Sigma aims to prevent cracks in concrete

Sat, 25 Oct 2003

Saudi Review

Sigma aims to prevent cracks in concrete

DAMMAM

The protection and decoration of cementitious exterior substrates has given the paint manufacturer many different and difficult issues to resolve, among the most problematic being the cracking of the rendered surface and concrete carbonation, says Dammam-based Sigma Paints.

Concerned by the needs of its customers, and in response to the cracking and carbonation issues, Sigma Paints has added Sigmaflex Premium to its already extensive range of decorative products. According to the company, the product has been made following extensive research, development and testing in Europe, Africa and the Middle East.

Cracks that appear on freshly applied cement rendered substrates are commonly caused by one or more of the following, says the company:

Accelerated drying of the applied render: Often caused as a result of exposure to high ambient temperatures, typical of those experienced in the Middle East.

Settlement of the building: All new structures are prone to very slight movement or settlement. Construction materials contract when they dry out. This differential contraction of the various materials may continue for a number of months even after the construction has been completed.

Overly thick application of the render: When the face of the render dries out before the underlying render, it creates stresses in the entire render application.

The use of poor quality raw materials: Use of such material - and in some instances, materials that contain impurities such as desert sand or brackish water - often has an adverse effect on the hydration or drying process of the cement render.

Bad mixing of raw materials: When the mixing method adopted does not produce a homogeneous mix of materials, this can result in re-hydration of the cement.

Re-hydration of the cement can occur when the surface is exposed to a source of moisture, humidity, rain or irrigation water and again causes expansion and contraction of the applied render, resulting in cracking.
Concrete is alkaline by nature owing to the materials used in the concrete manufacture. The steel reinforcing bars are passivated, or protected from corrosion, by this natural alkalinity, pH 12- 13.

The penetration of acidic gases leads to carbonation and a reduction of alkalinity in the concrete when the pH levels are less than 9.5.
At a pH of less than 9.5, the steel reinforcing bars are no longer protected from corrosion and rust forms on the steel bars. As corrosion of the steel reinforcement progresses, the bars may expand to up to five times their original size; the result is initial cracking followed by the forcing off of the covering concrete.

The company says that the Sigmaflex Premium is the perfect coating to resolve all of these exterior issues, and is particularly suited to the climatic conditions experienced in the Gulf region. It is a water-based, pure acrylic, elastomeric coating with excellent UV (ultraviolet) resistance.

'Sigmaflex Premium is easy to apply, has excellent flexibility and elongation properties and has been independently tested and certified by Bureau Veritas, for its ability to bridge cracks of up to 2 mm,' the company says. The product also provides the required anti-carbonation properties for the protection of reinforced concrete and has been tested independently by the University of Dortmund, it adds.

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