Drywall repair is mostly about matching the repair method to the size of the damage. A tiny screw hole does not need a patch panel, while a fist-sized hole will not be fixed properly by packing it with filler. In the UK, the same type of sheet material is usually called plasterboard, so the methods below apply to ordinary plasterboard and drywall walls with a painted or skimmed surface.
Before repairing anything, make sure the damage is only cosmetic. A hole caused by a leaking pipe, electrical fault, structural movement or repeated damp needs the underlying problem fixed first.
Check what is behind the damaged area
Do not start cutting a larger square around a hole until you know what may be hidden in the wall. Pipes and electrical cables commonly run through stud walls. If the damage is near sockets, switches, radiators, bathrooms or kitchens, take extra care. Use an appropriate detector where useful and keep cuts shallow. Also check whether the board is damp, soft or mouldy. Wet plasterboard loses strength and may need replacing beyond the visibly damaged patch.
Repairing nail and screw holes
For a clean small hole, scrape away loose paint and raised paper. Press a small amount of fine surface filler or joint compound into the hole with a filling knife, then draw the blade across the surface to leave it slightly proud or level, depending on the product. Allow it to dry fully. Sand lightly with fine abrasive paper, remove dust and check the repair in side light.
Deep holes may shrink if filled in one thick application. Two thin applications usually give a flatter result than one large blob. If an old fixing remains loose in the wall, remove it before filling unless it is designed to stay permanently in place.
Repairing a small dent or torn surface
Trim away loose, fuzzy plasterboard paper with a sharp knife. Do not keep pulling once you reach firmly bonded paper because the tear can spread. A damaged paper face can bubble when wet filler is applied directly over it. If the exposed paper is badly torn, seal it with a suitable problem-surface or drywall sealer before filling. Apply filler in thin layers, feathering each layer beyond the edge of the previous one. Sand only once it is fully dry.
The aim is not merely to fill the depression. The edge of the repair has to disappear into the surrounding wall.
Small holes that need a patch
For holes too large for filler alone, use a purpose-made self-adhesive mesh or metal-backed repair patch if it is appropriate for the size and wall type. Remove loose material and clean the surrounding surface. Centre the patch over the hole and press it flat. Apply joint compound or suitable filler over the patch, extending beyond its edges. The first coat anchors the patch. Let it dry as instructed before feathering on another wider layer.
Once dry, add one or more wider, thinner coats. Feathering the compound farther out with each coat prevents a visible hump. Sand lightly between or after coats as the product requires.
Larger holes need new board
A larger hole is usually best repaired with a piece of plasterboard rather than layers of filler and mesh. Mark a neat square or rectangle around the damaged section. Before cutting, check for services behind the wall. Cut away the damaged board carefully. The replacement piece needs solid support. If the edges of the opening do not land on studs, fix timber backing strips inside the opening so they bridge behind the existing board. Screw through the existing plasterboard into the backing, leaving enough backing exposed to support the new patch.
Cut a replacement piece of plasterboard to fit the opening with a small workable gap around it. Screw the patch to the backing or studs. The screw heads should sit just below the paper surface without tearing through it.
Tape the joints
Bed paper tape in a suitable joint compound, or use mesh tape with the filler specified for that system. British Gypsum's EasiFill 60 instructions call for a first coat embedding tape followed by wider feathered coats. Paper tape is commonly bedded into joint compound; self-adhesive mesh is used differently, so follow the product instructions. Cover the taped joint with compound, keeping the first coat fairly narrow. Once dry, add wider coats to feather the change in level across a broad area.
This widening is what makes the repair disappear. If all the compound is piled directly over the seam, the patch will show as a raised square after painting. Use a wide jointing knife for the final coat if you have one.
Sand without damaging the wall
Dry joint compound sands easily, which is helpful but also makes it easy to overdo. Use fine abrasive paper or a sanding block and light pressure. Stop once the edges of the compound blend smoothly into the surrounding wall. Avoid sanding deep enough to expose the joint tape or damage the paper face of the plasterboard. If that happens, another thin coat will be needed.
Wear suitable dust protection and control the dust. Joint-compound dust is extremely fine and travels through the house. A damp-sanding method can reduce dust with some products, but only use it where the filler or compound manufacturer says it is suitable.
Prime before painting
Fresh filler and joint compound absorb paint differently from an already painted wall. If you paint straight over an unprimed patch, the repaired area can flash: it looks duller, shinier or a slightly different colour even though the topcoat is the same. Remove sanding dust and apply a suitable primer or mist/primer system for the material used. Then repaint the area. For a very small repair, touching in may work, but on walls with older paint the colour and sheen can have changed enough that repainting the whole wall gives a less visible result.
Repairing a drywall crack
A fine stable crack can sometimes be opened slightly, filled and finished. A crack that keeps returning deserves more investigation. Movement at a plasterboard joint may mean the tape or joint has failed. In that case, simply smearing filler over the line is likely to produce a temporary repair. Remove failed material as necessary, re-tape the joint and build up fresh joint compound. Cracks associated with significant building movement, doors suddenly sticking or widening gaps should not be dismissed as cosmetic plasterboard damage.
When to replace rather than patch
Replacement is usually the better option when the plasterboard is:
- soaked or repeatedly damp;
- badly mould affected;
- crumbling;
- damaged over a large area;
- unable to hold securely to the framing;
- contaminated by a problem that requires specialist treatment.
Do not close a wall while a leak remains active. The visible patch may look finished while moisture continues to damage timber, insulation or wiring behind it.
Sources checked: www.british-gypsum.com, www.british-gypsum.com.