There are some finishes which can be classed as part of the structure of a building because they are fixed more easily if they are considered at the design stage and provision for fixing them is made during the construction of the building. If walls are to be panelled instead of plastered, provision for fixing the battens or grounds can be made by building pallets into the joints of the brickwork at regular intervals.
These pallets are made of preservative treated softwood and are about 100 mm square. They are the thickness of the mortar joint which will be about 10 mm. It is usual to bed them so that the nails will be driven into the side and not the end grain. They should be made of rough sawn timber to provide a grip in the brickwork.
The alternative to building-in these pallets is to plug the wall after the building has been completed and this can be a long and tedious task. Masonry bits in electric drills can be used, or even the hardened steel masonry pins driven into the wall by hammering or by fixing guns which fire the hardened masonry nails into the brickwork. All this extra work can be avoided if the type of finish to be used is considered at the design stage and proper provision is made during construction.
Grounds, as these supporting battens are called, are usually fixed horizontally, but where wide boards are to be fixed, such as sheets of decorative plywood, vertical grounds will be needed at the vertical joint of the boards. When fixed, the grounds must be plumb and straight, so that it will be necessary to pack them at the nailing points, using a straightedge and a string-line to keep them all in line.
Extra vertical grounds will be needed around window and door openings as well as at angles. The finish at external angles can be a problem when plywood or hardboard sheets are used, because the edge of one of the boards would show unless the two boards were mitred together. This would hardly be practical, as getting a perfect mitre on such thin material over such a long length would take a very great deal of time and patience.
The easiest way of overcoming the problem would be to fix a cover strip at the corners, but this may not be acceptable where the rest of the finish is flush. An alternative is to fit an angle bead, either square edged or rebated, so that the decorative sheeting has something to butt up against. Internal angles do not present the same problem as one board butts against the other.
Spacing between the grounds depends, of course, on the thickness of the sheets being used and as a rough guide the spaces for hardboard would be not more than 400 mm centres. Plywood up to 6 mm thick would need spacings of not more than 450 mm to 600 mm centres.
It is best if sheet materials are fixed with adhesive, because nails are likely to show, however carefully they are punched below the surface and then filled with a coloured filler. Matchboarding and similar tongued and grooved boardings are nailed through the tongue edge into the grounds, so that the grooved edged of the next board will cover the nail head.
The spaces between the grounds can be filled with either thermal or acoustic insulation. This can be glass-fibre mat or mineral fibre mat, in which case it will need fixing to the battens to hold it in place otherwise it will eventually slide down to the bottom of the cavity. An alternative for thermal insulation is sheets of expanded polystyrene, which is, of course, stiff enough to hold itself in place once the boards have been fixed.
Ideally, the panelling would be made in the more traditional form of a framework with each panel fitting into grooves. This offers more scope for secret fixings. If one or two of the panels are left out at the outer edge of the framework, then the fixing screws can be inserted through the rebates of these panels or the angles can be screwed together through the edge of the frame . When the whole frame has been fixed, the loose panels are then fitted into the rebates and beaded into place. Sheet materials are usually faced with hardwood veneers or they have a printed woodgrain pattern to resemble hardwoods, and can have the joints covered. Close boarding such as matchboard is usually carried out in softwood such as pine or redwood. In this case the knots seem to have some decorative value. Cedar planking and parana pine planking are two other materials which can be used to provide a permanent interior finish, but they have rather straight grain and can be monotonous if used over too large an area.
Plastic panelling imitating mediaeval or other historic mouldings can be obtained, along with imitation oak beams, nearly all of which require some form of grounds for fixing them to the walls. Provision made for these fixings during construction will save much time after the structure has been completed; it only takes a little care in setting out.
Where a wall is to be panelled, the door linings must be wide enough to come flush with the finished panels or the framework if the panels are in the traditional framing. Then the architrave will fit over the joint between the lining or door frame and the panelling in the same way as it is used to mask the joint between the lining and the plaster.
Sheet plastics nearly always have to be fixed by adhesive, as nails would spoil the finished surface. Joints in these hard-surfaced materials are rarely successful and some form of plastic, metal or wooden moulding has to be used as a cover strip. It is better to arrange the flat areas so that they can each be covered with one complete piece of decorative material so that no joints will be needed.
Where pre-finished panels or timber are being used, secret fixings are called for, if the appearance is not to be spoiled. In many cases the framing can be screwed to the grounds with the heads of the screws sunk below the surface and the hole filled in with a wooden pellet. However carefully the colour and grain of the timber is matched, the pellet will show, if the finish is to be varnish. This method only works successfully when the finish is to be paint.
Among the secret fixing methods, two, nailing through the tongue of the leading edge of matchboarding, and screwing or nailing through rebates before fixing a panel with beads, have already been mentioned. Slot screwing is another method, and this is done by driving stout screws into the grounds leaving the heads of the screws projecting about 10 mm.
A dab of paint is applied to the heads of the screws and while it is still wet the moulding to be fixed is packed up about 25 mm off the floor and is then pressed against the screw heads so that their positions will be marked on the back.
Holes are then bored at these points about 12 mm deep and slightly larger than the diameter of the screw heads. Next, a gauge is made by driving a screw into a block of hardwood allowing it to project exactly the same amount as the screws in the grounds. A slot equal to the width of the shank of the screws is cut upward from the hole in the back of the moulding, so that the hole now resembles an upside-down key hole. The gauge is put into the hole and driven along the slot so that the head of the screw cuts a dovetail shaped groove in exactly the same position in each of the slots.
The screws in the grounds are given an extra half-turn more and the moulding is placed on the screw heads and driven down to the floor, the screw heads following the grooves in the slots will draw the moulding tightly to the wall. This method of secret fixing is useful for cover strips, architraves and other mouldings as well as for decorative wooden brackets which are not intended to carry any weight.
If skirting boards are fixed to wooden grounds at the top and bottom edges, then the space between can be used as ducting for electric cables or for pipework. These grounds are, of course, fixed before plastering the wall and they are placed just below the top edge of the skirting so that the skirting will cover the joint between the ground and the plaster. Fixing wooden grounds prior to plastering is the best way of providing fixing points for most fittings as there is no need for messy drilling and plugging of the finished wall surface and the nails or screws used for the fitting can be placed at any point along the grounds.
Where pallets are not built into the wall the brickwork joints can be raked out while the mortar is still fairly soft. Where concrete is being cast, dovetail blocks are set into it at the required points. For instance, lintels over windows need provision for curtain track and casting these blocks into the concrete is a quicker and easier way of providing the fixing points than drilling the hardened concrete after the structure is complete would be. After the wall is plastered the blocks can be located either by careful measurement or by probing at the approximate place using a thin nail or bradawl. Another method of ensuring that the little blocks are not lost is to drive a small nail partly into them before the wall is plastered. The nail is left protruding through the finished plaster so that the fixing block can be found.
Careful locating of the fixing points will enable decorative fittings to be screwed directly to the wall instead of having to have a wooden strip fitted first. The metal or plastic rose can then be positioned so that the fitting will be in the exact place that it is required as well as being upright. It is because drills often wander out of position when holes are being made in walls, causing fixing plates to be off-centre or even making it impossible to use all the available screw holes, that making early provision for the fixtures and fittings is so important.
Where possible, shelf bearers and cupboard framing are fixed before plastering, as this enables a neater finish to be made without resorting to cover strips or scribing which are needed when the frames are fixed after the plastering is complete.
All the woodwork and preparation carried out before plastering the walls is called the first fixing. Door linings are made up by cutting housings in the head-piece to take the jambs.
These are then fixed to the wooden plugs or pallets built into the door openings. The linings project at each side of the brickwork, by the thickness of the plaster. They must be levelled and plumbed carefully as well as being checked with a straight edge and packed out accordingly. Where only narrow skirtings are being fixed and grounds are not used, and there are no pallets, the brickwork has to be plugged at intervals using wide plugs to take nails at the top and bottom edge of the skirting. These plugs are cut off so that they project from the wall the thickness of the plaster, a straightedge being used to ensure that they are all in line.