Plastering is the step that turns a raw, uneven wall into a surface ready for paint or decoration. Contractors spread a mortar layer over the coarse faces of walls and ceilings, then work it to the required texture, and the finishing treatment chosen at the end determines how the wall looks for decades. Builders group these treatments as plaster finishes, and the range runs from a flat, polished skin to rough, aggregate-studded coats that hide joints and add texture. Before picking one, compare finishes by application effort, durability, and upkeep. For projects that want more than a standard trowel job, decorative plaster finishes such as Venetian and clay plasters add colour and depth.
Finishing coats go on only after the base coats have cured, and the final layer is the one the eye sees. Its mix, thickness, and working method change with the finish you select. This article covers the standard finishes, the special materials available for the finishing coat, and the practical questions that come up when plaster walls are specified or renovated.
How a Plaster Finish Is Built Up
Plastering is not a single-coat operation. On masonry walls the sequence runs from a rendering coat that keys onto the substrate, through a float coat that brings the surface to a true plane, to a thin finishing coat that carries the final texture. Each layer is thinner than the one before it and must cure first.
The Three Coats of Traditional Plastering
- Rendering or scratch coat: 10 to 12 mm of mortar, scratched while wet to give the next coat a key.
- Float coat: 6 to 8 mm, levelled with a straightedge and float.
- Setting or finishing coat: 2 to 3 mm, trowelled to the specified finish.
Total thickness usually lands between 12 and 15 mm for a finished plaster wall, with a 15 mm coat standard on block walls. Estimate material volumes by measuring the wall area in square metres and multiplying by the coat thickness before you order.
Preparing the Surface for a Clean Finish
Workmanship shows at the edges. Corners, reveals, and junctions between plaster and door frames are the first places to crack or look untidy, so many finishers reinforce external corners with metal profiles. On drywall-backed partitions, the same role falls to drywall corner beads, whose main types and installation sequence are covered in this guide. The surface preparation that follows decides how well the coats bond:
- Remove loose material, dust, and grease.
- Dampen the substrate so it does not suck water from the mortar too quickly.
- Apply the scratch coat and comb it while wet.
- Let it cure, then float the second coat level.
- Trowel the finishing coat and work the chosen texture before it stiffens.
The Seven Standard Plaster Finishes
Standard finishes fall into seven families, each defined by how the final coat is applied and worked. The same base coats serve all of them; only the finishing treatment differs.
Smooth Coat Finish
A smooth coat is trowelled flat until the surface is even and ready for paint. It is the default choice for plain, low-maintenance interior walls and ceilings. The finishing mortar is richer than the base coats, often with a higher cement proportion, so it trowels to a dense, closed skin.
Sand Faced Finish
Sand faced finish uses coarser sand in the finishing coat and works the surface with a sponge float while the mortar is still green. The result is an evenly gritty texture that hides minor defects and gives paint something to grip. It suits both interior feature walls and exterior elevations.
Rough Cast and Aggregate Dash Finishes
Rough cast finish, also called spatter dash, is made by dashing coarse aggregate onto a wet mortar bed so the stones stand proud of the surface. The coat is thick and tough, shrugs off weather, and is a common exterior treatment.
Pebble Dash Finish
Pebble dash, sometimes written as peddle dash or day dash, follows the same principle with clean pebbles thrown onto the fresh coat and pressed lightly so they stay exposed. The finished wall reads as a field of small stones, which hides cracks well.
Depeter Finish
The depeter finish embeds crushed stone or grit into a freshly trowelled bed, producing a dense surface popular on decorative facades. Because the aggregate is pressed in rather than dashed, the texture is flatter than rough cast.
Scrapped Finish
The scrapped finish is worked with a steel blade or saw edge after the mortar begins to set, creating fine, parallel scrape marks that can run vertically, horizontally, or diagonally. It is a low-cost way to give a plain wall texture.
Textured Finish
Textured finishes cover any pattern produced with brushes, rollers, stencils, or shaped trowels while the coat is still plastic. The range of patterns is limited mainly by the applicator.
Finish selection often comes down to the binder. Cement-based finishes dominate exterior work because they withstand weather, while gypsum-based finishes set faster and are preferred indoors. The practical differences in mixing, drying, and service are set out in this comparison of cement plaster and gypsum plaster.
| Finish | Texture | Application method | Typical use |
|---|---|---|---|
| Smooth coat | Flat and dense | Steel trowel | Interior walls and ceilings |
| Sand faced | Fine grit | Sponge float | Interior and exterior walls |
| Rough cast | Coarse aggregate | Dash onto wet coat | Exterior walls |
| Pebble dash | Exposed pebbles | Throw pebbles onto fresh mortar | House fronts and garden walls |
| Depeter | Crushed stone | Press into mortar bed | Decorative facades |
| Scrapped | Linear scrape marks | Saw blade over setting coat | Feature walls |
| Textured | Patterns | Brush, roller, or stencil | Feature walls and ceilings |
Special Materials for the Finishing Coat
Beyond the standard coats, a finishing layer can be formulated to absorb sound, block radiation, resist moisture, or deliver a decorative surface that plain mortar cannot.
Functional Plasters
Acoustic plaster contains lightweight, porous aggregates that absorb sound, so it is specified in auditoriums, offices, and corridors where echo is a problem. Barium plaster carries barium sulphate, which blocks X-rays, and is used to line radiology rooms in hospitals. Both are applied in thicker coats than standard finishes and cost more per square metre.
Decorative Aggregate Coatings
Granite silicon plaster blends granite chips with a silicone binder into a waterproof, self-cleaning facade coating that is trowelled on and sold in a wide colour range. Older specifications sometimes called for asbestos marble plaster, which used asbestos fibres as reinforcement. That material is now obsolete because of the health risks of asbestos, and existing asbestos-based finishes should be removed by licensed contractors.
Gypsum-Based Finishing Materials
Plaster of Paris, also called gypsum plaster, sets quickly and gives a brilliant white surface, but it softens when repeatedly wetted. Keene’s cement plaster is a harder, denser gypsum product burned at a higher temperature; it resists moisture much better and is used in bathrooms and kitchens.
Water Resistance and Wet Areas
Bathrooms and kitchens need cement-based or Keene’s cement finishes rather than plain gypsum. Where a plaster finish must tolerate steam and splashes, specify the moisture-resistant option and back it with a vapour-permeable paint.
Mixing ratios and application technique differ between interior plaster and exterior stucco even when the materials look similar, and water content errors show up as cracking or poor adhesion. The full mixing and application sequence for both is covered in this guide to plaster and stucco materials.
Plaster vs Drywall: Which Wall Finish Fits?
Most modern interiors are built with drywall, but plaster still wins on several counts. The decision comes down to cost, schedule, durability, and the finish you want to live with.
Cost and Speed
Drywall goes up fast and costs less per square metre than a three-coat plaster finish, which is why it dominates new housing. Plastering a room typically costs more than hanging and finishing drywall, but the gap narrows when labour rates rise or when walls have curves and recesses that drywall cannot follow.
Durability and Sound
A well-kept plaster wall is denser than drywall, gives better sound insulation, and shrugs off knocks that would dent a board. Plaster also handles moisture better when the right material is specified. The trade-off is repair: a cracked plaster wall needs patching with matching material, while a damaged drywall panel is cut out and replaced.
Hanging Things on Plaster Walls
Plaster walls are hard but not structural. A screw driven straight in crumbles the finish, so use masonry anchors or toggle bolts:
- Locate the stud or cavity with a detector before drilling.
- Drill a pilot hole with a masonry bit.
- Fit a wall plug or toggle anchor.
- Drive the screw and stop before the fixing over-tightens.
In-Situ Mouldings and Profiles
One advantage plaster keeps over drywall is the ability to form cornices, coves, and architrave profiles in place, cast directly against the wall rather than bought as prefabricated trims. Custom profiles are run with a mould and template; the technique is explained in this guide to making plaster mouldings.
| Criterion | Plaster | Drywall |
|---|---|---|
| Installed cost per square metre | Higher | Lower |
| Ready for paint | After drying, days | Same day |
| Impact resistance | High | Low to moderate |
| Sound insulation | Better | Standard |
| Repairs | Patch with matching plaster | Cut out and replace |
| Curved and recessed surfaces | Formed in place | Difficult |
Lime Plaster: A Natural Alternative Finish
Lime plaster is one of the oldest wall finishes and it is coming back in renovation work. It breathes, letting moisture pass through the wall instead of trapping it, which suits old stone and brick buildings designed to dry out. Lime is softer and more flexible than cement, so it moves with the structure and resists cracking on traditional buildings. For homes with timber-framed or drywall partitions, lime plaster can still be applied over the boards, and the process is covered in this guide to lime plaster installation over drywall.
Working with Lime
Lime plaster sets slowly and needs longer between coats than gypsum. The trowel matters more than with modern plasters because lime is sticky and drags when the blade is not shaped and flexed correctly. Different trowel types suit different stages of the work, from laying on to burnishing, and the options are compared in this guide to lime plaster trowels.
Eco-Friendliness and Health
Lime is produced by burning limestone at lower temperatures than cement clinker, so its embodied carbon is lower, and the plaster is naturally mould-resistant. Historic finishes sometimes carried lead-based paint layers, and some old plasters contained asbestos, but modern lime plasters are free of both. Finish lime with a breathable paint so the wall keeps its vapour-open behaviour.