Intergrain UltraPrep Timber Cleaner 4 LitreIntergrain UltraPrep Timber Cleaner 4 Litre Intergrain UltraPrep Timber Cleaner (previously known as Reviva) is a high strength cleaner that contains oxalic acid and citric acid, both naturally occurring, bio degradable organic acids. Use UltraPrep Timber Cleaner to clean all timber prior to coating. UltraPrep Timber Cleaner will help restore and prepare weathered, grey, rust or tannin stained, mould or mildew affected timber to a clean appearance