Painting is the process of applying a layer of colour or pigment to a surface, such as walls, wood, canvas, or metal, using tools like brushes, rollers, or sprayers. It serves both functional and aesthetic purposes.
Types of Painting:
- Artistic Painting: Used in fine arts to create visual expressions or narratives on mediums like canvas or paper.
- Decorative Painting: Enhances the aesthetics of a space, typically for homes, offices, or public buildings.
- Protective Painting: Applies coatings to surfaces to prevent damage, corrosion, or wear, commonly in industrial or exterior settings.
Benefits:
- Aesthetic Enhancement: Improves the visual appeal of spaces or objects.
- Protection: Shields surfaces from moisture, sunlight, and other environmental factors.
- Customization: Allows for personal expression and design in residential or commercial settings.
Painting combines creativity and utility, making it an essential element in both art and practical applications.
Various Painting Terminology and their definitions should be known to Civil Engineers/Supervisors/Painting Experts:
- Bleeding:
Bleeding in painting refers to the undesirable diffusion of colour or resinous substances from the undercoat into the topcoat, resulting in discoloration or staining of the surface. This problem commonly arises when painting over wooden surfaces or when improper preparation and techniques are used.
Causes:
- Knots in Wood: Substances in the knots of wood dissolve in the paint’s oil and migrate through the surface.
- Improper Sealing: Failure to apply a knotting solution or primer allows substances to seep through the paint layers.
- Undried Undercoat: Applying a topcoat over a not fully dried undercoat leads to colour migration.
- Incompatible Paint Layers: Interaction between certain types of paint, such as solvent-based paints over specific undercoats, can result in bleeding.
Prevention:
- Sealing Knots: Use a shellac-based primer or knotting solution to seal wood knots.
- Proper Drying: Ensure each coat of paint is fully dry before applying subsequent layers.
- Use of Stain-Blocking Primer: Apply a specialized stain-blocking primer before the final coats.
- Surface Preparation: Clean and prepare the surface thoroughly to minimize contamination.
By following these steps, bleeding can be effectively controlled, ensuring a clean and uniform finish.
- Bittiness:
Bittiness refers to a condition in painting where small particles or foreign substances are embedded in the paint or varnish film, resulting in a rough, uneven surface. This defect can occur due to several reasons:
Causes:
- Dirty Surfaces: Dust, dirt, or grease on the surface before painting.
- Unclean Tools: Contaminated brushes, rollers, or other painting tools.
- Polluted Atmosphere: Presence of airborne particles during the application process.
- Paint Contamination: Mixing or stirring old paint containing dried skin or impurities.
Prevention:
- Thoroughly clean surfaces and tools before use.
- Ensure the painting area is free of dust and debris.
- Use strainers to filter paint to remove any skins or particles.
- Store paint cans in a sealed and clean condition.
Proper preparation and attention to cleanliness can significantly reduce the occurrence of bittiness, ensuring a smooth and professional finish.
- Blooming or Blushing:
Blooming or Blushing refers to the appearance of a whitish, cloudy film on the surface of varnish or enamel, often accompanied by a loss of gloss. This defect impacts the aesthetic appeal and can compromise the quality of the finish.
Causes:
- Humidity During Application: Moisture from the atmosphere gets trapped in the varnish or enamel during application, leading to cloudiness.
- Defective Composition: Poor-quality varnish or paint formulation that reacts unfavourably with environmental factors.
- Improper Application: Application of varnish or enamel under unsuitable conditions, such as high humidity, cold temperatures, or inadequate drying times.
- Incompatible Materials: Using materials that don’t bond well together can exacerbate blooming.
Prevention:
- Control Humidity: Avoid painting or varnishing in damp or humid conditions.
- Use Quality Products: Ensure the paint or varnish used is of good quality and suitable for the application environment.
- Surface Preparation: Properly clean and prepare the surface to avoid contamination.
- Additives: Use anti-blooming additives in varnishes where recommended.
Remedies:
- Polishing: Buffing the surface can sometimes restore gloss.
- Reapplication: Strip the affected layer and reapply under proper conditions.
- Controlled Drying: Allow the material to dry in a controlled environment with low humidity.
Addressing blooming promptly is crucial to maintaining the durability and aesthetics of the finish.
- Blistering:
Blistering is a paint defect characterized by the formation of bubbles or swollen spots on the paint film, which often lead to peeling. This occurs when moisture, grease, or volatile substances are trapped beneath the paint layer, causing the film to lose adhesion and swell.
Causes:
- Moisture Trapped Beneath Paint:
- Painting over damp or unseasoned wood.
- Painting on wet surfaces, such as newly plastered walls or ironwork.
- Contaminants on Surface:
- Presence of oil, grease, or dirt on the substrate before painting.
- Failure to prepare knots or resinous areas on wood.
- Improper Application:
- Using gloss or oil-based paints over surfaces that are not adequately prepared, such as damp plaster or poorly primed wood.
- Environmental Factors:
- High humidity or damp conditions during or after paint application.
- Rapid drying of the paint surface due to excessive heat, trapping solvents underneath.
Prevention:
- Proper Surface Preparation:
- Thoroughly clean and dry surfaces before painting.
- Apply primer or sealer on knots or resinous wood.
- Suitable Environmental Conditions:
- Paint in dry conditions with moderate temperatures and low humidity.
- Ensure proper ventilation during and after application.
- Choose the Right Paint:
- Use paints suitable for the specific surface and conditions.
- Avoid non-porous coatings on surfaces prone to moisture.
Remedies:
- Identify and Remove:
- Remove the blisters by sanding or scraping.
- Address the underlying issue (e.g., moisture, grease, or contamination).
- Repaint:
- Allow the surface to dry completely.
- Reapply primer and topcoat with appropriate techniques and materials.
Blistering not only affects the appearance but also compromises the durability of the paint. Proper preparation and application are key to preventing this defect.
- Bleaching or Saponification:
Bleaching or Saponification refers to a chemical reaction that occurs when oil-based paints are applied to highly alkaline surfaces, such as newly plastered walls. The alkalinity reacts with the binders in the paint, particularly oils, leading to saponification—a process that creates soap-like substances.
Effects:
- Discoloration: The paint film loses its color and appears faded or bleached due to the chemical action.
- Softening and Stickiness: The paint becomes soft, sticky, and less cohesive.
- Washability: The weakened paint film can easily dissolve or wash away when exposed to water.
Causes:
- Alkaline Surfaces: New plastered walls contain high levels of lime or cement, making them highly alkaline.
- Incompatible Paint: Using oil-based or alkyd paints without proper priming on such surfaces.
- Insufficient Curing: Painting on plaster that has not been allowed to fully cure.
Prevention:
- Surface Neutralization:
- Allow new plaster to cure for at least 4-6 weeks.
- Wash surfaces with dilute acidic solutions (e.g., vinegar or mild muriatic acid) to neutralize alkalinity, then rinse thoroughly.
- Proper Primer:
- Apply a high-quality alkali-resistant primer before painting.
- Use of Appropriate Paint:
- Opt for water-based paints like acrylic emulsions on newly plastered walls.
Remedies:
- Removal:
- Strip off the affected paint layer completely.
- Neutralization:
- Neutralize the surface alkalinity before repainting.
- Repainting:
- Use suitable primers and paints to prevent recurrence.
Proper curing of plaster and selecting compatible materials are critical to avoiding bleaching or saponification.
- Brush Marks:
When paint is applied with a brush, bristle marks may appear and in some cases these marks are deep and permanent and further aggregate in a glossy surface. This is generally due to unskilled application, sometimes aggravated by unsuitable paint.
- Cracking:
It is the chipping of paint film which is due to the cracks developing throughout the entire paint system and extending right down to the original surface. This is often found on exterior work after long exposure. On interior work, this is due to faulty application of paint and insufficient drying between coats.
- Chalking:
Chalk like substance appears on the painted surface and paint film becomes powder due to insufficient oil in primer (white patches on the surface). This is caused by the effects of sunlight and oxygen in the atmosphere and also by salty air.
- Colouring off or Not Matching:
This is when the dried paint shade does not match.
- Cissing or tiny craters:
Cissing is a defect in which a wet paint film recedes from small areas on the surface leaving them apparently uncoated and tiny craters are visible in the centre of hole on the painted surfaces. This occurs due to painting over glossy, oily or waxy surface or lack of preparation of hard and glossy ground.
- Dry Spray:
Sprayed paint film sometimes dries to a rough gritty finish.
- Erosion:
Erosion is the weathering away of the top layer of a painted surface. It starts with chalking and ends with the removal of paint film in dry powder form.
- Efflorescence:
Efflorescence is the appearance of salt-like deposits commonly observed on masonry substrates.
- Floatation:
During drying, one or more of the pigments separate or float apart from the other and concentrate in streaks or patches on the surface of the film.
- Fading/Spotting:
The total discoloration and loss of gloss is known as fading.
- Feeding or Livering :
Paint thickening to a very high viscosity, one which cannot be reduced by thinning.
- Flaking:
Flaking is the detachment of paint film (the breaking of coating system right from the primer to the top finishing coat) from the underlying surface in the form of flakes or scales.
- Hiding or Opacity:
The ability of a paint film to obliterate the underlying surface is called hiding or opacity.
- Holidays or Misses:
Holidays represent the patches where paint has not been applied.
- Microbial growth:
It is in the form of bacteria and fungus growing on the painted surface.
- Orange peel:
This defect is associated with spray painting. The painted surface will be rough with ups and downs.
- Pin holes:
The formation of very small holes on the paint film during application and drying. It generally occurs on the applied surfaces.
- Patchiness:
The uneven finish or scratch like thing appears on the putty-applied surfaces. Presence of foreign matters in the putty leads to this defect.
- Pattern Staining
The accumulation of dirt on certain broad surfaces, usually ceilings, appearing as light and dark patterns is called pattern setting.
- Poor adhesion
Poor adhesion of paint on the substrate or between different coats of the paint itself can originate.
- Peeling
Peeling is the swelling of paint film that is due to located loss of adhesion between one or more coatings or between primer and parent surface and moisture on the surface. It occurs in non-porous coatings such as oil based paints and enamels.
- Putty
Putty is a kind of paste prepared for applying on walls to fill in any minor dents or surface imperfections.
- Rain-spotting or cratering
These are minute pits, also called craters, on the surface of a dry film.
- Slow drying
This is a defect, which slows down the process of drying the paint film in its required time period.
- Setting
Setting is a condition in which the pigments in the paint separate and settle at the bottom of the container.
- Sagging/run down/tears
A downward movement of the paint film between the time of application and setting (drying) resulting in an uneven coating having a thick lower edge. This excess paint runs down and gives an uneven surface.
- Skinning
Skinning is a term used when the top surface of paint or varnish in a container dries.
- Wrinkling
Surface of the paint wrinkles and gathers together when thick coat of paint is applied. The lower portion of the paint does not dry due to greater thickness of the paint film that shrinks due to drying in course of time. It is more pronounced with enamels and varnishes.
- Yellowing
It is loss of whiteness, which develops the yellow colour on ageing. This is most noticeable on dried film of white paints or clear varnish.