Cement mortar can be ‘fattened up’ – made more plastic and easier to lay – by adding a squirt of washing-up liquid to it. This must be a soap liquid, such as Fairy liquid, and not a synthetic detergent.
When checking that a course of brickwork or other work, is horizontal, ensure that there are no lumps of mortar sticking to the spirit level. Even a small piece would make it inaccurate enough to affect the job. To compensate for any inaccuracy in the level itself, use it once, then turn it end for end and use it again. Do not use a short level for checking a long run.
Never wash cement-covered tools in a plumbed-in sink: the cement will set in the pipe and block it. Wash them in a bucket and empty it where the dried cement won’t show.
Structural Engineers are not celebrated like the Architects are – because what they do is not a glamorous job. Crunching numbers, loads and weights, resistance and making sure the designs are safe to built – makes them a bit unpopular.
Where very heavy furniture and timber used for construction purposes are to be attached to solid walls, expanded masonry bolts should be used for secure fixing. These are inserted into a suitable hole and, when the bolt is tightened, it draws a plug up into the outer body of the bolt, which then expands and grips the masonry. When positioning the holes, avoid drilling in the mortar between bricks and in the corners of the bricks themselves.
Lined walls are obviously weaker than solid ones, and great care must be taken when fixing up heavy objects. If there is too much stress on an unsupported wall board, it could rip away from the studs. To make a secure fixing, locate the timber studs and attach a batten to the surface of the wall. The object can then be screwed to the batten.
Many interior wall and ceiling surfaces are created by fixing some form of lining, such as plasterboard, to timber supports. The fixings described above, except for the Rawlnut and some nylon plugs, are not suitable for use on these surfaces as they would simply fall out. In some cases, objects can be attached by screws passing through the lining into the timber supports. To locate the position of the studs or joists, tap along the wall or ceiling with a hammer-a ‘dull’ sound will indicate a stud. Before drilling the screw hole, probe with a fine drill or bradawl to confirm you are in the right position. Often, however, the proposed fixing point will not correspond with a timber support (or you may not be able to find them!) and you will have to use a special fixing.
Fixings for hollow surfaces
A large number of fixings are available and all are designed so that some form of support is provided behind the panel when the bolt or screw is tightened. A metal type of fixing is the metal ‘toggle’. These either rely on gravity to open the toggle when the fixing is pushed through the wall, or are spring loaded. Gravity toggles should be used for hollow wall fixings only as they would not spread the load evenly on a ceiling. Spring toggles, however, are suitable for both walls and ceilings. To attach an article with both these fixings, first undo the toggle and then insert the bolt through the object to be fixed.
Attach the toggle to the end of the bolt, fold it flat, and push it through the hole. Once on the other side of the panel, the toggle opens and is drawn against the back of the panel when the bolt is tightened. Unfortunately, these can only be used once, as withdrawing the bolt will cause the toggle to fall into the cavity. This feature also applies to nylon or plastic anchors, which are used with screws instead of bolts. For a more ‘permanent’ type of fixing, a nylon toggle is available that remains in place when the screw is removed. This is made up of a toggle bar, a slotted collar which remains on the outer surface of the panel, and a ridged nylon strip which joins the two. The toggle is first pushed through the wall panel and the collar is slid along the strip into the hole. The strip is then cut off flush with the collar and the screw is inserted. Alternatively, you can use one of the anchor devices with a flange which remains on the outside of the wall to prevent the body of the fixing being lost in the cavity if the bolt is removed.
Solid walls are generally made of either brick, concrete, or lightweight cellular or aggregate building blocks. Attaching objects to brick and concrete is usually straight forward, and a secure fixing can be made with masonry nails or any of the standard types of plug and screw fixings in the case of cellular blocks, an adequate fixing can be made by simply drilling and driving in a screw. Care is needed, however, when fixing to aggregate blocks as these do not provide as secure a bedding as the other materials.
These can be used to fix such things as shelving battens, picture rails, skirting boards and studs for wall panelling to most types of solid surface in the home. They are tempered to prevent bending and can be nailed straight into the wall with a hammer. Special cartridge tools which fire the nail into the wall can be obtained. These are particularly useful where large quantities of nails need to be driven. Two types of nail are available. One has a straight shank and the other a twisted one, which improves penetration into hard materials and helps keep the nail firmly in place. When nailing, always drive the nail in at right angles to the wall and ensure that the nails are long enough to penetrate at least 13mm and not more than l9mm in into the masonry. If the wall is plastered add the thickness of the plaster to the length of the nail required. To prevent them from snapping, nails with straight shanks should be gently driven into the wall with light hammer blows aimed to hit the head of the nail straight on. With twisted shanked nails, start the nail off with light hammer blows, and then use heavier blows to drive the nail home they are stronger than straight shanked nails and will not break so easily if possible, wear goggles as protection from flying chips of masonry or broken nails.
Most household objects can be firmly attached to solid walls with one of the many types of plug and screw fixings available. They all require a pre-drilled hole, which can be made with either a hand boring tool or a tungsten carbide-tipped masonry drill. To make a hole with a hand tool, first tap the tool with a hammer through any plaster and then use firmer blows when the masonry is reached. Twist the tool slightly after each blow to ensure a neat hole and to stop it jamming. Once the required depth for the plug has been reached, remove the tool and blow out any dust. If you are using a masonry drill, you must use either a hand brace or an electric drill with a speed reducer. With some drills this is built in but an attachment is available to reduce the revolutions of a fixed speed drill. As you drill, press firmly so that the bit bites into the masonry. Remove it from the hole a few times and clear away any debris. Take care to keep the drill steady or the hole will become larger than required. If this does happen, you will have to pack it with a suitable filler. A percussion drill is desirable for use with concrete as it saves time and wear on the drill bit. This can be hired but, again, an attachment for converting an ordinary drill is available.
Second, the screw shank must never be allowed to enter the plug; this would weaken the fixing and the masonry. If the thickness of the article to be secured is less than the length of the screw shank, sink the plug further into the wall. When the hole has been made, first insert the screw a couple of turns into the plug and then push the plug into the wall. Then tighten the screw until the shank is about to enter the plug. Withdraw the screw, attach the fixture and then screw it up tight. Plastic wall plugs are also available and come either as strips which you cut yourself, or in pre-cut lengths. They have the advantage of being rotproof and waterproof, and are colour coded for size.
The main problem encountered when attaching objects to walls made of aggregate building blocks is obtaining a firm anchorage for the fixing. Although light objects can often be adequately fixed with standard plugs and screws, it is safer to use one of the many nylon plugs designed for the purpose. These have ‘teeth’, or ridges, which grip the surrounding material, and ‘fins’ which prevent the plug rotating while screwing. They will also take screw shanks with little distortion, and can be used in normal masonry. Another device that is useful for fixing to aggregate blocks is the’Rawlnut’. This has a rubber sleeve which, when the bolt is tightened, expands and compresses against the surrounding material. lt can also be used for fixing to other types of masonry and is suitable for hollow surfaces.
Lath can be used as an alternative to plasterboard as a base for ceiling plaster. Various types are available, but the most common are ‘expanded metal lath’ and ‘K-lath’. Wood lath has largely been replaced by these. Expanded metal lath is a metal diamond shaped mesh which is fixed in position with galvanised clout nails, screws or staples. It comes in 2.7m 600mm sheets and can be cut with tin snips. When fixing to the joists, stagger the sheets to avoid long joins, and overlap each about 13mm. Wire any unsupported joins with galvanized wire at frequent intervals. K-lath consists of a mixture of metal wire and paper. It is also cut with snips and fixed with galvanized nails or staples. Wood lath is made up of strips of timber about 1.2m x25mm x6mm. The strips should be nailed about 6mm apart across the joists, and the joints should be staggered wherever possible.
Plastering on lath
Before the normal floating and setting coat, a ‘rendering’ coat has to be applied directly to the lath. If you are using a lightweight finish coat, a plaster such as Carlite Metal Lath should be used. If using this plaster, however, you must use the same material for the floating coat. Using a sanded mix is more complicated, but it does enable you to use a slower-setting finish plaster. To mix a sanded rendering coat, first prepare a lime mortar by mixing three parts of sand and one part of lime with water (use a bucket as a measure). Hair, or a special nylon fibre made for the purpose, should be added to this mix to strengthen the finish mortar. As a guide, if you have used three bucketful of sand and one of lime mix in about one handful of hair or fibre.
Allow this mix to stand for about 24 hours, then mix six parts of it to one part Portland cement. Add water, but only enough to make the mix fairly stiff. When applying the rendering coat, press it on firmly with the laying trowel so that the plaster firmly ‘keys’ with the lath. If you are plastering over wood lath always apply the plaster in the direction of the joists, so that you plaster across the ‘run’ of the lath. Once the lath has been covered to a depth of about 6mm, key the surface well and leave it to set. Now mix your floating coat and lay screeds around the edges of the ceiling with the laying trowel. Rule them in with the featheredged rule. Divide the ceiling into manageable sections with further screeds if required.
Then proceed to fill in the sections and rule them flush with the screeds. Smooth over and key the surface with the devil float, and clean out the corners with the laying trowel. When dry, skim on a thin layer of finish plaster with the steel trowel. Go around the edges first and then apply strips from one side to the other. Follow up with the wood float, using strokes in the same direction. Then put on another layer, this time crossing the previous strips at right angles. With the steel trowel, lay on a final coat and then smooth all over. Clean out the corners where the ceiling meets the walls with the angle trowel and, finally, wash down adjacent plasterwork if required.
Red plasterboards are fire rated
Plasterboard consists of a gypsum core sandwiched between paper liners. Various types are designed to take plaster, and it is advisable to read the manufacturer’s instructions regarding fixing and plastering before you start work as there can be small variations to the instructions given below. Most plasterboards, however, have square edges and these need ‘scrimming’, or reinforcing, after the boards are placed in position. Most can also be plastered with one ‘thick’ (about 5mm coat of finish plaster.
The plaster must be a hemi-hydrate. Various sizes of boards are available and it is sometimes useful to obtain a variety to minimize wastage. But as it is easy to cut, one of the standard sizes, say 1.2m x 2.4m (4ft x 8ft) is a convenient size to work with. Plasterboards also come in two thicknesses 9.5mm and 12.5mm. The first is suitable for most situations, but where the distance between the centres of the ceiling joists exceeds about 350mm, the latter should be used. Some ceilings are very uneven and it may be necessary to counter batten them to provide a new level surface on which to nail the plasterboards. The first battens are nailed at any convenient, spacing and are used to form fixing points for a second set of battens which are then fixed at right-angles to the first ones. This second set of battens are fixed at centres to suit the width of the plasterboard and they are levelled by driving thin wooden packing pieces between the battens where necessary.
The ends of the boards can be butted up to the walls or the plaster can be chipped away so that the boards can go right up to the brickwork. In the former method jute scrim is applied to the angle to reinforce the plaster. When flxing the plasterboards to the joists do not use ordinary galvanized clout-head nails as these large, flat heads cut the paper covering of the boards.
If you are not using plasterboard screws, use only the proper plasterboard nails which have a slight bevel underneath the head rather like a countersunk screw head. These small-headed galvanized nails should be 30mm long for 9.5mm thick boards and 40mm long for the 12.5mm boards. Place the nails 12.5mm from the edge and at 150mm centres.
Fixing to the ceiling
Plasterboards over which you intend to plaster can normally be nailed either across or along the joists. For large areas it is often desirable to position them in both directions so that long joins, which may cause cracking, are avoided wherever possible. It is particularly important to ensure that the joints are adequately nailed to the joists. You should leave an 3mm gap between the boards for scrimming. Before starting work, it is a good idea to draw a plan of the ceiling and work out roughly how your boards will be placed. This will help you to arrange them to minimize cutting, and also to ensure that they are sufficiently staggered.
If you are working alone you will need the help of a ‘dead man’s hand’ in addition to the normal tools and working platform. This is simply a long piece of straight-edged wood, about 50mm x 25mm to which is fastened a cross piece about 600mm wide. The bottom of the batten rests on the floor and the cross piece is wedged against the plasterboard to hold it in position. Your hands are then free to nail or screw the board to the joists. The easiest way to cut plasterboard is to score the face side deeply with a knife along a straight edge and then lay the board, with the cut side uppermost, over the edge of a table or bench so that the cut is in line with the edge. Snap the core by pressing down sharply, turn the board over and cut the paper on the other side along the crease. Alternatively, you can use an old saw, but this is slower and more tedious.
Solid ceilings are plastered in basically the same manner as walls. Solid ceilings are rare, however, and either plasterboard or some form of lath is usually fixed to the ceiling joists before plastering.
Repairing cracked plaster sometimes turns into a much bigger job than expected: you find a whole wall that needs replacing. Plastering a complete wall or ceiling is a fairly ambitious job and some skill is required to produce a true, flat surface. If you doubt your ability, it would be a good idea to experiment first on a suitable ‘hidden’ surface like a garage wall or ceiling or get a Plastering Company to do it for you.
Plastering a wall
It is unlikely that your wall will be perfectly flat and upright, so the first job is to find the high spots and determine whether or not the wall is out of true.
To do this, hold a spirit level on the back of a long straight-edged rule and move it systematically over the wall. Once you have prepared your surface, taking particular care to ensure that it has a good key, mix your mortar floating coat and start to lay ‘screeds’ on the wall. These are strips of plaster about 200mm wide which act as depth guides. They also break up the wall surface into easily manageable sections. With the steel laying trowel, lay the first screed a little over 13mm deep, from the floor to the ceiling on one side of the wall. Take it right up to the end of the wall. If this is a reveal corner, and you are using a length of angle bead to make a neat edge, place the bead in position before you lay the screed. If you are using the more traditional method, leave the reveal until you have floated the whole wall.
When you have laid the first strip, use a straight-edged rule about 1.8m long to rule it off. Hold the rule vertically and move it gently up and down from the outer edge of the screed inwards. Test for plumb with the straight edge and spirit level, and adjust, if necessary, with a little more careful ruling. Add more mortar if required. The ruling should reduce the thickness to about 13mm if the surface is good. A screed similar to the first one should then be laid on the other end of the wall. You should lay a minimum of two vertical screeds although, for ruling off later, it will help you to lay additional screeds at about 1.5m intervals. Now lay a horizontal screed about 50mm from the floor to join the vertical ones. Use the latter as guides when ruling off this screed. Another horizontal band should now be laid about 1.5m from the floor and ruled in the same way. The final screed should be laid across the top of the wall, flush with the ceiling, and ruled.
The screeds should now be smoothed with the plastic float. The sections between the screeds are then to be filled in flush. Deal with one section at a time and apply the floating mortar with the laying trowel. Rule off each section using the screeds as guides. Fill and re-rule if necessary. The 50mm strip at the bottom of the wall can be left if skirting board is to be used). When the whole wall is covered, clean the internal angles with the laying trowel, and wash down any adjacent surfaces smeared with mortar. Finally, go over the entire surface with the devil float to flatten any small bumps and to key the surface.
If you are using a sanded floating mix, allow it to dry for 24 hours; a lightweight plaster will take about four hours. If you are using the traditional method, any reveals in the wall should now be plastered with both the floating and the setting coat. Before applying the finish plaster, it is wise to test the surface for suction. Brush water on to a small section of the wall and watch what happens. If it is ‘sucked’ straight through, there is excessive suction. As this can have a disastrous effect by weakening the final coat, it will have to be remedied. Throughly dampening the wall will be sufficient in many cases, but if the suction persists, brush on a weak mixture of water and pva bonder-one part bonder to six parts water is about right-arid follow up immediately with the setting coat. When you are ready to apply the setting coat, mix up some finish plaster in a bucket and pour it on the spot board. Then clean out the bucket and fill it with clean water so that it is ready for another mix. Start to skim on the plaster with the laying trowel. First skim a band, about a trowel width, along the top. Then skim over the whole wall in vertical strips, up to the band already laid.
When the wall is covered, use the wood float to put on another thin application, again with vertical strokes. Work systematically from the left to the right (if you are right handed) and keep the seams well pressed down. Now, still using the wood float, Put on another thin application, but this time use horizontal strokes. At this point use the feather-edged rule to rule out the internal angles. Any seams still visible should be smoothed over with the wood float. If you are using an anhydrous plaster such as Sirapite, a little water will help for this, but do not use any at this stage if it is a hemihydrate. The final application of finish plaster should now be put on the wall. Use the steel trowel and lay a ‘tight’, or firm, coat with long vertical strokes. Then wash the trowel and sprinkle a little water over the plaster. Quickly follow up with the trowel and smooth over the whole area. Use the angle trowel to finish the internal angles and, finally, scrape any unwanted plaster off the floors, adjoining walls and the ceiling before it sets.