Correct check and preparation of substrates for external basement waterproofing

A well-done waterproofing can be only as good as the substrate will allow. Therefore the substrate must be carefully checked before the waterproofing is applied. The substrate must be true-to-size and suitable for receiving a well-functioning waterproofing system in a sustainable way. Substrates must have following features: sufficiently even, load-bearing, clean, dry resp. slightly damp, dimensionnally-stable and free of adhesion-impairing particles.

Step by step

  1. 1. Removal of dust and all kinds of dirt prior to subsequent works. The substrate must be clean

  2. 2. Water is acting like a separating film on a damp substrate. Water prevents from the penetration of the primer and the bonding of the waterproofing layers with the substrate. Carry out suitable measures like foil protection, heating etc. for obtaining a dry or at least slightly damp substrate. Afterwards apply a preliminary waterproofing layer with the watertight mortar weber.tec 933. Alternatively wait for better weather conditions.

  3. 3. A scratch test must be carried out in order to determine if cement laitance is existing on concrete surfaces.

  4. 4. Existing cement laitance layers are to be removed mechanically. Often they pull off from substrate and their porosity is so low that bitumen coatings do not propely bond.

  5. 5. Remove the cement laitance on the forpart of concrete slab and its external angle with a diamond rotative disc.

  6. 6. Via hammer test hollow parts must be identified.

  7. 7. Hollow parts or hollow layers must be removed eventually be replaced by an appropriate mortar.

  8. 8. Via wipe test by hand or with a cloth surface dirt must be identified.

  9. 9. In case of remaining dirt or loose particles make sure to remove them.

  10. 10. Carry out a permeability test: Spray some water on the substrate. If it does not penetrate some residues of formwork oil or other sub-stances may subsist on the top surface. They must be removed by high pressure water jet in order to obtain a porous surface.

  11. 11. Open joints and cavities > 5 mm are closed with the mortar weber.tec 933.

  12. 12. Pores and honeycombs up to 5 mm are closed with a full-surface scratch layer of the chosen waterproofing thick coating.

  13. 13. Surface profiled substrates or subtrates with porous aggregate particles (e.g. concrete or lightweight concrete blocks) must be egalized with a filling layer of the 2-comp. reactive, thick and quick-setting waterproofing coating weber.tec. Superlex D 24 mixed 3 : 1 parts by volume with silica sand (0.1 - 0.5 mm).