Check and preparation of substrates in case of renovation works

The renovation works of old waterproofing needs a careful evaluation of the substrate, since it must be matched with several types of substrates and old waterproofing materials, for example different masonry types, different bitumen or tar paints or coatings etc.

Step by step

  1. Scratch test

    1. Via a scratch test it must be evaluated if cement laitance is existing on the concrete surface.

  2. Hammer test

    2. Via hammer test hollow parts must be identified.


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

  4. Bitumen or tar?

    4. Pour some white spirit on a sponge or a cloth. Bitumen can be dissolved by white spirit (it becomes a brown colour), tar cannot. New bitumen material can be applied on old anionic bitumen.


    5. Tar is not suitable as substrate and must be removed mechanically by sandblasting.


    6. The bonding of old bitumen materials (coatings or paints) must be checked. If it is not sufficient, they must be removed down to the sound substrate.

  7. Removing existing layers of cement laitance

    7. Existing layers of cement laitance must be removed mechanically, since they pull-off from substrate. Furthermore, their porosity is so low, that subsequent waterproofing layers will de-bond.

  8. Chamfering the external fillet between wall and concrete slab

    8. The external fillet between wall and concrete slab must be chamfered, in order to allow a smooth connection without "break" with the waterproofing on main surfaces; this provides the same layer thickness like on walls, and allows a homogeneous drying of the waterproofing.

  9. Removing old paint or coating

    9. In all cases the old paint or coating must always be removed down to the sound mineral substrate completely upwards from the groove area (angle wall/concrete slab) on approx. 25 cm on both sides and also downwards till to the forepart of concrete slab.

  10. Preliminary waterproofing coat

    10. In case of high residual moisture always apply a preliminary waterproofing coat with the watertight mortar weber.tec 933. If at the same time the substrate shows deep unevenness, use the waterproof render weber.tec 934 for levelling works. Prior to these operations remove the old waterproofing layers completely.

  11.  Application of render

    11. In case of quarrystone masonry the application of the render weber.tec 934 is necessary, too.