Surface Inspection Before You Paint: Moisture, Cracks and Choosing the Right System
When a paint job fails, the paint is usually the last thing that went wrong.
The outcome was decided before anyone opened a tin. Whether the wall carried moisture. Whether the plaster was sound. Whether the cracks were opened and filled, or simply painted over. A proper inspection catches all of it, and it is the highest-return hour on any project.
Start with the surface, not the product
On most jobs the product comes first: someone picks a range, prices it by the square metre, and the surface gets whatever preparation the schedule allows. That is the wrong way round. The substrate determines which system can be specified at all. A wall holding moisture rules out certain coatings. Friable plaster must be made sound first, because a coating is only ever as well attached as what lies underneath.
Moisture is the first question, and it has a number
Moisture problems are not interchangeable. Penetrating moisture comes through the wall from outside. Rising damp travels up from the ground. Positive and negative moisture describe which side the water is pushing from, and negative is harder because the water arrives from behind the surface you are coating. All of them must be identified and addressed with a reputable waterproofing system before painting.
There is a number attached to this. Moisture levels in any wall surface to be painted should not exceed 15%. Not dry to the touch. Under 15%, measured.
Where Damp Cure helps, and where it does not
Prominent Paints Damp Cure is a premium quality primer that can withstand moisture up to 40%. It is built for new plaster still drying. A wall reading 40% after a week can be primed with Damp Cure by brush and roller, then allowed to dry to 15% before top coats. In that window it prevents moisture ingress if it rains while the wall dries.
What it will not do is hold back constant moisture. It is not a solution for negative moisture from a retaining wall, or water from the back fill beneath the damp proof course. Those need waterproofing, not a primer.
Cracks and the sequence that fixes them
Cracks form from moisture ingress combined with heat: water gets in, the sun raises the surface temperature, and the escaping moisture opens the surface. A crack is a symptom, so filling it without addressing the cause produces a wall that cracks again. The repair sequence has waiting periods that are not optional:
- Open the cracks a minimum of 5mm
- Wash the surface with Prominent Paints Fungal Wash
- Prime with Damp Cure and allow the full 24 hours drying time
- Fill with a cementitious filler or Prominent Paints Ready Mix Crack Filler
- Once dry, prime again with Damp Cure and allow another 24 hours
- Then apply the top coats
Two separate 24-hour intervals, both of them real. Compressing them is how the repair fails.
Reading the rest of the surface
Four conditions dictate the preparation required. Chalkiness means the coating has broken down. Friable plaster means the substrate is failing and will take the new coating with it. Loose and flaky paint has lost adhesion. Fungus grows back through a coating if covered rather than treated. The standard is the same throughout: sound, clean and dry.
Choose by exposure, not by colour
The system must be selected on what the coating will be exposed to. Wind, humidity, rainfall and harsh South African UV rays all influence performance, and a product formulated for one set of conditions will not necessarily hold in another.
Coastal work deserves particular mention. Near the coast, intercoat washing is necessary, because salt contamination between coats leads to adhesion failure of the entire system, not a patch. So think about the features of the system, not the colour, and choose fit for purpose from the Prominent Paints range.
Frequently asked questions
How do I know if my wall is under 15% moisture?
You measure it. A meter reading is the only reliable method, because walls can feel dry while carrying moisture well above the threshold.
Can I use Damp Cure to fix rising damp?
No. Damp Cure tolerates moisture up to 40% while a wall dries down, which is a different job from stopping water. Rising damp requires a waterproofing system and attention to the source.
Why wait 24 hours twice when repairing a crack?
Damp Cure is applied twice and needs its full drying time each time: once on the opened crack before filling, once on the repaired surface before top coats. Cutting either short undermines the adhesion of everything above it.
What is intercoat washing and do I need it inland?
Washing between coats to remove contamination settled since the previous coat. It is necessary near the coast, where airborne salt causes adhesion failure across the whole system if coated over.
My wall is chalky. Can I just paint over it?
No. Chalking means the coating is breaking down into powder, so anything applied over it bonds to loose material and lifts with it. Remove the chalk and bring the surface back to sound, clean and dry.
Getting it right before you start
Almost everything that goes wrong on an exterior job was visible before work began. For specification support, contact Prominent Paints customer care on 0861 77 66 46, or find your nearest branch on the Prominent Paints website.