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How to Choose the Best Underlay for Mould

Updated 16/10/2023

Choosing the right underlay for a new floor can be confusing. You may have bought a new floor or are replacing an existing floor; it’s essential to choose the right underlay. And you’ve come to the right place to learn about underlay and how to choose the right one!


What is the Underlay? 

The underlay (also called the flooring underlayment or underlayment) is a thin layer of material made from rubber, fibre, felt, or foam. This thin layer acts as a cushion, absorbs sound, insulates, and reduces wear and tear on your flooring.


What’s the Purpose of the Underlay? 

The underlay can be made of different materials and works to create a flat surface for the floor covering. It provides a smooth surface that allows for easy installation of the surface covering.

When used under engineered wood flooring or laminate, the underlay provides a vapour barrier to keep moisture from coming through and damaging your floor.

Here are the main purposes of the underlay:

Smooths the surface: the underlay provides the floor covering with a smooth surface that acts as a cushion between the subfloor and the surface covering.

Improves adhesion: the underlayment also improves the adhesion of ceramic tiles. A cement board may be used as the underlayment. It offers a better surface for the tile to adhere to. Tiles can’t be directly installed on a subfloor. The subfloor doesn’t provide the stable surface needed for tiles to adhere. Subflooring tends to expand and contract, which could cause tiles to crack and shift.

Improves structural stability: a hard underlay provides stability for the entire floor. It’s often used in older homes where the subfloor may have been constructed with boards rather than OSB or plywood sheets.


Where is the Underlay Installed? 

When most people think of flooring, they’re focused on the top layer that’s visible. They usually don’t think about the different layers that go to make up the flooring in their homes. Most residential homes use four layers, including:

Floor covering: this is the visible part of the flooring surface and the part you walk on.

Underlayment: is installed just under the visible floor covering. This layer is usually about ¼- or ½-inch thick. The purpose of the underlayment is to provide a smooth, flat surface for the floor covering. It can be made of different materials, depending on the floor covering.

Subfloor: is the layer of OSB or plywood that’s a part of a home’s structure; it is under the underlay and works to improve the strength and rigidity of the flooring system when attached to the joists.

Joists: are wooden framing pieces that rest on the foundation walls and beams. They provide structural support for the entire frame of the home.


Is Underlayment Always Needed? 

That’s a great question! In most flooring installations, an underlay is required to install the surface flooring correctly. The underlay may be very thin.

In some cases, such as with brand-new construction, the subfloor may be sturdy and smooth enough that no underlay is required. Carpeting may be laid directly on carpet padding attached to the subfloor.

In other cases, the existing floor covering may be able to serve as the underlay. Existing flooring may be used as an underlay for laminate flooring, or vinyl flooring may be laid over older vinyl flooring without issues. Carpeting is sometimes installed over existing hardwood floors with no underlayment other than carpet padding.


Which Specs Should You Choose for the Underlay? 

The quality of underlay is determined by its TOG rating. TOG stands for Thermal Overall Grade, which is a measurement for insulation, warmth of sleepwear, and bedding. In the case of underly, the TOG rating measures the thermal insulation and its effectiveness. The higher the TOG rating, the better the insulating factor.

Next, it’s important to review the underlay’s DPM. The DPM stands for damp proof membrane and is usually installed under a concrete subfloor. It works to keep moisture from travelling through the floor. New homes and homes built since the 70s should have a DPM already installed beneath the concrete.

Thickness is the next consideration for choosing the right underlay. There are several factors to consider when choosing the thickness of the underlay. For instance, if you’re installing underfloor heating, an underlay that’s too thick will make it too difficult for heat to come up with the floor. It’s necessary to choose an underlay with the right thickness for your space.


What Material is Best for an Underlay? 

Here are the different materials used for underlay and how they’re used.


Foam Underlay

Foam underlay is a great choice if you have a tight budget. It’s affordable, warm, and practical and it can add more comfort with laminates. Foam is also a sustainable choice because it’s made from recycled scraps of foam. And it works great for dampening sounds; it even takes care of squeaky floorboards.


Thermal Underlay

Thermal underlay is a great choice for vinyl, laminate, and engineered wood flooring. It’s also a great choice if you’re installing underfloor heating. Thermal underlay keeps the floor warmer longer and creates a thermal barrier that keeps moisture from damaging the floor, and your home stays free of damp.


Fibreboard Underlay

Fibreboard underlay is often one of the best choices. It helps smooth uneven floors, reduces noise, and helps trap heat. In addition, this is the best underlay to use with laminate and wood flooring.

If you’re dealing with an uneven subfloor, fibreboard also gets rid of dips and dents that are impossible to level. And remember to include a DPM if you’re installing fibreboard over concrete subflooring, to keep moisture from causing damage to the surface covering.

One last point, fibreboard is not an optimal material to use in wet rooms, such as the bathroom, laundry room, and more.


Cork Underlay

A cork underlay is best for tile and stone flooring. It works to dampen sound and is a hygienic choice, too. Cork naturally prevents the growth of bacteria, mould, and mildew. It’s also an eco-friendly option for anyone concerned about the climate. It can also improve the energy efficiency of your home.

The main issue with this material is that cork is not waterproof. So, it’s best to avoid installing cork underlay in bathrooms or other wet spaces.

Cork is a great choice for hardwood floors, and it works well under linoleum, stone, tile, and carpet.


Summing It Up

So, there you have it! We hope this information helps you choose the right underlay for your project! If you have any questions about the right underlay for your flooring, be sure to reach out to a professional flooring installer. They can guide you on which underlay is the right option for your flooring.

FAQs about Choosing Underlay for Mould

What causes mould under flooring?
Mould under flooring is typically caused by moisture or humidity. It thrives in damp environments.

Can any underlay prevent mould?
No, not all underlays can prevent mould. Choosing the right material and thickness is essential.

How often should I replace my underlay to prevent mould?
Underlay replacement frequency depends on the material and wear. Generally, it’s recommended every 5-10 years.

Can I install underlay myself?
Yes, many underlays are DIY-friendly, but professional installation may be necessary for complex cases.

Is cork underlay a good choice for preventing mould?
Yes, cork underlay is an excellent choice as it resists moisture and inhibits mould growth.

Does underlay thickness affect mould prevention?
Yes, thicker underlays with higher density create a more effective barrier against moisture and mould.

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