Lime Plastering Inside: Base Coats for Brick and Stone Walls
Liverpool School of PlasteringLiverpool School of Plastering · Lime guide 2 of 4
If an internal wall needs substantial levelling, it needs more than a thin skim. Internal lime base coats build a suitable background before the finishing plaster is applied. The work is sometimes called “internal lime rendering”; lime plastering is the more usual term indoors.
Why the whole wall matters
Traditional walls exchange moisture with their surroundings through both liquid water movement and vapour movement. Appropriate lime finishes can support that behaviour, but adding lime over an unsuitable layer does not automatically improve the entire wall. Internal moisture also needs sensible ventilation. Identify leaks, water entry and other defects before treating a new plaster surface as the solution. [1]
Check the background
Solid brick or stone, timber laths and manufactured boards require different approaches. Do not specify them as though they were interchangeable. Board systems need an approved combination of board, fixings, base coat and reinforcement; a lime label does not guarantee compatibility. Historic lath work and ceilings deserve a separate assessment, particularly where material is loose or sagging. Cornish Lime’s background guidance illustrates why the construction must drive the choice. [2]
The application sequence
- Prepare and repair. Carefully remove failed plaster and loose contamination. Investigate defects and make compatible repairs before covering them.
- Dub out deep hollows. Build local repairs using the specified backing mortar instead of forcing the entire depth into one heavy coat.
- Manage suction. On suitable masonry, pre-dampen with clean water as directed, checking how evenly the background absorbs it.
- Apply the specified key or bonding coat. Some systems need one; others do not. Follow the system rather than adding an extra layer by habit.
- Build the base coats. Apply the scratch and float coats, or the approved alternative build-up, before moving to the finish.
Mike Wye’s internal plastering guidance uses separate backing and finishing materials and stresses preparation and damping. The method and thickness must be selected for your actual wall. Keep tools and mixing equipment ready before beginning; wear eye protection, protective gloves and clothing when handling lime. [3]
What each coat does
- Scratch coat: forms the first substantial backing layer and provides a key.
- Float coat: establishes the shape and level, with a suitable texture for the final plaster.
- Finish coat: produces the visible surface using a finer material.
Conserv describes this traditional three-coat arrangement while recognising that some situations need different build-ups. Use backing material to correct depth. A finishing plaster should not become a thick levelling coat. Allow the earlier coats enough time and protection to reach the condition required before recoating. [4]
A simple room-by-room job sheet
For each wall, record its construction, condition, approximate area, repair depth, specified products and planned finish. Add a separate line for junctions, corners and openings. Ask the supplier to confirm:
- Whether the existing surface can remain.
- The permitted thickness of each coat.
- Where fibres, mesh or other reinforcement are required.
- What readiness for the next coat looks like.
- The curing and decoration requirements.
Common questions
Will lime plaster cure damp? It can form part of an appropriate moisture-management approach, but it will not stop a leaking pipe or defective gutter. Diagnosis and repairs come first. [1]
Can I use the same method on plasterboard? No automatic substitution. Some proprietary products have a board specification; others do not. Get the complete approved system for that background. [2]
When is it ready to skim? When your backing coat meets the finishing product’s requirements for firmness, moisture and surface key. There is no single waiting period for every lime mix and room.
Continue learning
- Lime Rendering Outside: A Beginner’s Guide to Preparation, Coats and Curing
- Lime Skimming Inside: How to Prepare and Finish Internal Walls
- Lime Skimming Outside: Choosing an Exterior Lime Render Finish
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Technical references
Checked 23 September 2026. This introductory guide is not a specification for an individual building. Use the current product instructions and an appropriate project specification.