What is the difference between S1 and S2 tile adhesive?

Understanding the value of tile adhesive

When embarking on a tiling project the preparation is key and using the right tools for the job is essential!

For preparing your space for tiling, you can read our guides on preparation, these guides cover how to plan your space, levelling your surface and preparing various types of substrates ready for your tiles. The next step then is to talk about how to fix your tiles.

Choosing the right adhesive for your specific tiling job can sometimes be a little confusing, in this article we breakdown the technical jargon and provide you with the key points on how to choose the right adhesive for your job and why sometimes it’s worth investing a little more for a better finish.

Cementitious tile adhesive classifications

When looking at a cementitious adhesive, various letters are used to help describe the products added efficiencies, we’ve mapped them out for you.

C = Cementitious

1 = Normal characteristics

2 = Improved characterises (usually this means its flexibility, referring to additional polymers or such like to improve the performance of the adhesive)

T = Reduced slip (so how effective is the product’s grab, aka keeping the product on the substrate)

E = Extended opening times (how long can you work with the product)

F = Fast setting (how quickly after application can you grout your tiles)

S1 = Deformable (in conjunction with all the above features, this adhesive also has added flexibility, a deformability of between 2.5mm & 5mm)

S2 = Highly Deformable (this product has high flexibility, a deformability of above 5mm

To put these letters in a bit of context, if you’re tiling a wall with large format tiles, you’d need to look for an adhesive that is C2T as a minimum, as this has reduced slip. If you’re tiling a floating floor, you’ll need a C2TES1 as a minimum (as it depends on how much movement is in your floor).

If the product you’re looking at has a ‘D’ (for Dispersion) classification, then this is not a powdered adhesive (aka ready mixed) and not suitable for a project that requires the properties of a cementitious adhesive, for example, large format tiles or flexibility.

Why choose an S1 or S2 adhesive?

Although typically more expensive than the standard C2 adhesive, S1 and S2 adhesives are designed to cope with movement within a substrate and ultimately preventing the final surface (aka tiles) from de-bonding or cracking. If a non-flexible adhesive is used and movement or vibration occurs within the substrate the adhesive is likely to crack or fail, resulting in a damaged floor and tiles lifting.

All materials are subject to some form of movement, most commonly expanding and contracting with changes in temperature therefore for a long-term investment like tiles it makes sense to secure your project by reducing the risk of tile failure.

Even in substrates you would normally expect no movement, such as concrete, over a few years they can continue to cure creating even the slightest movement. This is often why you see cracks appearing in floors some years later after being laid. But this issue can be prevented by investing in your preparation and the right adhesive..

Why choose an S1 adhesive?

A S1 adhesive has increased deformability when compared to a regular adhesive. It has added flexibility, a deformability of between 2.5mm and 5mm.

A S1 adhesive will therefore safeguard against tile adhesive failure by coping with smaller types of movement.

Why choose an S2 adhesive?

Similarly, to S1 adhesives, S2 products are designed with flexibility in mind. The difference being the amount of deformability the product allows. Typically, an S2 allows for 5mm or more deformability, for example the BAL Fast Flex allows for movement of up to 20mm, one of the best available.

S1 adhesives can be used for most tiling projects, however those that have more movement and/or vibration an S2 product should be used. Those circumstances are typically

- Tiling directly onto tongue and groove floorboards

- Floating floors

It is essential that any existing timber floor is stable, clean and in good condition with adequate ventilation beneath to prevent atmospheric moisture distortion. It should be sufficiently rigid and stable, as any unsupported movement in the subfloor can cause tiles to crack, and the floor should be able to support the additional weight without any deflection (bounce in the floor).

To check whether there is any deflection in the floor and how to solve it, read our guide on tiling onto a floating chipboard floor.

Once movement has been resolved, timber floors that require strengthening ready for tiling can be overlaid using a suitable, flooring grade, 15-18mm thickness WBP plywood (to be primed on the underneath and sides, not on the top side).

Where floors require further strengthening, you may wish to fit additional noggins within the joists beneath the subfloor or floorboards.

Please note plywood should ONLY be used as an overlay and not fixed directly to floor joists.

Which product is for you?

Now you know what the classifications means and the difference between flexible and non-flexible adhesive, we’ve provided a product breakdown of our key ranges to help narrow down your final choice.

Product Name: BAL New Floor. Classification: C1S1. Capabilities: For new cement and concrete floors (after just 7 days for fast-track installation on new concrete, 24 hours on sand/cement screeds). Can be used for most tile types and rigid insulating materials in wet or dry / interior and exterior environments. Enhanced adhesive to low porosity substrates.

Product Name: BAL Single Part Fastflex. Classification: C1S2. Capabilities: Highly flexible, can be used as isolating, anti-fracture underlay for tiles . Water and frost resistant. For fixing ceramic, porcelain, mosaics, and natural stone in wet or dry / interior and exterior environments. Sound reduction properties for most tile types and rigid insulating materials in wet or dry / interior and exterior environments. Enhanced adhesive to low porosity substrates.

Product Name: BAL PTB Fibre Plus. Classification: C2FES1. Capabilities: Pourable Thick bed Adhesive. Suitable for large format tiles. Can be used with UFH, in wet rooms and most tile types. Ideal for natural stone with differing thickness. Can be used on timber floors. Sets in 3 hours.

Product Name: BAL Rapid-Flex Fibre Plus. Classification: C2FES1. Capabilities: Walls and Floors. Improved flexibility, strength, and grab. Fast setting . For fixing ceramic, porcelain, mosaics, and natural stone in wet or dry / interior and exterior environments. High polymer content allows for direct fixing to plywood walls. Suitable for UFH.

Product Name: BAL Flex Fibre Plus. Classification: C2TES1. Capabilities: Walls and Floors Up to 20mm thickness. Non-slump and non-slip properties. Ideal for fixing large ceramic and porcelain tiles. Extended open time of 60 minutes. Working time of 30 minutes.

Product Name: BAL Rapid XP Plus. Classification: C2FTES1 . Capabilities: Combines the use of a PTB and adhesive in one easy to use product. Walls and Floors. Up to 25mm thickness. Fast Setting Non-slip properties. Lightweight Rheology for smoother application. Ideal for fixing large format tiles and natural stone. Working time of 30 minutes. Extended open time of 60 minutes.

When exploring our full range of tile adhesives, you can find the classification in the product description under ‘classification’. The identifying letters are found at the end of the British Standards coding as per the example here:

Grout After: 5 Hours

Classification: BS EN 12004 C1S2

Coverage for 12.5kg bag:

For more information on adhesive types to use for your project as well as tiling tools and a quick how to, see our adhesive guide.

With a little more knowledge, it’s clear to see the importance of not only selecting the right adhesive for your tiling project but also investing in a higher quality product for a long-lasting finish. Shop our full range of adhesives now.

What is the difference between S1 and S2 tile adhesive?

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What is the difference between S1 and S2 tile adhesive?