Painting a plastered wall is a long and sometimes dangerous job. Depending on whether it is a plaster located inside the building or an exterior plaster, a living room or a service room, a fine plaster or a strongly structured, paperwork, products and application methods can change dramatically.
For this work, you will need the usual painter’s equipment. However, to facilitate the application of the products on these rough surfaces, brushes and rollers with long hairs are essential. The most pronounced hollows may even require action by tapping the brush. However, the most efficient and fastest option is still to spray the paint using a low-pressure gun (air less), available from all good equipment rental companies.
Painting a plastered interior wall
First of all, remove the removable elements and protect the joinery, electrical appliances, baseboards and other fixed parts with masking tape. Finally, never apply paint (including water-based) before the surface has completely dried thoroughly (±24 hours).
Very fashionable in the 1960s, especially in large real estate programs, interior plasters generally have a relatively low relief and spaced and rounded points. These characteristics make it easy to cover with a standard paint for interior walls. Another solution is to smooth these protuberances using a filler, sanded if necessary, to obtain a smooth surface with a more modern appearance. In one case, as in the other, you will have to carefully prepare the bottom, for an aesthetic and lasting result.
Preparing an interior plaster wall
All surfaces must be freed from impurities, grease and other traces of pollution which accumulate with remarkable tenacity. The relief of the plasters increases the difficulties and the time required for this task. Inside, there is no question of implementing the pressurized water jet, so you will have to arm yourself with a brush and… courage. Remember to protect the surrounding floors and furniture from dust and water splashes by covering them with waterproof tarpaulins. Work on successive small surfaces ( ±1 m²), rather than on large sections of walls, the drying of which will collect the impurities, thus making them even more difficult to rinse.
1)- For surfaces already coated with a washable paint, the use of washing soda applied with a soft brush, then carefully rinsed, gives the best results.
2)- For porous plasters tinted in the mass, cleaning is done dry by brushing using a brush with hard synthetic bristles. Traces of grease are neutralized by applying a suitable product (alcohol, acetone, highly diluted acid, etc.).
3)- Lime and porous paints only require dusting with a vacuum cleaner brush. Greasy stains are removed by stripping the paint.
Caution: the use of certain strippers or solvents is contraindicated on vinyl and acrylic plasters, which they disintegrate.
Once the cleaning phase is over, it’s time to repair the small imperfections in the wall:
- The cracks are widened with a triangular scraper before being filled with acrylic masonry putty (especially no silicone, on which few paints stick) or with a special filling filler.
- The flaking or poorly adhering parts must be unstuck, then filled with a smooth coating.
- Unused dowels are torn off. To do this, insert a screw of suitable diameter over half the length of the dowel, then use pliers to pry it out. The fulcrum of the pliers must be protected with a board. In hollow walls, driving the dowel into the wall a few millimeters is sufficient. Fill the hole.
- Traces of mold or saltpetre are signs of latent humidity. The cause must be found and treated, because no paint will hold up under these conditions and they will systematically reappear at short notice.
Whatever the method used, the aesthetics of the wall requires a restructuring of the freshly applied plaster, in coherence with the existing relief.
Paints for plastered interior walls?
To know the type of paint suitable for your wall, identify the nature of the support. Most interior plasters are based on acrylic or vinyl resins. Good news, all paints on the market are compatible with this type of product!
For mineral-based plasters (cement, lime, stucco, etc.), acrylic paints are recommended. It is advisable to deactivate the surface with a specific suitable product or to apply a universal undercoat.
On plasters already covered with oil or glycerophtalic paint (wet rooms), vinyl paints are incompatible (poor adhesion) and acrylic paints are not recommended (random hold and blistering). In this case, 2 main options are available to you: repaint with a solvent-based emulsion (glycero or other) or apply a primer compatible with the new paint.
Whatever the nature of the plaster, you can choose a paint called “all supports”. These products are reliable, hold very well on a wide variety of substrates, sometimes without an undercoat, and are resistant to splashing water. Unfortunately, they are very expensive, therefore poorly suited to large surfaces and, for two-components, difficult to use.
Painting a plastered exterior wall
To screen against bad weather, facade renderings are most often made of coatings, sprayed mechanically. Based on mortars (cement and/or lime) with strong additives. This material offers a surface with a very pronounced relief. Deposits of mould, fungus and other atmospheric pollution accumulating in cavities and crevices can penetrate the core of the plaster. Unsightly black spots, refractory to any treatment, then remain permanently. If the plaster body is sound and resistant, the paint will make the facade look like new for many years.
Attention danger : working at height, in sometimes acrobatic conditions, requires the use of specialized scaffolding that is firmly anchored.
Preparing the facade for painting
Painting an exterior plaster does not constitute a facelift. It is therefore necessary to accurately assess the condition of the support, because the best performing paint will only resist if the walls are hard, healthy and clean. It is therefore imperative to carry out a thorough preliminary examination, or better, to have a professional establish a diagnosis of the state of the facade.
Overall, the implementation processes remain identical to those developed above, this time with the efficient help of a very high pressure water jet. This device presupposes, of course, a certain erosion of the surfaces, but does not modify the general appearance and strips the parts that are not very adherent, with the beneficial effect of avoiding loading the brushes and rollers with grains of sand, which quickly renders them inoperative.
Pay particular attention to the remedial treatment of mold and fungus, using thoroughly rinsed anti-foam products. Saltpeter is a cancer that eats away limestone and certain mortars and concretes. The only lasting solutions consist of locally peeling off the coating to treat the body of the wall and sometimes creating underground drainage around the building. In these extreme situations, simple painting is unlikely to be sufficient. It is necessary to consider, after treatment of the causes, a facelift, at least on a certain height from the ground.
On facades or exterior walls, cracks must be filled using a non-silicone masonry mastic or a filling filler specially formulated for facades or concrete.
Exterior plaster paints
For this type of work, which is heavy, time-consuming and expensive, it is essential to choose a quality paint that has proven its durability over time.
If, despite serious cleaning, the bottom seems unstable and flakes or crumbles slightly with the passage of the hand, apply an undercoat to fix the surface and ensure the adhesion of the finishing paint. Also remember that this coating must let the wall breathe, which excludes lacquers.
Pliolites® are effective paints, but generally cover badly. Made from solvents, they are environmentally unfriendly and give off a lingering odor. Better suited to smooth surfaces than to plaster, their use can be envisaged on an already painted wall. Provide a breathing mask protecting solvents and thinners in quantity for cleaning tools.
“Special façade” acrylic paints are a judicious choice for covering a roughcast. A resin-free single-coat product, with more coverage and better quality, will save a lot of time. Painting light on a dark background or one with large color variations requires at least the application of two coats or more if it is a standard paint.
- Painting over roughcast absorbs larger amounts of paint. So plan for 20 to 30% additional product, compared to the estimates written on the cans.
- If your facade changes color or if you live near a historical monument, this work modifying the exterior appearance of the facade requires administrative authorisation. Information from your town hall.