# What is rough rendering?
**Rough rendering (also known as scratch coating or the first coat) is the process of applying an initial, coarse layer of plaster or render to a masonry wall to create a flat, even base for subsequent finishing coats.** This first coat fills gaps, irregularities and open joints in the brickwork or blockwork, providing a solid key for the topcoat.
## How is rough rendering done?
The process follows a clear sequence:
1. **Preparation** — the wall is cleaned of dust, loose mortar and efflorescence. Dry masonry is dampened to prevent rapid moisture absorption from the render
2. **Mixing** — a relatively coarse mortar is prepared, typically cement-sand (1:3 or 1:4) or cement-lime-sand, depending on the substrate and exposure
3. **Application** — the mortar is thrown onto the wall with a plasterer’s trowel (a technique called “throwing on” or “harling”) in a layer of approximately 10-15 mm thick
4. **Levelling** — the surface is roughly levelled with a straight edge or darby but left with a textured finish
5. **Scratching** — while still wet, the surface is scored with a comb scratcher to create grooves that give the next coat mechanical grip
6. **Curing** — the coat is kept damp for several days to prevent cracking from rapid drying
## Application
Rough rendering is used in:
– **External wall rendering** — as the first of two or three coats in a traditional render system
– **Internal plastering** — providing a flat base on rough blockwork or old brickwork before the skim coat
– **Renovation work** — levelling uneven historic masonry before finishing
– **Wet rooms** — as a substrate for tile adhesive on masonry walls
### Common mistakes to avoid
– Applying the coat too thickly in one pass, which causes cracking and slumping
– Rendering onto a dry wall, which draws moisture from the mix too quickly
– Skipping the scratch marks, resulting in poor adhesion of the finish coat
– Using too rich a mix (too much cement), which leads to shrinkage cracks
## Related terms
– Rendering
– Plastering
– Scratch coat
– Finish coat
– Mortar
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