Why primer/sealer is needed on surfaces after wallpaper and border removal
Wallpaper paste often gets absorbed into wall surfaces, especially surfaces that are unprimed or previously coated with flat finish paint. Cleaning removes the surface paste but will not always remove absorbed paste. Staining material contained within the absorbed paste can be drawn from beneath the surface causing staining of newly-applied paint. Staining can occur as absorbed paste comes in contact with the moisture from applied paint.The mixing of absorbed paste and the moisture from applied paint often causes a rusty-colored cloudiness, or areas of solid color staining in the applied paint. The application of one coat of oil-based quick-drying primer/sealer, after cleaning wallpaper paste residue and completing all surface preparation techniques and repairs, seals the surface and prevents any absorbed paste from mixing with newly applied paint. In extreme cases where wallpaper or border removal has caused extensive drywall cover damage, a coat of oil-based quick-drying primer/sealer should be applied after surfaces are cleaned, dry and lightly sanded after wallpaper paste residue removal. A second coat of primer/sealer should be applied after all surface preparation techniques and repairs are complete.
Note: If oil-based products are no longer available in your area, use a high-quality latex primer/sealer capable of sealing previously wallpapered surfaces.
This information can be found on page 101 of the book:
The Homeowner's Guide to Surface Preparation for Interior House Painting.
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