ITI/NCVT Painter General (AITT Theory) cheat sheet

Solvent vapour hazard is rated by flash point: liquids with flash point below 23 °C (e.g. acetone, toluene) are highly flammable; keep ignition sources away and bond/earth containers during transfer.

Paint mixing and spraying areas need forced ventilation sized so solvent concentration stays well below the occupational exposure limit; typical thinner exposure limits are in the 100–500 ppm range depending on solvent.

Respiratory protection: use air-purifying respirators with organic-vapour cartridges for low concentrations; use supplied-air or airline respirators for isocyanate hardeners, confined spaces and spray booths without adequate airflow.

Skin contact with two-pack isocyanate hardeners can cause sensitisation; nitrile gloves, coveralls and eye protection are minimum PPE, and barrier cream is not a substitute for gloves.

Fire triangle: fuel + oxygen + heat. Extinguish solvent fires with dry powder, CO₂ or foam; never use a water jet on burning solvent because it spreads the fuel.

First aid: solvent on skin - wash with soap and water, no solvent washing; solvent in eye - irrigate with clean water for at least 15 minutes and get medical help; inhalation - move to fresh air, keep warm and resting.

Paint waste, empty tins and used rags are hazardous waste: drain residues, close lids, store in labelled containers away from heat, and never pour thinners down drains or onto soil.

Lead-based and chromate pigments are toxic; removal by dry sanding or burning frees toxic dust/fume, so use wet methods or dust extraction and approved respiratory protection.

Putty knife (scraper) blade widths commonly range 25–150 mm; flexible blades for filling, stiff blades for stripping; a worn, rounded edge causes ridges and drag marks.

Spatula/trowel for stoppers and fillers should be held at about 30–45° to the surface; a lower angle spreads thicker material, a higher angle leaves a thin scrape.

Paint brushes: bristle (natural) for oil-based and solvent paints, nylon/polyester for water-based; brush sizes are stated by width in mm and thickness.

Wire brush and abrasive paper grades follow grit numbers: lower number = coarser. Typical sequence for bare wood is 60–80, then 100–120, then 150–180 grit.

Shave hook and scraper are used for removing old paint; a shave hook with a triangular blade reaches mouldings and corners that a flat scraper cannot.

Chipping hammer, chisel and needle gun are used for removing rust, mill scale and old coatings on steel; always work away from the body and wear goggles.

Stirring rod and mixing paddle: add hardener to base at the maker's ratio by weight or volume, mix for the stated time, and use a clean container each batch to prevent gel lumps.

Tool care: clean brushes with the correct thinner (water for emulsion, white spirit for oil paint), comb bristles straight, and store handles-down or flat so bristles do not deform.

Steel rule: read to 0.5 mm; always measure from a true edge and keep the rule flat to avoid parallax error.

Vernier calliper least count = 1 main-scale division (1 mm) ÷ number of vernier divisions. For a 50-division vernier, least count = 1/50 = 0.02 mm.

Micrometer least count = pitch of screw ÷ number of thimble divisions; for a 0.5 mm pitch and 50 divisions, least count = 0.01 mm.

Vernier calliper reading = main scale value before the vernier zero + (coinciding vernier division × least count).

Moisture content of wood is measured with a moisture meter; acceptable level for interior painting is usually 12–15 %, and for exterior joinery around 12–18 % depending on specification.

Surface profile (anchor pattern) on blast-cleaned steel is checked with a comparator or profile gauge; typical profile for a protective coating is 50–75 µm.

Wet film thickness is measured with a comb gauge immediately after application; dry film thickness = wet film thickness × volume solids fraction.

Workshop practice: mark with a scriber or pencil, prick-punch hole centres before drilling, and keep files clean with a file card; never use a file without a handle.

New wood: sand along the grain, remove dust, knot and resin pockets sealed with knotting (shellac) before priming; moisture content must be below about 15 %.

New plaster and masonry must be fully cured - typically 4–6 weeks for cement render - before painting; alkali-resistant primer is used where free lime is present.

New steel: remove mill scale, rust and grease; blast cleaning to Sa 2½ is the usual specification for protective coatings, giving a grey-white surface.

Galvanised steel needs a mordant/etch primer (e.g. T-wash or zinc phosphate primer) because the zinc surface is smooth and alkaline, causing poor adhesion.

Aluminium: abrade, degrease and apply an etch or chromate-free conversion primer; bare aluminium forms an oxide film that paint will not grip.

Hand-tool cleaning grades: St 2 = thorough hand and power tool cleaning, St 3 = very thorough; blast grades Sa 1, Sa 2, Sa 2½, Sa 3 in increasing cleanliness.

Previously painted surfaces: wash to remove grease and dirt, sand to key the gloss, feather edges, and spot-prime bare areas; check for lead before sanding old paint.

Concrete floors: check for laitance and moisture; a polythene sheet test (sealed 24–48 h) shows whether moisture vapour is trapped and a moisture-tolerant coating is needed.

Paint = pigment (colour, opacity, corrosion inhibition) + binder/resin (film former) + solvent/thinner (viscosity control) + additives (driers, anti-skin, dispersants, biocides).

Oil paints cure by oxidation and polymerisation of drying oils (linseed, tung); the process is accelerated by driers such as cobalt, manganese and zirconium soaps.

Varnish is a clear coating of resin in oil or solvent; lacquer is a coating that dries mainly by solvent evaporation (e.g. nitrocellulose), so it can be re-dissolved by its own solvent.

Two-pack (2K) products cure by chemical reaction between base and hardener; pot life is the usable time after mixing, and the mix must not be thinned beyond the maker's limit.

Thinners must match the binder: white spirit for oil/alkyd, water for emulsion, xylene/toluene for some epoxy and chlorinated systems, and proprietary thinner for nitrocellulose lacquer.

Volume solids is the percentage of the wet film that remains as dry film; it is used to calculate spreading rate and dry film thickness.

Primer, undercoat and finish have different jobs: primer for adhesion and corrosion inhibition, undercoat for filling and opacity, finish for colour, gloss and weather resistance.

Water-based emulsion dries by coalescence of polymer particles; it must not be applied below the maker's minimum temperature (commonly 5–10 °C) or the film will not form properly.

Brush application gives the best penetration and control for edges, corners and small areas; laying off means finishing with light strokes in one direction for a uniform film.

Roller covers are chosen by pile length: short pile (about 5–10 mm) for smooth surfaces and gloss, medium for walls, long pile for rough masonry.

Spreading rate in m²/L = (volume solids % × 10) ÷ required dry film thickness in µm; this gives the theoretical coverage before loss allowances.

Wet film thickness (µm) = dry film thickness (µm) × 100 ÷ volume solids %.

Practical coverage is lower than theoretical: allow roughly 10–20 % loss for brush/roller and more for spray, depending on overspray and surface texture.

Dip coating and flow coating suit small parts and regular shapes; the film thickness depends on viscosity and withdrawal speed.

Airless spray uses hydraulic pressure (typically 100–250 bar) to atomise paint without air, giving high build and less overspray but requiring tip-size selection by product.

Recoat time is temperature-dependent: too early recoat can lift the previous coat, too late recoat can cause poor intercoat adhesion; follow the product data sheet.

Conventional air spray atomises paint with compressed air; typical gun inlet pressure is 2–4 bar, and fluid pressure and air cap setting control pattern and atomisation.

Spray gun pattern defects: a split or banana-shaped pattern indicates a blocked or damaged fluid tip or air cap horn; a heavy centre shows too little atomising air or too much fluid.

Distance from gun to surface is normally 200–300 mm, held perpendicular, with 50 % overlap per pass and a consistent speed to avoid stripes and sags.

Fluid viscosity for spraying is measured with a flow cup (e.g. Ford No. 4 or DIN 4); typical spraying viscosity is around 18–25 seconds flow time, adjusted with the correct thinner.

HVLP guns transfer paint at high volume and low pressure, giving better transfer efficiency (often above 65 %) and less overspray than conventional guns.

Electrostatic spraying charges the paint so it wraps around the workpiece, giving high transfer efficiency and good coverage of edges, but it needs an earthed workpiece and Faraday-cage areas may need touch-up.

Common spray faults: orange peel from too little thinner or too much air; dry spray from too much distance or too fast a pass; runs from too slow a pass or too much fluid.

Clean the gun immediately after use with the correct solvent, back-flush the fluid passages, and never soak the whole gun in thinner because it damages seals.

Compressor output is rated as free air delivery (FAD) in L/min or m³/min; the spray gun's air consumption must not exceed FAD or pressure and atomisation will drop.

Air pressure at the gun = compressor/tank pressure minus losses through hose length, fittings and filters; use a regulator at the gun for consistent pressure.

Moisture and oil in compressed air cause fisheyes, blisters and poor adhesion; fit a coalescing filter and a refrigerated or desiccant dryer, and drain the receiver daily.

Compressor safety: fit a pressure relief valve and a pressure gauge, drain the receiver regularly to prevent corrosion, and never exceed the rated working pressure.

Spray booth airflow must be from clean to dirty: downdraught booths pull air from the ceiling through a filter floor, keeping overspray away from the wet film and operator.

Booth filters must be replaced when pressure drop rises; a loaded extract filter reduces airflow, raises solvent concentration and increases the risk of dirt in the finish.

Booth lighting should be bright and colour-correct so that colour and film defects can be seen; the booth must be clean, and the floor kept free of dust and paint build-up.

Before spraying in a booth, confirm the extraction is running, the interlock works, and the correct filter media and PPE are in place; never spray in a booth with the extraction off.

Decorative finishes include scumble glazes, rag rolling, stippling, sponging, dragging and marbling; the ground coat must be fully dry before the glaze is applied.

Wood graining: apply a ground colour close to the lightest grain tone, then a glaze or scumble, and draw grain with a graining comb, rubber or brush; overgrain with a fine tool and soften with a badger softener.

Scumble is a translucent oil glaze used over a dry ground to imitate wood grain; it stays workable for some hours and is protected with a clear varnish.

Stencilling: cut the design in stencil card or acetate, apply with a stencil brush using a near-dry stipple motion, and use a different brush or clean edge for each colour to avoid bleeding.

Sign writing: lay out letters with a pencil and rule, keep strokes consistent, and use a mahl stick to steady the hand; enamel sign paints flow out and dry glossy.

Marbling: build veins over a light ground with a sponge or feather, use a softener to blur edges, and finish with a clear glaze for depth.

Gold leaf: apply gold size, let it become tacky (about 12–24 h for oil size), then lay leaf with a gilder's tip and burnish; water size is used for glass and gilding on sized surfaces.

Masking for decorative work: use low-tack tape on freshly painted surfaces, remove tape while the paint is still soft to avoid tearing the film.

Sagging/runs: too much paint, too slow a pass, or too much thinner; remedy by sanding back and recoating with thinner coats.

Orange peel: paint too thick, insufficient atomising air, or wrong thinner; remedy by sanding smooth and spraying with correct viscosity and pressure.

Blistering: moisture trapped under the film or solvent trapped by recoating too soon; remedy is to strip, dry the substrate and recoat with correct intervals.

Fisheyes/cissing: oil, silicone or moisture contamination of the surface or air line; remedy is to clean with a degreaser, filter the air and add a fisheye eliminator only as a last resort.

Chalking: binder breakdown from UV and weather, common with underbound exterior paint; remedy is to clean, remove chalk and recoat with a weather-resistant finish.

Flaking and poor adhesion: inadequate surface preparation, dust or grease, or coating over a glossy surface; remedy is to strip, abrade and prime correctly.

Blooming: loss of gloss and a milky haze from moisture condensing on the film during drying, common with varnish in damp cold conditions; remedy is to rub back and recoat in dry conditions.

Wrinkling: a thick skin dries over a soft underlayer, common with oil paint applied too thickly; remedy is to remove the film and apply thinner coats.

Primary colours of light are red, green and blue (additive); primary colours of pigment are cyan, magenta and yellow (subtractive), with red, yellow and blue used in traditional art teaching.

Hue is the colour name, value is lightness/darkness, and chroma (saturation) is the strength or purity of the colour.

Complementary colours lie opposite on the colour wheel; mixing them dulls the colour and moves it towards grey or brown.

Tinting strength is the colouring power of a pigment; strong pigments such as phthalo blue and carbon black need small additions when matching.

Hiding power depends on refractive index difference between pigment and binder and on particle size; titanium dioxide gives high opacity in white and tinted paints.

Metamerism: two colours match under one light but differ under another because their pigment spectra differ; always match under the specified light source.

Colour matching steps: identify the dominant hue, adjust value with white or black, then adjust chroma with a complementary or neutral; check a drawdown against the standard under standard light.

Pigment classes: inorganic (titanium dioxide, iron oxide, zinc phosphate) are generally light-fast and heat-stable; organic pigments (phthalocyanine, azo) give brighter colours but may be less durable.

Epoxy coatings give excellent adhesion and chemical resistance but chalk under UV; use a polyurethane topcoat for exterior colour and gloss retention.

Polyurethane (PU) coatings based on isocyanate hardeners give good gloss and weather resistance; they require correct mixing ratio and induction time.

Zinc-rich primers protect steel by galvanic action; typical specification is at least 80 % zinc in the dry film, applied over a blast profile of 50–75 µm.

Intumescent coatings swell on heating to form a char layer that insulates steel; the dry film thickness is calculated from the steel section factor and fire rating.

Powder coating is applied electrostatically and cured in an oven; it gives a tough film with no solvent, but the substrate must be able to withstand the cure temperature.

High-build and high-solid coatings reduce solvent emission and can reach 100–250 µm per coat; they need careful thickness control to avoid solvent entrapment.

Heat-resistant coatings use silicone or aluminium pigments; aluminium flake coatings are used on hot surfaces such as exhausts and stacks.

Non-slip and floor coatings use aggregate or a textured profile; the surface must be sound, dry and primed, and moisture tests must be done before sealing concrete.

Corrosion of steel is an electrochemical cell: an anode, a cathode, an electrolyte and an electrical path; coatings break the circuit by sealing the surface.

Barrier protection depends on low permeability and sufficient dry film thickness; thicker films resist moisture and oxygen ingress but must not crack.

Galvanic (sacrificial) protection: zinc-rich primers and galvanising corrode preferentially to protect the steel beneath.

Inhibitive pigments such as zinc phosphate, zinc chromate (now restricted) and tannin passivate the steel surface and slow corrosion at breaks in the film.

Coating life depends on surface preparation more than on the paint: blast cleaning to Sa 2½ removes salts and mill scale and is the single biggest factor in durability.

Total dry film thickness is the sum of the coats; a typical protective system for steel is primer 75 µm + intermediate 100 µm + topcoat 50 µm, giving about 225 µm.

Cathodic disbondment and holiday (pinhole) testing: a spark or high-voltage holiday detector finds breaks in the film on buried or immersed steel.

Coating selection must match the environment: C1–C2 (low) inland, C3 urban/industrial, C4 coastal, C5 marine/offshore, with increasing film thickness and better resin systems.

Area of a rectangular surface = length × width; for walls, measure perimeter × height and subtract door and window openings.

Paint quantity (litres) = total area (m²) × number of coats ÷ spreading rate (m²/L per coat).

Theoretical spreading rate (m²/L) = (volume solids % × 10) ÷ dry film thickness in µm.

Cost of paint = quantity in litres × rate per litre; add labour, scaffolding, surface preparation and consumables to reach the total job cost.

For pipes, external area = π × outside diameter × length; for a cylinder, add the two end areas if they are coated.

Allow for practical loss: add about 10 % for brush and roller, and 20–30 % for spray depending on overspray and shape complexity.

Labour cost = area (m²) × labour rate (m²/h) × hourly rate, or area ÷ daily output × daily wage; always state the assumed output.

Estimate scaffolding and access separately, and add a contingency of about 5–10 % for unforeseen preparation and repairs.

Attendance and punctuality: arrive at the workplace before the shift start, record attendance, and inform the supervisor in advance of any absence.

Workplace discipline means following the job card, the safety permit and the supervisor's instructions, and reporting errors instead of hiding them.

5S housekeeping: Sort, Set in order, Shine, Standardise, Sustain; it reduces accidents and material waste in a paint shop.

Teamwork: share the correct information with the next shift, keep the work area clean, and never leave a mixed two-pack batch unlabelled.

Time management: sequence preparation, priming and finishing so recoat windows are met, and keep a simple record of materials used.

Right to information and grievance: raise unsafe work through the supervisor or safety committee; refuse work that is immediately dangerous to life.

Continuous improvement: record defects and their causes, and suggest changes to tools, mixing or masking that reduce rework.

Basic documentation: fill job cards, material issue slips and inspection records accurately, with date, quantity and signature.

Technical communication should state the product, batch number, thinner, mix ratio and conditions; vague instructions cause coating failures.

Active listening: repeat back the instruction (e.g. the required dry film thickness) to confirm understanding before starting work.

Email basics: use a clear subject line, one topic per message, attach files under the size limit, and do not open unknown attachments.

Computer file management: use meaningful folder and file names, keep a backup, and save work before shutting down.

Spreadsheets are used for estimation: enter area, spreading rate and rate per litre in separate cells and use formulas so changes recalculate automatically.

Safety data sheets (SDS) are read for hazard, first aid, storage and disposal; the sections are numbered 1–16 and Section 2 covers hazards.

Digital measuring and records: photograph completed coats with a dated record, and log dry film thickness readings against the specification.

Password and data hygiene: use unique passwords, lock the screen when leaving, and never share company product data or customer details.