Mould and Algae – Trouble Brewing

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Many excellent painting projects are spoiled by the infection of mould or algae. Mould can be found on exterior

surfaces but is generally encountered inside. Different types of mould can be found but the most common can be identified by colour. The three most common types are black, green or

one with a pinkish tone.

Mould is a living fungus that thrives on substances often used in paints such as placticisers and cellulose thickeners that are incorporated in water-borne products.  In addition to this, any substance that contains vegetable oils can also encourage growth. To make matters worse, the spores are airborne and can settle onto a partially formed paint film .

When work is undertaken black  mould can often look like dirt and if not fully removed prior to painting the spores can be encapsulated within the wet coating. If this does occur, very soon after the work has been completed the growths can re-appear. It is because of this that when removal of the spores is eventually attempted, the paint film can be stained. This is most noticeable on whites and pastel shades.

Mould is often referred to as mildew and can survive and grow in damp rooms such as bathrooms, laundries, breweries and cellars. Factors that can also encourage mould growth include areas where the relative humidity is in the region of 75% plus.

Therefore a combination of  high humidity, lack of light and lack of air flow is an ideal environment for this type of problem to be prevalent and is particularly noticeable when standard emulsion paints are used. The absorbency of the surface can also have a bearing on this matter, whether it be smooth or textured, painted or untreated. While water­ based coatings have fungicides incorporated within their formulations they should not be confused with specialised products designed to deal with potential mould growth.

Mould growth requires light to grow, in fact it will photosynthesise in the same way as any other plant. The main problem of paint coatings being affected by algae can be related to wall surfaces that are continually damp due to defective guttering, areas at ground level subjected to continual wetting.

In all cases where mould or algae is encountered then, it is necessary during the preparation work to ensure the spores are completely killed.

Where mould and algae are  present then it is important to remove all of the spores; this may involve power washing or if the spores are incorporated within the paint film , complete stripping may be necessary.

An interesting situation occured many years ago when a Brewery decided to repaint the cold storage rooms. At that time the ceiling, walls, steelwork and woodwork were all painted pale grey with the tank ends being black. The maintenance manager decided to have all the surfaces including the tank ends repainted in white.

As there did not appear to be anything untoward the contractor carried out the usual preparation tasks and painting commenced. The actual work took approximately 2 weeks and everyone was delighted with the results. Some 4 weeks after completion urgent meetings were arranged as mould was visible on all the surfaces.

It was decided that remedial work was necessary and the entire area washed down with a proprietary fungicidal wash. A programme was introduced to monitor the situation to establish where the fungi

was originating. After several days it was established that the mould growth was stemming from the tank ends. As these were metal it baffled everyone, and the tanks were said to be dry with no condensation present prior to or during painting. At a meeting the maintenance operator was asked “How did you keep the tank ends so black” “Easy”, was the reply, “l used boot polish.” Vegetable oil is found not only in paint, but also in boot polish.

A lesson to be learned when  dealing with problems, the cause may not be the most obvious even to the experienced tradesman.



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