16 Steps to Self-build: Plastering
Step 9: finishing first fix and plastering
Self-build expert David Snell talks us through what needs to be done before and during plastering, and the different options available at this stage in the build
Our step-by-step guide to building your own home reaches the next stage: plastering. David Snell explains what needs to be done before and during plastering, and the options available
W hile work has been going on outside to put in the drains and the drainage system, work should also have been going on inside, gearing up for the arrival of the dryliners and plasterers. To a large extent, many of the trades naturally work alongside each other but the exception is, perhaps, these two. Once dryliners, tackers and plasterers are in an area, everybody else has to clear out. However, in our build there are a few remaining first fix tasks that still have to be carried out before the plastering trades arrive. If the staircases haven’t already been fitted then this ideally needs to be done and, once in place, protective measures have to be taken to cover up all treads to prevent impact damage and staining from plastering and, later, decorating materials. Stringers against the walls can sometimes be left off and many choose not to fit newels, balustrading and handrails until a later date. The carpenters will also fit the loft trap at this point but may leave the architrave surround until later. If you have chosen to leave the screeding of any floors until this stage then now is the time to get that done. Many feel that it is better to carry out this task at a much earlier time, especially as underfloor heating should not be run until most screeds have had at least three months to cure. Bricklayers need to build the fireplaces and hearths in either brick or stone and these then need to be covered and protected. Surface-mounted fire surrounds can, however, be fitted after plastering. Insulation also should be fixed between intermediate flooring joists and between the studs of all studwork partitioning. This is typically installed for the purposes of soundproofing rather than insulation, although some thermal insulation between floors, and between some rooms, can be beneficial.
Tackers and Dryliners
To start with, any soil vent pipes or service boxings should be boxed in with either plasterboard or plywood and the cavity packed with insulation to deaden any sound. The tackers can now commence fixing the plasterboard to the ceiling. Some tackers prefer to work from a full board scaffold, set at a height that enables them to reach the ceiling at any point. Others prefer a single board arrangement, and others are happier working from the floor with hop-ups and floor-to-ceiling props, also known as a ‘dead man’. Joints should be staggered and all boards should be tacked to each joist they cross and fixed to a noggin at both ends. The joints in all ceiling boards should be taped and filled. This can be done in one of several ways: a proprietary paper scrim tape fixed up with a finish plaster mix; a proprietary self-adhesive tape; or a mesh scrim tape (often referred to as ‘silk scrim’), which is fixed to the joints using a mix of topcoat plaster. The latter is often considered to be the best. Next, all of the external windows and joinery should be sealed from the inside using a foam gun, and you should ensure that all cavity closers are firmly fixed back and sealed.
The dryliners can then come in and fix the plasterboard to all of the internal and external walls to be plastered. Studwork walls will be tacked in much the same way as the ceilings and their joints taped and sealed, while blockwork walls that are to be drylined will have plasterboard affixed to them using ‘dots and dabs’ of a fixing mixture. This is technically a misnomer as, strictly speaking, the fixing material should be continuous at the top and bottom of the board. Occasionally the boarding is fixed to the walling using vertical battening. All external angles, joints and junctions should be scrim taped. If coving is not proposed, care needs to be taken to ensure that the joint between the wall boarding and the ceiling boarding is taped and filled, otherwise cracking is certain to occur at this point in the future. skim All coat boards or finish should plaster, now receive starting a with coat the of ceiling boards. This should be smooth and not show any trowel marks or undulations as it is, essentially, the finished surface of the walls and ceilings of your new home. These days, most external walls are drylined, regardless of whether the main construction is timber frame or masonry. However, there are situations where wet plaster is still used.
Wet Plaster
At any point where there is a change of walling medium from, for example, blockwork to brickwork, or blockwork to timber or ply, or where there is a straight joint, expanded metal mesh should be firmly attached to bridge the change. Angle beading should be fixed to all external corners and angles too, while gaps around the windows and external joinery should be filled with proprietary foam and all cavity closers should be firmly fixed and sealed. It is usual for the ceilings to be set with plaster, as above, before work commences on the walls. All blockwork walls to be plas- tered should receive one coat of sand and cement render, known as a ‘scratch coat’. This is left to set and then scratched, using a float with nails in it, in swirling fashion to provide a stable key for the next coat, which is applied when the first scratch coat is still green but before it has dried out completely. These two coats can be used to ‘dub’ out and fill any indentations or undulations in the wall. (Both of these undercoats of sand and cement render can be substituted for proprietary brands of plaster undercoatings.) At a point where the plasterer judges that the render has set sufficiently, the topcoat plaster skim finish is applied in much the same way as for the drylined house, save that a longer time will need to be left for it to dry out sufficiently for decoration. Once the plasterers have finished, the second fix trades can be geared up to come in and commence their finishing work. But before that there are a couple of little jobs that need doing. The decorators should take advantage of empty rooms to set up their trestles and paint the back of all skirting boards and architraves with undercoat or preservative. The loft trap, its surround and the loft ladder, should be fitted. And any mineral wool insulation destined for the roof void can be taken up into the loft and laid out. The home now awaits the arrival of the second fix and finishing trades.