cloth, clean off any loose debris or residue from the siding; the paint thinner must be applied evenly to a smooth surface.
Remove any chipped areas of the old paint with a scraper or putty knife to reduce the amount of thinner required for removal. Scraping off large sections will save time in the process.
Put on the solvent-resistant gloves to protect your skin against alkaline burns. Apply paint thinner to the surface of the clapboard using a brush, paint roller or aerosol spray can.
Allow the old paint to soften for the instructed period of time. Begin lifting it gently with the scraper blade and use a scouring pad or steel wool to scrub the remainder.
Rinse the loose paint and solvent with water and allow the clapboard siding to air dry overnight before applying a new coat of paint.