Successful Exterior Installation: Water In, Water Out.
By Wilfried Sitzler
As published in Tile Design and Installation
Tile has a long history of exterior applications but the difference between a successful installation and one full of problems is the proper evaluation and design of a water drainage system. Severe weather exposure, freeze/thaw-cycle stresses, inadequate drainage design, and improper installation practices can contribute to saturation, efflorescence, deterioration and total failure of the covering. No tile covering can be permanently waterproof. None can guarantee that a covering will never crack, or that liquid water will not percolate. The laws of physics prove that water vapor diffusion is very essential concerning the absolute quantity of condensed (liquid) water in the substrate. Therefore it is necessary that a sealing layer be laid underneath the screed. Waterproof membranes, as used on balconies and terraces and in interior wet areas, are sealings against non-pressurized water.
In keeping with physical laws, as well as international construction standards, it is essential to protect waterproofing membranes from environmental and weather-related influences, and from water pressure. Environmental influences (e.g., mechanical stress) are prevented by screed and covering structures; together, these form the necessary protective layer. Where ceramic tiles are being installed, this protective layer doubles as a working surface.
If no preventive measures are taken to permanently drain off the water at the level of the waterproofing membrane, this screed will soon be saturated, causing water pressure on the sealing and various forms of frost damage and efflorescence.
Effective drainage of the percolating water is key for the long-term stability of the overall assembly. This requires the following construction features:
Sufficient incline from the sealing level to drainage points. Insertion of a drainage layer between the sealing and protective layers so as to allow water to run off under normal gravitational force. Drainage systems are available which are functional and designed to meet these requirements.
The only way to retain—or, in many countries, to win back—terraces and balconies as potential ceramic applications is to build them in accordance with the laws of physics, construction standards, and the most advanced technology available.
Many thinkers have already focused on the problem of water. Regardless of whether there is too much or little of it, water is always a problem. Especially in the construction field, water must be regarded as one of the primary causes of damage; damage-free construction therefore means waging a successful battle against water. This can be accomplished using a drainage systems under ceramic coverings in order to improve their ability to carry off water.
It must be stressed from the outset that no tile covering is permanently waterproof; nothing, moreover, can guarantee that a covering will never crack. It is important to understand the way water is transported within ceramic covering structures, and the resultant necessity of draining this water in a controlled fashion so as to prevent it from causing any damage. This necessity holds true for tiled surfaces in wet rooms, and especially for outdoor installations.
Balconies and terraces, by definition, are directly exposed to the effects of outdoor climates. The task of a tiled surface over such areas is to protect the underlying structure from environmental and climatic influences, and to produce a surface which is usable for its intended purpose.
To achieve this, certain construction principles must be respected. The German (DIN) construction guidelines are the most detailed. The German Practice Code offers directions for planning and execution, including references to the flat roof guidelines. The code clearly states: "The sealant must surround or cover the structure to be protected and prevent the penetration of water." The same section stipulates: In the planning of the structure which is to be waterproofed ... the prerequisites for a professional layout and execution of the sealant must be created. In doing this, the interaction between the sealant and the structure must be taken into account and, if applicable, the stresses imposed on the sealant layer must be kept within acceptable limits through appropriate construction measures.
The standard further states, "Permanently effective drain-off of the water which affects the sealant must be assured through technical construction measures, e.g., by the lay-out of gradient." Moreover, in regards drainage systems:
Protective layers must permanently protect structure sealants from damaging influences, whether these be of static, dynamic or thermal origin. They may, in individual cases, form functional layers of the structure.
In other words, the tile covering, as a protective layer designed to use, is actually a component of the sealant system.
It is important to understand the water transport processes in screed and cement. The transport of water or water migration in cement and in other porous, mineral-bound construction materials can, in principle, be triggered by the following transport processes:
- Laminar percolating flow.
- Capillary water transport.
- Water vapor diffusion.
These processes can occur individually, but are often found to occur in combination.
Laminar percolating flow requires extensive water saturation of the cement or the screed, and a hydrostatic pressure difference as the impelling force. Such transport can only take place in hollow spaces of a certain minimum size.
As an impelling force, capillary water transport requires differential moisture levels in the construction material, which then attain an equilibrium via the capillaries. A screed can never completely fill with water through capillary water transport alone; hollow spaces and pores cannot suck up water in this way. Partial pressure is equilibrated via water vapor diffusion. As a rule, the moisture present in the form of vapor moves from warmer areas toward colder ones.
For our purposes, water vapor diffusion must be regarded as the essential transport process. First, let’s return to the topic of laminar percolating flow. If you take a tube, shape it in a form of a "U" and introduce water at one end, the water will rise at the other end to the same height. If you create additional branches, each of them will fill to the same level as the others (of course, the greater the number of branches, the lower this common level will be). Now, if you attach a run-off drain at a certain level (to any of the branches), the tube as a whole will empty down to the level of that outlet. This principle applies to mortar beds. The porous mortar bed functions like the tubes and will saturate completely with water.
Now, if under such a water-saturated covering the sealant is perforated at only one point, water will escape at that point. A vacuum develops which automatically draws more water after it as long as the water lasts.
If a drainage system is laid between the sealant layer and the covering structure, the water percolates in accordance with the hydrostatic pressure gradient down to the sealant, and can then flow off there. Yet what happens to the remaining water in the capillaries? Capillary moisture can only escape from the covering structure via water vapor diffusion.
As mentioned earlier, vapor normally moves from the warmer part to the colder part. The source of warmth normally comes from the covering surface, e.g. through sunshine beating down on it. Thus, there is usually a temperature gradient running from the surface in the direction of the sealant. The water vapor diffusion therefore moves toward the sealant layer. If a drainage system has been installed there, the water can escape either in the form of vapor or in fluid liquid form. Since the ceramic tile surface is to a great extent vapor-proof, almost none of this moisture can escape upwards anyway.
Now, if there is no drainage system underneath, the water vapor condenses on the sealant layer and percolating water begins to develop, until the covering structure is completely saturated with water. Accordingly, DIN 18195, Part 5, states, "A permanently effective drain-off of the percolating water which affects the sealant must be assured through technical construction measures." With respect to ceramic coverings, this requirement can only be fulfilled by installing a drainage system.
Remarkably, it is virtually certain that the scientific community has, until now, done astonishingly little basic research in this area, i.e., the fact that water vapor diffusion is the most important moisture penetration process. This fact is very often underestimated, even by specialists. Of course, this diffusion also has its positive sides and undeniably contributes—together with capillary water transport—to maintaining the moisture which the screed requires.
Thus, the important thing is to limit the magnitude of these moisture values through the installation of a surface drainage system. Whoever fails to act in accordance with this is working contrary to the recognized technical rules. In light of the potential warranty claims, this is a decisive importance for companies carrying out this type of work. From this perspective, it may be that until now, the wrong people have been paying for a lot of damage.
Surface drainage system are available which are functional and designed to meet practical requirements. The functional ability of surface drainage system has also been demonstrated in a comprehensive series of research studies. The result of these studies form a sort of standard for any drainage system:
Under identical test conditions, when [the drainage system] was not used and the ceramic protective covering’s bedding material was instead simply applied directly over the sealant layer, a period 80 times longer was required for the same quantity of released water to flow off.
And further: The research finding cited was also confirmed through test variations conducted with lime cement....The intended leaching out of easily soluble CaO components could thus be achieved during the test.
And: No impairment of the drainage capacity of the (drainage system) installed in the test coverings was determined at any point during the test period. The load imposed by a whirling arm tester with 12,000 point loading of 337 lb. (150 kg) each had no negative impact on the sealant, the covering or the function of the drainage system. The test results also corresponded to nine years of Schluter-Systems’ practical experience with balconies and terraces, parking surfaces, breweries, underground garages, pedestrian zones, etc.
We regard it as the task of all those involved with such ceramic surfaces, to work towards structures which function in accordance with the laws of construction physics and the most advanced technology, in order above all to hold onto—or win back—terrace and balcony applications as potential markets for ceramics. Installers, architects, and tile manufacturers must themselves make the effort to understand the laws of construction physics.
Further information