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Introduction

In this Head Scratcher, we are going to show you five scenarios/problems from some developing markets in Africa that have similar yet slightly different causes.

Scenario 1: Colour-changing exterior coating in Mauritius

A customer built a luxurious house by the coast in Mauritius, but by the time he had finished the plastering stage, not only was he in a hurry to complete his house, he was beginning to run of money. So instead of the plaster and two coats of sheen that was on the original painting specification, he just applied two coats of a 72% PVC matt coating in a pastel beige/grey colour made up of yellow oxide, organic violet, and carbon black colourants.

In less than three months, some of the panels (mostly in the sun) look like the pictures below. The customer blamed the paint/colourant but what really happened? Hint: the moisture readings in some areas are 30-35 percent.

Cause: This is mode 1 of alkali attack. The pebbledash plaster was still damp when the high PVC matt paint was applied. The water carried the alkali salts (Calcium Hydroxide) from the plaster into the paint film in patches, where it was exposed to both light and shade. Further, the Calcium Hydroxide attacked the organic structure of the violet pigment, cleaving to it and making it change colour, leaving only the yellow oxide and carbon black behind.

If the builder would have let the plaster dry for six weeks and/or used the agreed-upon plaster primer, this would not have happened.

Scenario 2: Red oxide house in Kenya

A building contractor built a multi-story house in the very humid seaside city of Mombasa. The paint company told him that he would have to wait six weeks for the plaster to dry, and that he would need scaffolding to paint the very tall walls in the red oxide/white-only pastel sheen colour. However, he only waited two weeks and used ladders to reach the walls.

A few weeks later, the walls looked like the pictures below. The contractor wants the paint company to pay for the repainting but what is the real problem?

Hint: Application and sheen play a role but there is also another issue. Moisture readings in places around the windows are above 20 percent.

Cause: Although there is evidence of lapping, the wet edge problems were due to the use of ladders instead of scaffolding, plus the plaster was still wet and contained a lot of lime/Calcium Hydroxide which is not very soluble in water. The lime deposited in the paint film as white material, which caused those patches (in both sun-exposed and shaded areas) to look lighter or whiter. This is mode 2 of alkali attack.

Scenario 3: Shopping centre with stone finish in bright colours by a major freeway in Pretoria, RSA

About 15 years ago, a new shopping centre was built by the N1 Freeway in Pretoria East, one of busiest roads in the Southern Hemisphere traversed by many thousands of cars every day. The architects chose a trowel-applied stone finish with 1-2 MM marble chips at 75% PVC on an adhesion-promoted pure acrylic in very bright colours (blues, yellows, and oranges).

For the first four to five years, the colours were ok, but then they started to lighten, as seen in the picture below. The applicator/paint company states that inferior pigments were used to tint the stone finish and they are fading with the sun. But if you look into the film with a magnifying glass, you see a white deposit. What is really happening?

Cause: The stone-filled textured paint was painted on fresh cement which contained Calcium Hydroxide. Small amounts were deposited into the open micro-pore structure of the stone-filled coating, which over time reacted with the carbon dioxide/water from the exhaust fumes of the nearby traffic. This reaction forms white Calcium Carbonate and precipitates in the film, causing the observed white patches. This is mode 3 of alkali attack. The whole building has since been expanded and recoated or tiled.

Scenario 4: Four-Year-Old Houses in Namibia

A housing developer built a complex of cluster houses in Walvis Bay, Namibia. For the main houses, he used a plaster primer and a sheen paint in a pastel blue-grey colour. On the garden walls separating the units, he did not apply plaster primer and used a higher PVC (55-60%) matt paint in the same colour.

For the first two to three years, everything was ok, but then there was a slight ground subsidence and cracks appeared in the boundary walls. Within a year, the walls had white patches and discoloration on them, especially after the water table rose after heavy rain. See the pictures below. What caused the white patches/discoloration and why didn’t it affect the main houses?

Cause: When the matt coating was painted on the slightly damp wall, its slightly-above-CPVC structure allowed the liquid water to leave the paint film so everything looked normal. When the wall moved with the land subsidence, the matt paint film cracked. This then allowed moisture to enter into the cement and start reacting with the deeper unreacted cement present, producing Calcium Hydroxide by-products, causing a mixture of pigment degradation and white Calcium Hydroxide salt deposits. This is mode 4 of alkali attack.

Scenario 5: Fish warehouse in Beria, Mozambique

A Warehouse owner in Mozambique built a warehouse for Fish storage, on the Docks in the very Humid Sub-Tropical Costal Port of Beria in Mozambique. The Company, who leased the Ware house wanted the whole warehouse painted in their Corporate Colours, which were a Bright/deep Blue based on White and Pthalocyanine Blue tinted from a high-quality Sheen Paint Deep Base. The building was Completed and handed over but in less than 6 Months the leasing Company is complaining that the whole Building is Fading Turning white in patches, see the Pictures Below the Asset owner is Blaming the Paint and the Paint Company is blaming the Tinter Supplier but what went wrong and more importantly how do you fix it?

Cause: When the Blue paint was applied the substrate was slightly damp and the Calcium Hydroxide started to attack the Blue pigment in the Paint film leaving it exposed which then reacted with chlorine and Ozone  Free Radicals which are present in the salt laden humid air of this area which react together to quickly attack the blue pigment even further/accelerating the break down. This is mode 5 alkali attack and is the rarest form of Alkali attack as it only happens in humid coastal/salt laden atmospheres when Pthalocyanine Blue is present if such a blue is required by the sea than the more inert but far more expensive cobalt blue pigment should be used.

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