Building? Why the outside wall plaster should NOT be smooth
There is no user manual for all aspects of homeownership, from moving, to taking occupation and to maintaining and understanding common and uncommon defects. Albert van Wyk has more than 38 years’ worth of building experience and has put all he has learned into a concise, easy-to-use reference book entitled, The Proud Home Owner. He has granted HomeTimes exclusive access to republish portions of his book to help homeowners make better decisions around buying and selling, as well as maintaining their properties.
Request that the plasterer do an example of finished plaster for you to approve and as a specimen for the rest of the walls.
A wood float finish is acceptable on the inside. This finish is achieved with a wooden trowel. A smooth wood float finish is not recommended for the outside walls because it will always look uneven in the sun, and it is inclined to develop small shrinkage cracks on the surface.
When a steel trowel is used, a smoother finish than using a wood float, is achieved.
A hard broom is used to make vertical lines and stripes in the wet plaster after the wood float has been used.
A hand-held machine is used to spray a pure cement and water mix on the wall. After that a steel trowel is used to smooth the edges. The machine’s settings are adjustable in order to obtain different finishes. I regard this as an art and not every plasterer can do it well. You will hardly ever get hair line cracks in this finish. A fine texture on the inside and a rougher one on the outside give an excellent finish.
Rhinolite (referred to as 2 coats plaster)
Rhinolite is a gypsum product which is applied onto the plaster as a second coat in order to achieve a high-quality, smooth finish on the inside walls and the ceilings. A rubber-faced float is used to apply Rhinolite.
TOP TIP: When the application is finished, the surface should have small, pin-sized black spots visible as an indication that the product was applied correctly. The plasterer should then not carry on floating the surface.
This is the trade name of a texturised wall coating product. It is a composition of acrylic resins, plasticisers, quarts and other chemicals which give the product its water-repellent, durable, flexible and colourfast qualities. It is applied as a second coat onto the plaster on outside or inside walls.
The history: Gamma Zenith came on the market during 1979. It was very popular, and in great demand. Plasterers and contractors tried to copy this type of finish, not the product only, but the appearance too. This was achieved by adding the correct quantity and quality of river sand to the plaster sand and then they used the same technique to apply the product. There are many different variations and attempts made today, but none are able to match this Gamma Zenith look. Most plasterers do not know what the finished product should look like.
It is important that the river sand is washed in order to remove all the fine material and dust. Only the small stones which remain after the washing are used and mixed with the plaster sand.
Ask the contractor to make a trial mix by mixing one spade full of washed river sand with 3 wheel barrows of plaster sand. The quantity of the river sand will change and alter the texture (appearance).
The plaster must be fairly dry before the plasterer can start to remove the excess plaster with a straight edge.
“Scratch” finish is popular, as it is strong and will not develop hairline cracks because of the river sand in the mixture.
Albert says: “This is the secret” – The movement of the straight edge must only be vertical (up and down) in order to achieve the “pitted” look.
The pattern will not be uniform when the straight edge is also moved sideways.
I hope that you will realise the importance of your supervision and presence on the day when they start with the plastering. Do not arrive on site a few days later only to discover that the work is not to your satisfaction. It will then be too expensive to remove the plaster from the walls.
Next time: Why gutters and down pipes still have a very important role to play