Rheology modifiers are the additives that set a paint's viscosity at every shear rate, from storage in the can to the drying film, and paint formulators choose them from 6 classes. They decide whether a latex (emulsion) paint keeps its pigment suspended in the can, loads onto a roller without spatter, and gives good levelling without running on a vertical wall. In solventborne alkyd, epoxy and polyurethane paints, clays and organic thixotropes build the structure that holds a thick film in place.
The 6 classes are cellulosic thickeners, HEUR and other associative thickeners, alkali-swellable thickeners (ASE and HASE), clays, organic thixotropes and anti-settling agents. Rheology modifiers are one of the 15 families of paint additives, and this page covers how each class thickens, which class suits which paint type, all 9 substances with a page on this site, the 4 defects the family prevents, the CLP, REACH and US rules, the ASTM and ISO tests and how to source a grade.
How we check: regulations and classifications are read at the body that issues them, standards at the standards body, and every additive level names its basis and its source; the full method is in methodology and fact-checking.
What Are Rheology Modifiers in Paint and Why Does Every Paint Need One?#
A rheology modifier is a paint additive that controls viscosity and flow at low, mid and high shear, so the paint resists settling, loads onto the brush or roller, levels without sagging and builds film. Rheology itself is the science of how a material flows and deforms under shear. A paint needs a high viscosity at rest and a low one under the brush, and the rheology modifier supplies that difference.
Rheology modifiers carry 4 working names, each pointing to the shear region it serves. "Thickener" or "paint thickener" names the agents that raise mid-shear viscosity in waterborne paint, such as HEC, HEUR and HASE. "Thixotrope" and "sag control agent" name the structure builders of solventborne paint, such as organoclays, castor wax and diamides. "Anti-settling agent" names the additives that keep dense pigments suspended in the can.
The share of a rheology modifier in a finished paint is small. In the PCC EU Ecolabel indoor white guide formulation, 0.10 % HEC (dosed as 10 % of a 1 % solution) plus 0.4 % polyether thickener add up to 0.5 % of the total formula by weight (calculated). That share sits beside binder, pigment, extender, solvent or water and the rest of the additive package; the place of each group is set out on paint raw materials.
Which Shear Rates Must Rheology Modifiers Control, From Can to Film?#
Paint needs 3 viscosities: low-shear viscosity in the can and on the wall, mid-shear viscosity in stirring and loading, and high-shear viscosity under the brush, roller or spray gun. Each region has its own instrument, and the 3 regions are listed below.
- Low shear (Brookfield): storage in the can and the wet film on the wall. Low-shear viscosity controls settling, sag and leveling.
- Mid shear (KU, Stormer viscometer): stirring, pouring and loading the brush or roller. Krebs units describe how the paint feels when it is stirred and how much it picks up on the brush or roller.
- High shear (ICI): brushing, rolling and spraying, measured at 12,000 s-1 on the cone and plate.
How Do Paint Thickeners Work? Volume Exclusion, Association and Particle Networks#
Paint thickeners work in 3 ways: volume exclusion, where water-soluble polymers such as HEC and ASE swell and entangle; association, where hydrophobic end groups of HEUR, HASE and HMHEC bind to each other and to latex particles; and particle networks. Particle networks form when clays, fumed silica and organic thixotropes build a structure that breaks under shear and rebuilds at rest.
Volume exclusion thickens by taking up space in the water phase. Cellulose ethers and ASE polymers swell with water, entangle, and push latex particles into loose flocculation, and their thickening efficiency rises with molecular weight and with concentration. Association instead links hydrophobic end groups with each other and with latex particles into a three-dimensional network.
Associative thickening depends on everything else in the paint that has a hydrophobic surface. Surfactants with a high HLB lower associative viscosity, an effect that can appear only after months of storage. Colorant surfactants with a high HLB displace associative hydrophobes in the same way, which is why HASE added to a HEUR paint holds viscosity in medium and deep tint bases.
6 Types of Rheology Modifiers for Paint Compared#
The 6 types of rheology modifiers for paint are cellulosic thickeners, HEUR and other associative thickeners, alkali-swellable thickeners (ASE and HASE), clays, organic thixotropes and anti-settling agents. The first three thicken waterborne paint, and the last three build structure mainly in solventborne paint, with hectorite, bentonite and attapulgite also used in waterborne paint.
The table compares the 6 classes by chemistry, paint types, one sourced product level with its basis, strengths and limits.
| Class | Chemistry and members | Paint types | Example level (product, basis, source) | Strengths | Limits |
|---|---|---|---|---|---|
| Cellulosic thickeners in paint | HEC, MHEC, EHEC, HMHEC (nonionic); CMC (anionic); water-soluble cellulose ethers | Interior, exterior, silicate and silicone resin emulsion paints | SE Tylose (producer statement for its cellulose ethers in paint): 0.2-0.5 % on total formula, system dependent | Water retention; associative grades cut spatter | Cellulase attack; spatter with plain high-MW HEC |
| HEUR and other associative thickeners | Polyethylene glycol backbone, urethane linkers, hydrophobic end groups; nonionic; RHEOLATE NiSAT grades (Elementis leaflet): 20,000-50,000 g/mol | Gloss and semigloss latex paints | See the HEUR class page; supplied at 17.5-35 % solids (Dow HEUR range) | Flow, leveling, low spatter, early water resistance | High-HLB surfactants, hydrophilic glycols, tinting |
| Alkali-swellable thickeners | Methacrylic acid and ethyl acrylate copolymers (ASE); HASE adds hydrophobes | Interior and exterior emulsion paints | Rheovis AS 1126 (BASF TDS): 1.1-3.5 % as supplied on total formula; ACRYSOL RM-7 (Dow TDS): 9.6-35.9 g/L (8-30 lb per 100 US gal) as supplied | KU and sag; resistant to enzymes | Needs a neutralizer (Dow guide ASE grades thicken at pH 8 or higher); can displace an acid-copolymer dispersant |
| Clay rheology modifiers | Organoclays, bentonite, hectorite, synthetic hectorite, attapulgite | Solventborne (organoclays); waterborne (hectorite, bentonite, attapulgite) | BENTONE 34 (Elementis TDS): 0.2-0.5 % dry on total system; LAPONITE RD (BYK product page): 0.1-2 % as supplied on total formula | Low-shear structure, syneresis control | Conventional organoclays need high shear and a polar activator |
| Organic thixotropes for solventborne paint | Hydrogenated castor oil, diamide and polyamide waxes, modified ureas | Solventborne industrial, epoxy, polyurethane, road marking | THIXATROL MAX (Elementis TDS), diamide: 0.5-2.0 % on total system; THIXATROL ST (Elementis TDS), castor wax: 0.2-0.8 % on total formula | Film build; fast recovery | Activation window; seeding; NMP in some urea grades |
| Anti-settling agents | Polyamide pastes, PE wax pastes, low-dose diamides, fumed silica | Primers and paints with dense pigments | M-P-A 1078 X (Elementis TDS): 0.5-1.0 % on total formula; M-P-A H105 (Elementis TDS): 3.0-10.0 % as supplied on total formula | Prevent hard settling; H105 without viscosity rise | Water in pastes gasses zinc-rich primers |
The organic and inorganic split cuts across these 6 classes. Cellulose ethers, HEUR, ASE, HASE, castor wax, diamides and modified ureas are organic; bentonite, hectorite, attapulgite and fumed silica are inorganic; organoclays are both, a mineral clay carrying an organic quaternary ammonium coating. Carrier and mechanism decide where a grade works: an inorganic hectorite thickens waterborne paint, while the castor waxes on this page are solventborne thixotropes.
Which Classes Thicken Waterborne Paint?#
Cellulosic, HEUR and alkali-swellable thickeners are the 3 classes that thicken waterborne paint. Cellulosic thickeners are water-soluble cellulose ethers that hydrate, swell and entangle in water in interior, exterior, silicate and silicone resin emulsion paints. Plain HEC is susceptible to the enzyme cellulase, and enzyme-resistant grades exist; hydrophobically modified HEC (HMHEC) adds association to entanglement, and Natrosol HMHEC grades are described with outstanding spatter resistance and improved high-shear viscosity.
HEUR thickeners are nonionic polymers with a polyethylene glycol backbone, urethane linkers from an isocyanate, and hydrophobic end groups, soluble at any pH. The end group sets the profile: strongly hydrophobic end groups give pseudoplastic grades with low-shear viscosity and elasticity for sag control and storage stability, while less hydrophobic end groups give Newtonian grades with high-shear viscosity, flow, leveling and reduced roller spatter that leave low-shear structure to a co-thickener. The RHEOLATE NiSAT leaflet reports less water pick-up for its grades than with anionic acrylic thickeners.
Alkali-swellable thickeners are acrylic emulsion copolymers that stay insoluble until a base neutralizes their acid groups. ASE is a copolymer of methacrylic acid and ethyl acrylate; for the ASE grades of the Dow thickener guide, the ratio is about 50:50, the product is supplied below pH 5 and below 100 mPa·s (cP) at up to 35 % solids, and it thickens at pH 8 or higher. HASE adds hydrophobes to the same backbone and thickens by association as well; both are synthetic and resist microbial and enzymatic attack.
The table lists product examples behind the waterborne classes, each value tied to its product and data sheet.
| Product (producer, data sheet) | Class | Example value (basis) |
|---|---|---|
| Rheovis AS 1126 (BASF TDS) | ASE | 1.1-3.5 % as supplied on total formula; pH kept at 7.5 or above |
| ACRYSOL RM-7 (Dow TDS) | HASE | Thickening begins at about pH 6 and is complete at about pH 8; at least 0.1 part by weight of 28 % ammonium hydroxide or 0.15 part of AMP-95 (aminomethyl propanol) per part of thickener (0.1 or 0.15 lb per lb); 2 % (dry) or less on binder solids in exterior paint |
| ACRYSOL DR-1 (Dow product page) | ASE | Low-cost alternative to cellulosics in interior flat latex paints |
| ACRYSOL RM-3000 (Dow product page) | HEUR | 20 % solids; high-shear Newtonian grade |
| Bermocoll EHM 300 (Nouryon product page) | Associative EHEC | 0.3-0.5 % on total paint weight; high resistance to enzymatic degradation |
| Natrosol B grades (Ashland) | HEC | Enzyme-resistant grades for architectural paint |
Which Classes Build Structure in Solventborne Paint?#
Clays, organic thixotropes and anti-settling agents are the 3 classes that build low-shear structure in solventborne paint, each after its own activation step. Clays used in paint are organoclays (bentonite or hectorite made organophilic with a quaternary ammonium compound), natural and synthetic hectorite, sodium and activated bentonite, attapulgite and mixed-mineral organophilic phyllosilicates. Conventional organoclays need high shear plus a polar activator, such as methanol or ethanol with 5 % water, propylene carbonate or acetone, to delaminate their platelets; self-activating grades need neither and go straight into the grind.
Organic thixotropes are castor wax (modified hydrogenated castor oil), diamide and polyamide waxes as powders or pastes, and modified urea solutions. Powder castor waxes and diamides form a fibrous network only inside a temperature window: too cold gives no activation, too hot dissolves the wax, which then re-crystallizes as gritty "seeds". Castor waxes carry a higher risk of seeding and false body than diamides. Modified ureas are liquids that can be post-added without temperature control.
Anti-settling agents keep dense pigments such as zinc dust, micaceous iron oxide (MIO), aluminum paste and anticorrosive pigments from forming a hard cake. Polyamide pastes, polyethylene wax pastes, low-dose diamides and fumed silica serve this role.
The table lists product examples behind the solventborne classes, each level tied to its product and data sheet.
| Product (producer, data sheet) | Class | Example value (basis) |
|---|---|---|
| BENTONE 34 (Elementis TDS) | Organoclay | Polar activator 33 % on dry clay for methanol/water 95/5, propylene carbonate or propylene carbonate/water 95/5; 50 % for ethanol/water 95/5; 60 % for acetone/water 95/5; pregel 5-10 % in solvent; 0.2-0.5 % dry on total system in house and industrial paints, 0.5-1 % in primers |
| BENTONE 38 (Elementis TDS) | Organo-hectorite | 0.2-0.5 % dry on total system; 0.5-1.0 % in epoxy and polyester systems; needs high shear and a chemical activator |
| BENTONE SD-3 (Elementis TDS) | Self-activating organoclay | 0.2-1.0 % on total formula; no pregel, no activator; grind only |
| THIXATROL MAX (Elementis TDS) | Diamide | 0.5-2.0 % on total system for flow and sag control; 0.2-0.5 % for anti-settling only |
| RHEOBYK-410 (BYK product page) | Modified urea | 0.2-1 % (anti-settling) and 0.5-2 % (anti-sag) as supplied on total formula; 52 % active in NMP |
| M-P-A 1078 X (Elementis TDS) | Polyamide paste | 0.5-1.0 % on total formula; 40 % in xylene; minimum activation 43 °C (109 °F) in aromatic and polar solvents |
| M-P-A H105 (Elementis TDS) | Polyethylene wax paste | 3.0-10.0 % as supplied on total formula; prevents hard settling without viscosity increase; anti-silking in metallic and flat paints |
How to Choose a Rheology Modifier by Paint Type#
Choose a rheology modifier by the paint's carrier and application method first: cellulosic, HEUR and HASE thickeners for latex paints, organoclays and organic thixotropes for solventborne paints, and an anti-settling agent where dense pigments must stay suspended.
The table matches 9 paint types to their main rheology modifier class, a sourced level with its basis, and the point to watch.
| Paint type | Main class | Level example (basis, source) | Watch-out |
|---|---|---|---|
| Emulsion (latex) paint formulation | Cellulosic plus associative | HEC 0.10 % + polyether thickener 0.4 % by weight on total formula (PCC EU Ecolabel indoor white guide formulation); ASE/HASE thickener 0.3-0.8 % by weight of total batch (distributor guide formulation, Raykem) | Cellulase attack on cellulose ethers; tint-base viscosity loss with associative grades |
| Water-based enamel paint formulation | Newtonian HEUR and HASE for flow and gloss | See the water-based enamel page | HASE gives a smoother film with fewer brush marks and higher gloss than HEC |
| Alkyd paint formulation | Organoclay | BENTONE SD-1 (Elementis TDS): 0.2-2.0 % on total formula | Cold, low-shear let-down disperses poorly |
| Distemper paint formulation | Cellulose thickener | See the distemper page | Cellulase attack on cellulose ethers |
| Epoxy paint formulation | Organoclay plus fumed silica | Heubach guide formulation 132-01: BENTONE 38 0.25 + TIXOGEL-VP 0.25 + AEROSIL R 972 0.40 pbw per 100 (% on total mixed paint) | Fumed silica raises high-shear viscosity and can impair spraying |
| Polyurethane paint formulation | Organoclay plus fumed silica | Heubach guide formulation 687-03: BENTONE 38 0.45 + AEROSIL R 972 0.15 pbw per 100 | Castor wax only in PU without free isocyanate (THIXATROL ST TDS) |
| Road marking paint formulation | Organoclay, castor wax, attapulgite | BENTONE SD-1 0.2-2.0 % and THIXATROL ST 0.2-0.8 % on total formula (Elementis TDS) | Activation window of castor wax |
| Primer formulation | Organoclay (solventborne), fumed silica with HEUR (waterborne) | Heubach guide formulation 299-03 alkyd primer: BENTONE SD-3 0.40 pbw per 100 in the premix; PCC waterborne direct-to-metal guide formulation: fumed silica 0.2 %, two HEUR solutions (50 %) at 4 % and 0.1 %, all % by weight on total formula | Water-free anti-settling pastes for zinc-rich primers |
| Wood stain and varnish formulation | Organoclay | BENTONE SD-1 (Elementis TDS): 0.2-2.0 % on total formula | Clarity of clear finishes |
In the guide formulations of the table, waterborne paints pair a cellulose ether or an ASE with an associative thickener, and solventborne epoxy and polyurethane paints pair an organoclay with fumed silica. Spray application sharpens the choice between classes: fumed silica raises high-shear viscosity, which can impair spray atomization, while organic thixotropes give higher low-shear viscosity, which builds film. Each paint type's full additive package, with the rheology modifier as one line of it, is on paint formulations by paint type. Film build sets the bar in high-build marine and protective paints, which the THIXATROL PM 8058 paper puts at about 1,000 µm (39.4 mils) or more per spray pass.
In zinc-rich primers, water in an anti-settling paste can cause gassing, so these primers take water-free grades (M-P-A 1078 X TDS).
Which Thickener Combinations Work?#
Waterborne paints combine 2 thickeners where a single class covers one shear region well and leaves the other weak. The 3 combinations with a documented reason are listed below.
- HEUR with HASE: a high-shear HEUR improves the flow of a HASE paint, and HASE improves the stain resistance, sag resistance and tint-viscosity retention of a HEUR paint in medium and deep bases.
- HEUR with clays or cellulose ethers: associative HEUR grades combine with clays, cellulose ethers and acrylic thickeners, so attapulgite or hectorite supplies the low-shear structure a Newtonian HEUR lacks.
- ASE with HASE: Dow guide formulation SH-7-1, a low-VOC interior satin, combines about 13.7 g/L ACRYSOL DR-1 (ASE) and 12.8 g/L ACRYSOL RM-7 (HASE) (11.4 and 10.7 lb per about 100 US gal; calculated with 1 lb/gal = 119.83 g/L) and reaches KU 93 ± 2 and ICI 120 mPa·s (1.20 P) at pH 9.0, PVC 48 % and VOC below 10 g/L.
One combination fails: HASE can displace an acid-copolymer dispersant from the pigment surface and flocculate the paint, and HEUR with a polyacid dispersant can destabilize as well.
When and How to Add Each Class: Let-Down, Pregels, Activators and Activation Temperature#
Cellulose ethers go into the premix, liquid HEUR into the let-down, conventional organoclays into the grind with a chemical activator, and castor wax and diamides into the grind inside their activation window. For its own paste, the M-P-A 1078 X data sheet sets one order of addition: the solvent and binder of the millbase, then the organoclay or castor wax, then the chemical activator, then the paste and the rest of the millbase.
The table lists stage and activation conditions for the main product forms, each tied to its data sheet.
| Product (producer, data sheet) | Stage of addition | Condition |
|---|---|---|
| SE Tylose cellulose ethers (producer page) | Premix | Interior, exterior, silicate and silicone resin paints |
| Natrosol FPS pourable HEC suspension (Ashland) | Let-down and post-thickening | Grind also possible |
| Liquid HEUR (Elementis NiSAT leaflet) | Let-down, under moderate shear after the millbase and before the binder | Predilute very hydrophobic grades |
| LAPONITE RD synthetic hectorite (BYK) | Premix | 2 % predispersion in demineralized water at 20 ± 5 °C (68 ± 9 °F) |
| BENTONE DE hectorite (Elementis TDS) | Grind or let-down | Pregel up to 14 % in water |
| BENTONE SD-1 organoclay (Elementis TDS) | Let-down | 21-35 °C (70-95 °F); minimum dissolver tip speed 4 m/s |
| THIXATROL ST castor wax (Elementis TDS) | Grind | 38-54 °C (100-130 °F) aromatic, 63-74 °C (145-165 °F) aliphatic |
| THIXATROL MAX diamide (Elementis TDS) | Grind | 71-85 °C (160-185 °F) aliphatic, 60-70 °C (140-160 °F) aromatic, 49-54 °C (120-135 °F) oxygenated |
| M-P-A 1078 X polyamide paste (Elementis TDS) | After the thixotrope and activator | Minimum 43 °C (109 °F) in aromatic and polar solvents |
The activation temperature of a diamide rises as solvent strength falls, so an aliphatic paint needs a hotter grind than an oxygenated one, and seeding follows when the grind overshoots. Premix, grind and let-down are the stages where each additive enters, and the full sequence is explained on how paint is manufactured.
Complete Table of Rheology Modifier Substances Used in Paint#
The table lists all 9 rheology modifier substances with a page on this site, with CAS number, class, function in paint, an example level with basis and its source, and the CLP hazard line.
| Substance | CAS | Class | Function in paint | Example level (product, basis, source) | CLP hazard line |
|---|---|---|---|---|---|
| Hydroxyethyl cellulose (HEC) in paint | 9004-62-0 | Cellulosic | Nonionic thickener, water retention aid and stabilizer for emulsion paint | SE Tylose (producer statement for its cellulose ethers): 0.2-0.5 % on total formula | No Annex VI entry; ECHA C&L notified classification: STOT SE 3 H335, Skin Irrit. 2 H315, Eye Irrit. 2 H319 (58.19 %) |
| Hydrophobically modified HEC (HMHEC) | 80455-45-4 (cetyl hydroxyethyl cellulose) | Cellulosic (associative) | Associative cellulose ether for spatter resistance and high-shear viscosity | See the HMHEC page | No Annex VI entry; ECHA C&L notified classification: not classified (84.06 %) |
| Methyl hydroxyethyl cellulose (MHEC) | 9032-42-2 | Cellulosic | Thickener and water retention aid for interior, exterior and silicone resin paints | SE Tylose (producer statement for its cellulose ethers): 0.2-0.5 % on total formula | No Annex VI entry; ECHA C&L notified classification: not classified (100 %) |
| Ethyl hydroxyethyl cellulose (EHEC) | 9004-58-4 | Cellulosic | Thickener and stabilizer for latex paint; associative grades improve high-shear viscosity and spatter | Bermocoll EBS 481 FQ (Nouryon product page): 0.2-0.7 % on total paint weight | No Annex VI entry; ECHA C&L notified classification: not classified (100 %) |
| Carboxymethyl cellulose (CMC) | 9004-32-4 | Cellulosic (anionic) | Anionic cellulose ether thickener | See the CMC page | See supplier SDS |
| Fumed silica in paint | 7631-86-9; treated grades 68611-44-9 (DDS), 68909-20-6 (HMDS), 67762-90-7 (PDMS) | Anti-settling | Inorganic thixotrope and anti-settling agent in solventborne and solvent-free paint | See the fumed silica page | 7631-86-9: No Annex VI entry; ECHA C&L notified: not classified (85.67 %); also notified by a minority as STOT RE 2 H373 (8.59 %). HMDS-treated (68909-20-6): Annex VI index 014-052-00-7, STOT RE 2 H373 (lungs, inhalation), ATP18, applicable since 2023-11-23 |
| Hectorite in paint | 12173-47-6 | Clays | Swelling clay for low-shear viscosity, pigment suspension and syneresis control | BENTONE DE (Elementis TDS): 0.1-1.0 % on total formula; LAPONITE RD (BYK product page), synthetic: 0.1-2 % as supplied on total formula | No Annex VI entry; ECHA C&L notified classification: Eye Irrit. 2 H319 (71.85 %); synthetic grade (EC 701-573-6): not classified |
| Attapulgite clay in paint | 12174-11-7 | Clays | Non-swelling mineral thixotrope; viscosity does not fade under prolonged shear | See the attapulgite page | No Annex VI entry; ECHA C&L notified classification: Carc. 2 H351 (69.39 %) |
| Hydrogenated castor oil (castor wax) | 8001-78-3 | Organic thixotropes | Heat-activated thixotrope for sag control and pigment suspension | THIXATROL ST (Elementis TDS): 0.2-0.8 % on total formula; THIXATROL GST (Elementis TDS): 0.4-1.5 % on total formula | No Annex VI entry; ECHA C&L notified classification: not classified (97.06 %) |
| All other paint additive substances |
Four further rheology modifier substances are sections of their class pages rather than pages of their own: bentonite and organoclay on the clay page, polyamide wax on the organic thixotrope page, and methacrylic acid-ethyl acrylate copolymer on the alkali-swellable page. Organoclay of CAS 68953-58-2 has no Annex VI entry and is notified as not classified (98.79 %), and bentonite (CAS 1302-78-9) has no Annex VI entry and is notified as not classified (65.9 %).
Which Paint Defects Do Rheology Modifiers Prevent?#
Rheology modifiers prevent 4 paint defects: sagging, settling (with syneresis), roller spatter and viscosity loss in storage, each by restoring the viscosity that the defect shows is missing at one shear rate.
The table links each defect to its cause and the rheology fix.
| Defect | Cause at which shear | Rheology fix |
|---|---|---|
| Paint sagging and runs | Low-shear structure recovers too slowly after application; the THIXATROL PM 8058 paper measures the sag window as the time after 1,000 s-1 until tan delta falls below 1 | Solventborne: organoclays, fumed silica, castor wax, polyamide or diamide, urea; waterborne: hectorite, synthetic hectorite, attapulgite with associative thickeners |
| Pigment settling in paint | Low-shear structure in the can too weak to hold pigment | Waterborne: hectorite, synthetic hectorite, attapulgite, bentonite; solventborne: organoclays, fumed silica, polyamide and polyolefin pastes, castor wax, urea |
| Roller spatter in latex paint | Elastic high-molecular-weight networks (plain HEC) break into droplets at the roller nip under high shear | HMHEC, associative EHEC and Newtonian HEUR; measured by ASTM D4707-24 |
| Viscosity loss in latex paint | Tinting surfactants, cellulase, pH drift below the activation pH (ASE, HASE), hydrophilic glycols | Enzyme-resistant grades, HASE or HEUR, HASE in HEUR deep bases, in-can preservation |
Settling and sagging sit at the same low-shear end of the scale, so one low-shear additive can address both, while roller spatter is a high-shear problem of waterborne paint that a change of thickener class solves. Dense pigments raise the demand on low-shear structure: zinc dust, micaceous iron oxide, aluminum paste and anticorrosive pigments need an anti-settling agent.
Cellulose ethers lose viscosity in storage when cellulase attacks them, so the fix for viscosity loss includes in-can preservation. Rheology covers only part of the defect list; all other defects and their additive fixes are collected under paint defects.
How Are Paint Thickeners Regulated? CLP, REACH and US Rules#
No rheology modifier substance on this page carries a harmonized CLP classification except HMDS-treated fumed silica (Annex VI index 014-052-00-7, STOT RE 2 H373, applicable since 2023-11-23). The regulatory load of the family sits in what grades carry: in-can preservatives that count toward the paint's EUH208 label, NMP as a urea thixotrope solvent, and ethyl acrylate, the monomer of ASE and HASE, which carries the harmonized entry 607-032-00-X with Flam. Liq. 2 H225, Acute Tox. 3 H331, Acute Tox. 4 H312 and H302, STOT SE 3 H335, Skin Irrit. 2 H315, Eye Irrit. 2 H319 and Skin Sens. 1 H317, as amended by ATP21, Regulation (EU) 2024/197, applicable since 2025-09-01. The copolymer itself (CAS 25212-88-8) has no Annex VI entry and no notified majority; see the supplier SDS.
The table lists the instruments that reach rheology modifier grades, with their dates.
| Instrument and date | What it requires | Rheology substances affected |
|---|---|---|
| CLP Annex VI, ATP18 (Delegated Regulation (EU) 2022/692), applicable since 2023-11-23 | STOT RE 2 H373 (lungs, inhalation) for HMDS-treated pyrogenic silica; the generic limit for STOT RE 2 in a mixture is 10 % | HMDS-treated fumed silica only; never untreated, DDS- or PDMS-treated grades |
| CLP labeling of paints: EUH208 and H317 thresholds | BIT (Annex VI 613-088-00-6, ATP21, from 2025-09-01): EUH208 from 36 ppm, H317 from 360 ppm in the paint; CMIT/MIT 3:1 (613-167-00-5): EUH208 from 1.5 ppm, H317 from 15 ppm | In-can preservatives in liquid HEUR, HASE and ASE grades (isothiazolinone-free grades exist) |
| REACH Candidate List (since 2011-06-20) and Annex XVII entry 71 (Regulation (EU) 2018/588, from 2020-05-09) | NMP (CAS 872-50-4, Annex VI 606-021-00-7: H315, H319, H335, H360D, ATP09, since 2018-03-01): not placed on the market at 0.3 % or more unless worker DNELs of 14.4 mg/m3 (inhalation) and 4.8 mg/kg/day (dermal) are met | Modified urea thixotropes supplied in NMP; NMP-free variants exist |
| REACH Annex XVII entry 78 (Regulation (EU) 2023/2055) | Synthetic polymer microparticles at 0.01 % by weight or more in mixtures where present for a sought-after characteristic, unless derogated; instructions for use and disposal from 2025-10-17 | Polyethylene waxes; silica is outside (no carbon) |
| VOC: VOC in paint (Directive 2004/42/EC Art. 2(5); 40 CFR 51.100(s)) | EU: organic compound with an initial boiling point of 250 °C (482 °F) or less at 101.3 kPa; US: federal definition with its exempt list | Cellulose ethers, clays and silica are non-volatile; propylene carbonate activator is US-exempt but an EU VOC |
| US TSCA and California Proposition 65 | Inventory listing; Prop 65 warning for listed chemicals | Prop 65 listed: palygorskite fibers, NMP, ethyl acrylate; amorphous silica not listed. TSCA: see the paragraph below |
VOC status depends on the jurisdiction: cellulose ethers, clays and silica are non-volatile and count nowhere, while propylene carbonate, an organoclay activator, is exempt from the US federal definition but counts as a VOC in the EU, because its boiling point of 242 °C (468 °F) lies below 250 °C.
Attapulgite has no Annex VI entry, but 69.39 % of ECHA C&L notifications classify it Carc. 2 H351. When a supplier classifies its grade Carc. 2 H351, the generic CLP concentration limit of 1 % applies, so a paint containing 1 % or more of that grade is itself labeled H351. Under Proposition 65, "Palygorskite fibers (>5 µm in length)" are listed for cancer since 1999-12-28, ethyl acrylate since 1989-07-01 and NMP for developmental toxicity since 2001-06-15; amorphous silica is not listed. On the US TSCA Inventory, HEC, CMC, MHEC, EHEC, hydrogenated castor oil, organoclay 68953-58-2 and silicon dioxide are listed, attapulgite and natural hectorite count as naturally occurring minerals (40 CFR 710.4(b)), and 80455-45-4 is on no TSCA list. VOC, biocide, CLP label and restricted-substance rules for every family are on paint additive regulations.
The microparticle restriction of REACH Annex XVII entry 78, set by Regulation (EU) 2023/2055, reaches the polyethylene waxes of the family but not silica, which contains no carbon.
How Is Rheology Modifier Performance Tested? KU, ICI, Brookfield and Sag#
Rheology modifier performance is measured with 4 test groups: viscosity at low, mid and high shear, sag resistance and leveling, fineness of dispersion, and settling and package stability.
The table assigns each test group its current ASTM or ISO designation and what it shows for rheology modifiers.
| Test group | Standard and edition | What it shows for rheology modifiers |
|---|---|---|
| Paint viscosity: KU, ICI and Brookfield | ASTM D562-10(2023) (KU, Stormer-type, load for 200 r/min); ASTM D4287-00(2023) (ICI, cone and plate at 12,000 s-1); ASTM D2196-20(2026) (rotational, non-Newtonian); ASTM D7394-18(2023) (three-viscometer profile of architectural paint); ISO 2884-1:2024 | Mid-, high- and low-shear viscosity; shear thinning and thixotropy |
| Sag resistance and leveling tests | ASTM D4400-18(2025) multinotch applicator; ISO 16862:2003; ASTM D4062-24 draw-down leveling | Thickest wet film that does not sag; flow-out of brush marks |
| Fineness of grind (Hegman gauge) | ASTM D1210-05(2022) | Dispersion of organoclay and fumed silica; 0 Hegman = 100 µm (4 mils), 8 Hegman = 0 µm |
| Paint storage stability tests | ASTM D869-21 (degree of settling); ASTM D1849-95(2019) (package stability) | Pigment suspension, ease of remixing, change in consistency on storage |
ASTM D7394-18(2023) combines three viscometers into one rheological profile of an architectural paint. No general conversion from KU to mPa·s exists for a non-Newtonian paint, because KU is defined by the load that turns a paddle at 200 r/min, while ICI converts exactly: 1 P = 100 mPa·s, so 1.20 P equals 120 mPa·s. Every other paint test method is described under paint test methods.
The ISO counterpart for high-shear viscosity is ISO 2884-1:2024 (EN ISO 2884-1:2024), which replaces the 1999 edition and covers cone-plate measurement at 9,000 to 12,000 s-1. Sag resistance has ISO 16862:2003 as its ISO method beside ASTM D4400, while leveling by ASTM D4062-24 has no ISO equivalent. ASTM D1309, the accelerated settling test for traffic paint, was withdrawn in 2020 and is historical only; roller spatter has ASTM D4707-24 (see the defect table).
Sourcing Rheology Modifiers: Product Forms, Specifications and Quote Requests#
Rheology modifiers are bought as powders, granules, pourable suspensions, aqueous solutions and pre-activated pastes. A request names the class, the grade or a performance target (KU, ICI, sag rating), the paint type, the annual volume, the packaging and the delivery country.
Product form changes the plant step: HEC comes as powder, as surface-treated grades with delayed hydration that disperse without lumps at neutral pH, as pourable suspensions and as direct dry-add grades; HEUR comes as liquids and as powders at 100 % active; liquid ASE and HASE arrive at about 25 to 35 % solids. Annual volume follows from the paint output: product mass equals paint output times level divided by 100, so a worked example of 1,000 t of paint at 0.3 % HEC on total formula needs 3 t of HEC (calculated).
US suppliers deliver an English safety data sheet of 16 sections with the initial shipment and after an update (29 CFR 1910.1200(g)). Grand View Research estimates the paint additives market at USD 10.1 billion in 2025, with rheology modifiers the largest product segment at 30.2 % of revenue. Sourcing and qualifying producers and distributors is covered on paint additive suppliers and manufacturers.
Two related pages cover regional sourcing and the market.
- Producers and distributors in India: paint additive manufacturers in India
- Market size, segments and leading producers: paint additives market
How Rheology Modifiers Interact With Other Additive Families#
Rheology modifiers interact with 7 other paint additive families, because neutralizers activate ASE and HASE, dispersants and wetting agents compete for associative hydrophobes, and coalescents, biocides, leveling and matting agents depend on the thickener. The 7 interactions are listed below.
- Neutralizers: ASE and HASE thicken only once a base such as ammonia or AMP (aminomethyl propanol) neutralizes them; see neutralizing agents for waterborne paint.
- Dispersants: HASE can displace an acid-copolymer dispersant and flocculate the paint; see dispersing agents for paint.
- Wetting agents: surfactants compete with the hydrophobes of associative thickeners; see wetting agents in paint.
- Coalescents: hydrophobic ester-alcohol coalescents raise the Brookfield viscosity of a HEUR paint, while propylene glycol and butyl diglycol lower it; see coalescing agents for latex paint.
- Biocides: in-can preservation protects cellulose ethers from cellulase; see paint biocides.
- Leveling agents: HASE gives a smoother film with fewer brush marks and higher gloss than HEC, and Newtonian HEUR grades add flow and leveling; see leveling agents and flow additives.
- Matting agents: synthetic hectorite prevents the settling of pigments, fillers and matting agents in waterborne paint; see matting agents for paint.
How Much Rheology Modifier Does a Paint Contain?#
Rheology modifier levels depend on class and product: SE Tylose cellulose ethers (producer page) 0.2-0.5 % on total formula, BENTONE 34 (Elementis TDS) 0.2-0.5 % dry on total system and THIXATROL MAX (Elementis TDS) 0.5-2.0 % on total system.
A distributor guide formulation from Raykem for an interior mid-sheen emulsion paint uses 0.3-0.8 % ASE/HASE thickener by weight of total batch. Ladder studies that start from such a level and step it up and down are explained under paint additive dosage.