Waterproofing systems

Cementitious coatings are quite thin, from 1–3mm, and so have little integral tensile strength. It follows that they must be applied to a sound substrate, or a prepared render base coat. So brickwork, unless in excellent condition, needs a render coat first before the coating application. Some manufacturers recommend use of a mesh (e.g. stainless steel) to strengthen the coating. Cementitious coatings can usually be laid directly onto a concrete substrate, following priming and sealing of cracks. At the very least, brickwork requires flush pointing and any holes and imperfections making good. Certainly brickwork with many spalled bricks needs to be rendered first prior to application of coating. Cementitious coatings can include additives for improved elasticity and flexibility.

Coatings are pre-mixed, comprising cement, graded aggregates and chemical additives. There is therefore no risk of contractors using unsuitable sands, which often occurs when multi-coat renders are used in waterproofing.

Sovereign Chemicals Ltd (Hey'di system) recommend removal of unsuitable (e.g. hollow) renders prior to coating application, and in some cases recommend application of a new render coat before coating.

The fact that a render base coat is often needed when applying a cementitious coating to, say, brickwork or stonework means a substantial additional cost in the waterproofing application. Some savings in space can be gained by using a cementitious coating due to its potential very limited thickness. The BRE, in their Good Repair Guide 23, do not specifically mention the thinly applied type of coating available in today's market.

Cementitious coatings are commonly used for waterproofing underground car parks, swimming pools and service tunnels.

Product literature by Sovereign Chemicals Ltd claims the Hey'di system can cope well with hydrostatic pressure (having been tested to 65m hydrostatic head of water). To achieve reliable waterproofing to withstand hydrostatic pressure, Sovereign specifies a 'special system application'. Where there is a significant head of water we must be sure the basement walls have sufficient structural integrity to sustain the applied loads.