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Water blasters can damage your home

There is growing concern at the damage that water blasters can cause when used to clean the outsides of buildings - especially New Zealand houses.

Where water blasters were once the preserve of professional cleaning specialists, now anyone can buy one at the local hardware store, or hire one, and without any knowledge or understanding of how to use them properly, point them at their homes and 'blast away'.

While it is important to regularly clean and maintain roof and wall claddings to keep them looking good and prolong their life so they continue to do their job of keeping weather out, it was never intended that this be done with the indiscriminate use of high pressure water blasters.

Most claddings simply are not designed to withstand the water pressures generated by even the smallest of these pieces of equipment. For example, cladding systems and joints described in the Acceptable Solution for External Moisture E2/AS1 (most New Zealand homes) are designed to withstand maximum pressures in the 1.5-2.5 kPa range, which is the pressure you might expect from a 180 km/hr (or kph) wind gust. But a relatively small 1200 psi water blaster has a nozzle pressure of 8300 kPa that would cause a tremendous 'punch' on walls and joints!

The materials, joints and seals used for cladding the average New Zealand house are simply not designed to withstand these excessively high pressures. Water blasters can etch out soft weatherboard, tear out mortar from brick joints, knock off paint film along cladding edges, dislodge sealant, force water into joints where water would never otherwise get to, etch away paint film thickness - and much more. If the building did not leak before it was 'cleaned' by water blasting, there is a high chance it will afterwards. Where buildings are regularly cleaned in this way, parts of them may never get a chance to dry out, and decay of materials and framing may result.

Water blasters, used indiscriminately, will damage your home. Banning their use (even if it was possible to do so) might avoid this damage occurring, but there are occasions where the proper use of water blasters, on some materials, may be appropriate. The best method of cleaning the house will always be with the garden hose and a soft brush or broom. However, if you are going to use a water blaster, there are some simple rules you should follow to reduce the risk of damaging claddings and joints.

  • Always read the operating instructions first.
  • Check the maintenance requirements of your cladding or roofing material - many exclude the use of high pressure cleaning (ie, water blasters).
  • Use the lowest pressure setting available.
  • Set the nozzle on 'wide spray' and maintain it at least 500 mm clear of the building's surfaces.
  • Don't hold the nozzle up close to a surface to dislodge stubborn dirt - use a brush or broom for that.
  • Never point the nozzle directly at joints or aluminium joinery, because many of these rely on sealants for their weathertightness, which can be dislodged by high pressures.
  • Use cold water only.
  • Use infrequently. It is better to wash down your home more frequently with a low-pressure garden hose and soft broom
    than to use high-pressure water blasters occasionally.

If you want to have your home cleaned, there are professional water blasting companies with experience in building cleaning. References from their previous work should help provide you with proof of competence. If you are concerned that a water blaster has been improperly used on your home, do not wait for the potential leak to cause damage. Have a building professional check your home with moisture meters to detect the presence of moisture in walls or roof.

A leak found early is an inconvenience. A leak ignored can result in more serious problems.