Waterproofing – FAQ

What kind of primers should be used before the waterproofing application? How to apply the waterproofing correctly upon the gypsum plasters? Below we present the answers to the most frequently asked questions concerning water tight membranes.

Can the waterproofing coating be left uncovered for some time or is it necessary to apply the adhesive and tiles onto it just after?

Tiles, beside the aesthetic function, fulfill also a protective one. They protect the waterproofing against mechanical damage. Therefore, if the waterproofing is not covered with tiles, it needs to be protected against mechanical damage in some other way.

It is recommended that the set waterproofing coating is covered with lining after 24 hours since application. In addition, the waterproofed areas must be protected against water access within three days. This is the course of action when ATLAS Woder W or ATLAS Woder E (Aval KL 51) are in use. When it comes to ATLAS Woder S, the set waterproofing should be covered with lining after 24 hours and then it should be protected against water under pressure within seven days.

When using ATLAS Woder Duo, the waterproofed areas should be protected against rain and free water flow within 12 hours and within 7 days if water is under pressure.

Is it really necessary to rub the first waterproofing coat with a brush into the substrate?

Yes, it is absolutely necessary. When using ATLAS Woder W, Woder E, KL 51, Woder S or Woder Duo, the first coat must be rubbed into the surface to be waterproofed. Only this technique of application guarantees that the material fills all the existing pores in the substrate. If the pores are not properly sealed, one cannot assume that the substrate is effectively protected against moisture.

What primers should be used under single-component and two-component waterproofing?

ATLAS Woder S (cement based waterproofing) requires that the substrate is initially intensively wet and kept matt-wet during the mortar application. For ready-made single-component waterproofing masses, like ATLAS Woder E (Aval KL 51) and Woder W it is obligatory to prime particularly absorbent surfaces (e.g. cement-lime plasters) with ATLAS Uni-Grunt (Aval KT 17) emulsion. In case of very smooth substrates of low absorption, one should use ATLAS Grunto-Plast mass as a primer.
If one uses two-component waterproofing Woder Duo, then the substrate should be initially intensively wet and kept matt-wet during the application. Highly absorbent (e.g. aforementioned cement-lime plasters) or dusty substrates should be primed with ATLAS Uni-Grunt (Aval KT 17) emulsion. On the other hand, smooth or hardly absorbable substrates (e.g. OSB) should be coated with ATLAS Grunto-Plast mass.

What type of waterproofing should be used on gypsum plasters?

It is preferable to use single-component waterproofing masses ATLAS Woder E (Aval KL 51) and ATLAS Woder W. These waterproofing materials do not contain cement. Gypsum cannot be combined with cement – if so, strongly expansive etryngite is formed.

Salts swell and increase in volume even by 168% when they crystalize. The effect of direct connection between gypsum plaster and cement based waterproofing is the destruction of the top layer. ATLAS Woder Duo should be applied upon primed substrates. The primer separates the gypsum plaster from the waterproofing layer. In conclusion, the gypsum plasters should be used with single-component waterproofing masses: ATLAS Woder E (Aval KL 51) which is more universal (can be used indoors and outdoors) or ATLAS Woder W (used indoors only).

What type of adhesives should be used on waterproofing and whether is it obligatory to use C2S1 class mortars?

It is recommended to use adhesives of C2 class (such as ATLAS Elastyk (Aval KM 16), ATLAS Geoflex or from ATLAS Plus line) when fixing the tiles on the waterproofing. Due to high deformability, this type of adhesives perfectly compensates thermal stress which occurs on balconies, terraces, underfloor or wall heating as well as mechanical stress (on flexible waterproofing: ATLAS Woder E (Aval KL 51), ATLAS Woder W and ATLAS Woder Duo).

Which waterproofing is resistant to negative water pressure?

Among waterproofing products manufactured by ATLAS, Woder Duo is resistant to negative pressure of water. This results from a very high bonding to the concrete substrate – over 1.0 MPa. The application of the waterproofing coating, when there is the negative water pressure expected, must be done extremely carefully and precisely.
One should remember that the element protected by waterproofing exposed to negative water pressure is permanently kept damp. This in turn negatively affects its performance. Therefore, every time one faces such situation, it is recommended to elaborate a technical design which takes into account local hydrotechnical conditions and technical condition of the building elements to be waterproofed.

How to apply the waterproofing coat of appropriate thickness?

This question is very important, as after all the thickness of waterproofing determines its type, e.g. heavy type of waterproofing must be at least 3 mm thick over the entire proofed area in order to make it resistant against water under pressure. In practice, the appropriate thickness of waterproofing is determined by the second coat application. The first coat rubbed into the substrate with a brush forms the contact coat and it can be assumed that its thickness is about 0.2 mm. When applying the second coat with a notched trowel, one needs to choose a matching size of the notches, i.e. for the 3 mm thick waterproofing it is “safe” to choose 8 mm notches. The trowel is led at an angle of 45 degrees. Therefore, the height of the furrow reaches approx. 5 mm. After smoothing, and taking into account the thickness of the first coat, one obtains the assumed thickness of 3 mm.

Another way to verify the thickness is to apply the polypropylene or fibre mesh of adequate thickness (we recommend mesh normally used for thermal insulation of buildings) on the contact coat. The second coat of waterproofing can be applied with a plain float. The amount of the applied material must be chosen so that the mesh precisely embedded in the waterproofing.

This method is obviously more expensive as the contractor needs to buy the mesh. However, some manufacturers oblige the contractors to embed the mesh because, apart from the thickness control, it is also the reinforcing element. When using ATLAS Woder Duo one does not need to buy the mesh, as the mortar has the reinforcing polypropylene fibres distributed in its composition – they make more than enough reinforcement. 

Why the tiles cannot be applied on the bitumen membranes?

Bitumen membranes, unlike two-component or single-component waterproofing materials, are not so deformable. To make the matter worse, the bitumen membranes tend to stick to each other on the contrary to ready-made and two-component waterproofing, which do not stick but maintain slip.

Bridging the scratches is a very desirable feature of waterproofing, especially outdoors, but is not a feature of bitumen membranes. On top of it all, bitumen membrane is not a rigid and stable substrate for the tiles fixing.  The material which performs the best under the tiles in case of outdoor applications (e.g. terraces, balconies) is a two-component waterproofing.

Why the single-component waterproofing materials are not recommended for use on balconies and terraces, despite that the manufacturers place such information on the products packaging?

Single-component waterproofing materials generally offer light type of waterproofing, i.e. damp-proofing. They protect from water which flows freely across the surface of the protected element. Therefore, one could assume that they are good enough for use on balconies or terraces.  Given that the balcony/terrace slab has 1.5 % slope towards the edge, the rainwater can be easily drained from the surface. The balcony or terrace proofed with single-component waterproofing can be safely used for many years. However, if there is much snow which cannot be quickly removed from the tiles, it is very likely that puddles will form under the snow. Hence, the waterproofing should be selected not only to resist the water free flow over the surface, but also to resist the water which remains on the tiles surface for some time. For this reason one must apply medium type of waterproofing represented by a two-component product (e.g. ATLAS Woder Duo).

Let’s then keep the principle: waterproofing of a terrace or a balcony is a medium type of waterproofing, that is why one must use two-component products(e.g.ATLAS Woder Duo).

Having in mind the climate change and frequent unexpected weather conditions, the design and technique of application of building materials should be provided in a way assuring protection of the building structure during the extreme conditions.

Is there any outdoor application where one can use a single-component, dispersive waterproofing, when we already know that a balcony or a terrace is too demanding for them? Absolutely yes, it is 100% safe to use such materials to waterproof vertical surfaces, i.e. plinths, building supports or walls just above the ground level.

Is it necessary to apply special sealing tapes in the corners if we know that ATLAS Woder Duo is already reinforced with fibres?

Yes, of course. The fibres used in ATLAS Woder Duo and special dispersion of appropriate viscosity provide bridging of scratches up to 0.75 mm wide. The sealing tape laid in the corners or at the connection with a terrace profile is able to transfer much larger deformations caused by movement of the terrace slab at the junction with a wall or on the joint between waterproofing and other materials, e.g. aluminum – from which the profiles are made, or cement screeds.

Is there a need to secure the flashings before application of ATLAS Woder Duo?

It is a logical question with a view to a potential problem which is the corrosion of the flashings made of galvanized steel used to finish the edges of terraces or balconies.

Each two-component waterproofing product containing cement produces heavily alkaline environment with high Ph coefficient – over 11. Is galvanized flashing resistant to corrosion in alkaline environment? The answer is clear – sooner or later it will corrode. Here, the corrosion speed depends on the coating and cannot be stopped in any way. One can extend the flashing life span by means of additional protection, for example: painting the sheet with an epoxy resin. Unfortunately, there is a misconception that, as the galvanized steel performs well as the roof flashing, it will also do just fine on the balconies and terraces where its function is the same. However, the membranes based on bitumen or asphalt does not produce the alkaline environment in contrary to cement mortars.

The best solution is to use specialist terrace profiles made of aluminum, which are additionally coated with powder paint. This is currently the most effective protection against corrosion. The drawback of this solution is the price of the aluminum elements, nevertheless the effectiveness of this solution is guaranteed.

Original text: Krzysztof Szyszko, ATLAS Group

English text: Piotr Marciniak, ATLAS Group