Check and preparation of substrates in case of renovation works

The renovation works of old waterproofing need 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.

Simple & safe to the goal

  1. Check of substrate

    1. The scratch test: it must be carried out in order to determine if cement laitance is existing on concrete surfaces.

  2. 2. The hammer test: its scope is to identify hollow parts. The substrate should be scraped and tapped with a blunt hammer.

  3. 3. A dark sound can be heard in the area of hollow spots. Hollow layers must be removed, eventually be replaced by an appropriate mortar.

  4. 4. Bitumen or tar? 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. 5. Tar is not suitable as substrate and must be removed mechanically by sandblasting.

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

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

  8. 8. The external angle of the 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. 9. In all cases, remove all old paint or coating from the whole grove area up to approx. 25 cm above the concrete slab and from the socket part.

  10. 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. 11. In case of quarry stone masonry, the application of weber.tec 934 is necessary, too.

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