How to render a wall with Cement Plaster?

How to render a wall with cement plaster? This is the question of a basic finishing technique that is being applied at every construction site. Cement plaster works are the most extensively used finishing technique for the rough surface of walls or concrete structures. Cement plaster is the mixture of fine sand & cement which is mixed together with the inclusion of water. This cement plaster is used to spread over the surface that requires a finished surface. Plaster of pairs is yet another type of plaster. However, in this blog post, we are covering how to plaster a wall with cement.

Detailed procedures of cement plaster

• Surfaces of undercoats shall be well prepared and cleaned to provide a good key for subsequent and/or finishing coats.
• Screed marks or making good on undercoats shall not show through the finishing coats.
• All surfaces to be plastered shall first be dashed with a mixture of Portland Cement and Sand (450 kg cement: 1 m3 sand) to form a key.
• Plastering shall normally be applied in two coats. Surfaces shall be wetted before the application of the first coat, which shall be finished flat and vertical by a straight edge and scored to form a key.
• The second coat shall not be applied until the first coat has dried out completely.
• Immediately before application of the second coat, the surface of the first coat shall be thoroughly wetted again.
• The second coat shall be finished to a smooth hard and dense surface, which is truly flat and vertical. An approved plasticizer may be used in both coats.
• Mortar joints in block and brickwork must be racked out to a depth of at least 15mm. Concrete surfaces have to be roughened prior to plastering and — like any other surface as directed by the Employer/ Engineer shall be treated with an approved bonding agent to provide an adequate key and bond.
• Joints between differing materials (other than the main reinforced concrete members and the block walls) shall be reinforced. This shall apply where walls join stiffeners, concrete frames, etc., meet and where cracks are likely to develop, and/or wherever directed by the Employer/ Engineer.
• Reinforcement shall consist of a strip of approved galvanized or stainless-steel wire
• mesh (10 to 15 mm hexagonal mesh), min. 150 mm wide, or of an approved expanded metal with galvanized or stainless-steel nails and washers or galvanized or stainless-steel staples or similar.
• Any reinforcing mesh shall be fixed at both edges at intervals not exceeding 50mm, or as
• required, and the reinforcement shall be completely embedded in the undercoat of plaster.
• If any joint is between the main concrete elements (columns, beams, etc.) and blockwork, a definite break should be made through the back to stop beads, chamfer, or rebate in the plaster finish.
• Any remaining gap between plaster and concrete, etc. shall be filled with mastic to cover unavoidable cracks between these materials.
• Surfaces described as troweled smooth shall be finished with a steel or celluloid trowel to a smooth flat surface free from trowel marks.
• Surfaces described as floated shall be finished with a wood or felt float to a flat surface free from trowel marks.
• Applied plaster shall be floated as smooth as possible and then steel-troweled. Steel troweling shall be delayed as long as possible and used only to eliminate the uneven points and to force aggregate particles into the plaster surface.
• Each plaster coat shall be applied to an entire wall or ceiling panel without interruption to avoid cold joints and abrupt changes in the uniform appearance of succeeding coats. Wet plaster shall abut set plaster at naturally occurring interruptions in the plane of the plaster, such as corner angles, openings, and control joints where this is possible.
• Finished grooves shall be neat, of uniform width and depth, sharp straight edges, and exact vertical and horizontal lines. Elevation grooves shall be cut before plaster sets by using a molded guide or wooden strip and fixing it in temporary grout and screed. Regarding recessed, follow the procedures same as grooves.

For complete article on how to do cement plaster, its tools requirements, handling & storage of material, safety requirements etc, please visit our blogpost. Cement Plaster | How to plaster a wall