Plastering the Bedrooms

It’s been a real pleasure watching and recording the plastering work on this job. I guess plastering is just one of those very watchable trades. As you’ll see from the pictures, plaster gets built up in layers – depending on the surface being worked on.

The ceiling and the new stud wall between the rooms have had plasterboard fixed to them earlier. As we saw, screws are used nowadays for this as they provide a more resilient fixing. Galvanised plasterboard nails are more likely to ‘pop’ with any minor surface movement and spoil the decorations. The joints have been taped up and external angles already set with plasterboard beads. These provide a good edge to work the plaster up to and make the corners more durable.

Finish plaster is mixed to a creamy consistency in a bucket of clean water using a power mixer. The plaster is scooped out onto the hawk ready for work to start. The rooms are relatively small and working off a ladder is a reasonably practical option. For larger rooms it would be beneficial to set up a staging at the right height. Having loaded the steel trowel, the plasterer holds it at a shallow angle and sweeps it across the surface to distribute a thin layer of plaster on the boards. Working overhead requires a good deal of skill to maintain the thickness and deliver even amounts of plaster with each pass. He works in bands across the room butting each section with the previous one. In what seems like no time, the whole ceiling has been coated and left to dry off. The stud walls are skimmed in the same way – working in bands across the surface and using a sweeping motion to apply the plaster.

By now, the ceiling has set up sufficiently for the second coat to be applied. A fresh mix of finish plaster is mixed with clean water and the hawk loaded. The process is the same as for the first coat except that the plaster is worked even smoother so that there are almost no irregularities. Once the whole surface is covered it is immediately trowelled again – this time with a little more pressure and longer sweeps. This leaves a pretty good finish ready for polishing up in a while. A second coat is also applied to the walls in the same fashion and allowed to set up.

The final process for the ceiling and stud walls is to polish them up to remove and minor marks. Water is flicked sparingly over the surface and the steel trowel used with a little pressure to work the surface to a fine finish. A long sweeping action is used for this and the resulting work looks first class.

The remaining walls are a mixture of brickwork, block work and patched up surfaces. For these areas, the first job is to seal them with diluted pva. This evens out the porosity of the surfaces so that the amount of suction is constant. As the plasterer explained, failing to seal the walls first would mean that areas dried out at different rates making it very difficult to work. There would also be problems with adhesion between the surfaces and the plaster. The pva is mixed with water in a bucket then applied with a roller. This is a quick job and once it’s completed it’s allowed to dry off.

At the top of the walls in one of the rooms, the new timber wall plate is slightly lower than the new ceiling and, in order to ensure that the plaster adheres properly and doesn’t crack along this section, a strip of expanded metal lathe is used. Strips are cut to length with tin snips and stapled straight to the timber.

The undercoat plaster used for these walls is hardwall. This is a good general purpose plaster suitable for use on a variety of masonry backgrounds. It has high impact resistance and is fairly fast drying. Half a bag of hardwall is poured into a bucket part filled with clean water and thoroughly mixed. The plasterers use a plaster mixing drill for this which makes light work of the job and also ensures the powder is fully mixed. The plaster is mixed to what can best be described as a thick creamy consistency - fluid enough to spread well but still firm enough to hold its shape.

The plasterer wets in his tools ready to start work and uses a bucket trowel to scoop out some of the mix onto his hawk. Bucket trowels, as the name suggests, are designed to make scooping out the plaster from a bucket reasonably easy. The end of the trowel is squared off allowing plaster to be scraped out from the bottom of the bucket.

With a quick flip of the wrist, he loads the hardwall onto his steel trowel and begins spreading the plaster. Work starts at the top of the wall and continues in a band about a metre deep going across the wall. For the central areas, the trowel is swept at a shallow angle across the surface leaving a thickness of around 5mm. To fill in the top section, the trowel is loaded, placed flat at the top of the wall, then drawn downwards with the blade tipped slightly. As each trowel full is spread, the plasterer works back over it to smooth it – Watching, you notice how the front edge of the trowel is always lifted slightly. This ensures that the trowel floats smoothly over the surface rather than digging in or lifting the plaster.

The plasterer continues with a second band between this section and the floor – all the time keeping the thickness even. The electrical points in the room are all disconnected from the mains and the cables tucked in allowing the trowel to pass straight over them. Once this first layer has been applied, it is allowed to set up a little before applying a second coat. The second undercoat brings the surface up to the required level – the conduits are fully covered and the edges of socket boxes are flush with the finish. The application of this second coat is much the same as the first with the plasterer working across the wall in two bands.

To ensure a good flat surface, the second coat is smoothed out with a long steel straight edge. This tool is held against the surface at a slight angle, and drawn gently over to remove any excess as it passes. After each pass, excess plaster is cleaned off the straight edge. It’s clear to see what a good surface is achieved with this tool and the wall is left perfectly flat. The plaster is allowed to set up for a while and then scratched up. It seems odd to scratch up such a good smooth wall but, as the plasterer explains, scratching up the undercoat plaster improves the mechanical adhesion between it and the finish plaster.

To scratch up the surface, an old plastic float is used. It’s similar to the one we saw yesterday being used when they were laying a screed downstairs except that it has a row of plasterboard nails driven through one edge so that they protrude a few millimetres. The float is worked over the surface in a semi circular motion. This leaves a trail of scratches in the surface as you can see in the images.

Once the hardwall undercoat plaster has set up, the plasterers are ready to apply the finish plaster. Once again, this is built up in two layers. This allows for a superior finish than can be achieved with one thicker coat. All the tools used earlier were thoroughly cleaned as soon as they were finished with. The plasterer tells me how important it is to keep the tools clean and use clean water for the mix. Old plaster getting into a new mix will affect the drying time and can cause it to set up too quickly to be able to be worked smooth.

Finish plaster is poured into a bucket of clean water and thoroughly mixed with the power mixer. The consistency of finish plaster is surprisingly fluid. DIY plasterers often make the mistake of mixing finish plaster too dry and this makes in near impossible to work. Finish plaster is poured from the bucket onto a spot board. The hawk is then loaded and the plasterer sets to work, coating the wall. He works methodically across the surface starting at the top. The trowel is held at a slight angle as he spreads the plaster using upward strokes. As before, short downward strokes with a freshly loaded trowel are used to fill in the very top section of the wall as he goes. The surface is left pretty smooth but final finishing will be left for the second coat.

Once the first coat has set up a bit, a second batch of finish plaster is mixed. This is applied in the same way as the previous coat but is left even smoother. Once the wall has been coated up it is retrowelled – this time with longer strokes and a bit more pressure leaving it very smooth. It’s then allowed to dry for a little while. There is now a window of an hour or so to get the surface finally polished up.

The plasterer equips himself with a steel trowel, a bucket of clean water, and a large wetting in brush. Using the water sparingly, he wets up one area at a time and works over the wall with the trowel held at a slight angle. Using a little pressure and long sweeping strokes, the surface gets finely smoothed. Any minor irregularities and tram lines are worked out leaving a first class finish.

If you live in the Hertfordshire area and are looking for a professional building contractor, you can get in touch with G L Smith and Sons via their website: http://www.glsmithandsons.co.uk/