Hollow or Delaminating Plaster
Causes, Risks & Re-Plastering (2026)

What hollow or delaminating plaster is

Most Malaysian walls are brick or block finished with a sand-cement render, then a thin skim coat and paint. ClickBina's render guide describes cement render as a thick mortar coat of about 10–25 mm applied directly to masonry, and skim coat as a thin finish layer of 1–3 mm on top. When the render loses its grip on the wall behind, it becomes a separate shell with an air gap underneath. That is what “hollow”, “drummy” or, in Malay, “kopong” plaster means.

A hollow patch can sit quietly for years, or it can crack, bulge and eventually drop off in pieces. The difference usually comes down to its size, where it is, and whether water is involved.

The tap test: finding the hollow areas

Tap the wall lightly with a coin, a knuckle or the handle of a screwdriver, working in a grid. Sound plaster gives a solid, short knock. Hollow plaster gives a duller, echoing sound, and you can usually trace its edge by tapping outwards until the sound changes. Mark the outline in pencil so you can see how large the area is and check later whether it grows.

Look at the surface too: a fine crack tracing the outline of the hollow area, a slight bulge you can see when you shine a torch along the wall, or paint that cracks in a map pattern over the patch all confirm what the sound tells you.

Why plaster loses its bond

When water is the real cause

If the hollow area is on a bathroom wall, near a kitchen sink, below a window, on an external wall or low down on a ground-floor wall, suspect water first. Leaking concealed pipes, failed bathroom waterproofing, rain driving through cracked render and damp rising from the ground all soak the render from behind. Salts carried by the water crystallise in the plaster and push it off, which is why hollow damp plaster often comes with white powder. ClickBina's guides on rising damp and white powder on walls explain those two sources.

Re-plastering a wet wall without fixing the water is money wasted: the new render loses its bond the same way, usually within a few rainy seasons.

When hollow plaster becomes a safety issue

• Ceilings and soffits: any hollow or cracked render overhead can fall on someone; treat it as urgent.
• External walls above walkways, porches or a neighbour's property: falling render is a risk to people passing below.
• Bulging or cracked-around patches: the shell has already moved and may drop soon.
• Plaster over a crack in a beam or column, or with rust stains: the problem may be the concrete, not the plaster; see the spalling concrete guide.

A small hollow patch on a dry internal wall, with no crack and no bulge, is not an emergency. Mark it, date it and deal with it at the next repaint or renovation.

Common places it happens

In older terrace houses, hollow plaster shows up most often on the lower part of ground-floor walls, around bathrooms and kitchens, and on the west-facing external wall that takes the sun and rain. In newer homes it tends to follow concrete elements: columns, beams and the edges of slabs where render went straight on to smooth formwork concrete. Walls that were chased for new wiring or pipes and then patched are another classic spot, because the patch and the old render rarely bond perfectly.

Patch repair or full re-plaster?

Filling or injecting behind hollow render is sometimes offered as a shortcut. For a home wall it rarely makes sense: the shell is usually cracked already, and a proper hack-back is the repair that lasts.

How re-plastering is done properly

1. Find and fix any water source; let the wall dry.
2. Tap-test and mark the area, then hack off the hollow plaster back to firmly bonded edges, cutting the edges square.
3. Clean off dust and loose material; rake out weak mortar joints.
4. On smooth concrete, roughen the surface and apply a bonding coat before rendering.
5. Dampen the background so it does not suck the water out of the new render.
6. Render in coats rather than one heavy coat, then keep it from drying too fast while it cures.
7. Skim coat once the render has cured, then prime and paint.

Hacking is noisy and dusty, so on strata property check the house rules on working hours first. ClickBina's hacking guide covers the demolition side.

What re-plastering costs

These indicative Klang Valley figures (2026) are from ClickBina's published cement render and skim coat guide:

Fixing a leak or damp problem behind the plaster, scaffolding for external walls and painting are priced separately.

Preventing it next time

• Insist on a clean, dampened background and a bonding coat on smooth concrete before any render goes on.
• Ask for render in coats of sensible thickness, not one heavy coat to hide an uneven wall.
• Keep new render from drying too fast in sun and wind.
• Deal with leaks, cracked external render and rising damp early.
• When walls are chased for wiring or pipes, have the chases filled and rendered properly, not just packed with mortar.

How ClickBina can help

ClickBina is an experienced KL & Selangor contractor for whole-house refurbishment and trade coordination, including the hacking, re-plastering, skim coat and painting that a hollow-plaster repair involves. WhatsApp us your job details for a quote: the wall size, where it is, and whether it is damp. We reply within the hour, the price we agree is a flat price with no hidden charges, and a site visit is RM150, waived if you go ahead.

Sources & methodology

• ClickBina cement render and skim coat cost guide — render and skim coat thickness, prices and the hacking add-on.
• ClickBina rising damp, white powder and spalling concrete guides — related causes.

How we estimated prices: every RM figure on this page is quoted unchanged from the ClickBina render and skim coat guide; they are indicative Klang Valley ranges for 2026, not fixed rates. Causes and repair steps are general good practice; the condition of your wall decides the scope.