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Be Alert – Not Awash!

Waterproofing Requirements for Rimless and Stand Alone Baths

by John Rathbone, current member of BD-13 Committee working on Australian standards for Waterproofing

New Zealand was the first country in our area to strike problems with these baths.  The first wave of imports were “budget baths” which could be produced cheaply, as rimless baths.  They are less complex moulds than standard baths, so production is quicker.  They were installed against the wall sheets with the shower over the bath.  Shortly after the shower went into service the problem became apparent – water from the shower rose was penetrating at the junction between the wall sheet and the bath, damaging the bathroom floor.  Various “band aid” solutions have been tried with no success.  This caused our Waterproofing Committee to introduce a new procedure in the 2010 edition of AS 3740 to address this type of bath which at the time was marketed in Australia.

However, since then many new types of rimless and free standing baths are being marketed in Australia.  Many of them are often installed under showers, with resulting damage to the bathroom floor and water penetration to adjacent rooms.  The committee has addressed this problem in AS 3740 amendment one (re-issued 12/12/2012) which was referenced in May 2013 in 3.8.1.1, by the National Construction Code (NCC).

The updated requirements for rimless and free standing baths where there is a shower fitted above the bath are as follows:

For both types – the floor of the bathroom must be waterproofed and drained to a waste.

  1. A rimless bath with shower over is treated as  type two shower (e.g. the waterstop shall be a minimum of 1500mm from the wall connection of a shower rose** and must finish flush with the finished surface of the floor.
  2. Waterproof the whole bathroom floor (including waterstop in the bathroom doorway)

** I should point out that in bathrooms this method is very rate, as home owners don’t like seeing the top of metal angle in their tiled floor, so invariably the second method is chosen (e.g. the full bathroom floor waterproofing and the waterstop is in the doorway as shown in AS 3740-2010 (amendment No. 1) on page 19.

(I was in Europe a few years ago where rimless baths below showers are very common, and nearly all that I came across were leaking like sieves).

Australia can avoid this expensive mess simply by following the new requirements (and by always using a professional to install the waterproofing).