Types of render and plaster: which to choose for your home

Render and plaster are the final layer we see and touch, but their job goes far beyond looks. They protect the wall from rain and sun, regulate moisture, hide irregularities and define the character of a facade or a room.

The choice in a builders’ merchant can be confusing, though: acrylic, silicone, silicate, mineral, Venetian, “bark-effect”, “scraped”… In this article we sort out the types of render and plaster, look at where each one is used and explain how to choose the right one for your home.

What types of render and plaster are there?

Renders and plasters are classified by two independent criteria: the binder, which determines their technical properties, and the texture, which determines their appearance.

• By binder: mineral (cement, lime, cement-lime), gypsum, acrylic, silicate, silicone and hybrid.
• By purpose: base coats (levelling) and finish coats (decorative); interior and exterior.
• By texture: smooth, scraped, bark-effect, sprayed, Venetian and other decorative effects.

So, for example, a “silicone bark-effect render” means a silicone binder with a bark-effect texture. The grain size, usually stated in millimetres on the packaging, determines how coarse the surface will be.

What are the main facade renders and how do they differ?

In Bulgaria, four types of thin-coat decorative render are most often used on facades, especially as the finishing layer of external wall insulation systems.

Mineral render

Made with a cement or lime base, sold as a dry mix and usually painted after application. It is vapour-permeable and well suited to mineral substrates and old buildings. It can crack if the substrate moves and needs paint to achieve a saturated colour.

Acrylic render

A ready-mixed paste based on synthetic resin, available in a wide range of colours. It is flexible and crack-resistant, but less vapour-permeable. It is better suited to substrates that do not need to “breathe” much, such as EPS insulation.

Silicate render

Based on potassium water glass. It bonds chemically with the mineral substrate, is vapour-permeable and holds less dirt. It needs more experienced applicators and has a more limited colour range, especially in saturated tones.

Silicone render

Based on silicone resin. It is water-repellent yet vapour-permeable, keeps the facade cleaner and suits almost every type of insulation. It is usually the most expensive of the four.

What is the difference between them, in brief?

If we had to sum up each one in a sentence:

• Mineral – the most natural and “breathable”, but more brittle.
• Acrylic – the most flexible and colourful, but less vapour-permeable and more prone to soiling.
• Silicate – mineral durability and a clean facade, but more demanding to apply.
• Silicone – the best balance of water repellency, vapour permeability and cleanliness, at a higher price.

With mineral wool insulation, vapour-permeable renders are preferred – mineral, silicate or silicone. Manufacturers of insulation systems specify which products are compatible, so the safest course is to use components from a single system.

Which plasters should you choose for interiors?

Indoors the requirements are different – smoothness, a pleasant feel and regulating the room’s humidity matter more.

Gypsum plaster

The most widespread interior plaster in new construction in Bulgaria. It is quick to apply, gives a smooth surface and is ready for skimming and painting. It is not suitable for permanently wet areas.

Lime plaster

A traditional material that absorbs and releases moisture and is naturally alkaline, which inhibits mould growth. It is preferred when restoring old houses and in interiors with a natural character.

Clay plaster

A natural material with a soft, matt appearance and a very good ability to regulate humidity. It is not suitable for areas in direct contact with water.

Venetian plaster

A decorative lime-based technique with marble powder which, after multi-layer application and polishing, resembles polished marble. It requires an experienced craftsman, but creates depth and sheen that are hard to achieve with paint. Related techniques such as microcement give seamless surfaces in bathrooms and kitchens.

Textured decorative plasters

Effects such as concrete, travertine, sand or relief surfaces. They suit a feature wall in the living room, behind the bed or in the entrance hall.

How do you choose a render or plaster, step by step?

1. Identify the substrate. Brick, concrete, old lime plaster, EPS or mineral wool – each requires a compatible product.
2. Assess the moisture. Facades exposed to heavy rain, plinths, bathrooms and basements need more resistant systems.
3. Consider vapour permeability. Walls must be able to release moisture outwards; do not “seal” mineral and old walls with impermeable products.
4. Choose the texture and grain size. A coarser grain hides irregularities; a finer one looks cleaner.
5. Choose the colour carefully. Very dark facade colours heat up strongly in the sun; manufacturers often limit how dark a colour may be on insulated facades.
6. Follow the correct procedure. Primer, suitable temperature and humidity during application, and no direct sun or rain in the first few days.

What are the most common mistakes with render and plaster?

Most problems with render do not come from a poor product but from the wrong choice or poor application. This is what we see most often on facades and in interiors:

• Incompatible materials. Acrylic render over an old lime wall or over mineral wool traps moisture in the wall, leading to stains and detachment.
• Application in unsuitable weather. Strong sun, wind, cold or rain in the first few days cause stains, uneven shades and cracks.
• Skipping the primer. Primer evens out the absorbency of the substrate and is often tinted to the render colour – without it the facade can look patchy.
• Stopping partway along a wall. Each facade wall must be rendered without a break, from corner to corner, or the joins will show.
• Insufficient protection of the plinth. The lower part of the facade gets wet from splashback and snow and needs a more resistant render, such as a mosaic or silicone render.
• Colour chosen from a small sample. On a large facade and in direct sun the colour looks lighter and more saturated than in the catalogue.

How we approach it at DARCH Projects

Facade render is part of the architecture, not just a finishing trade. In our energy renovation projects and in new buildings, we propose a system, texture and colour suited to the insulation and the setting, and show them in a 3D visualisation before anything is ordered.

Frequently asked questions

Which render is best for a facade?

There is no single best render for every case. Silicone render is often preferred because it is water-repellent, vapour-permeable and stays cleaner. Silicate render is a good choice for mineral substrates and mineral wool, acrylic for EPS on a tighter budget, and mineral render for old buildings. What matters is that the product is compatible with the insulation system.

What is the difference between acrylic and silicone render?

Acrylic render is based on synthetic resin; it is flexible, comes in a wide range of colours and costs less, but lets less water vapour through and picks up dust more easily. Silicone render is water-repellent yet vapour-permeable, soils more slowly and suits more types of substrate, but it is more expensive.

Which render goes over mineral wool insulation?

Over mineral wool, vapour-permeable renders are used – mineral, silicate or silicone – so that moisture can escape from the wall. Acrylic renders are generally not recommended in this case. The safest approach is to use adhesive, mesh, primer and render from the same system by a single manufacturer.

What is Venetian plaster?

Venetian plaster is a decorative technique in which a lime-based plaster containing marble powder is applied in several thin layers and polished with a trowel. The result is a smooth, glossy surface with a depth that resembles marble. It is used for feature walls in living rooms, entrance halls, bathrooms and commercial interiors, and requires an experienced craftsman.