Cleaner can be used undiluted or diluted 1:4 with water. Simply apply, leave to take effect and rinse. Mix in the wash bucket, apply to the areas to be treated with a sponge or pre-wash brush. Then rinse with water or neutral shampoo. Avoid galvanized surfaces. The No Yellow Cleaner does not work on yellowing caused by UV light. We recommend closing the open-pored gelcoat after thorough cleaning by polishing and sealing to prevent rapid yellowing.