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True stone paint is widely used in new building exterior walls and renovation projects of old residential areas due to its realistic texture, high cost-effectiveness, excellent breathability, and wide adaptability. However, in practical engineering applications, uneven color difference, batch color difference, color difference between the inner and outer surfaces of walls, and color difference between new and old walls are the most common and difficult quality problems in the application of real stone paint, which seriously affect the overall aesthetics of building facades and the quality of engineering acceptance. To systematically solve the problem of color difference in real stone paint exterior walls, this article conducts multivariate traceability analysis from six dimensions: raw material system, formula compatibility, construction technology, environmental factors, post maintenance, and supporting system, clarifying the internal mechanism and external manifestation rules of color difference caused by different variables. By combing the action mechanism of key influencing factors such as natural color sand batch fluctuation, lotion film forming difference, uneven color paste dispersion, spraying thickness deviation, temperature and humidity disturbance, and inconsistent overlay construction, a five in one color difference prevention and control system of “raw material control – formula standardization – construction refinement – environmental adaptation – later uniform color maintenance” is established to form a landing and replicable color difference quality control scheme for stone like paint. The research results can provide theoretical basis and practical guidance for the standardized construction of exterior real stone paint, the control of exterior color uniformity, and the treatment of common engineering quality problems.

1 Introduction

Stone like paint is a kind of sand like stone like paint, which is composed of natural quartz sand and colored ore particles as aggregates, acrylic acid lotion, silicone acrylic lotion and other water-based resins as film forming and bonding substrates, and functional additives. After the coating is cured, it has the rough texture and three-dimensional texture of natural stone, as well as the advantages of light weight, good breathability, strong crack resistance, convenient construction, green environmental protection, and low cost. It is currently the mainstream decorative material for replacing dry hanging stone and ceramic tiles on the exterior walls of buildings, and is widely used in high-rise residential buildings, villas, public buildings, industrial parks, and urban renewal and renovation projects.

However, in a large number of engineering practices, real stone paint exterior walls commonly have problems such as overall discoloration, local color difference, color difference between yin and yang surfaces, color difference between new and old repairs, and batch color difference. Unlike delicate coatings such as sand in water and latex paint, real stone paint is formed by stacking particles to form a film, and its color is formed by the combination of natural colored sand base color, resin filling color, and transparent coating color. It is highly sensitive to fluctuations in raw materials, construction thickness, environmental conditions, and film formation degree. A slight deviation in variables can lead to visible color differences, greatly reducing the overall appearance of the facade, and even causing problems such as engineering rework, failed acceptance, and increased maintenance costs in the later stage.

At present, the treatment of color difference in real stone paint in most projects is mostly limited to post repair and local rework, lacking systematic cause analysis and a pre control system for the entire process. In order to solve the common problem of color difference in real stone paint from the root, this article adopts a multivariate layered analysis method to comprehensively analyze the color difference induction mechanism of raw materials, formula system, construction technology, environmental climate, supporting system, and maintenance stage, clarify the primary and secondary influencing factors, and construct a full process, standardized color difference prevention and control system, providing technical support for improving the quality of exterior wall real stone paint coating and achieving uniform and unified exterior color.

2. Classification of Color Differences and Characteristics of Genuine Stone Paint

By reviewing a large number of exterior wall engineering cases, the color difference defects of real stone paint can be classified into five typical forms, with different types of color differences corresponding to different triggering variables. The specific characteristics are as follows:

(1) Batch color difference: The overall color tone deviation of real stone paint materials from different production batches after spraying is manifested as the overall wall being darker, lighter, yellowish, and grayish, mainly caused by fluctuations in raw material batches and differences in factory color matching;

(2) Local color difference on the wall: The same bucket of material and the same facade may have light and dark spots, block like flowers, which are often caused by uneven mixing, uneven spraying thickness, local bottom leakage, and differences in base color;

(3) Color difference between yin and yang surfaces: The difference in lighting between the sunny and shaded surfaces of buildings, as well as the shaded areas of eaves, leads to visual color difference. At the same time, it is affected by the different speed of dry and wet film formation, resulting in brightness deviation;

(4) Color difference between new and old repairs: There is a clear boundary between the later repair area and the original wall surface, and the degree of coverage, aging, and sand particle density of the new and old coatings are inconsistent;

(5) Late stage color difference: In the initial stage of completion, the color is uniform, but after several months of rain erosion and UV aging, local fading, whitening, and graying occur, which belongs to the long-term color difference caused by insufficient film density and differences in weather resistance.

Multivariate analysis of color difference in real stone paint

3.1 Raw Material Variables: The Core Source of Color Difference

The color system of real stone paint highly relies on natural colored sand, which is also the main source of color difference. Natural colored sand is made by crushing and screening natural ores. There are natural differences in the background color, mineral impurities, and crystal luster of ores from different mines, layers, and mining periods. Even for colored sand from the same manufacturer and color number, there will be slight fluctuations in whiteness, yellowness, and grayscale in different batches, which will be magnified into obvious color differences after stacking into a film. At the same time, uneven particle grading and fluctuation in the ratio of coarse to fine sand particles can cause differences in the density of wall particles, resulting in visual depth deviation.

The performance fluctuation of lotion substrate will also induce color difference. There are batch differences in light transmittance, film plumpness, and resin base color between acrylic lotion and silicone acrylic lotion. When the content of lotion is high, the resin is filled plump, and the coating is dark and bright; When the lotion content is low, the sand grains are exposed more and the coating is dry and white. In addition, small fluctuations in the dispersibility of the color paste and the concentration of the color masterbatch can cause overall color tone shift, resulting in systematic batch color differences.

3.2 Formula and Production Process Variables: Differences in System Stability

The real stone paint system belongs to a high solid content, heavy aggregate, heterogeneous suspension system, and the stability of formula compatibility directly affects color uniformity. Fluctuations in the dosage of thickeners, wetting dispersants, and antifreeze agents in the additive system can alter the suspension state and construction thixotropy of the coating, leading to sedimentation of sand particles, resin enrichment and layering during the spraying process, and uneven local depth after wall application. Insufficient mixing speed and time in production can cause uneven dispersion of the color paste, local accumulation of colored sand, and the formation of hidden color patterns and base colors, resulting in irregular color differences after construction.

At the same time, fluctuations in the moisture content of the system can affect the film-forming shrinkage rate. Coatings with higher moisture content have greater drying shrinkage, more surface pores, stronger diffuse light reflection, and a lighter white appearance visually; The coating has a low moisture content, high compactness, and a darker color, resulting in a phenomenon of different colors on the same wall.

3.3 Grassroots and supporting system variables: color difference induced by background color differences

The base layer of the wall is an important color difference variable that is easily overlooked. Uneven thickness and uneven polishing roughness of exterior wall putty can cause differences in the absorption rate of the base layer. Coarse areas have a higher absorption rate and darker color, while flat and dense areas have a lower absorption rate and lighter color. Local alkali bleeding, whitening, and moisture absorption at the grassroots level can cause the coating of the real stone paint to turn white and flower, forming irregular color spots.

Inconsistent base color between the sealing primer and intermediate coat is also an important cause of color difference. The omission or false application of primer causes alkaline precipitation on the wall, which damages the color stability of the coating; Uneven thickness of the intermediate coat and partial exposure of the base layer can cause the thin layer of the real stone paint to penetrate the base color, resulting in staggered hair defects of varying depths.

3.4 On site construction process variables: the main cause of on-site color difference

The construction process is the biggest variable that causes color difference on site, and it is also the focus of engineering control. Unstable spraying pressure, uneven distance between spray guns, and uneven speed of gun movement can directly cause differences in coating thickness. The sand particles in the thick spraying area are densely packed, the resin is full, and the color is darker; The thin spray area has sparse sand particles, obvious exposed bottom, and a lighter color. Single thick spraying, repeated overlapping spraying, and local supplementary spraying can all cause significant color differences in the color blocks.

Improper mixing methods can also cause color differences. Static storage of real stone paint may result in sand water separation. If only simple stirring is done before construction and the bucket is not thoroughly stirred, there will be a layered color difference of more resin and darker color on the upper part, and more sand and lighter color on the bottom. Directly applying different bucket coatings without mixing them evenly can cause segmented deviation in the overall color tone of the facade.

In addition, improper pasting of dividing seams, improper timing of tearing off paper, pause in local joints, and unnatural connection between new and old construction interfaces can all form linear or strip-shaped color difference marks.

3.5 Environmental Climate Variables: Dynamic Color Difference Disturbance Factors

The temperature, humidity, light, and wind in the construction environment can significantly affect the drying and film-forming speed of real stone paint, inducing dynamic color differences. The surface of the coating dries extremely quickly in a high-temperature and dry environment, and the resin cannot be evenly leveled in time, resulting in a dry and white surface; Under low temperature and high humidity conditions, film formation is slow, and the resin fully infiltrates the sand particles, resulting in a darker and more transparent color. The sunny side of the same facade dries faster and shallower, while the shaded side dries slower and darker, forming a typical color difference between the yin and yang sides.

Construction in windy weather can lead to flying sand during spraying, uneven atomization of paint, sparse and uneven particles on the wall, and overall whitening and whitening; After the rain, the base layer was not completely dried during construction, and the moisture was trapped inside the coating, which later precipitated and caused local whitening, fading, and color difference.

3.6 Cover and Later Maintenance Variables: Causes of Long term Color Difference

Inconsistent application of topcoat is a key factor in color difference in the later stage. Uneven thickness, missed spraying, and virtual spraying of the topcoat can cause uneven glossiness of the wall, with darker glossy areas and lighter matte areas; The difference in light transmittance between different batches of covers will amplify the slight color difference of the original wall surface. Real stone paint without surface protection can accumulate dust outdoors for a long time, be washed away by rainwater, and undergo UV aging. The exposed areas of sand particles will powder and turn white first, while the resin rich areas will have stronger weather resistance. After long-term service, serious aging color difference will occur.

During the maintenance period of finished products, exposure to rain, dust pollution, and external friction can damage the uniformity of the initial film formation, resulting in local fading and discoloration of the wall surface, and permanent color defects.

Summary of Color Difference Formation Mechanism under Multi factor Coupling

The color difference of real stone paint is not caused by a single factor, but rather by the coupling effect of multiple variables such as inherent fluctuations in raw materials, unstable formulation systems, differences in base color, construction process deviations, dynamic environmental disturbances, and inconsistent post maintenance. The raw materials and formula determine the color stability of the coating itself, which is the source of congenital color difference; The uniformity of the wall is determined by the grassroots and construction technology, which is the main cause of color difference on site; The environment and surface maintenance determine the consistency of film formation and long-term weather resistance uniformity, which are the core causes of color difference during later aging. The variables overlap and magnify each other, ultimately resulting in visible defects such as uneven color, blurred appearance, and uneven depth on the exterior facade.

Construction of a refined color difference control system for the entire process

5.1 Raw Material Source Control System

Establish a designated supply and batch sealing system for colored sand. The same mine and batch of colored sand must be used for the same project and on the same facade to prevent fluctuations and color differences in raw materials. Materials entering the site shall be compared with samples in batches, and materials with deviations in grayscale, whiteness, and hue are strictly prohibited from entering the site. Unify the brand and model of lotion, color paste and additives, fix the production formula parameters, lock the lotion content and sand grading ratio, and realize the standardization and homogeneous control of raw materials.

5.2 Factory Production Standardization Control

The solidification production mixing process ensures uniform mixing speed, mixing time, and feeding sequence to ensure that each batch of coating is evenly dispersed, suspended stably, and has no layering or color difference. Each batch of products is made into on-site samples, which are confirmed and sealed by Party A and the supervisor before mass production to ensure uniform color tones for each batch. Strictly control the moisture content of the system and the amount of additives added to ensure consistent thixotropy and film-forming properties of the coating, and eliminate formula fluctuations and color differences.

5.3 Standardized construction of grassroots and supporting systems

Unified exterior wall putty brand and construction times to ensure consistent flatness and roughness of the wall surface; Thoroughly deal with alkali bleeding, hollowing, and powdering of the base layer, neutralize and remove alkali with oxalic acid, reinforce the interface, and prevent color differences caused by base layer defects. The sealing primer is sprayed thinly to cover the entire area without any omissions, and the base color is uniformly applied to ensure that the overall base color is uniform and consistent, eliminating the hidden danger of bottom bleeding from the bottom layer.

5.4 Fine control of on-site construction technology

Before construction, the entire bucket must be thoroughly turned over, and multiple buckets must be mixed evenly to eliminate color differences caused by layering; Standardize the spray gun model, spray pressure, spray distance, and gun speed, strictly implement the construction principle of “thin spraying multiple times, uniform crossing, no joints, and no pauses”, and eliminate uneven thickness and color difference. The same facade shall be completed continuously in one go, and it is strictly prohibited to pause or carry out segmented construction midway; Unified grid pasting and paper tearing timing to ensure neat lines and uniform interface. Establish a model first system, and determine the standard color tone and texture based on the model before large-scale construction.

5.5 Dynamic control of construction environment

Avoid construction in high temperature, low temperature, high humidity, strong wind, and rainy weather, and strictly control the construction temperature and humidity window. To address the differences between the yin and yang surfaces of buildings, fine tune the number and thickness of spraying, balance the speed of dry and wet film formation, and weaken the color difference between the yin and yang surfaces. After rain, it is necessary to wait until the base layer is completely dry and the moisture content of the wall meets the standard before resuming work, in order to avoid residual moisture causing white discoloration in the later stage.

5.6 Closed loop control of cover and finished product maintenance

Standardize the batch, spraying thickness, and number of application times of the topcoat to ensure overall gloss, uniform light transmission, and coverage of subtle base color deviations. Strictly implement the curing period of more than 7 days, and prohibit rain, scouring and dust pollution during the curing period, so as to ensure that the lotion is fully cross-linked and film-forming, and improve the color stability and weather resistance uniformity of the coating. Establish a post maintenance inspection system to promptly and uniformly repair areas that have faded or become discolored, ensuring long-term color consistency of the exterior facade.

6 Conclusion

The color difference of exterior wall real stone paint is a composite quality defect caused by the coupling of multiple variables such as raw materials, formula production, base layer matching, construction technology, environmental climate, and later maintenance. Among them, the fluctuation of natural colored sand batches, uneven spraying thickness, differences in film-forming environment, and inconsistent surface construction are the core dominant factors leading to color difference. Single link control cannot completely solve the problem of color difference. It is necessary to establish a full process color difference control system that includes source material control, standardized production, refined construction, environmental adaptation, and closed-loop maintenance. By solidifying raw material batches, unifying formulation processes, standardizing spraying parameters, balancing film-forming environments, and standardizing surface maintenance, common quality problems such as color difference, discoloration, and mottled on the exterior of real stone paint can be significantly reduced from the root, effectively improving the quality of exterior wall painting projects and the aesthetic of exterior walls. This provides reliable technical references for the green, high-quality, and standardized construction of real stone paint on building exterior walls.

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