Snot trimming (in Dutch: bijsnuiten) is the process of cutting or scraping away excess mortar (snots) that protrude from the back face of freshly laid brickwork. After bricklaying, mortar often squeezes through and projects from the joints on the inner side of the wall. These projections are removed with a trowel or jointing tool.
Why trim snots?
- Neatness — a trimmed wall looks tidy on the inside
- Plastering — if the wall is to be plastered, the surface must be reasonably flat. Protruding mortar lumps make it difficult to apply render or plaster
- Insulation — in cavity walls, mortar snots must not bridge the cavity, as this creates moisture bridges. Mortar droppings in the cavity are removed during trimming
- Services — a flat inner wall makes it easier to fix pipework and cables
Application
Snot trimming is carried out on:
- Internal walls — both loadbearing and non-loadbearing partition walls are trimmed
- Cavity walls — the inner leaf is trimmed before the outer leaf is built
- Chimneys — the inner face of masonry chimneys must be smooth for a good draught
Timing
The bricklayer or labourer trims the mortar while it is still fresh but has stiffened slightly. Trimming too early smears the mortar; trimming too late makes it hard to remove and may damage the joint.
Related terms
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