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. It must be true-to-size and suitable for receiving a well-functioning waterproofing system sustainably. Substrates must have the following features: sufficiently even, load-bearing, clean, dry resp. slightly damp, dimensionally-stable and free of adhesion-impairing particles and substances.

Simple & safe to the goal

1. Removal of dust: before any further work, it is necessary to ensure that such substrates are free of dirt and clean.
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. Alternative: wait for better weather conditions.
3. The scratch test must be carried out in order to determine if cement laitance is existing on concrete surfaces.
4. Existing cement laitance layers are to be removed mechanically. Often, they pull off from the substrate and their porosity is so low that bitumen coatings do not properly bond.
5. The outer corner of the floor slab is to be chamfered in order to obtain a clean transition to the forepart with a uniform layer thickness of waterproofing.
6. The hammer test: it is used to identify hollow parts. The substrate should be scraped and tapped with a blunt hammer.
7. A dark sound can be heard in the area of hollow spots. Hollow spots/layers are to be removed and, if necessary, replaced/refilled with suitable mortars.
8. The wipe test is used to identify surface contamination. This is done by wiping the surface with a dry cloth or by hand.
9. In case of remaining dirt or loose particles and substances, make sure to remove them.
10. The permeability test: spray some water on the substrate. If it does not penetrate, some residues of formwork oil or other substances may subsist on the top surface. They must be removed by high-pressure water jet in order to obtain an absorbent substrate.
11. Open joints and cavities > 5 mm are closed with the watertight mortar weber.tec 933.
12. Pores and honeycombs as well as butt joints up to 5 mm are closed with a full-surface scratch layer of the chosen waterproofing thick-layer coating.
13. Substrates with textured pattern or with porous aggregate particles must be levelled with a filling layer of weber.tec. Superlex D 24 (2-comp. reactive and quick-setting waterproofing coating) mixed with silica sand (grain size 0.1 - 0.5 mm) in a ratio of 3 : 1 parts by volume.