Rubber underlays

A right royal resurgence

By Gary Cowley Sales director Interfloor.

ALTHOUGH you can trace the evolution of carpets back to the earliest civilisations – archaeologists recently discovered a 2,000-year-old rug in a frozen tomb in Siberia – the use of underlay to protect and enhance floorcoverings is a much more recent invention.

But what the two do have in common is the motivation for their introduction: a desire to make interiors more luxurious.

Although the very first underlays were made of felt and used under carpet squares in the ‘40s, the development of wall-to-wall carpets in America in the ‘50s heralded the introduction of rubber underlays designed to help the carpet sit properly and wear evenly. But the main reason people opted for underlay was and continues to be for underfoot comfort.

And despite the introduction of PU underlays and their rise in popularity, there is still nothing quite like a rubber underlay to increase the comfort level of floorcoverings of all types.

Today’s consumers want quality products which offer high levels of comfort and are fit-for-purpose. They’re less concerned about price and more interested in long-term performance which is one of the benefits of traditional rubber underlays.

There are two types of rubber underlay: sponge rubber and crumb rubber.

Crumb rubber underlays are, as the name suggests, made from small crumbs of rubber which are bonded together. The rubber crumb comes from used car tyres, so the basic raw material comes from 100% recycled sources. In addition, crumb rubber underlays are fantastically durable and amazing at reducing impact and airborne noise.

They’re also dimensionally stable with regard to lateral forces. In other words, they don’t stretch or tear easily. Crumb rubber underlay offers outstanding recovery and longevity. This makes them ideal for high traffic and very large areas. They are, however, heavier than other underlay types and are not quite as comfortable underfoot as sponge rubber or PU underlays.

The manufacturing process starts with used car tyres, which are ground up and processed to produce tiny crumbs. These are mixed with latex foam and poured onto various types of backing material. The underlay is then passed through a large oven and then cured and cooled. Finally, it’s trimmed, cut, rolled and wrapped into strong and safe to handle packaging.

Sponge rubber underlays are one of the most traditional forms of underlay. They’ve been around since the ‘50s for very good reasons. They’re extremely comfortable: no other underlay produces quite the same feel underfoot.

They’re also exceptionally good at minimising impact sound and airborne sound between rooms. They’re incredibly flexible and cover more applications than any other type of underlay. They’re heavier and denser than PU foam. Specialist applications include low tog underlays for underfloor heating and thin and dense underlays for hard flooring.

Sponge rubber underlays are made from styrene-butadiene rubber (also called SBR). This is blended with oils, blowing agents and fillers to create the desired performance characteristics. This is followed by a process called calendarising, where the mix is converted to a smooth consistent paste. Once the paste is ready, it’s rolled into a wide thin sheet and this in turn is rolled onto a chain to produce the desired profile of either a flat, textured or waffle underlay.

The sheet is then heated, blown, cured and allowed to cool. Finally, it’s trimmed, cut, rolled and wrapped into strong and safe to handle packaging.

Why choose rubber underlay?
All types of floorcovering need the right underlay to ensure they perform well for as long as possible. There are a huge number of different rubber underlays which have been engineered to ensure they work together with each type of floorcovering to enhance it.
Underlays for carpets

The main reason people choose rubber underlay is for underfoot comfort. They also want it to make their carpet last longer, look better and reduce noise and add warmth.

The benefits of rubber underlay
Makes carpets feel better: provides the cushioning that makes the carpet so comfortable and luxurious underfoot.

Makes carpets look better: protects the carpet and helps prevent the pile from flattening thereby helping the carpet look new for longer.

Improves insulation: helps keep in the heat, which will reduce energy bills. Some studies have suggested that underlay can reduce energy costs by up to 15%.

Thickness, density and composition dictate the tog rating of underlay which is a measure of heat insulation. The lower the tog rating the better an underlay is for use with underfloor heating because more heat can rise-up through the flooring and into the room. Conversely, a higher tog rating gives a greater level of heat insulation which is perfect for use with conventional heating systems.

Helps reduce noise: acts as a barrier to sound. A carpeted floor is quiet but a carpet with an underlay can be 2.5 times quieter.

Makes carpets last longer: acts as a ‘shock absorber’ so carpets suffer less wear.

Improves hygiene: protects the carpet pile making it easier to clean and thus more hygienic.

Specialist acoustic rubber underlays for wooden and laminate flooring
Impact noise can be a real problem for areas where hard flooring has been installed, and with the current trend towards this type of floor in domestic and commercial settings, there are now specialist rubber underlays available.

Tests have shown in-room acoustics can worsen if inferior or lightweight underlays are used with hard flooring; putting a lightweight, air filled, cellular product under wood or laminate creates an echo chamber and more noise, whether it’s generated by scraping furniture, heavy footsteps or reverberation.

Special noise reduction rubber underlays for wood and laminate floors, with their superior weight and density, reduce acoustic noise levels by up to 30%.

Benefits of rubber underlay include:

  • Reduces impact sound. Specialist underlays for wood and laminate floors can reduce in-room noise by up to 30%
  • Reduces airborne noise being transmitted between rooms
  • Makes the flooring easier to install and helps to protect the joints
  • Helps keep moisture at bay for cold concrete or stone floors, protecting flooring from potential damage

Underlays for LVT
Luxury vinyl tiles have seen a massive growth in popularity in the commercial and residential sectors, thanks to their versatility. Like carpet and hard flooring, LVT performs better with the right underlay to protect and enhance performance.

The benefits of using rubber underlays with LVT flooring:

  • Improved noise reduction
  • Underfoot comfort
  • Easier installation as it provides an excellent subfloor, masking minor surface imperfections and helping prevent the overstraining of joints
  • Match the product to the customer’s needs

It’s always better to buy the right underlay to complement your choice of floorcovering and to maximise its performance according to its location. Keeping noise to a minimum might be important for people living in flats, or for those who have young children, while people with underfloor heating will want an underlay with a very low tog rating.

Areas such as stairs, halls and landings which see a lot of traffic will perform better with a more durable underlay, while a more economical underlay providing everyday comfort is perfect for a spare bedroom.

The combination of thickness and density is all important as a thick underlay with low density may not perform well. Typically, the thicker the underlay, the better quality it will need to be – 11mm is often used for luxury installations with 9mm and 7mm the common domestic thickness, but rooms with heavy traffic will need a thinner, denser pad.

Contract flooring
Durability is clearly a priority for floorcoverings in retail, leisure and hospitality environments, particularly high traffic areas such as retail showrooms, hotel receptions, casinos, corridors and offices.

A key performance enhancer is a good quality underlay, which will protect the floorcovering by absorbing the impact of foot traffic and, in the case of carpet, prevent the pile being crushed and destroyed. This is most easily assessed by looking at the measurements of ‘Work of Compression’ and ‘Compression Under Static Loading’ found on technical specification sheets provided by underlay manufacturers.

The trend for bolder carpet designs incorporating patterns and texture, particularly in hospitality flooring, means underlay systems need robust performance standards. Double-stick underlay systems are widely regarded as superior, helping to reduce the risk of rucking in high traffic areas. They’re also easier to install as they avoid the need for sewn or heatbond seams and gripper fixings and stretching aren’t necessary.

In terms of types, sponge and crumb rubber underlays are good for heavy footfall offering maximum protection and good levels of comfort (and they’re also very good over stair-nosings).

Commercial environments also need underlays which can keep impact and airborne sound to a minimum as well as help the floorcovering last longer.

In high traffic hospitality spaces, such as guestrooms, dining rooms and reception areas, there’s likely to be increased noise from footfall, trolleys, furniture scraping on the floor, doors closing, and dropped items.

Using a good quality crumb rubber underlay has been a popular choice to reduce impact sound and ensure durability in commercial environments since these types of underlays were first introduced. But in many cases, crumb or sponge rubber underlays will more than meet the performance requirements demanded by specifiers of contract flooring solutions.

In busy meeting spaces such as offices and theatres or halls noise levels can have a huge impact on the acoustics and the clarity of any speech.

Airborne noise is sound transmitted through the air, and underlays which work well for impact sound reduction will not normally be as effective in reducing airborne noise such as music and conversation. Adding more mass by using a rubber underlay will give more density to the final floor, thereby reducing airborne noise.

Another important consideration for public buildings is the fire resistance of floorcoverings including the underlay. Specialist contract rubber underlays are engineered to meet the stringent requirements of building regulations around the world.

The use of a resilient underlay can contribute to not only the tangible performance of a specified floorcovering, but also the installation’s environmental credentials which are becoming increasingly important particularly in the construction industry.

Given the current war on plastic it’s worth mentioning the green credentials of rubber underlays which are 100% recyclable at the end of their life, with many containing not less than 65% recycled content.

A flooring product’s green credentials are measured by several certification systems which assess buildings’ environmental performance. The most widely used around the world is Leadership in Energy and Environmental Design (LEED), a points-based system where building projects earn LEED points for satisfying specific green building criteria.

Flooring products are scored on their performance in several categories from use of recycled content, whether the product is 100% recyclable at the end of its life, indoor air quality and use of regional materials in the manufacturing process.

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