Can a “breathable” lime-plaster repair be defeated by wallpaper?

What the research found

Researchers tested lime plaster, bio-based wallpaper paste and five different wallcoverings. Most traditional papers, non-woven wallpapers and the bio-based paste had little measurable effect on vapour permeability or drying under the tested conditions.

Vinyl-coated wallpaper behaved differently. It reduced vapour permeability and slowed drying, while hygrothermal modelling indicated that low-permeability finishes can increase relative humidity inside a traditional solid wall. The effect was more significant when the wall already contained elevated moisture.

What this means on site

When surveying damp or slow-drying traditional walls, the inspection should record the complete decorative build-up—not simply the masonry and plaster. Wallpaper, adhesive, modern paint and previous coatings may be restricting drying.

A genuinely vapour-permeable lime-plaster specification can be compromised if the finished surface is subsequently covered with a resistant wallcovering. Intended decoration should therefore be discussed before the repair specification is agreed.

Practical contractor checklist

• Record existing wallpaper, paint and adhesive layers during the survey.
• Investigate and address the original moisture source before replastering.
• Confirm the proposed final decoration with the client or designer.
• Avoid assuming that all products described as breathable perform equally.
• Use representative sample areas where the wall is particularly damp or historically significant.
• Include the decorative finish within handover and maintenance guidance.