Cement spray - rendering for plaster

Cement Splash Coat – Bonding Coat for Plaster

Cement splash coat (bonding coat) for machine application is used as a base layer under cement-lime, cement, lime, and gypsum plasters.

It can also be used as a base for various wall coverings such as tiles, wallpapers, and skim coats (gypsum and acrylic).

It is also perfectly suitable as a substrate for decorative plasters – acrylic, silicone, and silicate. Intended for both interior and exterior use, it can be applied on a wide range of substrates: ceramic, aerated concrete, silicate, expanded clay blocks, as well as old plasters after preliminary removal.

The use of a cement splash coat helps to equalize surface absorbency and improves the adhesion of subsequent plaster layers. The product is easy to apply and work with, making it ideal for standard plastering works.

Preparation of the bonding coat:

Prepare according to the ratio: 3.0–4.0 l of water per 25 kg of dry mix.

The amount of water should be adjusted to the desired consistency, the type of substrate, and weather conditions, bearing in mind that adding an incorrect amount of water changes the properties of the plaster.

Application of the bonding coat:

The consistency of the mortar used for the first plaster layer, known as the bonding coat, should allow thorough filling of all uneven areas and cavities in the substrate, such as joints or installation grooves. After application, this layer should have a porous structure—it must not be smoothed or glazed. Best results are achieved by using a nozzle with a diameter of 10–12 mm and spraying from a greater distance from the wall.

The purpose of the bonding coat is to level the surface as effectively as possible—permissible deviations should not exceed 1.5 cm. Excessive thickness differences may lead to microcracks during drying. The minimum recommended layer thickness is 4 mm. It is important that the cement splash coat evenly covers the entire surface to be plastered, without gaps.

The mortar should be applied evenly using horizontal movements from bottom to top, with a trowel or plastering machine. After applying the splash coat over the entire wall, proceed to the first leveling stage, the so-called “first screed.” Using an H-shaped screed, pull it over the surface vertically, horizontally, and diagonally—always upwards. Any deficiencies are filled with excess mortar from the screed or with fresh mix.

After approximately two hours, when the mortar has set but is not yet dry (i.e., it is damp but does not soil the hand), perform the second leveling using a stiffer trapezoidal screed. If the splash coat serves as a base layer, it should be left to dry completely for a minimum of 24 hours. If it is the final layer, it should be finished with a polystyrene float. To achieve Class III plaster quality, lightly moisten the surface with water and then rub it with a felt or fine-pored sponge float.

During the drying of interior plasters, ensure good ventilation of the rooms. Exterior plasters must be protected from excessive sunlight, rain, frost, and overly rapid drying. During the setting period (approx. 24 hours), the air and substrate temperature must not fall below 0°C. Work should be carried out in dry conditions, without precipitation.