Block plastering is a decorative rendering technique in which a plaster coat is scored, incised, or moulded to imitate the pattern of dressed stone blocks or ashlar masonry. The finished surface gives the impression that a wall is built from individual stone units, even though the underlying structure may be brick, concrete block, or poured concrete.
Technique and process
The plasterer applies a base coat of lime or cement render to the wall surface and allows it to firm up slightly. While the plaster is still workable, the craftsman marks out a grid of horizontal and vertical lines using a straightedge, chalk line, or purpose-made jointing tool. These incised lines represent the mortar joints of an imaginary stone wall.
The depth and width of the scored joints, the size of the “blocks,” and the surface texture of the plaster between the joints can all be varied to imitate different types of stonework — from rough-hewn rustication to smooth ashlar. Once the plaster has set, the wall may be painted, limewashed, or left in the natural render colour.
Application
Block plastering has been used for centuries on public buildings, churches, and grand residential facades where the appearance of stone was desired but the cost of genuine cut stone was prohibitive. It remains popular in heritage restoration work, where damaged original block plaster must be replicated to match the building’s historic character.
In modern construction, block plastering is occasionally specified for feature walls, entrance facades, or boundary walls. It requires skilled craftsmanship, as the proportions and regularity of the incised joints must look convincing. Lime-based renders are preferred for historic buildings because of their breathability and compatibility with older substrates.
Related terms
- Ashlar masonry
- Rustication
- Lime render
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