What is the difference between plasterboarding and skimming?

Plasterboarding screws sheets of board onto studs, joists, and masonry to create a flat base, and is usually done by the builder's team. Skimming is the finish: the plasterer applies two thin coats of wet plaster over the board to give a smooth, paintable surface, often weeks later.

What is fireboard and why is it used around steel beams?

Fireboard is fire-rated plasterboard wrapped around structural steel beams to give the fire resistance that Building Regulations Part B requires for steels in a home. It usually has a pink face paper rather than the ivory of standard board, and building control inspects it before it is skimmed over.

How can you tell if an extension wall is dry enough to paint?

Judge it by colour. Wet plaster is a dark, muddy brown-pink, and as it dries it turns a uniform light pink. A single dark patch in a corner means that section still holds moisture and is not ready for topcoats.

Why do plasterers crack the joint between old and new walls?

The existing house and the new extension are two structures that move at different rates with temperature and moisture, so the join between them is prone to cracking. Expansion beads or flexible scrim bridging at the junction absorb that movement; filler alone will not hold and the crack returns.

What is dot-and-dab plastering?

Dot-and-dab sticks plasterboard straight onto a solid wall with dabs of adhesive instead of screwing it to battens or studs. It is faster on flat masonry, but the gap behind the board means heavy items need fixings that reach through to the masonry rather than ordinary wall plugs.

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Phase 7 · Second Fix · Task 01 of 09

Plastering Your Extension: What to Expect

Plastering costs £3,500 – £5,500 for a typical extension. How boarding, skimming, and drying work, what fireboard is, and why your plasterer won't do it all in one visit.

17 min readUpdated 2026Premium

Timeline infographic showing the plastering sequence from plasterboarding through bonding, skimming, drying, mist coat, and decoration, with time durations for each stage

Prerequisites

Complete these first

Plastering controls your finishing timeline. Every other second fix trade waits for it. Your electrician can't fit faceplates until the walls are plastered. Your decorator can't start until the plaster is dry. Your kitchen fitter needs dry, painted walls before fitting units against them. Get plastering wrong or late, and the entire completion date shifts.

The frustrating part? Plastering doesn't happen in a single visit. Your plasterer will come back repeatedly over several weeks, working room by room as each area becomes ready. And between the final skim coat and the first coat of paint, you'll be waiting. Possibly for weeks.

What this guide covers

01Two Stages, Not One
02Fireboard Around Steels
03The Bonding Question
04Drying: The Bottleneck You Can't Rush
05Scheduling: Multiple Visits, Multiple Headaches
06What Good Plastering Looks Like
07Should You Plaster It Yourself?
08Costs
09What Happens After Plastering

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