Solutions for waterproofing terraces and balconies

Winter, rain and ice are often symptoms of higher infiltration risk that, if not resolved, can cause damage to the building structure over time. Usually these types of problems arise from worn or poorly installed waterproofing. Below we’ll look at a few solutions used to avoid or resolve these issues in terrace and balcony floors.

What to consider before waterproofing

In new construction, the designer decides the best waterproofing solution for outdoor flooring. A Best Practice which has become commonplace is that of applying a drainage membrane on the underside of the substrate, serving as support for correct waterproofing. UNI11493-1 regulations, in fact, state that “the indication of a drainage and protection membrane, applied between the substrate and water barrier, is a measure with the objective of preventing water stagnation from penetrating the structure.”

On the other hand, in renovations, it’s important to evaluate different factors in order to choose the best solution based on certain basic conditions.

In this case, the first thing to analyze is the area where the intervention will take place:

• evaluate the state of conservation of the flooring and substrate
• verify the layered section of the structure
• make sure that the slope of the flooring is appropriate
• check that there are no fractures or separation between the various layers

Depending on the conditions of the terrace or balcony in question, you can choose the best solution between those described below.

Choose the most suitable waterproofing solution for renovations

Based on the conditions of the terrace or balcony, you can choose the best solution by evaluating several factors. If the flooring is in perfect shape, it might be enough to directly waterproof the floor covering.

However, if there are issues with the tile, such as cracks or holes, it’s a good idea to remove them and waterproof the underlying layer, that is, the substrate. If the condition of the substrate is also inadequate, the best solution is then to waterproof the layer beneath the substrate, hence preventing any possible future infiltrations.

Waterproofing solutions without removing the tile

If the flooring is in good condition, without cracks or tenting, liquid waterproofing is a good solution to employ without having to remove the tiled surface. It is easy to use and can be applied quickly with rollers or brushes onto the entire surface without leaving gaps, while creating a thickness of only a few millimeters. Such procedure, which should be carried out by carefully following the instructions indicated by liquid membrane manufacturers, is resistant to temperature changes, bad weather, chemical substances or stagnant water. A fundamental aspect to consider with the supplier is the suitability of the product the existing flooring.   

Waterproofing solutions between tile and substrate

If the flooring is damaged or unsuitable, it is necessary to completely remove it and intervene in the layer underneath, that is, on top of the substrate. Two main solutions stand out from what’s available on the market: waterproofing membrane rolls or waterproofing liquids.

Rolled membrane waterproofing systems

On the market, there are numerous solutions in which to use rolled membranes to waterproof the substrate. The most common are bituminous, rolled, self-adhesive waterproofing membranes, that can be applied with hot air welding on site.

The substrate must be clean, dry and free of dust and debris. Subsequent to the application of the adhesive membranes, thinset can be spread for the tile application.

If the waterproof layer under the substrate is undamaged, you can implement a cleaner and faster solution, such as a polyethylene rolled membrane. In order to use this type of waterproofing, we suggest using Floortec, a membrane composed of a base in polyethylene laminated with non-woven fabric on the underside. With a total thickness of only 3 mm, Floortec not only reinforces the waterproofness of the substrate without substantially influencing the interior of the flooring, it also compensates structural tension, manages moisture which rises up through the installation and provides additional load resistance. Upon the installation of the membrane with cement adhesive, the tiles can be installed.

Cement-based liquid compound waterproofing system

An alternative to a bituminous membrane may be the application of a cement-based liquid layer that is easy to apply on top of the substrate. The product is a cement-based mixture to which polymers and other elements impervious to water are added. The tiles can then be applied over this layer with the appropriate tile adhesive. This procedure is simpler than the previous one, but the cement layer, in practice, is not perfectly waterproof and could dilate or shrink as a result of changes in temperature, allowing a small amount of humidity to pass to the layer underneath. This technique is recommended in interventions where there is no doubt that the substrate is in perfect condition and does not present cracks or hairline fissures.

Waterproofing solutions under the substrate

The best solution to solve and prevent any type of infiltration and subsequent degradation is to intervene under the substrate. For optimal results, the procedure should include the application of a waterproofing layer, on top of which is applied a drainage membrane that provides protection and allows the outflow of water that percolates from the upper layer of the draining substrate, as suggested by regulation UNI11493-1.

Bituminous membrane waterproofing system

Bituminous membranes are the most popular system used to waterproof under the substrate of terraces and balconies. These membranes are derived from the distillation of crude oil and commercially sold in prefabricated rolls. In the thickness of the roll there is also an armature (in glass-fiber or polyester-fiber) to increase resistance. In pedestrian areas, such as terraces and balconies, the application of a bituminous membrane with a thickness of 4 mm is recommended, in order to increase mechanical resistance and maintain the elongation property that is characteristic of this material. The sheets of prefabricated rolls are easy to install and, due to flame bonding, guarantee complete adherence.

In application settings where an open flame is not permitted, the same membranes are available with an adhesive layer. These are easier to apply, yet provide slightly reduced effectiveness.

The importance of draining membranes

Draining membranes under the substrate are true lifesavers for the structure of the building.

The main cause for damage to terraces and balconies is, in fact, the presence of water when it inevitably infiltrates to the interior of the substrate and slowly wears the various waterproofing layers. The unique structure of the drainage membrane prevents this type of problem. For this reason we recommend Draintec 8, a membrane designed by our technicians to allow water drainage through a series of drainage channels, compensating hydrostatic tension in contact with the substrate and the bitumen-based membrane. Its particular shape supports and decreases load compression resulting from pedestrian or load passage. With a thickness of only 8 mm, Draintec 8 contains two glued layers. The first is a base in polyethylene with cone-shaped elements used to separate and drain liquids. The second layer is in non-woven fabric which is laminated above the base, with the function of blocking the passage of small particles and debris so that these do not obstruct the channels and decrease the effectiveness of the membrane.

When using a draining substrate, we suggest installing Draintec 8S, composed of a net with a looser weaving structure than that of Draintec 8.

Using a perimeter profile for optimal results

To complete an intervention with state-of-the-art results, we suggest installing the Bordertec BD profile along the perimeter of the terrace or balcony. The purpose of this edge profile is to guarantee the complete drainage of water through specifically designed drainage holes. Bordertec BD should be positioned under the substrate, precisely between the drainage membrane and the bituminous membrane. Together with the Draintec 8 drainage membrane, it is the ideal product to protect the terrace structure from infiltration and deterioration.