Before you paint any exterior surface it needs to be prepared correctly so that the paint will adhere to substrate. Often this can involve a number of processes such as, pressure washing, surface stabilisation, removing loose paint or algae. We often come across surfaces that haven’t been prepared correctly prior to painting, which results in damage to the surface and in some cases damage to the interior of a property, because the painted surface has failed. This damage is frequently caused by water or moisture penetrating through the exterior surfaces and into the interior of a building especially around window reveals.
It is standard practice for a building to be pressure washed prior to painting or any other processes taking place in order to remove any old flaky paint, dirt, grime, and algae. Pressure washing will often remove a great deal of the problems mentioned above, however other process will sometimes have to be applied in order to get a surface ready. Chalky, flaky, blistering or peeling painted surfaces cannot be painted over without compromising the effectiveness of the paint and as mentioned pressure washing will not always remove these problems completely.
Chalky surfaces always need to be stabilised prior to painting, either using an oil or water based stabilising solution. We normally use a water based stabilising solution with a water based exterior paint, and a oil based stabilising solution with an oil based exterior paint such as Pliolite. Stabilising solution helps bind powdery surfaces together by hardening it, so that when paint is applied it sticks. We often come across chalky surfaces that haven’t been stabilised prior to painting, which results in the paint coming away from the surface, often in huge segments or at numerous random points varying in sizes. This as you can imagine can make a building look incredibly rundown and cause severe damage to a surface.
Another common substrate we come across is bare cement render, which can absorb large amounts of paint due to the surface being predominantly porous. The surface can also be somewhat dusty if new. Bare cement render can have a number of difficulties with regards to preparation prior to painting depending on the age of the surface. As mentioned if the render is new it can be dusty, which as explained could cause paint to attach to the dust or sandy residue and not the surface. Therefore two approaches can be applied, the first approach is to water down a good quality masonry paint by about 50% and apply it to the fresh render to bind any dust or residue. This watered down coat will also soak into the surface and act as a primer, to allow subsequent coats to be applied to a stable surface allowing the paint to stick. The second approach can involve using a stabilising solution, which will basically do the same thing as a watered down coat but without the added benefit of blanking out the dark surface.
This is by no means a comprehensive overview of preparing every type of surface prior to painting but gives an insight as to what needs to be done to get a professional result.