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Balconies, Terraces and Patios


This section typifies pedestrian-trafficable areas such as balconies, patios and terraces under fully bonded tiles or pavers. These areas present some of the most difficult situations from a waterproofing point of view because there are often many complex situations in usually confined areas. The cost of the waterproofing is often but a fraction of the cost of the finishes - consider the cost/risk ratio and give high priority to the design, surface preparation and installation. Derbigum adopts a pragmatic approach and recommends the use of a dual-layer waterproofing system to reduce the risk of labour error and the possibility of subsequent damage.


As with most membranes and coatings, the substrate plays an integral part in the success of the system. Too often Waterproofing Contractors do or are compelled to install the waterproofing system on inadequate or poorly prepared surfaces. Surface preparation is essential to the success of the waterproofing system.

The substrate shall be surface dry, clean and smooth; free of voids, protrusions and contaminants. The area is then to be primed using a bituminous primer. Internal corners shall be coved and external corners rounded.
A screed to falls is to be laid on the concrete surface to receive the waterproofing membrane.


One layer Derbigum CG4 on one layer Derbigum CG3 laid staggered, with side laps of 75 mm and end laps of 100 mm, fully sealed to primed screeded surface by "torch-fusion", followed by one layer Derbigum Interdek with 50 mm laps, laid loose on waterproofing as isolation/protection layer, to receive fully bonded tiles/paving on a mortar bed of minimum 45 mm (elsewhere specified). Waterproofing to be installed by an Approved Derbigum Contractor.

 Isolation Layer

Tiles or Pavers bedded in mortar are to be laid on an isolating membrane, such as Interdek or a pvc sheeting, so as to reduce stresses placed on the waterproofing by possible movement in the paved finish. This further facilitates access for remedial work if required. Movement joints (soft joints) between the tiles/pavers are to be created at approximately 3 metre centres and at all abutments.

It is recommended that the minimum thickness of the mortar bed is 45mm.


The waterproofing is to be fully dressed into the drainage outlets to ensure a watertight seal.
A fully bonded soaker flange is recommended. Outlets are to be positioned so that they are easily accessible both for the Waterproofing Contractor at the time of installation and maintenance purposes at some future date. Ensure that the level of the flange is kept below the screed level so as to prevent ponding around the outlet.

Flood Test

The integrity of the waterproofing system should be established by means of a flood-test of 48hrs – 72hrs duration, prior to handing over to the contractor. A certificate is to be obtained from the professional team recording the date and time-period of the test and that the waterproofing system was handed over in a clean, proper and watertight condition.

Abutments and Edges

The height of the waterproofing membrane turnup is to be a minimum of 100mm and always above the height of the final tile or paving finish. Detailing of abutments requires careful attention to achieve a permanent, watertight and aesthetic finish. 
A soft joint must be created at all abutments to prevent damage to the waterproofing system caused by movement.   


The height of the door threshold is of paramount importance. The minimum height of the waterproofing turnup should be 100mm. The finished height of the waterproofing (turnup) is to be higher than the finished paving surface. This is to ensure that surface water does not penetrate behind the skirting.
Special precautions are to be taken so that wind-driven rain is prevented from entering the interior.
Door and window frame fixing methods require careful detailing and should be done in consultation with the frame manufacturer. Too often the frame is fixed mechanically through the waterproofing membrane.

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