Plastering and Painting a Ceiling for a Flat Finish

Preparing a concrete ceiling, plastering and skimming stages, why primer matters, choosing and applying paint, and avoiding defects that show in raking light.

A plastered and painted ceiling looks like the simplest of surfaces, yet it reveals a tradesman's skill more clearly than almost anything else. Light raking in from the window picks out every wave, every trowel mark and every roller line. Achieving a flat, clean ceiling requires each stage of work to be done in the right order.

Preparing the concrete ceiling

Work starts with removing old finishes completely. No old distemper or poorly bonded paint, loose plaster, rust stains or grease marks should remain. Any layer that is not firmly bonded will later pull the new plaster away with it.

Then the ceiling is inspected. On monolithic concrete, formwork marks and ridges are the main issue; in panel buildings, it is the joints between slabs. Slab joints are opened and cleaned, exposed reinforcement is protected from rust, and the joint is filled with a suitable compound and reinforced with tape. When these joints are not dealt with properly, long straight cracks appear on the ceiling after painting.

On smooth concrete, a bonding primer is applied so the plaster will adhere. It leaves a rough film on the surface and prevents the plaster from delaminating.

Plastering

If the ceiling is only slightly uneven, it can be levelled directly with skim coats instead of plaster. When differences are larger, the ceiling is plastered to screeding beads. The beads are set in one plane with a laser level and the plaster is ruled off between them with a long straightedge.

Thick plaster coats on a ceiling should be avoided. A heavy, thick layer can come away under its own weight. On very uneven ceilings, a suspended plasterboard ceiling is often the safer and more sensible option.

The next stage begins only once the plaster is fully dry. Drying time depends on the type of mix, the coat thickness and ventilation. Strong draughts and aggressive heating during drying can cause cracking.

Skim coats and sanding

Two types of filler are usually applied over plaster. A base coat fills small holes and marks, and a finishing coat creates a smooth layer ready for paint. Reinforcing mesh or tape is used at slab joints and at the corner with the walls.

After each coat dries, the surface is sanded with a fine abrasive. The most important tool at this stage is light: the tradesman holds a lamp almost parallel to the surface, and in that raking light every small defect casts a shadow. Defects are marked and reworked. Time spent here is always more efficient than making corrections after painting.

Primer: small but decisive

After sanding, all dust is removed and primer is applied. Primer evens out the absorbency of the filler. Without it, paint soaks in more in some places, and the ceiling ends up blotchy with uneven sheen. Primer also improves adhesion and reduces paint consumption.

Choosing and applying paint

Ceilings usually get a deep matt paint. A matt surface diffuses light and hides minor imperfections, while gloss and semi-gloss paints show every ripple in raking light. In humid rooms such as bathrooms and kitchens, moisture- and mould-resistant washable matt paints are used.

When applying paint, these rules determine the result:

• at least two coats are applied, each dried for the time the manufacturer specifies;
• the final roller pass runs towards the light, from the window into the room, so roller marks follow the light;
• each area is painted without stopping, keeping a wet edge, otherwise lap marks remain;
• corners and edges are cut in with a brush beforehand or at the same time;
• there should be no draughts or direct sunlight in the room during painting.

The overall sequence

Ceiling work is done before walls, because dust and paint drips from the ceiling spoil a finished wall. Electrical cables and light outlets must be in place before plastering. The final coat of ceiling paint is often applied after all dusty work is finished, at the same time as the walls' final coat, so that it is not damaged by later trades.

If the ceiling and wall colours differ, the line between them must be straight and neat. Masking tape is used for this, or a slim cornice is fitted at the junction.

Zaferoğlu İnşaat plans ceiling and wall work in stages in apartment and office renovations and checks the quality of each stage before moving on to the next. If your ceiling has been checked with a laser level, bring the figures and we can decide between plaster and plasterboard.