Often we cannot say right away, does the old paint coating on the wall adhere well to the substrate. It is enough to roll it over a roller soaked in paint, which we will paint the surface with. With poor adhesion, small flakes of old paint peeled off will remain on the painted surface. You then have to either completely remove the old coating, by scraping it and washing it with water and painter's soap, or prime it with preparation.
Another way to check adhesion is to place your thumb dampened with water on a dry wall. If it leaves a dark mark, this new paint will not stick to the substrate and after drying – and often while painting – will fall off in sheets.
A sign of poor adhesion of the old paint is also its sticking to the applied adhesive tape. Glue its short section to the wall and tear it off. No old paint particles should remain on it, if they stick – i.e. the substrate is weak - we have to harden the old layers of paint by soaking the wall with a preparation for deep priming. The layer of paint and the top layer of plaster then form a strong crust after drying, suitable for a base for painting.
In stores you can find many specialized spray preparations for isolating various types of water stains and stains. It is enough to spray them on and let them dry. At home, these types of stains can also be insulated with water glass or diluted with colorless spirit or nitrocellulose varnish..
This is also how molds or molds are removed from the walls – wider – mushrooms. However, if they penetrate deeply into the plaster, and that happens often, it must be broken off, insulate the substrate with a fungicide, e.g.. Boracol 10 Rh, and then apply a new layer of plaster.
But all this is removing effects, not causes, that is, a temporary measure. Effectively remove fungi, including molds, it is possible only by insulating the walls of the building in these places, in which they freeze. These organisms thrive on walls, especially at the corners, in places, where they freeze.
It is easiest to fill small holes in the walls with acrylic putty. We press it neatly with a narrow chisel or an ordinary kitchen knife. Fill the hole carefully, smooth the front surface.
Before painting, very carefully, high-quality, we must level the surface with special fillers. Currently, various types of gypsum materials are used most often for this purpose, intended for finishing plasterboard surfaces. After filling, we get a base for painting, called sztablatura.
For plastering walls and ceilings, we use a putty or stainless steel plastering trowel, preferably steel. The edge should be long. This makes it easier to apply the putty evenly. It is generally applied with vertical stripes. There should be no local thickening at their junction; their subsequent grinding would require a greater amount of work.
Priming can be carried out as early as one hour after applying the putty. If we putty an absorbent substrate, e.g.. from aerated concrete, they must be primed with a primer paint.
The repaired corner must have an even vertical line. To get it, we should use a wooden patch or a short and narrow board. We put it on one wall and fill the defect on the other with an assembly mortar. After applying the mortar, rub the surface of the putty thoroughly with a stainless steel trowel, we put the board away and wait, until the mortar starts to harden. Then we put the board against the second wall and fill the defect on the first wall, also thoroughly rubbing the surface.
When we can expect, that the repaired corner will be reflected from time to time, let's think about strengthening it by fusing one of the corner profiles into the mortar to cover convex corners made of plasterboard.