That was quicker than we thought. In our renovation series, we are already turning into the home stretch. But before we get there, let’s take a look at our house façade and/or balcony walls. Don’t they need a new coat of paint? And isn’t the plaster quietly trickling away in one place or another? Because painting a plaster façade is much more demanding than painting the interior walls, we explain how it can be done best and in the fastest way. Find out what preparatory work is necessary and how long the plaster has to dry before painting can even be considered.
Exterior walls should only be painted during the right season. In winter it is too cold for the paint to dry. On the other hand, it can be so hot in the summer that the paint dries much too quickly. And what is also very important: before the painting work can begin, the underlying surface must be thoroughly inspected. This is because painting the house exterior is a demanding and expensive task. If the façade is not properly prepared and any damage rectified, this will show up again after a short time. Therefore, the following 3 steps have proven to be the best way to proceed.
Step 1: Determine the quality of the plaster with various tests
The visual inspection
Immediately obvious are discolouration, loose paint layers, dirt accumulation and moss formation. While it is possible to remove plant residues with water and a brush, you should remove the dirt with a pressure washer. But be careful– before you begin painting after cleaning the façade, it must be completely dry. It is important to bear in mind that the water can penetrate quite deeply into the render and needs some time to dry out. To be on the safe side here, you should use our electronic moisture indicator BM31. With this instrument, the distribution of moisture in walls, floors and ceilings can be quickly located.
The wipe test
For this, brush your hand over the surface. Is there white dust on the inside of your hand? If so, this means that the wall is very chalky, which indicates the use of lime paint. If you would like to use a modern exterior wall paint, such as a water-based paint, you must first remove the lime paint.
The scratch test
Scrape firmly over the render or the old paint with an old screwdriver. If the render is friable or crumbly, you should strip back the render at the affected sites a few millimetres deep and apply a new coat of plaster. This also applies to old paint that will not support painting: if this flakes off in the test, it must be removed using a pressure washer and a sanding machine. Smaller cracks can be filled with acrylic filler or repair grout.
The knock test
Using a hammer, knock on a piece of wood placed on the render. If the render below begins to crumble, or if there are voids beneath the render layer, you need to break these open and clean and fill again with repair filler. If larger areas have broken off, you should use the original render. Please note: freshly applied mineral renders should only be painted over after four to six weeks, as the paint layer could otherwise be destroyed. Also, synthetic resin and dispersion renders must left for at least one week to completely set.
When determining whether the newly applied render has already dried sufficiently, you should use our electronic moisture indicator BM31. The instrument uses a dielectric measurement method, i.e. the moisture detection takes place non-destructively, as no electrodes or probes are inserted into the object being tested.
The absorption test
For this, apply water to the wall using a sponge. Now you can see by the discolouration, or by the fact that water runs off, how absorbent the façade is. If the water is directly absorbed, then you must in any case apply a primer, otherwise the paint layer will show stripes and its durability will be reduced.
Step 2: A good primer is the best basis for the new coat of paint.
Has the façade been inspected and repaired? Great – then you can begin by covering windows and doors with film. Attach the film carefully at the borders, for example under the roof gutters and at the windows. Apply the primer according to the manufacturer’s instructions. For a preliminary coat with the exterior wall paint to be used later, dilute it with 10 to 15 percent water.
Step 3: Now you can grab the paint bucket and paint roller
Use all your experience from interior painting: just as in this case, first paint the edges, corners and angles that you cannot reach with the paint roller. Do not paint all edges at once, but work successively so that you are able to paint the surrounding free areas with the paint roller before the paint is dry. Here you should paint generously into the free areas. This effectively “wet-in-wet” painting technique helps to avoid the later formation of patches.
To prevent further unsightly patches from forming in the first place, you should paint the façade in a crosswise fashion. First paint from right to left and back again, and then from top to bottom, or the other way around. This ensures that the exterior wall paint builds up in layers and the paint is applied evenly.
Moisture Indicator BM31 – with this, you paint on the safe side!
The BM31 is an electronic moisture indicator, that can be used to quickly and easily detect near-surface moisture in various materials and to localise moisture distributions in walls, floors or ceiling in a time-saving manner. Due to the dielectric measuring method, the moisture indication is absolutely non-destructive; no electrodes or probes need to be inserted into the material to be measured.
The BM31 is not only immediately ready for use, it also impresses with fast response times during measurement and shows the user not only the current real-time measured value but also helpful additional information such as minimum and maximum values on the easy-to-read display with back-light at the touch of a button. In addition, the current measured value can be recorded using the hold function.
Current offer recommendation
The moisture indicator BM31, reduced from €94.95 to only €69.95 incl. VAT
If you have any questions on this topic, please do not hesitate to contact us on +49 2452 962 400.
