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How to waterproof concrete floor

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18 Mar 2009

Rob Paddock scrutinizes the issue of waterproofing a concrete floor in case your sectional title unit is flooded.

I live in a sectional title scheme.

Recently I had the unfortunate experience of a kitchen sink pipe bursting in the apartment above mine, the resultant water managed to flow out of the kitchen, seep through the concrete floor, and flow directly onto my bed, welcoming me when I came home after a long day at work, looking forward to a good nights sleep.

This article is therefore rather close to my heart right now.
It is important to understand that concrete floors on their own are not in any way waterproof, in fact, as far as water is concerned, normal concrete behaves like a dense sponge. One cubic meter of good quality dry concrete will absorb the equivalent of roughly 60 liters of water in just 30 minutes!
Concrete therefore needs a waterproof membrane over it in wet areas of the apartment such as toilets, bathrooms and kitchens to stop water from getting to it in the first place. The usual materials used for internal waterproof membranes include a combination of tiles, waterproof grout, waterproof screeds, epoxy paints and waterproof plastic sheeting.

The most common cause of a ceiling leak is a failure in the waterproof membrane or screed in the floor slab of the upper floor apartment. The failure may be because of natural deterioration of the waterproof membrane, material damage or faulty construction/installation of the membrane. Whatever the cause, the membrane loses its waterproof properties and is no longer able to prevent water from penetrating the porous concrete floor slab and seeping into the lower part of that slab which forms the ceiling of the apartment below.

In order to repair the waterproof membrane, all tiles, fixtures and anything else which could obstruct the repair works must be removed. If the area is a bathroom, the shower base and toilet pan may need to be removed.

Then a layer of waterproof membrane and screed needs to be applied to the entire floor surface and, most importantly, extended up the surrounding walls, around pipes and over the base of any doorway. Only after these materials have been applied in accordance with the manufacturer's specifications should the fixtures and any surfacing be re-installed.

Ensure that your contractor follows the following basic steps:

1. Remove floor tiles, screed, any toilet pan, basin pedestal and shower base as well as outlet pipe fittings and any other fixtures. Areas around pipes should be hacked out slightly deeper (about 25 mm more).
2. Clean the hacked surface, removing all dust and loose particles.
3. Fill the areas around pipes with non-shrink grout.
4. Apply a good quality waterproof membrane onto the hacked surface. The membrane should be upturned (up to 150 mm) against the walls, kerbs and pipes.
5. Allow the membrane to set for between 6 to 12 hours depending on manufacturer's instructions.
6. Reinstall toilet pan and any other fittings.
7. Apply a new layer of waterproof screed, at least 20 mm thick, onto the surface. A gentle gradient should be provided for effective drainage. Screed should be left to harden for at least 12 hours. The use of pre-packed waterproof screed is recommended.
8. Reinstall any floor tiles, pedestals etc.

In sectional title living, internal water leaks are not as common as leaks through unenclosed balcony floors.

Rob Paddock works in the property development division of Paddocks, sectional title specialist firm.

For more information click here to visit the website.

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