Waterproofing is a tedious business. So is carpentry. But unlike carpentry, if you make a waterproofing mistake, the consequences aren’t visible and don’t become apparent until it’s too late.

Incorrect waterproofing at critical areas can jeopardise the whole system. Often these important detailing techniques are neglected (sometimes purposely) and slip through the cracks when inspected.

To help prevent waterproofing failures, building professionals should get heavily involved in the waterproofing process from the project's beginning to ensure proper preparation, detailing design and installation.

These 5 common design and installation pitfalls can be influenced before a drum of waterproofing is even cracked open – so get on top of them early and save yourself much heartache down the track.

1. Not installing a puddle flange

Many people think that a puddle flange is installed during screeding and tiling to allow water to freely flow from the tile surface into the drain. This is partly correct. There is another component of the puddle flange which is often overlooked and is required to be installed during slab/substrate preparation, before any waterproofing or screeding takes place.

The puddle flange provides the ‘bridge’ connecting the waterproofing from the floor substrate to the drainage pipe. This is a critical area where the membrane is vulnerable to failure due to the transition between building materials.

A puddle flange reduces this risk by providing a solid substrate to which the membrane can be applied and which eliminates the need to continue the membrane into the drainage outlet.

A common mistake when installing puddle flanges is that they are often not rebated into the floor to create a flush finish. This creates a weak point as the membrane is required to bend up over the thickness of the flange.

Rebating the puddle flange is often neglected as it is a messy and tedious job for the installer which they’d rather avoid to get the job done quicker. But it is an easy check you should undertake before any waterproofing begins.

Gripset’s Phil Scardigno provides more information about puddle flanges and their importance in this episode of Sealed for Good.

2. Not installing bond breakers at corners, transitions and cracks

Bond breakers are required to be installed at all corners, upturns, cracks or changes in substrate. They usually consist of a neutral-cure silicone and are one of the most important aspects of an effective waterproofing system. Often, however, their importance is underestimated. In fact, they are so important to the performance of the membrane system, that even a highly elastic membrane can be reduced to near zero elasticity without incorporating a bond breaker.

As the name suggests, bond breakers inhibit adhesion of the membrane to the substrate so that it has free movement. The bond breaker is what allows the membrane to perform at its full elastic potential. By providing an unbonded section in the membrane, the membrane is unrestricted allowing it to stretch to accommodate movement in the substrate.

ARDEX provides a good explanation of membrane elongation and flexibility and the role of bond breakers in accommodating cracks and movement.

Without a bond breaker, even a membrane with high elongation capabilities, will be restricted and not be able to stretch.

To use ARDEX’s example, if using a membrane with 200% elongation and the unbonded length of membrane is 2 mm, the membrane can stretch an additional 200% on the original gap of 2 mm, i.e. original unbonded length (2 mm) + 2 mm x 200% = 6 mm.

However, if there is no bond breaker, the length of unbonded membrane is 0 mm. So even with 200% elongation, the membrane won’t accommodate stretch,  0 mm + 0 mm x 200% = 0 mm.

Consider how much settlement and differential movement that a building undergoes in their early stages of life. Much of this movement is concentrated at wall-floor interfaces where different building elements meet (e.g. concrete floor and brick wall).

Bond breakers are critical in these areas to allow to membrane to accommodate this movement.

3. Insufficient membrane thickness

Carrying on from the previous point, when the membrane is stretched, it undergoes necking, or thinning, affecting its ability to withstand water.

As such, if the required dry film thickness is not met, the membrane's elongation properties are substantially reduced. Consequently, the membrane then loses its ability to withstand movement.

From a commercial point of view, clearly the installer is inclined to be conservative with the liquid product to reduce costs.

The installer also knows that this is a difficult one to enforce – it’s not readily visible and it requires a special gauge which is not found in a typical toolbox.

When specifying, ensure a DFT requirement is stipulated, not just the number of coats required.

Prior to application, do a calculation based on the area size and the manufacturer’s recommended coverage rates to estimate the amount of waterproofing required. Some manufacturer’s provide coverage calculators to make this calculation easier, such as Ardex’s coverage calculator.

The coverage rates will vary based on the porosity of the substrate so adjust it according to the manufacturer's data sheet.

After using the coverage calculator, estimate the number of drums required and check that the applicator has enough product on hand prior to commencement.

Directly after installation, use a wet film thickness comb or wheel to check the thickness and match it to the manufacturer's stipulated wet film thickness. Keep in mind that the use of the tool damages the waterproofing application so make sure the waterproofing applicator is on hand to touch up the damage.

If you are not present to take WFT readings, dry film thickness can be confirmed with an electronic gauge such as the Elcometer 456. However, if you leave it until the membrane is dry, it may be more difficult to rectify if the membrane does not meet the thickness requirement. Consult the manufacturer on the best method of rectification.

Insufficient thickness can compromise the performance of the membrane system so it is important that the membrane is applied in accordance or in excess of the coverage rates provided by the manufacturer.

4. Incorrect vertical terminations

Correct vertical termination details are important in external waterproofing to prevent ingress from rain percolating down the wall.

More often than not, liquid membrane terminations on the vertical is undertaken incorrectly – the waterproofing is just turned up and stopped with a skirting tile applied over it.

This creates a weak point where rain water dripping down the face of the wall can migrate between the membrane and the substrate, leading to delamination.

AS 4654.2 provides 3 options for vertical termination of external membranes.

The first option requires chasing the membrane into a 15 mm deep reglet within the wall and inserting an over-flashing to cover the top of the membrane.

The problem is that installing a reglet is not going to be feasible in all substrates such as when you are working on a heritage structure or where there are several services running down the wall. AS 4654.2 does not address an alternative for liquid membranes if a reglet is not possible.

The second option for vertical termination, using a pressure seal and sealant, is generally suited to sheet membranes.

And the third option, terminating underneath a cavity flashing, is only possible where you have an overhanging cavity flashing.

Although not technically compliant with AS 4654.2, some manufacturer’s will warrant the use of a bandage tape to terminate the membrane to assist with maintaining integrity and adhesion at membrane edges.

As additional protection, the installation of a skirting tile with a bead of silicone on top should be undertaken.

5. Incorrect balcony free edge detail

AS 4654.2 doesn’t give much guidance on detailing of free edge balconies when tiles are involved, and the design is often not given much thought prior to application.

The problems here don’t present themselves until much later when the tile joints start leaching efflorescence which looks unappealing and drips on the areas below. In worse cases, the balcony facing tiles can become drummy and start to delaminate as the crystallisation of salts and formation of calcium carbonate pushes them off.

This is usually because the membrane is installed along the balcony deck and simply turned down the face. Tiles are then applied on top and directly stuck to the membrane on the balcony face.

This detail pays little respect to the critical question of ‘where is the water going to go?’

The superior detail is to install a hob and drain the balcony through a floor waste. However, this is often not feasible or prohibitively expensive.

A more cost-considerate option to address this problem is to use a proprietary drip angle such as Stone Concept’s Durabal BK.

This provides an angle to turn the membrane up and over which stops water migrating from below the tile bed directly onto the balcony face. Moisture is then able to drip off the protruding flange without efflorescence accumulation compromising tile adhesion.


The thing to remember with any waterproofing install project is that proper preparation starts at the design stage. An easy trap is to leave all the waterproofing design and detailing to the applicator.

Develop the design and expectations of the waterproofing long before the applicator even steps foot on site. Then effectively communicate expectations and stipulate hold points for quality assurance inspections. The success of the membrane system depends on it.