According to Porter's Paints: paint problem solver & advice

generate bubbles
Air bubbles are created in the paint film, resulting in a localized loss of adhesion.
possible reason
– Substrate humidity is too high
– Paint on soiled or decayed substrates
– Paint on overheated substrates or expose to direct sunlight
– poor working or drying conditions (e.g. high humidity, condensation, rain)
solution
– Identify the cause and extent of the problem. Resolve the cause, strip off the old paint, make sure the substrate is properly repainted. (Some substrates are too damaged to be repaired, such due to replacement)

block
The surfaces of two freshly painted objects are glued together (eg a window is glued to a frame).
possible reason
– Close doors and windows before paint dries.
– poor working or drying conditions (e.g. low temperature, high humidity, condensation, rain)
solution
– Sand to remove affected area, repaint after ensuring proper substrate.
– Provide correct drying time according to paint label recommendations.
– Make sure the workmanship and drying conditions are in accordance with the manufacturer's recommendations.

Oil sweep/oil reel marks
Unintentional texture left in paint by an oil sweep or reel.
possible reason
– Painted with low quality/incorrect tools.
– Poor workmanship (eg too fast or too much paint).
– Repaint or reroll partially dried paint.
– poor working or drying conditions (e.g. overheated substrate, high temperature)
solution
– Lightly sand affected area until smooth, repaint
– Use consistent painting techniques (such as applying oil reel pressure evenly from top to bottom) while keeping the edges wet.
– Make sure to use high quality and recommended tools and equipment.
– Make sure the workmanship and drying conditions are in accordance with the manufacturer's recommendations.
– In hot or windy conditions, the recommended amount of thinner can be added to improve workmanship.

chalk
Powder on the surface of the paint film, produced by the degradation of the paint binder.
possible reason
– Use interior grade paint on surfaces exposed to UV radiation.
– Surfaces where the painted surface has been fully exposed to strong sunlight for a prolonged period of time, and/or has an elevated salt concentration (eg coastal areas).
– Use dark paint, which absorbs more heat and UV rays from sunlight than lighter colors.
– Paint lighter than recommended thickness.
solution
– Wash the affected area, remove all surface contamination and powder, and repaint with a UV–resistant paint system.
– Make sure to paint to the recommended coverage.
– To minimise chalking, have a maintenance schedule in place from the outset to ensure that painted surfaces are cleaned and repainted within scheduled times.

weathering
The salt migrates to the surface of the porous masonry substrate, forming a white scabbed deposit.
possible reason
– Excessive moisture in the substrate
– Paint on under–cured substrates.
solution
– Use a stiff brush to remove deposits, then clean the surface with a mild white vinegar solution (acetic acid). In severe cases, a stronger acid solution should be used by an experienced contractor to remove mineral salts and then allowed to dry.
– Identify and eliminate the source of moisture and repaint once the surface is intact, clean, dry and free of mold and algae. Alkali–resistant sealants and a suitable topcoat are recommended.

fade
Excessive tarnishing of the paint coat.
possible reason
– Use interior grade paint on surfaces exposed to UV radiation.
– The painted surface is exposed to high salinity (e.g. coastal areas).
– Colors such as bright blue, yellow, red are particularly susceptible to UV radiation.
– Add a colorant higher than the recommended coloring level.
– The paint film used is lower than the recommended thickness.
solution
– Thoroughly clean the affected area, remove all surface contamination and repaint.
– Use manufacturer–approved UV–resistant paint products and coating systems.
– Make sure to paint to the recommended coverage.
– To minimise fading, have a maintenance schedule in place from the outset to ensure that the painted surfaces are cleaned and repainted within the scheduled time.

foaming/foaming
Air bubbles formed during application and pits created when air bubbles burst in the paint film.
possible reason
– Painting with improper tools (eg oil reel fuzz length, material type).
– Poor workmanship (eg too fast or too much paint).
– Over–mix the product before use.
– Paint with old and/or improperly stored paint.
solution
– Make sure to use the correct application equipment and technology. If you notice excessive foaming in the can, allow the paint to settle before using.
– Correct foam in dry paint film, lightly sand affected area to a smooth surface and repaint. In some instances, lather in the wet film can be corrected by light application with a brush.

wear and tear
When the painted surface is worn or impacted, visible shiny spots or areas of polishing can appear.
possible reason
– Use low–gloss, matte and flat paint in heavy tones (dark or vivid), especially in high–traffic areas
– Fang.
– Frequent cleaning and/or spot cleaning, especially with abrasive cleaners or tools (wire balls).
– Unintentional bumps on painted surfaces (eg furniture rubbing coatings).
– Critical or low angle lighting may accentuate any worn look that has a chance.
solution
– Repaint with higher gloss or lighter color paint.
– In some instances, a durable clear coat may be recommended.

mold
Black, grey, brown spots on the painted surface.
possible reason
– Presence of moisture (condensation in the substrate, surface or high humidity).
– Paint on moldy substrates.
*TIP: Test for mold by putting a few drops of household bleach on the discolored area; if it disappears, it's likely mold.
solution
– To get rid of mold, scrub the surface with a diluted household bleach solution (one part bleach, three parts water) while wearing rubber gloves and goggles. Rinse thoroughly.
– To prevent mold, use paint with anti–mold properties.

crack
Deep, irregular cracks in the dry paint film.
possible reason
– Applying too much paint causes the surface of the paint film to dry faster than the rest (most commonly where paint can overlap, such as corners).
– Poor working or drying conditions (e.g. too cold substrate, too low temperature).
solution
– Sand the surface flat and repaint at the recommended coverage.
– In some instances, oil–based primers or high–concentration products may be required.
– Ensure application and drying conditions comply with manufacturer's recommendations

Rusty nail head
Red/brown rust on painted surfaces.
possible reason
– Paint on ungalvanized iron nails, which tend to rust in wet environments.
– Paint on galvanized nail heads that have started to rust from sanding or excessive weathering.
solution
– Wash off rust, sand nail heads, and follow new construction finishing procedures.
– When painting new exterior construction, if non–galvanized nails are used, it is advisable to countersink the nail head first and then caulk with a good quality exterior acrylic caulk.
– Each nail head area should be topically primed (preferably with an antifouling primer) followed by a good quality topcoat.

patch
Poor gloss or color uniformity, especially when looking flat from an angle.
possible reason
– Paint on surfaces with different textures and uneven porosity (joints between plasterboards).
– Failure to properly prime the substrate.
– Inconsistent workmanship
– Bad working or drying conditions (eg high temperature, high temperature).
solution
– Before applying the topcoat, the new substrate should be treated to ensure uniform porosity of the substrate.
– Use consistent painting techniques (such as applying oil reel pressure evenly from top to bottom) while keeping the edges wet.
– Make sure the workmanship and drying conditions are in accordance with the manufacturer's recommendations.

Cracking and peeling
The paint film forms a definite fracture, the local adhesion between the paint film and the substrate is lost, or the paint film is completely separated from the surface substrate.
possible reason
– Paint on unsound substrates (e.g. weathered wood, weak concrete or plaster)
– Paint on soiled or loose materials.
– Paint on overly smooth surfaces that are difficult to bond.
– No precoat (primer) used, poor quality or the wrong type for the substrate.
– Lack of maintenance of existing paint
solution
– Before starting any new paint, the extent and cause of the problem needs to be clearly identified, the cause removed, and the old paint stripped until the substrate is sound.

framing
A matter of appearance, areas where you paint with an oil brush look brighter or darker than areas where you use an oil reel.
possible reason
– Apply wet paint on dry or semi–dry areas
– Differences in gloss and/or surface texture due to different workmanship between oil brushes and oil reels.