GTA-004. S1 vs S2 Tile Adhesive: Understanding Deformability. The Guardian Tile Adhesive Series
Updated: Sep 14
By The Guardian
Chief Technical Advisor — GUGAFIX® Construction Chemicals
Introduction
You have probably seen tile adhesive classifications such as:
C2TC2TEC2TES1C2TES2
In GTA-003, we explained what the letters T, E, F and S mean.
Today, we focus on the S classification:
S1 vs S2
This is particularly important when dealing with movement, deformation, large-format tiles and demanding substrates.
But there is a common misconception:
“S2 is better, so I should always use S2.”
That is not the correct way to select an adhesive.
S1 and S2 indicate different levels of deformability. The appropriate class depends on the movement and stresses expected in the complete tile installation system.
Under EN 12004, S1 corresponds to deformable cementitious adhesive and S2 to highly deformable cementitious adhesive. The classification is based on the deformation measured in the relevant test.
The Guardian's Philosophy “I don't sell construction chemicals. I help people build stronger, safer, and longer-lasting structures.”
1. What Does “Deformability” Mean?
A tile installation is not always completely static.
The substrate and tile assembly can experience stresses caused by:
Temperature changes
Moisture-related movement
Substrate deformation
Vibrations
Flexing
External exposure
Thermal cycling
Differences in movement between bonded materials
A deformable adhesive can accommodate a degree of movement between the tile and substrate without losing its intended performance.
This is why deformability becomes an important characteristic in demanding installations.
Technical guidance identifies S1/S2 adhesives for situations where the adhesive needs to absorb stresses generated between the tile and bonding surface, including certain substrates subject to vibration or flexion and external applications.
2. What Is S1?
S1 = Deformable Cementitious Adhesive
Under the EN 12004 classification framework, an S1 adhesive meets the specified deformability requirement for the S1 class.
In simplified terms, S1 provides a greater ability to accommodate movement than a non-deformable cementitious adhesive.
The commonly referenced deformation range for S1 is:
≥ 2.5 mm and < 5 mm
under the relevant test method.
But remember:
This is a classification test result.
It should not be interpreted as saying that a tile installation can physically move 2.5–5 mm in service.
The test classification and actual project movement are two different things.
That distinction is extremely important.
3. What Is S2?
S2 = Highly Deformable Cementitious Adhesive
S2 represents the higher deformability class.
The commonly referenced classification threshold is:
≥ 5 mm
under the relevant EN 12004 test method.
Again, this does not mean:
“The adhesive can safely accommodate 5 mm of movement in every building application.”
The classification is based on a standardized laboratory test.
Actual project performance depends on the complete installation system, substrate, tile, joints, environmental conditions and workmanship.
4. S1 vs S2 — The Basic Difference
Characteristic | S1 | S2 |
Classification | Deformable | Highly deformable |
Relative deformability | Higher than non-deformable adhesive | Higher than S1 |
EN 12004 test classification | ≥2.5 mm and <5 mm | ≥5 mm |
Typical relevance | Applications requiring deformability | Applications requiring a higher degree of deformability |
Automatically suitable for every application? | No | No |
The important message is:
S2 is a higher deformability classification—not a universal recommendation.
5. Why Does Deformability Matter?
Consider a tile bonded to a substrate.
If the substrate expands, contracts, flexes or otherwise moves, stresses can develop within the tile installation.
A suitable deformable adhesive can help accommodate these stresses.
The simplified concept is:
SUBSTRATE MOVEMENT
↓
STRESS AT TILE/ADHESIVE INTERFACE
↓
ADHESIVE ACCOMMODATES PART OF THE MOVEMENT
↓
REDUCED STRESS TRANSFER TO THE TILE SYSTEM
This is one reason deformability can become important in demanding applications.
However, adhesive flexibility is only one component of the system.
6. Where Can S1/S2 Become Relevant?
Deformable adhesives may be considered where the installation is exposed to stresses or movement that require such performance.
Examples can include:
External installations
Outdoor surfaces can experience significant temperature variation and environmental exposure.
Heated floors
Heating and cooling cycles can produce repeated dimensional changes.
Large-format tiles
Large tiles can place greater demands on substrate flatness, coverage and movement management.
Certain deformable substrates
Some approved substrates may experience greater movement than conventional cementitious substrates.
Areas exposed to vibration or flexion
Where the substrate is subject to movement, an appropriate deformable adhesive may be required.
Technical installation guidance specifically identifies S1/S2 adhesives for applications where stresses from vibration or flexion need to be accommodated.
7. Large-Format Tiles: Is S2 Always Required?
No.
This is an important misconception.
Large-format tile installation requires consideration of several factors:
Tile size
Tile type
Tile thickness
Substrate
Substrate flatness
Location
Exposure
Movement
Installation method
Required adhesive performance
S1 may be appropriate for some large-format applications.
S2 may be specified for others.
The correct choice must come from the project requirements and product technical documentation.
There are commercially available S1 products specifically designed for large-format ceramic slabs, demonstrating that large format alone does not automatically mean S2.
8. Does S2 Mean the Adhesive Is “More Flexible”?
That is a useful way to understand the classification at a basic level, but technically we should be careful.
S1 and S2 are standardized deformability classifications.
They are not simply marketing descriptions such as:
“S2 is twice as flexible.”
Nor should the classification be used to compare unrelated properties such as:
Adhesion strength
Open time
Slip resistance
Setting speed
For example:
C2TES1
and
C2TES2
may both be C2 adhesives with T and E characteristics, but they differ in their deformability classification.
9. S1/S2 Does Not Replace Good Substrate Design
This is one of the most important lessons for installers.
A deformable adhesive does not mean that the substrate can be unstable.
If the substrate is:
Cracked
Poorly prepared
Structurally moving
Unsound
Excessively uneven
Inadequately cured
the correct response is not simply:
“Use S2.”
The substrate condition must first be addressed.
The Guardian's Technical Tip
An S2 adhesive is not a substitute for a sound substrate, correct movement joints or proper installation design.
10. Movement Joints Still Matter
A common misunderstanding is:
“If I use S2 adhesive, I don't need movement joints.”
That is incorrect.
Movement joints are part of the overall tile installation system.
Large-format installations and other demanding applications may require appropriate movement and perimeter joints according to the relevant design and installation requirements.
The adhesive cannot be expected to absorb unlimited movement.
Adhesive deformability and movement-joint design work together.
11. S1/S2 and Tile-On-Tile Installation
Tile-on-tile installations can create demanding bonding conditions because the installer is bonding a new tile over an existing finished surface.
Selection must consider:
Existing tile condition
Surface preparation
Existing substrate movement
New tile type
New tile size
Internal/external exposure
Required adhesive classification
An S1 or S2 adhesive may be appropriate in some situations, but the classification alone does not make tile-on-tile installation automatically suitable.
The substrate must still be properly prepared.
12. S1/S2 and Waterproofing
Another important distinction:
Deformable adhesive ≠ Waterproofing system
An S1 or S2 adhesive does not automatically make a tiled surface waterproof.
Where waterproofing is required, the appropriate waterproofing system must be designed and installed separately.
The tile adhesive then forms part of the overall tile installation system.
This distinction is particularly important in:
Bathrooms
Balconies
Terraces
Wet rooms
Swimming-pool environments
Exterior installations
13. What About GUGAFIX G6?
This is where the technical knowledge in the GTA series will eventually connect naturally with the GUGAFIX product range.
GUGAFIX has been developing G6 Nano-Graphene Series — Graphene-Flex S2 Active Waterproof Adhesive, positioned for large-format tiles and stone.
For this product, the important principle is not simply:
“G6 is S2.”
The professional question is:
“Where does an S2-class adhesive provide a technical advantage, and what installation conditions does the complete product specification support?”
That is exactly the type of question the Guardian Knowledge Series should teach.
We should always support any final product claim with the actual approved TDS/test documentation.
14. S1 vs S2: A Practical Selection Framework
Before choosing between S1 and S2, consider:
1. Tile
What type of tile or stone is being installed?
2. Size
Is it small, medium, large-format or slab?
3. Substrate
Is the substrate rigid, deformable, heated or otherwise subject to movement?
4. Location
Is the installation internal or external?
5. Exposure
Will it experience thermal cycling, moisture or other environmental stresses?
6. Movement
What level of movement is expected in the complete system?
7. Installation specification
What classification does the project specification require?
8. Product TDS
Does the selected product specifically support the proposed application?
This is a much more reliable method than simply saying:
“S2 is better.”
15. Common Mistakes About S1 and S2
Mistake 1 — Assuming S2 is always better
Higher classification does not automatically mean better suitability.
Mistake 2 — Thinking S2 allows unlimited movement
It does not.
Mistake 3 — Using S2 to compensate for poor substrate preparation
It cannot.
Mistake 4 — Ignoring movement joints
Adhesive deformability does not eliminate the need for appropriate joint design.
Mistake 5 — Choosing based only on tile size
Tile size is important, but it is only one part of the selection process.
Mistake 6 — Confusing deformability with waterproofing
They are different functions.
Mistake 7 — Ignoring installation technique
Even a high-performance adhesive requires correct mixing, application, coverage and curing.
The Guardian's Site Check
Before selecting an S1 or S2 adhesive, ask:
1. What tile is being installed?
2. What is its size and format?
3. What is the substrate?
4. Is the substrate likely to experience movement?
5. Is the installation internal or external?
6. Are there thermal or environmental stresses?
7. Are movement joints properly designed?
8. Does the project specification require S1 or S2?
9. Does the manufacturer's TDS support the intended application?
10. Is the installer following the specified installation procedure?
If these questions are answered properly, S1/S2 selection becomes an engineering decision rather than a marketing decision.
Conclusion
S1 and S2 are important classifications within cementitious tile adhesive performance.
S1 = Deformable
S2 = Highly Deformable
Under the EN 12004 classification framework, S1 corresponds to the specified deformation range of 2.5 mm to less than 5 mm, while S2 corresponds to 5 mm or more in the relevant test.
But these numbers should not be interpreted as the amount of movement an installed tile assembly can simply absorb in service.
The real question is:
What stresses will the complete tile installation experience, and what adhesive performance does the project require?
A successful installation depends on much more than adhesive deformability:
Correct adhesive + sound substrate + correct preparation + adequate coverage + movement joints + proper installation
The Guardian's Final Advice
“Choose S1 or S2 because the installation requires that level of deformability—not because a higher classification simply sounds better.”
About The Guardian
The Guardian — Chief Technical Advisor, GUGAFIX® Construction Chemicals
“I don't sell construction chemicals. I help people build stronger, safer, and longer-lasting structures.”
Knowledge Builds Stronger Structures
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