{"id":10358,"date":"2026-01-19T10:46:38","date_gmt":"2026-01-19T09:46:38","guid":{"rendered":"https:\/\/www.adesiviesigillanti.it\/?page_id=10358"},"modified":"2026-01-20T17:26:08","modified_gmt":"2026-01-20T16:26:08","slug":"2-sepiolsa-eng-1-26","status":"publish","type":"page","link":"https:\/\/www.adesiviesigillanti.it\/en\/archive\/__trashed\/issue-1-2026\/2-sepiolsa-eng-1-26\/","title":{"rendered":"2-SEPIOLSA ENG 1-26"},"content":{"rendered":"\t\t
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'The battle of clays'\nor Sepiolite vs. Bentonite: Choosing the right\nclay for mortars, tile adhesives and plasters<\/h1>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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David Giner
SEPIOLSA (MINERSA GROUP)<\/strong><\/span><\/h5>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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One of the most common questions I receive from clients concerns which clay is better to use\u2014sepiolite or bentonite\u2014in materials such as mortars, tile adhesives, putties, plasters, etc.
Traditionally, due to global availability and resource accessibility, bentonite has been more widely used, while sepiolite has played a more ‘shadow role’, being less known and less applied.<\/p>

MINERALOGICAL AND STRUCTURAL FUNDAMENTALS: THE ORIGIN OF RHEOLOGICAL DIFFERENCES
<\/span><\/strong>The different performance of bentonite and sepiolite in drymix mortars (DMM), tile adhesives, plasters, and putties is rooted in their crystal structures, which govern their gelation mechanisms upon hydration. These minerals are essential rheological additives, controlling viscosity, thixotropy, and sag resistance.<\/p>

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THE LAMELLAR STRUCTURE OF BENTONITE (MONTMORILLONITE)
<\/span><\/strong>Bentonite is a smectite clay, a 2:1 phyllosilicate with a lamellar morphology. Sodium bentonite is the most commonly used for rheological applications due to its superior swelling properties. Its gel structure forms through interlayer swelling, absorbing water between silicate sheets and expanding 15\u201325 times its original volume (or 30\u201350 times its weight). The thickening mechanism is predominantly electrochemical: dispersed platelets interact via attraction-repulsion forces (mainly edge-to-face), forming a 3D colloidal network known as the ‘House of Cards’.
This rigid network gives bentonite high static water retention, a high liquid limit, and notable plasticity.
In civil engineering applications, this plasticity is critical: bentonite enables plastic concrete, flexible waterproof plaster, and chemically resistant barriers, capable of moving with the substrate without cracking.<\/p>

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THE FIBROUS STRUCTURE OF SEPIOLITE (CHAIN-LAYER CLAY)
<\/span><\/strong>Sepiolite, in contrast, is a magnesium silicate, structurally related to palygorskite (attapulgite) and mineralogically distinct from montmorillonite. Its morphology is fibrous, needle-like. Sepiolite is non-expansive, highly porous, and very low in density, with a large surface area. Its thickening mechanism is primarily mechanical, based on the physical entanglement of its fibers, further reinforced by hydrogen bonding interactions between them, which enhance the stability and strength of the network. Unlike bentonite, sepiolite does not swell significantly; instead, it absorbs water in the microporous channels of its structure.<\/p>

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Viscosity and network formation arise from physical fiber interactions, especially under high shear. This gives sepiolite high absorption capacity, retaining its own weight in water. Its rheological mechanism makes it ideal for dry-mix systems, where consistency and stability are paramount.
The structural difference between lamellar swelling (bentonite) and fibrous entanglement (sepiolite) translates into a key functional trade-off for formulators: Sag control vs. Thixotropic Recovery.
Static gel strength and sag control: Vertical sag resistance (sag control) and stability against sedimentation at rest are directly correlated with the static yield limit (\u03c4\u2080) or the material\u2019s yield stress. Bentonite generates gels with higher initial static strength than sepiolite. The robustness of the bentonite ‘House of Cards’ network provides a high ‘Yield Point’, which is essential for the stability of freshly applied mixtures. This high Yield Stress is a fundamental requirement, particularly in large-format or heavy tile adhesives applied vertically, where preventing slippage or sag immediately after placement is critical. Bentonite, or its refined derivatives, is therefore the natural choice when the absolute priority is to maximize anti-sag performance at rest. Dynamic workability and thixotropic recovery: Workability is defined as the ease with which the mortar can be applied and spread under shear (low dynamic viscosity) and the speed at which it recovers its internal structure once the stress ceases (high thixotropy). Sepiolite exhibits a significant advantage in this regard, achieving superior workability at a gel strength comparable to that of bentonite. This improvement is evident in dynamic rheology: sepiolite shows a faster thixotropic recovery. When the fibrous structural network of sepiolite is broken by shear (e.g., during trowel application), it physically re-entangles almost instantly once the tool is removed. This rapid reconstitution of the structure is crucial to maintaining the shape of mortar ridges (layer thickness) and ensuring a uniform finish, preventing particle re-settling or ridge collapse, ultimately resulting in easier and faster application.<\/p>

STABILITY IN CEMENTITIOUS SYSTEMS: HIGH PH AND CALCIUM IONS
<\/span><\/strong>The performance of any mineral additive in construction is conditioned by high pH and Ca\u00b2\u207a ion concentrations released during Portland cement hydration.<\/p>