Indy Total Construction

You need only apply two very thin finishing coats directly over the drywall.

The plaster needed for the job is sold ready mixed or in a powder form requiring only the addition of water. It is mixed in the same way as other plasters and has a creamy texture.

Because you are only applying a finishing coat to the drywall board there is no need for thickness guides, except at any external corners.

It is a good idea to practice scooping the plaster from the hawk on to the trowel first, using a spare piece of drywall to try your hand at spreading the plaster and making it stick to the board_ The technique is to hold the hawk in your left hand (or right if you are left handed) so the top is level and set the trowel blade on edge, so it is at right angles to the top of the hawk. Use the trowel to push some plaster towards the edge of the hawk, scooping it off at the same time as tilting the hawk towards you. The whole is done in one smooth movement.

The first job is to seal the joints between the individual panels of gypsum board, reinforcing them with perforated paper tape or nylon tape to prevent the plaster cracking. The standard paper tape is available in 2in wide rolls of 50-500 feet.

Cut strips of tape to run the length of each joint, including any horizontal ones, before you begin plastering. They must be exactly the right length and should not overlap or be folded, otherwise the plaster will not grip the wall properly.

To seal the joint, spread a thin layer of plaster, about 4in wide, along it from bottom to-top. Hold the trowel so that the blade is at an angle of about 30° to the wall, reducing it as you move up the joint and the plaster on the trowel thins.

While the plaster is still wet, press the tape into it. The easiest way to do this is by draping one end over the blade of the trowel and pressing this into the plaster at the ceiling. Then gently slide the trowel down the plaster, positioning the tape with your other hand. Once the tape is in place, run the trowel carefully up the plaster to make sure it is bedded properly. Treat all the other joints between the panels in the same way.

When the taped joints have dried — which should take about 11/2 hours — fill in the areas between them with more plaster. Work upwards from the floor, spreading the plaster in thin vertical strips and being careful not to build up ridges at the joint positions. Stop just short of the ceiling and work downwards from there to get a clean, sharp angle.

Unless you are working on a very small area, by the time you have finished putting on the first coat, the area you started on will be ready for the second coat. This should be about 1/sin thick and applied with long, sweeping strokes to eliminate ridges. Start at the bottom corner of the wall and work upwards and along to make one continuous coating.

Allow the plaster to set slightly and then go back over it with a clean trowel to smooth off the surface. Finally, when it has hardened fully, “polish” the surface by splashing clean water on to it with a paintbrush (about 4in wide) then sweep the trowel back and forth lightly. This will give a smooth, matt finish ready for decoration.

Plaster is an excellent and inexpensive material for giving a smooth, hard surface to an internal wall so that it is ready for painting or wallpapering.

There are many types of plaster, but they can be divided into two basic types: gypsum-based and cement-based. The former are used solely for indoor work, whereas the latter are mainly used outdoors for rendering walls. Cement- based plasters do have a use indoors. however, and that is to finish external walls that might be subject to damp penetration; damp will attack a gypsum plaster and cause it to crumble.

Modern plasters come premixed with lightweight fillers such as perlite or vermiculite, which give a higher degree of thermal insulation and fire resistance and should be mixed with clean water.

Plaster is normally applied to the wall in two layers. The first, called a “floating” coat, is intended to even out the irregularities in the wall surface, so it is kept fairly thick — about 3/sin being usual. The second, finishing coat is spread much thinner Ysin or so — and carefully toweled off to a smooth finish.

Different types of building materials absorb water at different rates and if too much water is absorbed from the fresh plaster, it will dry too quickly and crack.

For example, bricks and lightweight building blocks absorb water quickly and are termed high suction surfaces. On the other hand, materials such as concrete and gypsum board do not absorb water that quickly and are termed low suction. You must choose a plaster to match the surface; but if in doubt, the best thing to do is coat the entire wall with a bonding agent which will make a low suction surface.

Browning plaster should be used for the floating coat on high suction surfaces and Bonding plaster on low suction surfaces. Finish plaster can be used for the finishing coat in both cases.

Only buy plaster as you need it since it has a limited shelf life. A 22lb bag of Browning or Bonding plaster should cover an area of about 1.8yd2 at a depth of 3/sin. The same quantity of Finish plaster, spread thinly, should cover an area about 6yd2.

In addition to a couple of clean buckets and a long level, you will need some special plastering tools: a spot board about 3ft square and supported on trestles or an old table to hold the mixed plaster while you work; a hawk for carrying small quantities of plaster to the wall; a rectangular metal plasterer’s trowel: a wooden float for producing flat surfaces (with a few nails knocked into the end it can double as a “scratcher” for scoring the floating coat before applying the finishing coat): and a 5ft length of 1 x 3in planed wood for leveling the plaster surface.

Cleanliness is essential when mixing plaster. since any dirt present in the mix will affect the drying time. Always use clean tap water for mixing and have a separate bucket of water for cleaning the tools as you work.

Mix the plaster and water in equal volumes in a clean bucket, adding the plaster to the water by sprinkling it on top and breaking up any lumps between your fingers. When the water has soaked into all the plaster, use a thick piece of wood to stir the plaster into a smooth consistency, (Finish plaster should resemble runny ice-cream). and make sure there are no lumps.

Wet the spot board and turn out the plaster on to it, kneading it with the trowel. If the mix appears too wet, sprinkle on a little more plaster and mix in with the trowel.