Metal Protection at the coast

Last week we were called to give a specification at a coastal installation - literally at the water's edge. Salt spray, wind and high humidity all challenging the integrity of metal gantries and equipment. Design of structures seems not to include the ease of maintaining metal components, and as it often happens we are asked "what now". Good stainless steel would surely have saved the day - but mild steel had been used to construct large moulds for concrete ramps and a series of beams forming an overhead delivery system some 100 metres long, down to the high water mark.
Priming had already been done, after in-house sand-blasting, using two coats of a high build epoxy-ester based anti-corrosive primer. The beams and moulds have to be coated in-situ, limiting application methods, as well as product types. Fortunately, the business has a full-time painter, dedicated to the maintenance of the installation. His days will be filled with removal of dried salt from the metal, sanding, spot priming with the epoxy ester primer and over-coating with Chlorinated Rubber Enamel for the next three years. While this should be music to a paint manufacturer's ears, use of a better material at the outset would have saved a lot costs down the line.

Some weeks are more intersting than others

This week has proved to be far busier and more interesting than most. In the Western Cape, winters are cold and wet, and painting slows down considerably. Spring is in the air now and it seems that business in this industry is set to begin the end of year rush earlier than in previous years.
Buildings visited this week for specifications and advice included an old multi-storey block in the centre of Cape Town (we had to reach the roof of this building through the top floor which proved to be a brothel), a 200 year old manor house in Stellenbosch, an 1800 square metre new luxury home in the farmlands outside Robertson and a fruit pack-shed re-furbishment on a well known estate in Somerset West.
Each of the above sites has its own set of requirements, budgets, and customer expectations. Giving the best advice to each individual owner is our goal, irrespective of the gain to our business. Not all we do as paint technologists is watch paint dry.

What are "snail-trails"

Snail trails can simply be described as shiny vertical run-marks seen on dry paint films. They are often seen soon after water-based paints have been applied, particularly if it has rained or after a heavy dew-fall.
Dry paint films are made up of pigment and binder, but to present the paint in a usable form, many additives are used in the formulation. These additives are mostly water-soluble and remain in the dry paint film until they are effectively washed out by water - be it via rain, dew or by irrigation sprinklers. If the amount of water falling on the surface is low, then only part of the water-solubles are washed out, and they can dry on the surface. This leaves what we call "snail-trails". They tend to be sticky, and can act as a dirt trap as seen in the photo below. Generally these additives are washed out of the paint after the dry film has been wet a couple of times.
Matt paints tend to show snail-trails more readily than sheen paints due to the fact that there is less binder in the dry film. Snail trails can also be seen in kitchens and bath-rooms due to the high humidity. Wiping with a damp cloth often can remove these snail trails.

How to sterilize contaminated surfaces

To support micro-biological growth, moisture, a food source and protection from u.v. light are required. Be it a poorly ventilated bathroom, kitchen, the interior of a wine cellar or fruit pack-shed, these requirements are met, and the growth of fungus and/or algae can be expected. Standard specifications generally call for an initial dose of a fungicide, followed by cleaning to remove the sterilised debris before a second application of the fungicide immediately before re-painting. This specification is sufficient for areas where moderate fungal contamination exists.
Where contamination is high, and where the growth has been present over a long period of time - such as in wine cellars - it is often necessary to repeat the application of fungicide, followed by the cleaning step several times, until all of the growth has been removed. The 'second' dose of fungicide can then be applied and re-coating can commence. These areas should be viewed as 'high-maintenance areas' and these walls should be washed down on a regular basis - as soon as growth re-appears. Installation of u.v. light in these areas will also help to slow down and limit re-growth. The 'one spec fits all' approach cannot be adopted in all cases.
The top-coat applied in these areas should contain a dry-film fungicide to ensure that re-growth is retarded for as long as possible. There is no guaranteed growth-free period, even when all of the above steps have been meticulously followed, as the rate of re-growth is entirely dependant on the conditions in that specific environment. Following the above steps will, however, ensure that you get the maximum benefit for the effort and costs incurred.

Getting prepared for the summer re-paint

With the feeling of spring in the air, it is a good time to start preparing for the summer facelift. Very often people leave painting of homes to the last minute, so that their home looks great for guests over the end of year holiday period. Contractors get booked up with work, and time runs out quicker than one thinks. This could leave you doing a rushed job using an unskilled painter, proving to be disastrous very soon after the fact. Identify what needs to be done now, choose the best contractor you can afford and do some product research so that you are informed when the contractor recommends his product of choice.
Peeling paint can be scraped off walls now, so that the affected areas have dried out completely at the time of recoating. Many times the high-pressure water jetting done by contractors removes paint from these areas, but at the same time forces water into the substrate. If over-coated the day after this has been done, as is the case many times, the coating - particularly if it is a high quality sheen paint - serves only to trap this moisture in the substrate effectively perpetuating the original problem.
Choose the best quality paint you can afford and save for it rather than settle for a cheaper option.
Planning time has begun!

How to remove bore-hole water stains from exterior walls

Often newly painted walls become stained from bore-hole water. The reason for this is that ground water often contains high levels of iron. This dissolved iron leaves brown stains on surfaces when irrigation water evaporates. Many home-owners resign themselves to the fact that they will have to repaint boundary walls on a regular basis to hide these stains. Fortunately this is not the case as we have a water-based degreaser - Tornado - that contains a metal complexing agent (EDTA) that removes these stains when used to wash the surface. The cost of the degreaser is very low, and the added benefit of having very clean, stain free walls after use is very noticeable. Check with your hardware outlet if they have a product containing EDTA for easy iron-stain removal before you repaint.

What happens if paint is applied to a wet surface

Instructions on packaging and in specifications will always call for surfaces to be dry before coating. Recently I saw a perfect example of the results if these instructions are not followed. A contractor had applied a water-proofing acrylic to a newly cast concrete roof, and blistering of the coating occurred in some areas within a week of application. The moisture, still present, in the underlying substrate was prevented from evaporating by the non-porous coating, and pushed the coating off the surface in water-filled blisters. On investigating the problem it was found that the moisture content of the slab was as high as 30%. Ideally, coating should only proceed when moisture levels are 12% or less.
Water-proofing contractors should carry a suitable moisture meter to ensure that the substrate is sufficiently dry before coating. Leaving a rubber mat on the surface over-night is an alternate method of detecting high levels of moisture. A dark patch will be present under the mat when lifted, if there is a high level of moisture in the substrate.
The moral of the story is to check first - rather than to make a costly error.

Apologies for break in transmission

Please excuse the break in postings - have been away for a week at the Kruger National Park. The best coating observed during this time is shown below.