ICF & Cracking
What You Should Know About ICF
A guide by the Insulating Concrete Formwork Association
There have historically been problems with concrete and cracking. Will ICF walls crack?
If you’ve ever bought a property, you’ll know that buildings naturally move and settle over time. This movement can cause anything from small hairline cracks on interior walls to more serious diagonal cracking. Minor issues typically present as flaking plaster or gaps appearing around doors and windows, but more significant wall cracks can indicate foundation movement or subsidence – problems no homeowner wants to face.
The choice of building material plays a critical role in how, when, and why these cracks appear. In a traditionally built new build, for example, hairline cracks in the plaster are almost inevitable as the materials settle and find their equilibrium. But not all construction methods are created equal – and that’s where Insulated Concrete Formwork, or ICF, enters the conversation.
ICF is a modern method of construction that uses interlocking foam forms, filled with poured concrete, to create structures that are exceptionally strong, thermally efficient, and inherently stable. Unlike traditional brick or timber frame builds, the reinforced concrete core at the heart of an ICF property gives it a structural rigidity that changes whether a building is likely to crack.
Is concrete a good build material to avoid cracks in walls?
For centuries, concrete has played an essential role as a build material in construction. Recognised for its superior strength, longevity, flexibility and cost-effectiveness, it has become a commonly used material on construction sites.
Recently, however, concrete has started to receive some negative press. Concrete structures can suffer from cracking, but it is the integrity issues with a specific type of concrete called RAAC that has really hit the headlines. Added to that, as we all become more conscious of our carbon footprint, there are negative perceptions about the environmental impact of using concrete as a building material.
Here we look at why these problems occur and if ICF walls crack. We also look at why concrete, when used with ICF, can be the ideal build material.
Reinforced Autoclaved Aerated Concrete (RAAC)
Firstly, RAAC is not as durable as traditional concrete, and the build material was only ever meant to have a lifespan of 30 years. Many buildings which used RAAC are now well past their sell-by date.
However, the biggest problem with RAAC is down to the structure of the concrete. Open it up and you will it is made up of approximately 80% air, giving the concrete a bubbly texture.
If water gets into the RAAC, it acts a bit like a sponge, enabling moisture content to quickly travel through the structure and affect the integrity of the steel inserts. Over time the water ingress caused the RAAC concrete to crumble which greatly impacted on the structural integrity of the building causing it to weaken and potentially fail.
Do you get wall cracks with concrete?
RAAC is a very specific building material, but not all approaches that use concrete should be seen in a negative light. In fact, the material has been successfully used for centuries but, as with any construction, incorrectly designed or specified concrete buildings can cause issues. One of these has been a problem with structural cracks and damaged walls, although it is worth saying that most issues related to poor construction of buildings over 50 years ago.
Concrete is formed by adding water to cement, sand and gravel. The concrete and water cause a chemical reaction that turns it into a paste and binds all the aggregates together. A bit like a sponge that expands when it soaks up water and shrinks again when it’s dry. However, concrete has a high compressive strength and a low tensile strength. When a tensile force such as thermal expansion, contraction, shrinkage or stress, is induced in the concrete it can cause it to crack.
Most of these issues are down to the incorrect mixture in the wrong conditions. For example, if there is too much water in the mix, it can weaken the concrete’s strength and durability, while not enough and the concrete will dry too fast and crack.
Problems can also occur in the setting process. If the water evaporates from the surface of the concrete, say in conditions that are too hot, the top of the surface dries out too quickly. As it tries to shrink the top of the concrete is restrained by the layers below that have not had the time to dry causing tensile stress.
Concrete is formed by adding water to cement, sand and gravel. The concrete and water cause a chemical reaction that turns it into a paste and binds the aggregates together. A bit like a sponge, the concrete expands when it soaks up water and shrinks again when dry. However, concrete has a high compressive strength and a low tensile strength. When a tensile force such as thermal expansion, contraction, shrinkage or stress, is induced in the concrete it can cause it to crack.
Do ICF concrete walls crack?
A big concern for many developers and architects is whether ICF walls crack.
When you build with an insulating solid wall construction method like ICF, it can mitigate any potential problems with the concrete.
During the build process, the ICF blocks are stacked to create the exterior wall structure before concrete is poured into a hollow core. The blocks are made from an insulating material, usually EPS or woodcrete, which creates the ideal environment for the concrete.
The insulating material allows the concrete to set quickly but cure very slowly while at the same time protecting it from extreme weather. This stops the concrete from drying too quickly and reduces the chance of cracking.
It is this same process that offers other benefits to the build. The slow curing process enables the concrete to gain additional strength. Tests have shown that a concrete block typically has a load pressure capability of seven newtons per square metre whereas an ICF wall is around five times greater at typically 35 newtons per square metre. This strength delivers on the longevity of the building with minimal maintenance requirements.
Environmental Cost – ICF Walls
Of course, not all concerns are related to the integrity of the concrete. With severe weather events now affecting the UK, the need to reduce carbon has become a key focus. Construction heavily contributes to the total global carbon output. To help combat this, the concrete industry has been making significant changes with a 53% reduction in emissions since 1990. Looking to the future, UK Concrete’s Roadmap details its aim to remove more carbon from the atmosphere than it produces.
Building with an insulated solid wall construction can accelerate this roadmap:
Why Choose An ICF System From An ICFA Member
The correct design and installation can play a big impact in promoting build quality with concrete and ICF structures. We always recommend getting expert guidance from an ICFA member involved early in the design process. They have the knowledge and technical resources to support your project and flag any areas that may require special considerations.
Contact Us
Interested to find out more about how ICF can help with cracking? Get in touch today!