What Is a Fire Rated External Render Board? Your Questions, Answered

In the 1920s, pebbledash was used in England and Wales as an exterior wall finish to cover low-quality brickwork and to provide protection from the elements.

Pebbledash is a plaster surface, consisting of sand, small gravel, and pebbles, which is then mixed with lime and water, and sometimes cement. It was the old form of rendering, and while it served its purpose, rendering a home is much easier and more efficient today.

An external render board provides the same function as the original pebbledash but to a much stronger degree. What is an external render board, though? Keep reading to learn all about render boards and tips for rendering your home.

What Is an External Render Board?

Render boards come in different materials, but they all perform the same function.

External render boards get applied to the exterior walls of a house or building. They can also be used on exterior ceilings and soffits. Once the render board is applied, then the exterior house rendering comes next.

Exterior house rendering entails applying plaster or another coating to the boards (the home's exterior) to protect it from cracks or erosion. Some render boards, however, still require additional coating. At that point, the plasterer would still need to fill cracks to protect the render surface.

What Does an External Render Board Do?

Different external render boards come with various properties. Typically, they're characterized by their high-tensile strength. That strength resists bending in order to prevent deformity and cracking. 

Render boards tend to be breathable too, which makes them perfect for moisture resistant, non-combustible, and breathable render systems. They're designed with the intention of withstanding impacts and weathering so that you can have peace of mind knowing your property is secure.

They give the house protection, the level of which depends on the type of board and the installation. 

Specific renders require significant maintenance to avoid cracking and penetration, or moisture through the render and into your building.

How Does Fibreglass Mesh Help?

Once a base coat gets applied, fiberglass mesh should almost always be used and embedded within that first coat. The mesh gets embedded from top to bottom, not from side to side. The layers of the mesh should always overlap the adjacent layers to ensure durability and strength.

The mesh ensures that the render primer and render protect the building's exterior as efficiently as possible. About 12-24 hours after the primer gets applied, you'll use the topcoat render. 

The topcoat render is the decorative layer that ensures the render system is both weatherproof and hydrophobic. Silicon renders are some of the most common, as they're breathable and hydrophobic. That means they're capable of self-cleaning, which inevitably lowers any future maintenance costs.

Types of Render

From sand and cement to lime or acrylic, there are many different types of render. Let's take a look at some of the most commonly used types.

Sand and Cement Render

Sand and cement renders are typically more durable and harder than lime renders. They're often painted too for a more appealing aesthetic.

Cement renders aren't suitable for older buildings, though, as any movement can start to cause cracks in the render. While additives can be used in the cement to increase durability and flexibility, cement is still naturally prone to cracking.

Because cement renders aren't waterproof, they're usually finished with a top finishing coat, like paint. The paint serves both decorative and protective purposes.

A few of the most significant advantages of opting to use cement render is that it's inexpensive, secure, and relatively easy to use.

Lime Render

Traditionally, the lime render has been applied to external walls built out of low-quality rubble or stone. Lime render has also been used for walls exposed to significant wind and rain.

While lime render doesn't create a barrier, per se, it does act like a sponge and absorb any water. Thus, it sucks it up and stops it from passing through the walls. When the rain dries up, that moisture evaporates into the air, and the lime render is once again ready for the next rainfall.

The curing process for lime render is eco-friendly, as the curing process absorbs CO2 from the air while the render "sets" to a limestone state. You can also color lime render in a variety of shades. It does require a unique skill set to apply lime render, though, which can make it a more expensive option.


Monocouche is a French term that translates to "one coat." It's also more of a modern render system and doesn't include any additives.

It's hard-wearing, weather-resistant, low-maintenance, and flexible. No additional painting is required, but the material is costly. Because there's no need for re-painting or sealing, though, you could save big on application costs. It is prone to cracking, though.

Acrylic Render

Lime and cement are both examples of thick render coatings. Acrylic render, on the other hand, is a thinner render. You start with a specially-engineered base coat and then apply a thin layer over the top.

Because the layer is so thin, you're guaranteed flexibility as your house moves because the application isn't too solid or thick to stop cracking. Acrylic render applications are perfect for homes that see cold and hot temperatures, as the house expands and shrinks.

Fiberglass mesh goes hand in hand with this type of render because it's also very flexible. Thus, as the building expands and contracts, the mesh holds the base coat together, preventing cracking of the thin acrylic coat render.

Of all the thin render types, acrylic is the cheapest. It's also the most impact-resistant! That means that it's powerful but loses some breathability.

Silicon Render Coating

Silicon render is a thin coat finish, just like an acrylic render. It offers the same strength advantages, but also boasts breathability and vapor permeability. In other words, this render coating allows water vapors to escape through it - a great way to prevent moisture buildup and home damage.

Once it's installed, silicon render is hydrophobic. If you live in an area where there are lots of trees and plant life, it's an ideal render choice.

It's another thin render, which means it's also very flexible.

It shouldn't be applied during harsh winter months, though, or when it's raining. The reason for this is that silicon render takes a few days to cure. Once it cures, though, you should expect to enjoy your maintenance-free render for at least 10 years.

How to Render a Home

Render carrier boards use cement or other human-made fibers and then press them together at high pressure. They provide a much more cost-effective alternative to applying layer after layer of mortar to create a base. 

For many external render boards, all you have to do is screw them in to get a more level, smooth surface.

Typically, these cement boards are applied to lightweight steel frame structures or treated timber. Once they're applied, then one of the render systems (usually a thin one) gets applied on top. They can also be used as an underlayment for flooring.