Removing a dividing wall — to create a through living-and-dining room, for example — leaves you with a rectangular opening formed by the RSJ and its piers. If you prefer a curved archway, you can buy ready-made metal formers that are fitted in the opening and plastered over. Alternatively , design the archway yourself, construct your own formers and cover them with wet plaster or plasterboard.

It is advisable to plan for the installation of an arch before you begin to make your opening. Choose the style of arch carefully: the shape will effectively lower the height of the opening at the sides, which may be impracticable and poorly proportioned for the room.

Expanded-metal mesh arch-formers are available from builders’ merchants. Various profiles are made —typically semi-circles, corner quadrants and ellipses, although Spanish, Oriental and Tudor styles are also available.

One-piece mesh frames are sold, but they are suitable only for walls 112mm (4′ in) thick. Segmented formers — half the face and half the soffit (underside) — are more versatile; some have a separate soffit strip and can fit any wall.

Fitting the former

Wedge a batten across the top of the opening, to which you can attach the mesh with nails. Hold the former in position and set it squarely, using a spirit level (1). Secure the mesh to the piers with galvanized masonry nails— you may have to hack off a margin of plaster at the sides so the mesh can be fixed flat against the bricks. Hold a spirit level diagonally against the fold of mesh at the curves and the hard plaster surface on the pier to check that it is set at the correct depth (2).

Corner arches round off the angle and do not encroach on headroom; semicircular types give a full, rounded shape, but eat into headroom at the sides; pointed arches make a distinctive shape without taking up headroom at the middle of the opening.

If you are fitting mesh segments, fit one half then the other (3) and tie the soffit strips together with galvanized or copper wire to prevent the mesh sagging under the weight of the plaster. On a thick wall, insert a soffit strip and tie it to the side pieces.

Mix up some metal-lathing plaster and spread a rough key coat on to the soffit with a plasterer’s steel trowel, working from bottom to top from both sides (4). Do not press too hard or excess plaster will be forced through the mesh. Apply plaster to the face of the arch, scraping it off level with the hard plaster edge on the pier and the rigid mesh fold on the arch curve. When the plaster has stiffened, after about 15 minutes, apply a thin coat of ordinary finish plaster. Apply a second coat immediately and trowel smooth.

MAKING A CUSTOMIZED ARCH

If you cannot find an arch former in the profile you require, make your own in one of two ways.

Using wet plaster

The arch may be a single curve, or it may incorporate intricate curves and points. Cut 12mm (1/2in) plywood ribs to the contour of the arch shape, but make them 12mm (’/in) less than the finished size. Nail or screw them to the beam fixings and piers. Nail softwood spacer battens between the ribs.

Cut and fix expanded-metal mesh sheeting across the faces and edge of the shape, moulding it around the curves (1). You may have to snip the mesh with tinsnips to enable you to fold it around tight shapes.

Make up plastering guides from hardboard. Cut these to the finished shape you require. Temporarily nail them, smooth side inwards, over the mesh with packing pieces behind. The packing should equal the finished thickness of the plaster. Set the edges of the guide to overlap the underside of the arch by 12mm (1/2 in), the required thickness of plaster. Spread plaster on to the underside of the arch between the overlapping edges. When this has set, remove the guides and plaster the wall faces, using the hard plaster edge as a level. Finally, apply finish plaster.