Rob_Paddock A friend of mine was recently looking to buy a sectional title unit on the Atlantic Seaboard in Cape Town. After many Sundays of viewing apartments and searching on the internet, he found a “pimping pad” within his budget that he was certain would result in gorgeous women queuing down the road just waiting to be his lucky girlfriend. But before he got too excited about this heavenly realm he was about to enter into, I advised him to phone the schemes managing agent and find out more about the scheme. As it turns out, the scheme had a severe spalling problem and a massive special levy was likely to be raised in the next two years. So, like the concrete falling off the walls of the scheme, his dreams of beautiful women were shattered in an instant.

“…severe spalling problem and a massive special levy was likely to be raised in the next two years…”

Concrete reinforced structures use steel reinforcing bars to strengthen the structure. Spalling concrete is largely due to a natural deterioration process called carbonation, in which the reinforcing steel rods embedded in the concrete slab corrode, causing the concrete cover to crack and bulge.  The rate of the advance of spalling will depend on a number of factors, including the humidity of the atmosphere, the CO2 content of the air and the quality of the concrete used.

An important fact to know about spalling is that it takes place below the surface and you generally won’t even know that it’s there until the symptoms appear. The early stages of spalling concrete will probably not affect the safety of the building. However, you must repair the spalling before the steel rods corrode further and damage larger areas of the ceiling or pillars.

“…it is far better to use an experienced and registered contractor to do the repairs for the scheme…”

If the spalling is relatively minor, you can repair it yourself according to the process set out below. However, I would not recommend this in a sectional title scheme, as more often than not, the spalling will appear in an area of common property. Repairs by individuals to areas of common property tend to result in fights down the line. It is far better to use an experienced and registered contractor to do the repairs for the scheme.

Step by step repairs of minor spalling:

  1. Remove the spalled concrete at the cracked areas to expose the steel rods.
  2. Scale and clean the corroded steel rods.
  3. Apply rust inhibitor to the steel rods, carefully following the manufacturer’s instructions.
  4. Apply a bonding agent to the affected surfaces before patching to ensure proper bonding.
  5. Patch the exposed area using polymer modified cement mortar or epoxy mortar.
  6. Paint the area to protect it from the elements.

 

Preventing and containing spalling

  1. Do not delay repairing spalling concrete as the affected area will become larger over time.
  2. Paint regularly
  3. Check pillars and concrete ceilings regularly. If there are holes that are no longer in use, they should be filled and sealed immediately to prevent moisture and oxygen entering the concrete. Cracks on the ceiling should likewise be filled and sealed as soon as they become apparent.
  4. A humid environment speeds up the carbonation process. Ensure that areas which could retain heat and moisture are properly vented.

Once the spalling process has started it will continue to weaken the structure over time. It is important to realise that these failures are aggressive in nature and should not be left to eventually undermine the structural integrity of you building. A specialist should be contracted to remedy these failures, as normal plaster repairs will not suffice.  Consult a specialist to determine the exact cause & extent of spalling in your scheme and to recommend a suitable reinstatement strategy. Once the cause and specification has been established, competitive quotes can be obtained from specialist contractors to perform the necessary repairs and maintenance. Due to the porous nature of concrete and the fact that this process is promoted by external factors, the general maintenance of your “building envelope” is your most effective prevention against spalling.

“…general maintenance of your “building envelope” is your most effective prevention against spalling…”

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