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.

How to coat previously lime-washed walls

A large number of old buildings, particularly in rural areas, have been coated with lime-wash ( also referred to as white-wash). Restoration of these buildings is a complex affair and needs to be undertaken by a skilled contractor who is prepared to pay attention to detail.
The external walls of many of these structures can be anything up to 50cm thick, built without a cavity or damp-proof course. Lime-wash does not seal these walls, so in winter months the walls get very damp, but due to their thickness this moisture never reaches the interior. During summer months the walls dry out, and the lime-wash allows this moisture to permeate though it unchallenged. The paint coatings applied to the exterior of these walls has to be breathable i.e. they should allow moisture vapour to pass through them at a high rate. Matt coatings, with an excess of pigment over binder content, are suitable, and less expensive than the sheen coatings usually used on exterior walls.
Before coating, all lime-wash needs to be removed from the walls. This is best done by scraper and bristle brush as high pressure water-jetting is not an option on old clay brick walls. This is a tedious process, requiring a lot of patience and perseverance. Once all the lime-wash has been removed, and the inevitable repairs to the plaster have been completed and dried, apply one coat of an alkali resistant Plaster Primer and allow to dry overnight. This primed surface can then be top-coated with an interior-exterior matt finish paint such as MattCoat 40.

What are 'high-traffic' coatings

Work-space floors can have very different requirements due to the activity that takes place in that particular area
From high people-traffic in school or office block passageways, to heavy vehicle load-bays or work-shop floors - each area has its own set of challenges. Substrates can vary from wood, to galvanised iron through to screeded concrete, and it is essential to take these factors into account when selecting a suitable coating.
When it comes to coatings (as opposed to self-levelling screeds), twin pack epoxies tend to be the product of choice. They are self-priming on cured cement (due to their chemical resistant properties) and can be applied directly to bright metal - although priming with a twin-pack etch primer would give better long term results.
On wooden floors - where high traffic is expected - it would be better to use a twin-pack polyurethane. They are, in general, more flexible and do not yellow over time so that the natural appearance of the wood is not affected.
Passageways, depending on the volume of traffic, the substrate, and in the case of schools - the budget, can be coated with twin-pack epoxies (best option) or single pack polyurethane enamels. The single pack polyurethane enamel, although not as abrasion resistant as the epoxies, is far cheaper and can be applied by less skilled applicators.

How to identify the type of coating currently on a surface

When selecting the coating type to apply to a previously painted surface it is important to know whether incompatibility could result. The best way to avoid this is to first identify the coating type currently on the surface. Quick tests can narrow the options down to a level where a potentially expensive compatibility problem is avoided.
Without becoming too technical, dry coatings exhibit solubility, or a lack thereof in certain solvents, and this can be used to identify the coating type on the surface.
The method used is to rub the surface of the coating with a rag wet by solvents 15 times back and forth (known as 15 double rubs), and inspecting the rag for dissolved paint.
If 15 double rubs using Lacquer Thinners as the solvent caused no dissolution of the paint coating, then the product on the surface would be a twin pack epoxy or polyurethane.
Similarly, if a high aromatic solvent dissolves the coating, a water-based coating is indicated.
If the high aromatic solvent does not dissolve the coating, but Lacquer Thinners does, then a single pack solvent based product is likely to be on the surface.
Although this is not a fool proof method of testing a paint film, it does give a good idea of what one is faced with, and helps when selecting a new top-coat option. Costly mistakes are avoided when the correct information is at hand when specifying coating systems to be applied to previously painted surfaces.