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Moisture and Membranes


Car Park Flooring Problems Part 3: Moisture and Membranes

In the last couple of posts in this series we’ve looked at how external factors like the sun and rain can affect a car park’s floor. In this post, we’ll take a look at how moisture can affect a deck coating system from both above and below (even in hot and dry countries like Australia!).

To fully protect a deck coating and its underlying structure, it’s important to guard against liquids seeping into the underlying concrete while simultaneously stopping moisture from inside the concrete rising up into the floor.

Apply a Membrane to Stop the Rain

Let’s start with the issue of water getting into the concrete, which is obviously more of a concern on exposed top decks than elsewhere.

We looked in the first post at how crack bridging properties are vital to maintaining a seamless, water resistant surface, but if the coating is chipped or otherwise compromised it’s vital that the concrete is still safeguarded to avoid potentially very dangerous corrosion issues.

To prevent water ingress, a membrane should always be installed underneath the finish that waterproofs the substrate. To achieve this, many contractors turn to liquid waterproofing membranes, which are applied like paint and when dry form an elastic layer across the concrete. These are often spray applied directly onto the substrate and create a thin, rubber-like coating.

While there are many liquid waterproofing membranes available, choosing the right one for a car park floor requires considering whether it will stand up to the rigours of a car park environment (such as heavy vehicle traffic, impacts, etc.)? If the answer to this is no, then not only could the membrane be ineffective, but it could lead to a domino effect of failures within the floor coating.

The MMA Way

To help ensure that the membrane ticks both of the above boxes, Deckshield Rapide ED has been designed to include an innovative MMA-based waterproofing membrane. This specialist system for external car park decks incorporates this membrane thanks to its ability to quickly form a robust layer between the floor’s primer and coating that stops any liquid in its tracks.

Deckshield Rapide ED has been specifically designed for external car park decks.

Slightly thicker than traditional, spray-on membranes, this solution is roller applied and thanks to its methyl methacrylate (MMA) formulation cures rapidly and is less affected by cold temperatures or high moisture levels during the application process.

Rising Moisture Matters

At the other end of the coating system, excessive moisture in the concrete slab can lead to significant damage. This happens because the moisture struggles to escape when it moves out of the substrate and so ends up forcing its way into the coating, causing issues such as adhesion failure and unsightly bubbles.

It might look innocent – but if there’s moisture lurking in the substrate it can cause a lot of issues!

It’s All Relative

These problems tend to occur when the moisture content of the concrete exceeds the critical moisture content of the materials that are in contact with it.

A material’s critical moisture content can be expressed as an Equilibrium Relative Humidity (ERH) value or a Moisture Content (%mc) value. ERH values are particularly suitable for this purpose because they convey the moisture condition of the material in question – essentially its degree of wetness.

ERH values are obtained by measuring the %rh of a pocket of air in moisture equilibrium with the material under investigation. Whilst the critical moisture content values vary for different materials, the problems outlined above are avoided when substrates have an ERH below 75%.

To clarify, humidity denotes the presence of water vapour (the gaseous form of water) in air and other gases. The expression relative humidity (%rh) of air expresses the degree of saturation with water vapour at a given temperature. For example, saturated air has 100%rh and so contains its full capacity of water vapour.

A Designer Primer

To make sure that the moisture lurking in the concrete doesn’t ruin the car park’s coating, the bond line between the substrate and the floor needs to be properly treated.

This is why the very first thing that’s put down for a Deckshield Rapide ED floor is a primer designed to prevent residual moisture diffusing out of the slab and into the other parts of the floor. Similar to the membrane, the primer uses an MMA formulation in order to quickly create a hardy layer that can resist moisture movement.

In this diagram we can see how the membrane is integrated into the Deckshield Rapide ED build up.

To make sure that a car park coating will protect against moisture from above and below, make sure to discuss the project’s specifics with both the applicator and supplier. If you’d like to learn more leave a comment or get in touch with a resin flooring expert.

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Ilona Osborne

Ilona Osborne is the Marketing Manager at Flowcrete Australia - a leading manufacturer of seamless resin floor solutions. In this role Ilona leads the regional marketing efforts in Australia and New Zealand to engage with construction professionals and to provide them with insights and information on resin flooring.

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