17th May 2022 What paint should I use to prime? An acrylic sealer-undercoat should be applied as the base coat if purchasing or using unprimed sheets. The back of my sheets are raw, do I need to prime them? Only if the sheets are likely to be exposed to moisture, e.g. Sheets on the inside of external walls where no sarking is provided; All sheets being used in bathrooms, laundries etc; Ceiling sheets.