SAMA: Guide - Most common wall flaws

Mould (spots and gray stains)	Dry brush with a sorghum-brush. Use 10% watered down bleach (sodium hypochlorite); let it dry completely then brush.
Bubbles or peeling of the wall	Remove with trowel or sandpaper. Smooth with plaster.
Black spots above the heaters	Strongly wash the surface with water, or sandpaper.
Moisture or saltpetre spots	Dry brush to remove efflorescences, then smooth the wall If you notice any saltpetre (white powder), after brushing wash with very watered down muriatic acid: 3 parts of acid every 100 parts of water
Cracks and holes	Click here with the mouse to see how can you eliminate cracks and holes both small and big

Even a large crack, must be first enlarged and deepened, beecause the edges are usually very fragile.
Then it must be wet and filled with plaster. Plaster sets quickly, and the crack will be sealed in 24 hours

Widen and deepen the crack with the corner of a trowel or with a light hammer, better yet using a three pointed scraper. Proceed with minor hits, keeping your trowel tilted.

Wall plaster is usually white or slightly coloured: it often stands out from the rest of the wall

Tiny nail holes are easily filled with wall plaster and a narrow trowel. Mind not to use too much plaster: it will likelty leave a thick layer on the wall. If that happens, use sandpaper to remove any excess thickness.

Bigger flaws must be enlarged with a stone chisel in order to remove the particles attached to the edges and the bottom. For gypsum walls fill them with powder of scagliola, mixed with water. Apply two or three layers, waiting for partial hardening between them.
You will avoid the typical filler deformation induced by the gravity, with the formation of a belly in the lower part.
For cement based plasters use a mortar prepared from pre-mixed powder.
Widen the crack or hole with a stone chisel, using light hits, but without fear to make it too big.

.Wet the surface with a brush, then apply the gypsum plaster or the mortar with the trowel and level flat. Don't be worried by color differences between the original surface and the filler. For long and deep cracks between wall and pillars or beams in reinforced concrete, use plaster mixed with gauze or a thin tissue. Push the plaster into the crack with a trowel for at least one cm (half inch). Then apply more plaster with your finger and level it flat with a thin trowel.