Instructions for external insulation of the cellar

In cellars where the outer wall seal is defective or insufficient, moisture is a permanent problem. The first important measure is in any case the complete sealing of the basement from the outside, since all other remedial measures otherwise remain ineffective. What you need and how to do it, read in detail here.

Background information

The basement wall is exposed to a great deal of moisture from the outside: from oppressive groundwater to seepage rainwater and rising soil moisture. A solid and effective seal is therefore fundamental.

In order to avoid condensation on cold basement walls, perimeter insulation of the cellar exterior walls is recommended, which you can then install together with the waterproofing.

High work and effort

Before sealing, you must expose the entire basement walls. This means a great deal of work and effort, with auxiliary equipment, such as a mini excavator, but this is a bit easier to create. Depending on the degree of moisture penetration of the basement walls, you must also set more or less elaborate drying measures.

Some expertise is needed in assessing damage and sealing properly, but having expert advice can be sufficient and at the same time help avoid costly mistakes. The costs for an expertise often pay off several times.

Step-by-step instructions for the external sealing of a cellar with perimeter insulation

  • Bitumen coating
  • Styrodur perimeter insulation boards
  • Bitumen insulation board adhesive
  • cement mortar
  • Foil and masking tape, if necessary sealing sleeves
  • if necessary, precoat, putty
  • ev. Mini excavator
  • Flat chisel, hammer
  • Spatula and notched trowel and a smoothing trowel and cleaning trowel
  • Hand saw for cutting the insulation boards
  • Bitumen brush or roller
  • mortar bucket

1. Digging the soil

The first and at the same time most complex step is the exposure of the soil. Dig the soil completely until all basement walls are completely cleared. A mini excavator is an invaluable help here. Otherwise, you can also commission this service.

2. Repair and sealing

Correct all damaged areas carefully, clean the outer wall and remove any moistened and crumbling areas and re-clean them with cement mortar. Then let the walls dry completely again.

3. Bitumen waterproofing

Spread the bitumen seal in two layers. You do not necessarily have to do a primer, but that depends on the condition of the cellar and its structure.

Then you can glue the Styrodur perimeter insulation panels with bituminous adhesive over the entire surface. Make sure you work as cleanly as possible.

Tips & Tricks

For very old buildings, especially with natural stone cellars, you have to be careful with external insulation. Be sure to consult an expert first.

Video Board: How to Insulate a Basement - This Old House