Cover the floor beneath the wall with the drop cloth.
Mix 1/4 cup trisodium phosphate with 2 gallons of warm water in a bucket. Wearing plastic gloves, apply the cleaning solution to the wall to wash the wood. Rinse away the chemicals with plain water and dry the wall with a towel.
Apply painter’s tape over adjacent surfaces that meet the wall to prevent paint from spreading as you work. Cover edges along the ceiling, adjacent walls, baseboards, windows and doorways.
Load the paintbrush with whitewash stain and apply it to the wood to cover a 3-foot area. Before the paint dries, rub it gently with the clean rag to spread it and remove excess paint. Continue rubbing the whitewash until you remove as much as you want to lighten the wood.
Repeat the same process to whitewash the wall in 3-foot sections. Blend the sections carefully with the rag to ensure you do not create visible seams in the whitewash application.
Allow the whitewash stain to dry for the time recommended on the product label. Remove the painter’s tape.