Plastering is one of those trades that looks deceptively simple but requires real skill to do well. A bad plaster job is immediately obvious once the paint goes on — ripples, hollows, edges, and shadows that no amount of painting will hide.

Types of Plaster and When Each Is Used

Hardwall

A gypsum-based backing coat used on masonry walls (brick, block, lightweight block). It builds out uneven surfaces and provides a flat key for the finish coat. Applied 8–11mm thick.

Bonding Coat

Used on low-suction surfaces such as concrete, painted walls, or where areas have been patched. It has a different texture to hardwall and provides the grip the finish coat needs on surfaces that wouldn't otherwise hold it.

Board Finish / Thistle Multi Finish

The thin finish coat applied over plasterboard (board finish) or backing coats (multi finish). This is the final 2–3mm skim that produces the smooth, paintable surface. This is what most people refer to when they say 'getting a room skimmed'.

Renovating Plaster

Specifically formulated for use after damp treatment. It contains salts-resistant properties that prevent the efflorescence from contaminated walls bleeding through the new plaster surface.

Skimming vs Full Re-Plaster — What's the Difference?

Skimming

Skimming refers to applying a thin finish coat over an existing surface — usually over plasterboard, or over sound existing plaster that just needs a fresh surface. It's quicker and less disruptive than a full re-plaster, but it only works if the surface beneath is solid, flat, and in good condition.

Full Re-Plaster

A full re-plaster involves hacking off all the existing plaster down to the masonry and starting from scratch — backing coat, then finish coat. This is necessary where the existing plaster is hollow, crumbling, contaminated with salts, or following significant building work.

If you tap a wall and hear a hollow sound, the plaster has delaminated from the wall behind it. Skimming over hollow plaster is not a fix — it needs to come off.

What Affects Drying Time?

Fresh plaster must dry completely before it's painted. Rushing this causes serious problems — paint that flakes, blistering, and ongoing moisture issues behind the wall finish.

• A freshly plastered room typically takes 3–5 days to dry fully in normal conditions
• Temperature and ventilation significantly affect drying time — plaster applied in cold, damp conditions takes much longer
• The colour of plaster is a good guide: dark (wet) plaster gradually lightens to a uniform pale pink/cream as it dries
• Mist coats (heavily diluted emulsion) should be applied first to allow the wall to breathe

Wittick Building Tip: Never use a dehumidifier or excessive heat to force-dry plaster. It dries too fast, cracks, and the finish is ruined. Open windows, keep the space ventilated, and be patient.

Preparing a Room Before Plastering

• All surfaces should be clean, dust-free, and free from loose material
• PVA bonding agent is applied to high-suction surfaces and allowed to become tacky before plastering
• Any services — first fix electrics and plumbing — must be completed and chased into the walls before plastering begins
• Beads (metal angle beads and stop beads) are fixed at all external corners and edges
• Rooms should be cleared, and floors covered, as plaster splatter is difficult to remove once dry

After Plastering — What to Do Next

• Apply a mist coat — 50% emulsion, 50% water — to seal and prime the plaster
• Allow to dry fully, then inspect for any minor cracks or hollows (minor shrinkage cracking is normal)
• Fill any cracks with fine filler, sand lightly
• Apply two full coats of your chosen finish paint

Gloss or oil-based paints should not be applied directly to fresh plaster. Allow a full 4–6 weeks and apply a water-based primer first.

When Will You Need Plastering?

• After damp treatment — contaminated plaster must be removed and replaced
• After a loft conversion or extension — all new walls and ceilings need plastering
• After knocking through walls — the reveals and edges need making good
• After electrical rewiring — chases cut for cables need filling and skimming
• General refurbishment — refreshing tired, cracked, or previously poor plastering