When And Where To Use Expanding Foam by Fastbuild Supplies


Expanding foam is a hugely valuable tool for contractors with many potential uses. Primarily, it is great for closing gaps and helping to improve insulation in buildings.

Here at Fastbuild, we sell a range of building supplies in the UK, including expanding foam, at great trade prices. Here, we look at its various possible uses to help you on your next job.

What is Expanding Foam?

Expanding foam is a substance made up of various chemicals, including polyurethane. Sold in cans as a liquid, it creates its own chemical reaction when sprayed, causing the compound to expand.

Some expanding foams can expand up to 30-60 times their liquid volume, although you should check the specifics of your product.

Different expanding foam products are used in different ways. They tend to be sold in two main styles:

  • Gun-grade expanding foam - to be used with a reusable foam gun.
  • Handheld expanding foam - comes with its own disposable nozzle.

Types of Expanding Foam

Standard B3 expanding foam is the most common type of expanding foam. However, there are other types of foam on the market which act in similar ways but have different properties. An example is B1 fire-rated expanding foam.

When choosing an expanding foam, ensure you have the right product for your job.

How to Choose the Right Expanding Foam for Your Project: Learn More at Fastbuild Knowledge Centre

When To Use Expanding Foam?

Expanding foam is a hugely versatile product that is incredibly useful for construction. Here are some common instances where expanding foam should be considered:

  • Closing Small Gaps
  • Insulation & Soundproofing
  • Leak Proofing
  • Pipe Stabilisation

Closing Small Gaps

Buildings rely on a lot of large, solid components which can’t always connect neatly. Expanding foam is often used to close small gaps to ensure standards regarding insulation and moisture ingress are met, while also providing a smooth finish.

Common instances where expanding foam is used include:

  • Filling gaps around the edges of walls.
  • Filling holes around plumbing fixtures, such as pipes.

Insulation & Soundproofing

Insulation is hugely important for homeowners, keeping buildings warm during the winter while also reducing energy bills. Windows and doors are often the primary culprits for heat loss, but expanding foam can fill the gaps around these installations, reducing heat loss and improving overall insulation.

In a similar way, expanding foam can be useful when soundproofing a room. By filling gaps around things like doors, expanding foam limits noise travel between spaces, making it useful alongside larger things like acoustic insulation.

Leak Proofing

When things like plumbing or extractor fans are installed, small gaps are often created for them to pass through walls neatly. Expanding foam is really useful for filling these gaps, helping to prevent any potential water ingress.

While expanding foam isn’t a long-term solution to persistent leaks, a waterproof foam can help plug gaps around new additions, such as plumbing work.

Pipe Stabilisation

Alongside helping to close gaps to minimise water ingress or heat loss, expanding foam can also be used to stabilise pipes when passing through holes.

Adding some expanding foam (although making sure not to pressure the pipes) delivers a more secure fit that minimises rattling and helps ensure long-term performance.

Where to Use Expanding Foam – Is it Waterproof?

There are expanding foams on the market that can be used both internally and externally. However, if using expanding foam outside, make sure you choose a suitable product that can withstand the elements.

The chemicals that make up expanding foam provide it with water-resistant properties, which make it very useful for stopping water ingress. However, a big problem with external use is UV rays on the foam, which can weaken it over time. Therefore, you often need to paint onto the foam once it's cured to give it the necessary protection.

Can You Plaster Over Expanding Foam?

Yes, you can plaster over expanding foam. However, you will need to take a few extra steps to ensure the plaster adheres to the surface correctly.

Although it may not provide as desirable a finish as plastering over a flat surface, such as plasterboard, for small areas or holes, it can be extremely useful.

Does Expanding Foam Stick to Any Surface?

Expanding foam sticks to pretty much anything – in fact, people often have more problems with removing expanding foam than making it stick.

There are certain materials that expanding foam is naturally more adhesive towards, while it can sometimes struggle with particularly oily or greasy surfaces. However, with a little preparation of the space, expanding foam can be made to stick to pretty much anything.

Where Not to Use Expanding Foam

Expanding foam is not a miracle cure. While it is hugely useful, it should not be used to solve all problems. Here are some common areas where expanding foam shouldn’t be used:

  • Structural repairs: Expanding foam doesn’t deliver the necessary strength to repair masonry cracks, for example.
  • Leak blocking: While most expanding foam can stop leaks, it doesn’t address the cause; using it to temporarily stop a leak can cause the water to spread to other areas and cause more damage.
  • Electrics: Expanding foam can damage electrical boxes and wires, while some expanding foams also pose a fire risk when near electricity.

Whether you’re looking for expanding foam products or other adhesives, we stock everything you need for your next job at unbeatable trade prices. Why not take a look at our range and see for yourself?

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