Wall Repairs, Heavy-Duty Patching (Rimano, Rotband, MVR Uni)

The difference comes down to how large and how deep the damage is, and what kind of room the wall is in.

• Standard patching (Rimano, Rotband) covers smaller spots in dry rooms: holes from wall plugs, chipped corners, filled cable chases and shallow dents. Gypsum plaster spreads easily, sets quickly and trowels to a smooth finish, so the wall is almost ready for skimming or paint.
• Heavy-duty patching (Rimano, MVR Uni) is needed when plaster has fallen off down to the masonry, when a larger area or a thicker layer has to be built up, or when the existing plaster is lime-cement and gypsum would not suit it. The work is done in several coats, often after holes in the masonry have been filled with mortar first.

Height also matters. A repair near the floor is a different job from one just below the ceiling of a tall older room, where scaffolding or a stable mobile platform is needed.

The choice should not depend on whatever happens to be on the shelf at the builders' merchant. The repair mix should be compatible with the original plaster and able to cope with the conditions in the room.

• Gypsum plasters (Rimano, Rotband) are for indoor use in dry rooms: living rooms, bedrooms and hallways. They can be applied in a fairly thick layer in one go. The exact maximum thickness is printed on the bag. They are not suitable outdoors, on damp masonry or where water splashes directly onto the wall.
• Lime-cement mixes (MVR Uni) handle moisture much better and can be used inside or outside. They suit cellars, utility rooms, plinths, repairs to old lime and lime-cement plaster, and any wall that will later be tiled. They dry more slowly, though, and thicker build-ups have to be applied coat by coat.

Why does this matter? Gypsum and cement-based materials do not always get on well together. In practice it often happens that someone patches a damp cellar wall with gypsum, and a few months later the repair swells and falls off. A lime-cement coat, on the other hand, should not go on top of gypsum. If you are not sure what the existing plaster is made of, ask a tradesperson or do a small test somewhere out of sight.

1. Checking the wall. Tapping the wall shows where the plaster sounds hollow and is only loosely attached. These areas are removed back to a solid base, otherwise the repair would come away with them.
2. Cleaning. Dust, old flaking paint, grease and loose grains are removed. Old wall plugs and nails are pulled out of the holes.
3. Filling deep spots. Larger holes and pockets in the masonry are first packed with mortar or pieces of brick, so the plaster does not have to bridge an empty gap.
4. Priming. An absorbent surface is consolidated and evened out with a primer. Smooth concrete usually needs a bonding coat, otherwise plaster will not stick to it. The type of primer follows the plaster manufacturer's recommendation.
5. Applying the mix. The mix goes on with a trowel or float and is ruled off with a straightedge so it sits flush with the surrounding wall. For heavy repairs it is built up in coats, each one going on only once the previous coat has set.
6. Corners and joints. Damaged corners are reinforced with an angle bead. Where two different materials meet, such as brick and concrete, glass-fibre mesh is embedded in the plaster to reduce the risk of cracking.
7. Finishing and drying. Gypsum can be trowelled smooth once it has set. Lime-cement plaster needs longer. A rough rule of thumb is about one day per millimetre of thickness, but the manufacturer's figures apply, and drying depends on temperature and ventilation.

Two walls that look similar can take very different amounts of work, and that affects the cost. The things that make patching slower and more demanding are mainly:

• Deeper damage that needs several coats
• Lots of small scattered spots rather than one continuous area
• Corners, window reveals, arches and areas around door frames
• Working at height, below the ceiling or over a staircase
• Weathered, crumbly plaster that has to be knocked off first
• Damp masonry that must dry out, or where the cause of the damp has to be fixed first
• A furnished home where furniture and floors need covering

An empty room, a dry and sound wall and continuous repair areas, on the other hand, let the work go quickly and cleanly.

• Plastering over a weak base. If hollow old plaster is left under the repair, the patch will later crack or fall off along with it.
• Skipping the primer. Absorbent brick or aerated concrete pulls water out of the plaster too fast, and the mix does not have time to set properly.
• Gypsum on a damp spot. With damp masonry or a leak, the cause has to be dealt with first. Only then does repairing the plaster make sense.
• Painting over a wet patch. On a repair that has not dried, the paint discolours, leaves stains or peels.
• Filling a structural crack. Diagonal cracks running from the corners of windows and doors, or cracks that keep reopening after repair, may be caused by movement in the structure. A structural engineer should look at such a crack first, because plaster alone will not solve it.

In a block of flats, agree any work on shared areas, the façade or load-bearing walls with the building management or owners' association beforehand. If the repair is part of wider building work, check with your local building authority what the regulations require in your case.

You can handle holes from wall plugs, small dents or a shallow chase in a dry room yourself. For large areas, thick build-ups and work below a high ceiling, it makes sense to call a plasterer.

1. Pull out wall plugs and nails, tap the wall to find loose areas and remove them back to a solid base.
2. Dust off the area with a brush or vacuum cleaner.
3. Apply primer as recommended by the plaster manufacturer and let it dry.
4. Mix only as much gypsum plaster into clean water as you can use before it starts to set.
5. Press the mix firmly into the hole and rule it off with a float or straightedge so it is flush with the wall.
6. For a deeper spot, let the first coat set and then add a second.
7. Once set, smooth the surface, let it dry fully and only then skim or paint.

Inspect the finished repairs in raking light, for example with a torch held flat against the wall. That way you will see every unevenness that paint would later reveal anyway.

• Repaired areas do not sound hollow when tapped
• The patch is flush with the surrounding wall, with no step or hollow under a straightedge
• Corners are straight and undamaged
• There are no hairline cracks or bubbles in the repair
• Mesh has been embedded where different materials meet
• The material suits the conditions, with no gypsum in damp or outdoor areas
• The tradesperson has told you when the wall can be skimmed or painted