How To Waterproof A Terrace With A Liquid System

How To Waterproof A Terrace With A Liquid System

Elastic, resistant, and long-lasting, liquid waterproofing systems are increasingly used in terrace waterproofing projects. Thanks to their low thickness, they can be applied to many existing surfaces of different natures and offer excellent mechanical resistance. Among their main features are the speed in installation, simplicity of cleaning, and the fact—very important when talking about terraces and balconies—that they are not susceptible to mold and bacteria. Furthermore, it is important to consider the breathability of the applied system, especially if the terrace is subject to moisture due to infiltration, in order to avoid trapping humidity beneath the waterproofing.

Here, we will analyse the basic concepts for correct waterproofing.



To apply a liquid waterproofing system, it is essential that the surface is suitable for the product used.

To apply a liquid waterproofing system, the surface must be consistent with the features of the product that will be used. Usually, these products are used on cement substrates or existing tiled floors. As with all waterproofing treatments, it is necessary to analyze the condition of the substrate and, if necessary, carry out operations to restore damaged parts to ensure the best linearity and continuity of the surface. Below are the four main steps for checking the substrate subject to waterproofing:

  1. Cohesion and resistance: The substrate must be cohesive and resistant, have good tear resistance, be free of crumbling or detaching parts, holes, gravel nests, and deficiencies. In this regard, it must be cleaned, restored with suitable products (for example, structural mortar for concrete, grout for tile joints, etc.), or leveled if it is not smooth enough.

  2. Roughness: The substrate must have roughness within a range suitable for adhesion of the liquid waterproofing product. Substrates that are too rough, such as staged concrete, must be smoothed out. Substrates that are too smooth, such as stoneware or clinker ceramics, must be treated by abrasion and sanding.

  3. Slope and flatness: Although good quality liquid waterproofing products are resistant to water stagnation, in order to guarantee correct flow of rainwater, it is necessary to guarantee a slope of the substrate equal to 1.5%, connecting drains and details to the waterproof system. Furthermore, it is useful to evaluate that the substrate is flat, avoiding the creation of depressions.

  4. Temperature and humidity: It is necessary to evaluate that the substrate has temperature and humidity conditions consistent with the chosen product. For example, high-performance products can also be used on humid supports and with temperatures close to 0°C. If you opt for less performing products, it is necessary to ensure that the support is dry and has a minimum temperature of 5°C. The same principle must be used in the evaluation of substrates exposed to the sun for many hours, which could even reach high temperatures. Consequently, it will be necessary to use products that guarantee stability and adhesion in such situations.



The components that require careful consideration, apart from the entire surface, can be broken down into three main areas: the edges, the joints, and the outlets. Prior to applying the liquid waterproofing product, it is essential to examine the following:

  1. Corners: due to the concentration of stresses and therefore potential movements, corners are among the fundamental points to be reinforced in waterproofing. Liquid systems are equipped with special “strips”, often self-adhesive, which are applied across the edge, ensuring continuity of the waterproofing. Recommended sealing system accessories: BC SEAL BAND.

  2. Joints: similarly to what has been described for the corners, due to the expansion brought about by the substrate, the joints are a critical element for the continuity of the waterproof covering. In order to create an elastic bridge, systems of straps or bands are set up to give flow. Typically, the prefabricated strips utilized for forming joints are installed using the product itself. They are applied with a brush or roller to the area directly neighboring the joint that needs to be treated, ensuring adhesion by embedding them into the resin. Recommended sealing system accessories: WINJOINT FOAM, WINJOINT SEAL, WINJOINT BAND.

  3. Drainpipes/or other installations: stormwater drains are certainly present or to be provided on the roof. Furthermore, there may be systems, shafts, vents, and various pipes constituting pass-through structure the waterproofing. To ensure continuity it will be necessary to treat these points with suitable accessories, self-adhesive or glued with specific materials. Recommended sealing system accessories: BC SEAL PAD, WINSEAL.



The application of the liquid waterproofing system can be done with different tools: by brush, with a short-haired roller, with a toothed trowel, or by spraying with an airless pump. "The first phase for an ideal outcome is achieved by laying down a layer of suitable material to ensure the waterproofness of the system." This film can only be guaranteed by controlling consumption of the product, according to the manufacturer’s technical data sheet. Usually, for products that involve the use of reinforcing mesh, it is applied in the first application layer to provide dimensional stability to the product and ensure an appropriate thickness. By completely submerging the reinforcement, you can ensure that the product is evenly spread. The second coat of liquid waterproofing, to be applied while adhering to the drying times indicated in the technical data sheet, will be laid in a similar manner to the first, fully covering the reinforcing mesh. There are some exceptions, noted in the technical data sheets, where products can be used in a single coat or with a double coat ‘wet on wet’.

N.B. If the existing terrace is covered in tiles, in order to avoid that the joints will also be highlighted on the surface of the final waterproofing, before laying the product it is possible to regularize the unevenness with a thixotropic product, compatible with the waterproof system (example: ONE Vertical for grouting the joints).



In conclusion, we will recap the key steps of a “typical” situation with one of Winkler's best-performing liquid waterproofing systems, One Winkler System. The breathable liquid system, suitable for floorings subject to high traffic, is laid in double hand with interposed armature.


The preparation of the surface involves: removal of dirt and parts in the detachment phase, sanding of existing tiles, pressure washing to remove dust particles.


Supply and laying of specific strips, including laying of liquid waterproofing for adhesion.


Supply and laying of specific self-adhesive strips.


Supply and laying of the specific tissue and self-adhesive strips.


Supply and laying with roller or brush of the material. Usually, it is a thixotropic product that does not drip when applied vertically (One Vertical).


Supply and laying in two hands. Reinforcing mesh is applied together with the laying of the first coat of product.