Two contractors apply the same product to the same building on the same day. Three years later one elevation looks like it was done last season, the other looks tired.
The difference is almost never the paint. It is how the surface was prepared and the conditions it was applied in. Both are within the applicator’s control, and both are first to be compressed when a programme runs late.
This article picks up where the previous one left off. Surface inspection tells you what condition you are dealing with. This is what to do about it.
Preparation follows condition
Preparation is not a standard step. It is chosen on what the inspection found, and the target is always the same: sound, clean and dry. It cannot sensibly be priced as one rate across a building. An elevation with chalking needs a different intervention from one with flaking paint, and pricing them the same means under-preparing the worse walls.
High-pressure washing, and why the nozzle matters
The most cost-effective way to prepare a building exterior is a high-pressure washer with a rotating nozzle. It removes chalking, dirt and loose material in one pass, and the rotating nozzle does a second job a fan nozzle does not: it opens up existing crack formation.
That is a feature, not damage. Cracks opened during washing can be repaired while access is still in place. Cracks that survive the wash intact will open later, under a fresh coating.
Tap the plaster before you trust it
Washing tells you about the surface. Tapping tells you what is underneath. Tap the plaster, particularly along parapet walls, to establish it is not friable. Parapets take weather from three sides and are the most neglected element on a building. Painting over loose plaster puts a new coating onto loose cement.
There is a related discipline on the repair side. The pot life of cement is two hours. Cement left beyond that should not be used, because material applied past its pot life will itself be friable, which makes the repair the next failure point.
Match the system to the environment
Selecting a system is a function of the environment it will face. An industrial area and a coastal location both present conditions an ordinary specification will not survive. Look at the product’s stated features and confirm the system can withstand that site. A client may have chosen a finish from a showroom board; whether it exists in a system appropriate to the site is a separate question.
Application conditions decide the film
A correctly specified system applied in the wrong conditions will underperform a lesser system applied properly.
- Surface temperature should be at least 3 degrees above dew point. Below that you are applying into condensation and the film will not form as intended.
- Do not paint later than 15:00. The afternoon temperature drop works against the cure.
- In spring and summer, start on the northern elevations and work anti-clockwise, so you and the coating stay in the shade.
That last one addresses a real cost. A hot substrate causes excessive paint consumption and streaky application, which shows in the finish. Working anti-clockwise from the north improves both the material cost and the visual result, at no cost at all.
Film thickness is where performance is decided
Overall performance depends on the film thickness achieved. Every product has a specified wet film thickness that delivers the correct dry film thickness, published on the data sheet. Applying below it means the coating lacks the material to do what the datasheet says. Coatings exposed to UV rays, rain, wind and wind-driven sand deteriorate far faster than interior ones.
Warranty and technical support
The warranty period applicable to a paint film is determined by the product or range used. Warranty periods and their terms are published on the Prominent Paints website at www.prominentpaints.co.za. For specification assistance, contact customer care on 0861 77 66 46. This is a free added service.
Frequently asked questions
Why does a rotating nozzle matter more than pressure?
Pressure removes contamination, but a rotating nozzle also works into crack formation and opens it, giving a true picture of the substrate before you coat it.
What happens if I paint closer than 3 degrees to dew point?
You are applying onto a surface where condensation is present or about to form. The film cannot form properly against moisture, and the result is not always visible on the day, which is what makes it dangerous.
Is the 15:00 cut-off a hard rule?
It is a strong recommendation based on how surface temperature behaves late in the day. As temperature drops, curing conditions deteriorate, and material applied in that last hour is the most likely to be queried later.
Why start on the northern elevations?
In the southern hemisphere the northern elevations take the most direct sun. Starting there and working anti-clockwise keeps you moving into shade as the day heats up, which lowers paint consumption and gives a more even finish.
How do I find the correct wet film thickness?
It is published on that product’s technical data sheet. Work to the wet film figure, because it is measurable while the coating is wet and determines the dry film thickness achieved.
Getting the controllables right
Preparation and application conditions cost nothing extra and change everything. A washer with the right nozzle. A tap on the parapet. A start time and a direction of travel. None of it is difficult, and all of it separates a coating that reaches its warranty from one queried in year three.