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5 Common Liquid Waterproofing Installation Mistakes

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 on your project, get heavily involved in the waterproofing process from the beginning to ensure proper preparation and detailing design.

Fortunately, most of these pitfalls can be addressed before a tin of waterproofing is cracked open – so get on top of them early!

1. Not installing a puddle flange

Many people think that a puddle flange is installed during screeding and tiling, well after the waterproofing installation is complete. But the first piece of a puddle flange is required to be installed before any waterproofing 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.

Link to site to buy standard or detail – maybe Master Builders

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 his video episode of Sealed for Good. https://www.youtube.com/watch?v=5ib81GYgEWs

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 and are often underestimated.

As the name suggests, 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 and can stretch to accommodate movement in the substrate.

ARDEX provides an explanation of membrane elongation and flexibility and the role of bond breakers in accommodating cracks and movement. http://cdn.ardexaustralia.com/pdf/tech%20bulletins/TB073%20-%20Misconceptions%20about%20Membrane%20Flexibilities.pdf

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. Now you can see how critical bond breakers are and how prone to failure the membrane is without them.

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 nominated dry film thickness is not met, the membrane does not possess the quoted elongation properties. This substantially 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 police – it’s not readily visible and it requires a special gauge which is not found in a typical toolbox.

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. The coverage rates will vary based on the porosity of the substrate but this is a good preliminary check that the applicator has enough product on hand.

This gauge used to measure wet film thickness are called a wet film thickness comb (https://www.youtube.com/watch?v=INnx7g5TF-k) or wheel (https://www.youtube.com/watch?v=_2X3Dp4g0yc). 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 https://www.elcometer.com/en/coating-inspection/dry-film-thickness/dry-film-thickness-digital/elcometer-456-coating-thickness-gauge.html. However, if you leave it until the membrane is dry, it becomes a much more difficult rectification method 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, I see incorrect liquid membrane terminations on the vertical – 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 further delamination.

AS 4654.2 provides one options for vertical termination of a liquid membrane. It requires chasing the membrane into a reglet within the substrate, and using an over-flashing to cover over the top of the membrane.


Installing a reglet is not going to be feasible in all substrates (e.g. where you are working on a heritage structure or there are several services running down the wall).

AS 4654.2 provides a second option to vertical termination, which is generally suited to sheet membranes, however, can be used on liquids. This is a pressure seal and sealant.

Some manufacturer’s will also recommend the use of a bandage tape to terminate the membrane to assist with maintaining integrity and adhesion at membrane edges.
In these situations, you can also install a skirting tile with a bead of coloured silicone instead of grout on top for additional protection.

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 both looks unappealing and drips on the areas below. In worse cases the tiles also become drummy and start to delaminate as the crystallisation of salts and formation of calcium carbonate pushes them off.

This is generally because the membrane is usually 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 always going to be to install a hob and drain the balcony through a floor waste. However, this is often not feasible or prohibitively expensive.

The best most cost-considerate option I have found to address this problem is to use a proprietary drip angle such as Stone Concept’s Durabal BK http://www.stoneconcept.com.au/product/details/78.

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 detailing to the applicator (see my article Risk vs. Reward in Specifying Construction Details).

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.

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