Technology Of Osmotic Renders In Waterproofing World

The concrete gets wet or water initially get below the membrane to create the osmotic cell by initial saturation, condensation and liquid water within holes and voids below the membrane and vapour diffusion from.

Osmosis is the chemical-physical phenomenon whereby two liquid solutions spread into one another through a semipermeable membrane and is caused by the difference in concentration between the two liquids.

Specially formulated cement systems, which are defined as ‘osmotic renders’, provided important waterproofing performances both in the occasional and permanent presence of rainwater, natural water, groundwater, etc.

Basic Working Principle

The particular adhesion of osmotic waterproofing systems, determined by the deep osmotic diffusion, also made them suitable for operating both in conditions of positive and negative water pressure.

In building materials (and not only) adhesion and adherence are the result of two different mechanisms that can be present both separately and as more often happens, in coaction: mechanical adhesion and chemical adhesion. The osmotic or diffusive adhesion also comes into play in the osmotic process.

Mechanical Adhesion

Mechanical adhesion depends, to a large extent, on the degree of preparation of the substrates, in particular on their degree of cleaning and roughening as well as on their saturation.

Chemical Adhesion

Chemical adhesion, pertaining to molecular interactions, depends on the nature of the adhesive, on its compatibility with the support and, in turn, on the degree of preparation of the surfaces.

Osmotic Or Diffusive Adhesion

In osmotic systems there is also a specific adhesion, which is realized through the two coagent processes, of diffusion and reactive chemical gel deposition, often defined osmotic or diffusive, dependent on the ‘osmotic capacity’ of the material and, once again, from the level of preparation of the surfaces.

Mapei‘s Osmotic Render: Planiseal 88

Mapei has one-component osmotic cementitious system, Planiseal 88 where osmotic, diffusive and mechanical adhesion is prevalent.

Some of the important features and highlights for the application of Planiseal 88 Waterproofing system are as below:

Surface Preparation: Among the essential conditions that must exist at the time of installation, it is absolutely necessary to consider the condition ‘saturated with a dry surface’, which can be defined as the ‘condition’ of a support which, having wet a few hours before, has completely absorbed the water that was applied to it, until it dried on the surface. In this way the support does not remove water from the material applied and the surface does not have veils of water that can interpose between the two materials, jeopardizing adhesion.

Proper Mixing: The wheelbarrow cannot be used in any way to ‘mix’ cementitious compounds and osmotic products in particular. The correct mixing must in fact take place either in special “mixers” and must be continued until a lump-free mixture is obtained, of the desired consistency. When mixed with water, Planiseal 88 becomes a fluid mortar that can be applied by trowel, brush or by spray with excellent adhesion to the substrate for complete waterproofing, even in the presence of negative pressure.

Prepation Of Mix: Preparing the mortar Pour 5-6 litres of water into a suitable container and slowly add the Planiseal 88 while blending with a mechanical mixer. Mix thoroughly for some minutes taking care to blend in all the unmixed powder deposited on the sides and bottom of the bucket, until the mortar is completely blended (free from lumps). Leave the mortar to stand for approximately 10 minutes, remix and apply.

Correct Distribution Of Stress: In order to obtain a correct distribution of the stress, in correspondence with the connections between horizontal and vertical structures, it is essential to make a preliminary construction of connection joints suitable for the shape and dimensions to the geometry of the structures. Mapei offers Mapeband tapes and non-shrinkable grouts as per the site conditions.

Application Methodology Of Planiseal 88

Apply Planiseal 88 with a brush, trowel or spray. Application by brush requires 2-3 coats. Make sure the previous coat is sufficiently dry before applying the next (generally 5-6 hours depending on the temperature and the absorption of the substrate. In order to have perfect adhesion between the coats, it is recommended not to exceed 24 hours).

Consumption: approx. 1.5 kg/m2 per mm of thickness.

Highlights Of Planiseal 88

Planiseal 88 corresponds to the principles defined in EN 1504-9

(“Products and systems for protecting and repairing concrete structures: definitions, requirements, quality control and conformity assessment. General principles for the use of products and systems”) and the requirements of EN 1504-2 coating (C) according to the MC and IR principles (“Protection systems for concrete surfaces”) Comes in White & Grey Color (Can be used for positive and negative both sides of basement waterproofing to handle low to moderate hydrostatic pressure.)

Final Performance

With 22% mixing water - thickness 2.5 mm: It is tested in accordance to EN 1504-2 (surface protection system for concrete, where this membrane comes in the category of Moisture Control and Increase Resistivity coating.)

Coefficient of permeability to free water (kg/m²·h0.5): Note w < 0.05 Class III (low permeability) according to EN 1062-1.

Permeability to water vapour - equivalent air thickness SD - (m): SD < 1 Class I (permeable to water vapour).

Bond strength on concrete (substrate in MC 0.40 - water/cement ratio = 0.40) according to EN 1766 (MPa): > 2

Advantage Of Osmotic Renders On Crystalline Coatings

- Osmotic renders are compatible for potable water tanks whereas crystalline coatings are not.

- Osmotic renders are recommended for both concrete & masonry structure, crystalline coating only react with the free lime present in concrete surface to give the reactive solution

- Osmotic renders bonding with concrete surface is more than 2M Pa gives extra assurance towards the integrity of the watertightness, whereas crystalline deeply penetrate in the pores and does not have any surface reaction.

- Osmotic renders can bear negative pressure too upto 1 ATM whereas crystalline coatings have no testing for negative pressure.

Conclusion

In order to protect the concrete surface, Selection of waterproofing Treatments are very much crucial. For protection against moisture ingress, Planiseal 88 an osmotic render works for waterproofing and useful for repairing underground masonries subject to water and moisture seepage in situations with negative pressure up to 1 atmosphere. Waterproofing basins, reservoirs and concrete or masonry tanks containing drinking water, waterproofing concrete or masonry tanks containing sewage water. Useful for both positive and negative side waterproofing. It can be applied on concrete or brick structure. Moreover, is classified as a protective protection coating for concrete as per EN 1504-2 guidelines.

For further information,
Rohini Malhotra
Business Development Manager
Mapei Construction Products India Pvt. Ltd.
www.mapei.co.in

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