How to Plaster a Wall
The application of traditional plaster is the benchmark in building work. If you master this one, you master everything!
Today, traditional plaster is used to cover old natural stone walls in renovation and cover modern materials such as concrete. Render gives the bare wall its final, smooth and regular appearance, suitable for a decorative finish (rendering, whitewash, paint).
Follow step by step how to apply a traditional rendering.
Composition of traditional rendering
Traditional rendering is composed of a binder and a mineral filler, the proportions of which can vary according to the supports, the constraints and the qualities sought. Its use dates back to Antiquity.
– On a natural stone wall :
◦ renderings and mortars are a mixture of lime and sand ;
◦ stuccos are special plasters made of lime and marble powder.
Good to know: lime brings together the best qualities required for a plaster. It is absorbent, essential for the walls’ breathing and prevents cracking. It is also sanitising, ecological, economical and aesthetic.
– On modern materials like concrete, lime can, however, be replaced by cement.
Application of the rendering
Traditional rendering is characterised by its application method, which is always the same. Only the proportions and drying times differ.
It is applied in 3 successive layers:
– the gobetis, very liquid ;
– the body of the rendering, of thick consistency;
– and the finishing coat.
Each stage requires different dosages for which it is advisable to refer to the specificities of the product: lime, cement, plaster or a mixture.
Equipment needed to apply a traditional plaster.
Brush for whitewash
Flat plastering knife
Thick protective gloves
1. Prepare the surface before applying the plaster
Before application, the surface must be clean, sound and free of dust.
– Remove any residues of old coatings with a flat knife, chisel or stiff brush depending on the nature of the wall.
– Scrape or brush between stones, bricks or breeze blocks to avoid unstable aggregate reserves.
– Wet the surface with a large sponge or a water sprayer to remove all dust.
Good to know: a Karcher can achieve good cleaning. However, be sure to control the pressure on old walls.
2. Apply the first coat
The gobetis is used to create a bonding layer for the next coat.
– Prepare a liquid mortar so that it can penetrate all the hollows and reliefs in the substrate.
Good to know: mortars are available in ready-to-use packages. They are much more expensive, but they are much easier to use if you are not used to mixing. For small surfaces, this can be a good option!
– Start by wetting the wall well so that it does not absorb all the water contained in the mortar.
Good to know: do not neglect this step because if the wall is not sufficiently wet, the plaster loses its power of adhesion and its perfect uniformity.
– Apply the first coat of plaster with a wide brush. Use a used broom brush or a whitewash brush.
– Cover the whole surface well, without trying to make a clean or smooth finish (difficult to achieve at this stage anyway!).
Good to know: you can use a tyrolean, a kind of mechanical sprayer, at this stage to avoid losing too much product.
– Leave to dry as is. Depending on the material used, the drying time is more or less long, from 1 to 3 days, but you must observe it at all costs.
3. Apply the second pass or “body of plaster
Made with a much thicker mixture, the second pass or body of plaster is used to dress the wall with its new coating for about 1 to 1.5 cm thick.
Good to know: this is where the helping hand comes in! If you have not yet acquired it, it will be done as you apply it.
– Load a supply of plaster with the trowel onto a large trowel held with the other hand and stand facing the wall.
– Take a small amount of plaster with the trowel and throw it at the wall in a quick, short, dry motion, like a backhand stroke in ping-pong.
– Moisten the surface thoroughly again before starting.
Good to know: if you cannot spray, place the trowel on the wall horizontally, held from underneath with its mortar reserve, and apply it to the wall by sliding it with the trowel.
– Continue applying the plaster by repeating these gestures.
– As you go along when the plaster is drying and starting to pull, use the trowel to smooth out the covered surface.
Necessary: you may need to start levelling before you have finished your wall. Identify the right time. Again, this is a matter of practice and observation.
– Allow the necessary time to dry before the topcoat (3 to 5 days).
Good to know: if you find it challenging to obtain an even surface in one go, work in two coats in the fresh (i.e. about 2 days apart). By coming back to work on the mortar while it is drying. And for an even more successful smoothing, finish with a sponge float in addition to the float.
4. Apply the third pass or “topcoat
This consists of a more delicate filler to obtain a softer finish. The plaster is prepared with a smooth consistency to be tested for good application comfort.
– Moisten the support.
– Apply the plaster by crushing it vigorously with a smoothing machine or trowel.
Good to know: do yourself a favour and take the time to create a beautiful effect by stepping back from the wall regularly to get an overall view.
– If you leave the plaster bare without any other covering, do this last coat by smoothing vigorously with a round-edged smoothing machine. Do this in the previous phase of the drying time, when the plaster starts to lighten.
Good to know: this step allows you to erase the reliefs caused by your tool during the application.
– Allow your rendering to dry entirely before considering the application of another finish.