1. Why is drainage important on a balcony, ground terrace or roof terrace?

The longer that water resides on the surface of an external application the more chance you have of encountering problems with floor covering. Water trapped in lower layers during the freeze/thaw cycle can cause issues such as cracking, staining, efflorescence and even weed growth. This is even more likely if surface water is able to penetrate the tiled surface without the ability to drain effectively. A water management system using Gutjahr System Technology from BAL provides rapid, immediate and high volume drainage of water. This  helps to protect tiles and natural stone from an array of problems. As well as frost damage, staining and water damage, the BAL external tiling systems also utilises thinner assemblies, promote lighter weight materials and limits water absorption and retention, in turn reducing the likelihood of standing water adversely affecting the installation.

  1. What is the minimum thickness of tile and type that I can specify with each system?

There are three different assemblies which can be specified depending on construction height you have available:

Standard Drainage Screed Assembly (height build-up from 68mm)                                                                                         

10mm porcelain
20mm natural stone
20mm concrete slabs or pavers

Thin, Lighter Weight Drainage Screed (from 43mm)

10mm porcelain
20mm natural stone
20mm concrete slabs or pavers

Thin Drainage Assembly (from 29mm)

20mm porcelain
30mm natural stone
30mm pavers

  1. Can I specify natural stone such as limestone for external projects?


When specifying Limestone and other types of natural stone materials it is important that certain considerations are made. According to BS 5385 Part 5 – 5.3.3 Selection of natural stone – General – “When selecting natural stone flooring at the design stage, apart from appearance the following should also be considered:

  1. a) proven track record in a similar environment;
  2. b) that the stone samples are representative of that to be used, having obtained information from the supplier about any significant variation in appearance that such stone can exhibit;
  3. c) abrasion and slip resistance;
  4. d) flexural strength;
  5. e) shape of stone unit selected;
  6. f) likely loading conditions. When the application is unusually demanding or if the designer or installer is not familiar with the type of stone, greater testing (including a petrographic examination) should be carried out……”

The best course of action is to speak to your supplier about usage and determine the suitability for not only the intended use but also the longevity of the installation. Note: some natural stone and resin based agglomerate stone are not recommended in areas where temperature and moisture fluctuate.

4. How does Gutjahr System Technology differ from traditional sand:cement fixing on ground terraces?

BAL’s external tiling solutions provide three fixing methods on ground terraces. Unlike traditional fixing methods, the BAL system from Gutjahr utilises a drainage mat with either a cement based or epoxy-based drainage mortar. This ensures that surface water is immediately taken away through the system and managed out towards the perimeter or primary drain outlet. Alternatively a direct point adhesion assembly is available for areas where height is an issue. The choice and thickness of tile would need to be increased.

5. Which of the three systems are better suited to roof terraces with a low threshold?

If it’s an existing roof terrace with a roofing grade membrane we would recommend the innovative ProFin V drainage profile that cover and accommodates the screed. Available in 22mm or 55mm height, the profile can be inserted into the screed without needing to be directly adhered to an existing roof membrane. Where height is an issue this can be combined with the AquaDrain T+ drainage mat and fixed using a direct point adhesion method as detailed in our Part B Installation Guides.

Please not that ProFin DP profiles cannot be used with an existing or heat applied roofing membrane system.

  1. Can this system be specified where there are weight and height limitations?

Yes. Both the Thin, Lighter Weight Drainage Screed Assembly and the Thin Drainage Assembly both provide options where there are weight and height limitations. The Thin, Lighter Weight Assembly utilises AquaDrain EK 8mm drainage mat sheets and MorTec DRAIN epoxy drainage mortar for strong and lighter weight constructions (when compared with the standard cement-base drainage screed). With this system build-up can be achieved from only 43mm.

Primarily suited for low construction height and external areas with reduced clearances, the Thin Drainage Assembly utilises a no-screed, direct point adhesion method for self-supporting break-proof tiles and stone. As there is no screed, complete construction height can be achieved from 20mm, while weight is significantly reduced without affecting the load-bearing capacity.

  1. What preparation might I need to consider before installing this a ground a or roof terrace?

For each assembly ensure that the Ground or roof terrace base you are fixing to/specifying is structurally sound and capable the static and dynamic loads expected. Ideally a cement:sand screed should be bonded/over the base with a fall of 1-2% and should achieve an SR1 finish. Once fully cured and, dried the screed should be suitably protected. All floor screed surfaces and upstand should be waterproofed using BAL TANK-IT. A PE foil is used to separate the assembly before loose laying the drainage mat or sheets..

When fixing onto a roof terrace always ensure that the insulation is suitable i.e.  >200k/Pa and is installed on top of a suitable damp proof membrane. A roofing grade membrane should then be installed directly onto the insulation. The PE foil is then loose laid before installing the preferred Gutjahr by BAL external tiling system.

  1. How do I tell the difference between the various assemblies?

Cantilever Balcony

A cantilever balcony is a projecting construction that extends outwards away from a building. A platform will sit on a number of beams that hold up to the structure. These are mainly secured at only one end – the building.

Ground Terrace

A ground terrace is considered to be an outdoor living area or patio where there is no living space or subterranean structure below.

Roof Terrace

A roof terrace is considered a platform or outdoor living space situated above an existing internal living area, this includes subterranean rooms, basements or garages.

  1. What waterproofing solutions do I need to consider for my assembly?

For ground terraces and cantilever balconies, BAL TANK-IT waterproofing kit protects the screed from water ingress. Easy to apply, dry within 90mins and conforms to EN Classification BS EN 14891 for external waterproofing, BAL TANK-IT provides long-lasting protection. The use of a thin PE foil is recommended for added protection.

For a roof terrace system a heat or cold-applied roofing grade membrane or coating should provide the primary waterproofing laying, further protected with an additional PE foil layer loose laid above.


Please contact BAL Technical Advisory Service (TAS) for information and queries on Gutjahr System Technology from BAL.

Email: info@building-adhesives.com

Call: 01782 591160