Inspection and Defect Rectification
Inspection questions ask when to check what, which instrument proves it, and how each common defect is diagnosed and cured rather than painted over.
Inspection points
- Before painting: moisture content, dust-free surface, alkalinity, rust removal grade, putty flatness under a straight edge, masking in place.
- During painting: wet and dry film thickness, thinning records, coat intervals, temperature and humidity.
- After painting: visual check under oblique light; adhesion by cross-cut tape test; hardness; gloss and colour uniformity; no sags, holidays, brush marks, pinholes; straight edges at junctions.
Defect diagnosis
- Blistering: moisture in the substrate, resin bleed, or solvent trapped by thick coats. Find the moisture source, strip, dry, re-prime.
- Peeling and flaking: poor adhesion from dust, grease, or the wrong primer on galvanised steel or bare plaster. Remove to a sound edge, feather, re-prime.
- Chalking or washing off: over-thinned paint or interior product used outside. Strip and use an exterior grade.
- Sagging and runs: film too thick or paint over-thinned.
- Cracking: putty laid too thick; keep individual coats to about 1-2 mm.
- Yellowing of alkyds in dark rooms; mildew in damp corners; rust bleeding through from unprimed steel.
Principle
Never paint over a defect. Remove material back to the cause, treat the substrate, then refinish.
Worked example
Emulsion bubbles on a bathroom ceiling. Check the moisture meter - it usually reads high. Trace the leak or ventilation fault, scrape the blisters back to sound film, dry the plaster, seal with a moisture-tolerant primer and finish with washable emulsion. Skipping the source repair means the same blisters return within weeks.
Traps
Blaming the paint when damp is the cause; touching up with a different batch; rejecting a whole job without a written checklist.