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Differences in Coating Layering, Water Separation, and Precipitation

All three belong to the category of storage stability problems, but their phenomena, mechanisms, causes, and solutions are completely different. Latex paint, industrial water-based paint, and solvent based paint can all occur. Below, we will summarize the reasons using a simple comparison, judgment methods, and additives/formulas.

1. Separate water (also known as water separation or effluent)

Phenomenon: A layer of transparent/semi transparent water appears on the upper layer of the paint tank, while the lower layer is still coated with paint, with a significant color difference between the upper and lower layers; After stirring, it can be mixed again without any hard residue.

Appearance: A layer of water phase on the top and a paste like coating on the bottom.

Mechanism: the system has low shear viscosity/thixotropy, water separates from the pigment filler lotion network, and the water phase floats upward.

Common triggers:

Insufficient addition of cellulose and HASE thickening, low shear viscosity too low;

HEUR polyurethane thickener is added in large amounts, but lacks low shear components, only high shear thickening, low shear thickening cannot be removed, and it is easy to separate water;

Excessive wetting/dispersing agents and surface active agents disrupt the binding network;

Too few pigments and fillers, and high proportion of lotion.

Features: Stirring can restore, generally without hard precipitation; Long term placement and repeated water separation will gradually develop into component layers.

Solution: Improve low shear viscosity, supplement cellulose/HASE/water-based bentonite; Do not rely solely on polyurethane thickening.

2. Layered

Phenomenon: The system is divided into two or more layers, which may not necessarily be clear water, but can be a thin material layer or a light colored slurry layer; The upper layer is a thin paint liquid, and the lower layer is a thick paste; Stirring can mostly mix well, but there are still particles after severe layering and stirring.

Dividing water is a special form of stratification (with clear water in the upper layer), with a larger range of stratification.

Mechanism: lotion, pigment and filler, and auxiliary network are separated as a whole, and the difference of two phase density causes phase separation.

cause:

Unreasonable combination of thickening system;

The compatibility of lotion and additives is poor;

PH drift, dispersant desorption, lotion stability decline;

Solvent based: Poor compatibility between resin and additives.

Different from dividing water: dividing water only has upper level clear water; The upper layer of the layer can be colored thin paint, not pure water.

3. Sedimentation (settling)

Divided into soft sedimentation and hard sedimentation (hard bottom) phenomenon: solid particles accumulate at the bottom of the tank.

Soft sediment: The bottom sediment is soft and can be easily dispersed and restored to uniformity by stirring.

Hard sedimentation (hard bottom): The bottom forms a hard block, which cannot be dispersed by stirring or high-speed dispersion, and the particles undergo coagulation and agglomeration.

Mechanism: The density of pigment fillers/heavy powders (titanium dioxide, heavy calcium, mica iron oxide, extinction powder) is higher than that of the base material, and they settle downwards under the action of gravity.

Soft sedimentation: Only gravity sedimentation occurs, and the powder does not undergo chemical flocculation, resulting in a weak thixotropic network.

Hard precipitation: The pigment undergoes secondary coagulation, the dispersant desorbs, and the particles bond and agglomerate with each other.

cause:

Insufficient dispersant and unstable pigment adsorption;

Insufficient anti settling/thixotropic additives (solvent based: polyamide wax, gas-phase silicon, bentonite; water-based: bentonite, cellulose);

The specific gravity of the filler is too high (mica iron oxide, quartz powder);

Insufficient grinding fineness leads to agglomeration of the original pigment.

⚠️ Key distinctions:

Split water: The water runs to the top, but the bottom coating is still normal;

Sedimentation: The solid runs to the bottom of the tank, and the upper paint becomes thinner;

Stratification: The overall two-phase separation can be accompanied by both water separation and precipitation.

Project water separation (precipitation) layer by layer sedimentation (settling)

Typical appearance: A layer of clear water is deposited on the top of the tank, which is divided into a thin layer and a thick layer. The upper layer has a colored thin paint, and the bottom of the tank is piled up with solids, soft sediment/hard bottom

The phase is separated by placing the water phase on top and the thick solid on the bottom

Core causes: insufficient low shear viscosity, overall phase separation of aqueous phase precipitation system, compatibility of lotion additives, gravity sedimentation of heavy powder, pigment flocculation

After stirring, it generally recovers completely and evenly, and most can be restored. In severe layering, there are particles and soft precipitates that can be dispersed; Hard bottom cannot break apart

The main adjustment direction is to increase low shear viscosity: cellulose HASE、 Water based bentonite adjusts pH, thickens and compounds, optimizes the compatibility of additives and dispersants, and provides anti settling and thixotropic additives

Common combinations in reality

Separation of moisture and slight soft precipitation: The most common drawback of ordinary latex paint is insufficient low shear viscosity, and priority should be given to adjusting rheological compounding.

Layering+Hard Precipitation: Dispersant desorption, pigment flocculation, not just viscosity issues, require reassessment of dispersant grade and dosage.

Solvent based epoxy/anti-corrosion paint: It rarely separates water and mainly exhibits delamination and hard precipitation at the bottom, mostly due to insufficient activation and dispersion of polyamide wax.

Quick on-site judgment tips

Open the jar without stirring:

If it’s clear water above, then separate the water

Above is a thin colored paint, below is thick paste → layered

Solid hard lumps can be felt at the bottom of the tank → sedimentation (hard bottom)

Project water separation (precipitation) layer by layer sedimentation (settling)

Typical appearance: A layer of clear water is deposited on the top of the tank, which is divided into a thin layer and a thick layer. The upper layer has a colored thin paint, and the bottom of the tank is piled up with solids, soft sediment/hard bottom

The phase is separated by placing the water phase on top and the thick solid on the bottom

Core causes: insufficient low shear viscosity, overall phase separation of aqueous phase precipitation system, compatibility of lotion additives, gravity sedimentation of heavy powder, pigment flocculation

After stirring, it generally recovers completely and evenly, and most can be restored. In severe layering, there are particles and soft precipitates that can be dispersed; Hard bottom cannot break apart

The main adjustment direction is to increase low shear viscosity: cellulose HASE、 Water based bentonite adjusts pH, thickens and compounds, optimizes the compatibility of additives and dispersants, and provides anti settling and thixotropic additives

Complete solution for coating water separation, layering, and sedimentation

There are three types of problems, including water-based architectural latex paint, water-based industrial paint, and solvent based coatings; Distinguish between formula adjustment, additive adjustment, and process adjustment, and specify what situation is a hard malfunction that cannot be salvaged.

1、 Separate water (clear water separates from the upper layer)

Essence: Insufficient low shear viscosity, water precipitates from the system; High shear viscosity may be normal, but thickening with HEUR polyurethane alone can easily occur.

Formula&Additive Adjustment

Improve low shear viscosity components:

Interior wall latex paint: increase the proportion of HPMC/HEMC cellulose ether or HASE alkali swelling thickener.

High end interior and exterior walls/industrial water-based paint: adding water-based modified bentonite to enhance static thixotropy.

Control the total amount of surfactants: reduce excessive addition of wetting agents and free dispersants. Surfactants can damage the HEUR binding network and exacerbate water separation.

The thickening system prohibits the use of HEUR polyurethane alone; Must be compounded: cellulose/HASE/bentonite+HEUR.

PH check: Maintain a pH of 8.0 and 9.0 in the system. If the pH is too low, HASE cannot thicken and will aggravate water separation.

Process Adjustment

Thickener should be added dropwise at the final stage of paint mixing; Dilute HASE stock solution with 1 to 3 times water and slowly add it, do not pour it all at once.

Do not add water later, as it will damage the rheological network.

Remedial measures for water splitting have already been produced

Slight water separation: Stir evenly at low speed, add a small amount of diluted HASE or water-based bentonite, and adjust the low shear viscosity.

Serious repeated water splitting: only thickening and treating the symptoms without addressing the root cause, it is necessary to modify the formula rheological compound system.

2、 Layered (upper layer with colored thin paint, lower layer with thick paste, not necessarily clear water)

Dividing water is a special case of layering; Layering belongs to overall phase separation, not only viscosity, but also lotion, dispersant pH、 Compatibility of additives.

Formula&Additive Adjustment

Check pH:

The ammonia water system is prone to pH drop during storage, so AMP 95 buffering neutralizer is used to stabilize the pH within the process range.

Check dispersants: Do not use excessive amounts of anionic dispersants; Check for any compatibility conflicts between cationic and anionic additives.

Optimization of rheological system: separate water and supplement low shear and thixotropic components.

Lotion compatibility: if layering occurs after replacing lotion, the brand of dispersant and wetting agent need to be slightly adjusted.

Solvent based coating delamination: check the compatibility of resin, dispersant, and anti settling wax; Polyamide wax is fully activated.

Process Adjustment

Neutralizer should be added in the early stage of grinding, and not concentrated in the later stage of paint adjustment.

It is forbidden to premix and feed multiple additives separately, and separate them with water/lotion in the middle.

remedy

Mild layering: Stir and mix at low speed, retest pH, and add buffer neutralizer and a small amount of bentonite for small-scale testing.

After mixing, there are still particles and flocculent substances: flocculation has occurred, and the entire batch cannot be salvaged and cannot be shipped.

3、 Sedimentation (tank bottom sedimentation, divided into soft sedimentation and hard sedimentation)

3.1 Soft sediment: Soft sediment at the bottom can be dispersed by stirring

Reason: Insufficient thixotropy/anti settling ability, powder gravity settling, and pigment not undergoing chemical flocculation.

Water based system: adding water modified bentonite and appropriately increasing cellulose/HASE; We cannot rely solely on HEUR.

Solvent based (epoxy, polyurethane, alkyd):

Polyamide wax: must be fully activated at 50-60 ℃ and establish thixotropy after cooling; Activation equals zero anti sinking effect.

High filler system combined with a small amount of gas-phase silica or organic bentonite.

Heavy pigments (mica iron oxide, quartz powder, matting powder): Properly increasing anti settling and thixotropic additives cannot rely solely on thickening and viscosity improvement.

3.2 Hard Sedimentation (Hard Bottom): Hard lumps that cannot be dispersed by stirring or high-speed dispersion

Core: Dispersant detachment, secondary coagulation and agglomeration of pigments, simple addition of anti settling agents cannot solve the problem of hard bottom.

Processing Steps

Verify dispersant:

Is the dosage insufficient; Does it not match the pigment; The amount of pigments such as carbon black and iron oxide added should be calculated based on the quality of the pigment, not the total formula.

Grinding process: whether the fineness meets the standard; The pigment aggregates have not been opened, and they will inevitably settle hard in the later stage.

PH drift: significant changes in pH, detachment of anionic dispersants, pigment flocculation; Replace the buffering neutralizing agent.

Excessive surfactant: Excessive wetting agent can displace the dispersant on the surface of the pigment, causing detachment and flocculation.

⚠️ The finished paint with a hard base has already appeared: the hard block has undergone pigment melting and agglomeration, and any additives added on site cannot be salvaged. It can only be scrapped and sent back to the furnace for re sanding.

Key points of general precipitation process

Dispersant should be added at the beginning of grinding, first adding dispersant and then adding powder. It is forbidden to add pigment first and then add dispersant.

Anti settling/rheological additives: added during the grinding stage of bentonite; Polyamide wax needs to be activated; Thickener is added in the later stage of paint adjustment.

Approach to handling combination faults (most common in actual production)

Separation of water+slight soft sediment

Prioritize improving low shear viscosity and thixotropy: increase bentonite/cellulose/HASE and control excessive wetting and dispersing agents.

Layered+Soft Sedimentation

Adjust the pH first, then optimize the rheological compound, and check the compatibility of the additives.

Layered+hard precipitation

It’s not a viscosity issue, dispersion system failure; Repeat the saturation adsorption test of dispersant and optimize the grinding process.

Solvent based epoxy/anti-corrosion paint: almost without water separation, mainly layering+hard precipitation, with a focus on checking polyamide wax activation and dispersant grades.

Small scale validation method (50 ℃ thermal storage acceleration test)

Prepare the test paint and place it in a sealed container. Place it in a 50 ℃ oven for 7 to 14 days.

Observation: Check if there is water flowing from the upper layer (separation of water), if the upper layer is thin and the lower layer is thick (layering), and if there is sediment at the bottom of the tank.

Remove and cool, do not stir, observe the appearance first, then stir at low speed to see if it can be completely dispersed.

If there is a problem with the thermal storage, storing it at room temperature will definitely exacerbate the problem.

Troubleshooting sequence (quick troubleshooting process for production issues)

Observe the phenomenon: distinguish between water separation/stratification/soft precipitation/hard precipitation

Measurement indicators: pH, Stomer viscosity KU、 fineness

Troubleshooting sequence: pH → dispersant dosage and grade → excessive wetting agent → rheological compound system → grinding process