Seal a damaged wall from the inside

When a plaster wall peels off, efflorescence or dark spots appear, the wall can be sealed from the inside to a certain degree. There must be no air- and watertight seal. Diffusible renovation plaster allows future moisture to escape. In some cases, only a renovation helps.

Assess the damage picture

In many older houses, especially in the basement lighter moisture damage caused by peeling plaster, stains and musty odor noticeable. This may be due to an overloaded or defective drainage of the basement wall. But even with well-designed exterior insulation often causes moisture by touching the earth.

The degree of soaking determines the necessary renovation or refurbishment measures. Superficial mildew does not necessarily mean complete renovation of the damp walls. If the wall can be drained by exposure and heat radiation, sealing from the inside can be sufficient.


The basis of the sealing is the complete uncovering of the masonry. The following work should be carried out:

  • Completely remove old plaster
  • Remove skirting boards, light switches and sockets
  • Scrape out joints with defective filling
  • Clean concrete or stone surfaces with a hard brush
  • Moisture measurement on bare wall
  • Dry the wall with a hot-air blower or radiant heater

Work equipment and steps

Renovating the wall is divided into five steps and tools:

1. When priming the wall, suitable means of painting the wall are painted on or sprayed on. They can also have fungicidal effects through appropriate ingredients, but they must be diffusible.

2. In order to impregnate and insulate the wall, waterproofing slurry is now evenly distributed with a painter's quast.

3. Possibly scratched joints are filled with joint mortar. Cement based mortars are waterproof. Acrylic or silicone-containing mortars are unsuitable.

4. The heart of the sealing is created by applying a special restoration plaster. He is "thrown" onto the wall with a cleaning trowel and roughly leveled with a trowel. When selecting the right product and mixing, follow the manufacturer's instructions for wall finish and instructions.

5. When the restoration plaster has dried, apply the final finishing coat. It should be about twice the thickness.

Tips & Tricks

If you have an old building basement, with individual masonry and stone types a sacrificial plaster can be an ideal helper, which is removed in an intermediate steps again.

Product Image: anastasiya parfenyuk / Shutterstock

Video Board: How to Seal and Waterproof Your Basement