How do I make good the wall after taking out a fireplace?

Taking a fireplace out is straightforward. Making the wall look as though there was never one there is the part people underestimate, and it fails in two predictable ways: the flue is sealed like a wall rather than ventilated like a chimney, and the plaster over the closure shows as a rectangle forever because the joints were not reinforced.

Safety

What you'll need

• Blocks and mortar, or timber framing and moisture-resistant board
• An air vent for the closure
• Scrim tape
• Bonding coat and finish plaster
• Dust sheets, P3 mask, goggles and gloves
• Rubble sacks
• A metal detector or scanner for the wall (optional)

Step by step

1. Establish what you are removing, and what you are not.A fire surround and a hearth come out. The chimney breast, the flue and anything supporting the structure above stay unless a structural engineer has said otherwise and it has been dealt with properly, including at every floor above.
2. Check whether the flue is still in use anywhere in the house.In a shared stack, another flue may serve a working appliance. Blocking or altering the wrong one is dangerous. If there is any gas appliance connected to any flue in that stack, that is Gas Safe territory.
3. Take out the surround and back panel carefully.Old surrounds are heavy and often held by lugs plastered into the wall. Cast iron surrounds are valuable and worth removing intact. Expect soot: seal the opening with plastic and tape before you disturb anything.
4. Lift the hearth and see what is beneath.A constructional hearth is often a slab of concrete below floor level and may not need removing. A superimposed decorative hearth lifts. The floor beneath is frequently unfinished, so plan for making it up to the level of the surrounding floor.
5. Ventilate the flue before closing it.A capped chimney with no airflow accumulates moisture, and that moisture appears as staining on the chimney breast in the room above. The rule is ventilation at both ends: a vent in the new closure and a vented cap, cowl or ridge vent at the top.
6. Close the opening.Blockwork bedded in mortar, tied to the sides, is the traditional answer and matches the mass of the wall. A timber frame with moisture-resistant plasterboard is quicker and lighter. Either way, set the face back so the finished plaster will be flush with the surrounding wall rather than proud of it.
7. Fit the vent into the closure.Low down, into the closed opening rather than into the room's outside wall, and left permanently open. It is not a draught problem in practice and it is what keeps the flue dry.
8. Scrim every joint between new material and old wall.All four sides of the closure, and any joint between board and plaster. This is the single step that decides whether the rectangle shows in five years.
9. Plaster across in two coats and feather well out.Backing coat to bring the closure up to level, ruled off against the existing wall, then finish plaster taken well past the joints onto the old surface.
10. Expect salt staining and allow for it.Soot and combustion salts in old chimney breasts migrate into new plaster and appear as brown or yellow staining. Where the breast has been used for years, a salt-resistant plaster or a suitable stain-blocking primer before decorating saves repainting three times.

Tips

• Photograph everything before you demolish it, including the position of the flue. Fireplaces are frequently reinstated by a later owner and the information is worth having.
• If you may want the fireplace back one day, close the opening with a removable boarded frame rather than blockwork, and note it somewhere.
• Soot is greasy and stains permanently. Sheet the whole room and bag the debris as you go rather than sweeping it later.

Common mistakes

• Sealing the flue airtight — Moisture cannot escape, condenses inside the stack, and comes through as damp staining on the chimney breast — usually in the bedroom above, months later.
• Not scrimming the joints — New material and old wall move differently. A rectangle-shaped crack appears around the closure within a year or two.
• Plastering straight over sooty brickwork — The staining comes through the plaster and then through the paint. Seal it or use an appropriate plaster specification.
• Assuming removing the chimney breast is the same job — The breast supports the stack above it, including in the loft and above roof level. Removing it requires structural support, building control involvement wherever you are in the UK, and, in a terrace or semi in England or Wales, likely a party wall notice.

Questions people ask