CSLB Painting (C-33) Trade — All Questions

Which roller nap length is best suited for a smooth surface such as new drywall or a fine finish?

• a.1 inch nap
• b.A short nap (about 1/4 inch)✓
• c.1-1/4 inch nap
• d.No nap is ever used on drywall

Short-nap rollers (around 1/4 inch) hold less paint and lay down a smooth, fine finish suited to smooth walls, doors, and trim. Longer naps are for textured or rough surfaces because they reach into the profile. Matching nap length to surface texture controls stipple and coverage.

For a heavily textured surface such as rough stucco, which roller nap is most appropriate?

• a.A 1/4 inch short nap
• b.A 3/16 inch mohair fine nap
• c.A long nap, 3/4 to 1-1/4 inch✓
• d.A smooth foam roller

Long-nap rollers reach into the deep texture of rough stucco or masonry so paint fills the profile and covers evenly. A short nap would skip over low spots and leave voids. The rougher the surface, the longer the nap needed.

What is the difference between an airless sprayer and an HVLP sprayer?

• a.Airless uses fluid pressure, HVLP uses air✓
• b.They are identical in every practical respect
• c.HVLP is only used on exterior masonry
• d.Airless cannot spray latex paint at all

Airless sprayers pump paint at very high pressure through a tip to atomize it, giving fast, high-production coverage on large areas. HVLP uses a high volume of low-pressure air to atomize gently, producing a fine finish with less overspray, ideal for cabinets and trim. Each suits different production and finish needs.

What is the difference between wet film thickness and dry film thickness?

• a.They are always exactly equal in thickness
• b.Wet is measured at once; dry is what remains✓
• c.Dry film is always thicker than the wet film
• d.Wet film only applies to spray work

Wet film thickness is the depth of the coating right after it is applied and is checked with a wet-film gauge. As solvents or water evaporate, the film shrinks to its dry film thickness, which equals wet thickness times the volume solids. Controlling wet film during application is how a painter hits the specified dry mils.

Why should exterior painting generally NOT be done when the surface temperature is below the coating's minimum application temperature?

• a.The paint will dry far too fast in cold
• b.It improves the final gloss level
• c.Cold blocks film formation and curing✓
• d.Cold has no effect on latex paint

Latex paints must coalesce as they dry, and temperatures below the product's minimum (often around 50 F, though some are lower) prevent the film from forming properly. This leads to poor adhesion, cracking, or a weak film. Always check the data sheet for minimum air and surface temperatures.

Why is the dew point important when spray-painting exterior steel?

• a.It determines the paint color to be used
• b.It sets the required film thickness
• c.Condensation forms and ruins adhesion✓
• d.It only matters for interior work

When a surface is at or below the dew point, moisture condenses on it, and painting over that invisible film causes blistering and adhesion failure, especially on metal. A common rule is to keep the surface at least about 5 F above the dew point. Painters monitor temperature, humidity, and dew point before coating.

What is a 'holiday' in spray or brush application?

• a.A missed or thin spot in the coating✓
• b.A scheduled day off the jobsite
• c.An intentionally thick area
• d.A type of shellac primer

A holiday is a skip or missed area where the coating is absent or too thin, leaving the substrate under-protected. Maintaining a wet edge, proper overlap, and adequate lighting helps prevent holidays. They are corrected by recoating the missed area.

What typically causes 'runs' or 'sags' in a paint film?

• a.Applying far too little paint per pass
• b.Applying too much so it flows downward✓
• c.Painting only in cold weather
• d.Using a nap that is too short

Runs and sags occur when too much paint is applied in one pass and gravity pulls the excess down before it sets. They are prevented by applying proper film thickness, maintaining spray distance and speed, and back-brushing or back-rolling. Sags can be brushed out while wet or sanded and recoated once dry.

What causes 'orange peel' texture in a sprayed finish?

• a.Perfect atomization at the spray tip
• b.Applying too many thin coats
• c.Poor atomization or wrong technique✓
• d.Using the correct thinner

Orange peel is a bumpy, citrus-skin texture caused by insufficient atomization, wrong tip size, incorrect pressure, holding the gun too far away, or paint too thick. Correcting pressure, tip, thinning, and distance produces a smoother lay-down. Severe orange peel is sanded and resprayed.

Why is maintaining a 'wet edge' important when brushing or rolling large walls?

• a.It blends strokes into still-wet paint✓
• b.It makes the paint dry a lot faster
• c.It increases the coating's VOC content
• d.It is only ever needed when spraying

Working to a wet edge means each new area of paint merges with an area still wet, so the overlaps blend invisibly. If the edge dries first, the overlap shows as a darker lap mark. Planning the sequence and working quickly across manageable sections maintains the wet edge.

When rolling a wall, what technique helps achieve even coverage and hide roller marks?

• a.Rolling one direction with a dry roller
• b.Load the roller and roll in a W pattern✓
• c.Pressing hard to squeeze the paint out
• d.Using only the very ends of the roller

Loading the roller and spreading paint in a W or M pattern distributes material, and back-rolling with light, overlapping passes levels it and removes heavy spots. Keeping the roller adequately loaded avoids dry, streaky application. Consistent technique produces a uniform stipple and hides seams.

How many coats does a typical high-quality paint job over a properly primed surface usually require?

• a.Always exactly one finish coat
• b.Never more than a single primer coat
• c.At least two finish coats over primer✓
• d.Five or more coats in every case

A standard quality system is primer plus two finish coats, which gives uniform hide, color, and the specified film build. A single finish coat often shows flashing and provides less protection. The exact number depends on color change, substrate, and product recommendations.

Why should you 'back-brush' or 'back-roll' paint that was sprayed onto rough or porous exterior surfaces?

• a.To add gloss to the finished surface
• b.To work the coating into the surface✓
• c.To remove all of the paint again
• d.To increase the amount of overspray

Spraying deposits paint on the surface but may bridge over pores and crevices without wetting them; back-brushing or back-rolling forces the coating into the substrate. This improves adhesion and fills pinholes on stucco, wood, and masonry. It is a common spec requirement on first coats over porous exteriors.

What is the purpose of masking and using drop cloths before spraying?

• a.To protect nearby surfaces from overspray✓
• b.To slow down the drying of the paint
• c.To increase the VOC of the coating
• d.To thin the paint before spraying

Masking with tape, paper, or plastic and laying drop cloths protects windows, floors, fixtures, and neighboring surfaces from overspray, drips, and splatter. This is especially important with airless spraying, which produces significant overspray. Good masking saves cleanup time and prevents costly damage.

High relative humidity during application of latex paint tends to do what?

• a.Makes the paint dry almost instantly
• b.Has no effect at all on drying
• c.Slows drying and extends recoat times✓
• d.Permanently changes the paint color

High humidity slows the evaporation of water from latex paint, extending dry and recoat times and, in extreme cases, causing runs or surfactant leaching. Painters allow extra dry time or avoid coating in very humid or damp conditions. Manufacturers publish acceptable humidity ranges on the data sheet.

What is the correct spray technique for keeping film thickness uniform?

• a.Arc the gun and vary the distance each pass
• b.Hold the gun square at a steady distance✓
• c.Hold it very close and move slowly
• d.Trigger only at the middle of a pass

A uniform film comes from holding the gun perpendicular to the surface, keeping a constant distance, moving at a steady rate, and overlapping each pass by about half. Arcing the gun or changing distance produces uneven thickness and stripes. Triggering at the start and end of each stroke reduces buildup at the edges.

When brushing trim, why is 'tipping off' with light strokes at the end helpful?

• a.It levels the paint and removes brush marks✓
• b.It adds a second color to the trim
• c.It thickens the film to double coverage
• d.It is only done when using a roller

Tipping off means making light, final passes with just the tips of the brush bristles in one direction to level the paint and eliminate heavy brush marks. It produces a smooth, uniform appearance on trim and doors. The technique is done while the paint is still wet.

Why should each coat be allowed to dry for the manufacturer's recommended recoat time before the next coat?

• a.To deliberately waste job time
• b.Coats can be applied with no wait
• c.Recoating too soon traps solvent✓
• d.Waiting changes the paint color

Applying the next coat before the previous one has reached its recoat window can trap solvent, wrinkle the surface, or lift the underlying film. The product data sheet lists minimum (and sometimes maximum) recoat times. Respecting these windows ensures proper drying and intercoat adhesion.

What is 'cutting in' when painting a room?

• a.Cutting the roller cover to size
• b.Brushing the edges a roller cannot reach✓
• c.Scoring the wall with a sharp utility knife
• d.Thinning the paint by half before use

Cutting in uses a brush to paint the edges along ceilings, corners, baseboards, and around trim where a roller cannot go cleanly. The rolled field is then blended into the cut-in border while still wet. Neat cut-in lines are a hallmark of quality work.

Why is adequate ventilation and lighting important during interior application?

• a.Only to keep the painters comfortable at work
• b.Lighting changes the paint chemistry
• c.Light reveals defects; air aids drying✓
• d.Neither affects quality or safety

Proper lighting lets the painter see missed spots, runs, and lap marks so they can be corrected while wet. Ventilation helps the coating dry, reduces the concentration of solvent vapors, and improves safety and comfort. Both contribute to a quality, uniform finish.

A specification calls for 5 mils wet film thickness. Which tool confirms this during application?

• a.A wet-film thickness gauge (comb)✓
• b.A moisture meter
• c.A caliper on the dried paint
• d.A pressure gauge on the sprayer

A wet-film thickness gauge, often a notched comb, is pressed into the fresh coating to read the wet mils applied. This lets the painter adjust technique in real time to hit the target and, with the solids content, the required dry film. Dry film gauges are used after curing to verify final thickness on metal.

What commonly causes 'brush marks' (ridges) to remain in a dried brushed finish?

• a.Using far too much paint thinner
• b.Overworking paint that is setting up✓
• c.Painting in ideal conditions only
• d.Tipping off with light final strokes

Prominent brush marks result from brushing paint that is already tacking up, using the wrong or low-quality brush, or a product with poor leveling. Using a quality brush, proper loading, working in the recoat window, and tipping off help the paint flow smooth. Some paints have leveling additives to reduce marks.

For an oil-based enamel on trim, which brush type is generally preferred?

• a.A synthetic (nylon/polyester) brush only
• b.A foam roller only
• c.A natural-bristle (china bristle) brush✓
• d.Any brush works equally, no difference

Natural China-bristle brushes hold and release oil-based (alkyd) coatings well and give a smooth finish, so they are preferred for solvent-based enamels. Synthetic brushes are used for latex paints because natural bristles absorb water and go limp. Matching brush type to the coating improves the finish.

Why should airless spray tips be selected based on the coating and orifice size/fan width?

• a.Tip size and fan width set flow and pattern✓
• b.Tip size only affects the paint's color
• c.All tips spray every coating exactly the same
• d.Tip choice has no effect on the finish

Airless tips are rated by orifice size (flow) and fan angle (pattern width), and they must match the material's viscosity and the surface. A tip too large for a thin coating floods the surface, while a worn or wrong tip causes tails, stripes, and orange peel. Selecting and maintaining the correct tip is key to a quality sprayed finish.

What is the benefit of 'boxing' (combining) multiple gallons of the same color into one larger container before starting?

• a.It thins the paint out for spray work
• b.It blends batch-to-batch color shifts✓
• c.It increases the coating's VOC content
• d.It makes the paint dry a lot faster

Boxing pours several containers of the same color together and mixes them so any minor shade variation between batches is averaged out. This prevents a visible color shift when one can runs out mid-wall. It is especially important on large jobs and with custom-tinted colors.

An airless tip is stamped 517. What does that number tell the painter?

• a.A five-inch fan and a .17 inch orifice opening
• b.A seventeen-inch fan at any working distance
• c.A five-thousand psi rating and a .17 gallon per minute flow
• d.A ten-inch fan and a .017 inch orifice✓

The first digit is half the fan width in inches sprayed about a foot from the surface, and the last two digits are the orifice in thousandths, so a 517 gives a ten-inch fan through a .017 opening. Reading the first digit as the fan width itself halves the pattern size. The number does not describe a seventeen-inch fan. Tip numbers describe pattern and orifice, not pressure rating or flow in gallons.

A painter is spraying interior doors and wants a controlled pattern with less overspray. Which tip change helps?

• a.A larger orifice with a wider fan width
• b.The same orifice with the pressure raised
• c.A smaller orifice and a narrower fan width✓
• d.A larger orifice with the pressure lowered

Small work calls for less material and a tighter pattern, so a smaller orifice and narrower fan give control and reduce the cloud. A larger orifice with a wide fan floods a door and puts paint everywhere else. Raising pressure with the same tip increases atomization and overspray. A large orifice at low pressure atomizes poorly and produces tails.

A tip that sprayed a twelve-inch pattern now sprays about eight inches and the film looks heavy in the middle. What is happening?

• a.The tip is worn, so the pattern narrowed and flow rose✓
• b.The pump pressure has drifted upward during the day
• c.The paint has thickened and needs additional thinner
• d.The gun filter has clogged and is restricting the flow

Orifice wear erodes the tip into a rounder opening, which narrows the fan and passes more material, so film build climbs in a shrinking band. Rising pressure would widen the pattern, not narrow it. Thicker paint tends to produce tails and a narrow ragged pattern rather than a heavy uniform stripe. A clogged filter starves the gun and reduces flow.

The spray pattern shows heavy tails at the top and bottom of each pass. What is the first correction to try?

• a.Reduce the pressure to soften the edges of the pattern
• b.Move the gun closer to the surface to fill in the tails
• c.Add a second finish coat to cover the tails from the first
• d.Increase the pressure until the pattern is a uniform fan✓

Tails mean the material is not fully atomizing, so raising pressure into the product's atomizing range is the first move, followed by checking for a worn tip, a clogged filter, or a too-thick material. Lowering pressure worsens atomization. Moving closer floods the center without fixing the pattern. Recoating over an uneven film keeps the defect in the system.

An operator sets the airless pump to maximum pressure by habit on every job. What are the consequences?

• a.Better hide because more material reaches the surface
• b.Slower tip wear because the material passes through more easily
• c.More overspray, faster wear, and lower transfer efficiency✓
• d.Lower material use because the coating atomizes more finely

Running higher than needed blows material into the air, accelerates wear on the tip and packings, and lowers the fraction of paint that lands on the wall. Hide comes from film thickness on the surface, which overspray reduces. High velocity through the orifice increases wear rather than reducing it. Finer atomization at excess pressure means more paint drifting away.

Why is the tip guard on an airless gun a required part of the equipment rather than an accessory?

• a.It keeps the tip aligned so the fan stays perpendicular
• b.It filters the last of the debris before the material reaches the tip
• c.It reduces overspray drift by shaping the edges of the fan
• d.It keeps the operator's body away from a stream that can inject through skin✓

Airless streams leave the tip at pressures that can penetrate skin and inject paint into tissue, and the guard exists to keep hands and fingers out of that zone. Alignment is set by seating the tip in the housing. Filtration happens at the gun and manifold filters. The guard does not shape the spray pattern.

A painter needs to clear a clogged airless tip. What must happen first?

• a.Reverse the tip and trigger the gun against a rag to blow it clear
• b.Raise the pressure and trigger the gun until the clog passes
• c.Loosen the tip housing slightly while the pump is still running
• d.Engage the trigger lock and run the pressure relief procedure✓

Any time the gun is opened or serviced, the trigger is locked and the system is depressurized, because a hose can hold injection-level pressure with the pump off. Triggering into a rag still puts a hand near the stream. Raising pressure to blast a clog is how injection injuries happen. Loosening fittings under pressure sprays material at whatever is in front of it.

The airless gun sputters and the pattern starves even though the pump is cycling. Where should the painter look first?

• a.At the gun, manifold, and inlet filters for clogging✓
• b.At the tip size, which is probably too small for the material
• c.At the paint, which probably needs to be thinned by half
• d.At the hose length, which is probably too short for the pump

Starved flow with a cycling pump usually means the material is being restricted, and the filters are the cheapest and most common restriction to check. An undersized tip reduces flow smoothly rather than causing sputter. Halving viscosity with thinner is both excessive and a VOC problem. Short hoses reduce pressure drop rather than causing starvation.

A crew will spray latex through a long hose run to reach a third-floor elevation. What should be anticipated?

• a.Pressure drop along the hose, needing more pressure at the pump✓
• b.Faster atomization because the material has more time to shear
• c.A lower pump setting because gravity assists the flow uphill
• d.No change, because airless pressure is constant along the hose

Every foot of hose and every foot of lift costs pressure, so long runs need a higher pump setting or a larger diameter hose to keep the material atomizing at the tip. Time in the hose does not atomize anything. Lifting material uphill costs pressure rather than saving it. Pressure is not constant along a hose carrying flow.

Why does a painter begin the gun's motion before pulling the trigger and release it before stopping?

• a.To avoid a heavy wet edge at the start and end of a pass✓
• b.To keep the pump from cycling more often than necessary
• c.To let the tip clear itself of debris between passes
• d.To reduce the wear on the trigger mechanism over a long day

Triggering while the gun is already moving keeps the deposit even, because a stationary trigger pull dumps material in one place and causes sags at both ends of the stroke. Pump cycling follows demand and is not the reason. Debris is handled by filtration, not by trigger timing. Trigger wear is trivial next to the finish defect.

A cabinet shop wants a fine finish with the least material waste in a small booth. Which method fits best?

• a.HVLP spraying, using a high volume of low-pressure air✓
• b.Airless spraying at maximum pressure with a wide tip
• c.Conventional high-pressure air spraying with a siphon cup
• d.Roller application with a foam cover and a flow additive

HVLP was developed for high transfer efficiency and fine atomization on small work, which is exactly the cabinet case. Airless at maximum pressure with a wide tip is a production method that wastes material on small parts. Conventional high-pressure air spray atomizes finely but has poor transfer efficiency. Rolling cannot match a sprayed cabinet finish.

A contractor sprays high-solids coatings on large commercial walls but wants less overspray than a conventional airless produces. What equipment addresses that?

• a.An HVLP turbine unit with a one-quart cup
• b.A conventional air gun with a pressure pot
• c.An airless with a larger tip and higher pressure
• d.An air-assisted airless gun✓

Air-assisted airless keeps airless production while using a small amount of air to soften the pattern edges, cutting overspray and improving the finish. A cup-fed HVLP turbine cannot keep up with large wall areas or high-solids material. A conventional air gun trades production and efficiency away. Bigger tips at higher pressure move the job in the wrong direction.

A stucco wall is being sprayed and the finish looks acceptable, but a specification requires the first coat to be back-rolled. What does the roller accomplish that the spray does not?

• a.It increases the wet film thickness beyond what was sprayed
• b.It removes the excess material and lowers paint consumption
• c.It works the coating into the surface texture and pinholes✓
• d.It raises the sheen of the finished wall

Sprayed material can bridge over the peaks of a rough surface, and back-rolling drives it into the valleys and pinholes so the film is continuous and bonded. Back-rolling redistributes material rather than adding thickness. It does not reduce consumption; a stucco wall consumes more, not less. Sheen is a coating property, and back-rolling tends to flatten it slightly.

A crew is spraying an exterior on a breezy afternoon and a neighbor's car is parked twenty feet downwind. What is the correct decision?

• a.Continue spraying and offer to buff the car if it is affected
• b.Continue spraying with the pressure raised for finer atomization
• c.Stop spraying or shield the work until the car is safe✓
• d.Continue spraying but switch to a lower-VOC coating

Overspray drift on a vehicle is an expensive claim and drifting paint is a nuisance and a compliance issue, so the work stops until the exposure is controlled. Promising to fix damage afterward accepts a loss that was avoidable. Raising pressure makes finer droplets that drift farther. VOC content has nothing to do with where the droplets land.

A production crew must repaint 12,000 square feet of smooth interior walls in a vacant building on a tight schedule. Which method fits?

• a.Brush application, which gives the highest quality on flat walls
• b.Spray and back-roll, which combines speed with a consistent film✓
• c.Roller application alone with a short-nap cover on every wall
• d.Spraying alone with no back-rolling to save the additional labor

On large open areas, spraying moves the material fast while back-rolling levels it and forces it into the surface, which is why the pair is standard on vacant production work. Brushing flat walls at that scale is not economically defensible. Rolling alone works but cannot match the schedule. Spray alone risks uneven build and holidays on the first coat.

A brand-new roller cover leaves lint in the first wall of an enamel job. What should have been done?

• a.Load the cover heavily so the lint is carried into the film
• b.Roll the first wall quickly so the lint does not settle
• c.Use a longer nap, which sheds less than a short nap
• d.Pre-wet and de-lint the roller cover before loading it✓

New covers carry loose fiber that comes off in the first pass, so wrapping with tape or washing and spinning the cover removes it before it lands in a finish coat. Heavy loading does not stop shedding; it just distributes the lint. Speed has nothing to do with fibers leaving the nap. Nap length is unrelated to whether a new cover sheds.

A painter rolls a large wall in one direction only and lap marks show under side lighting. What technique corrects it?

• a.Apply the paint with heavier pressure to force it to level
• b.Use a shorter nap and roll faster to outrun the drying
• c.Apply a third coat to bury the lap marks under fresh film
• d.Distribute the paint, then lay off in a single direction✓

Spreading the material first and then laying off in one direction with light, overlapping strokes produces a uniform stipple with the wet edge maintained. Pressing hard squeezes the cover dry and starves the film. A short nap and speed do not solve an edge that dried before the next pass met it. Another coat repeats the same technique and the same marks.

After painting a room, a distinct band of different sheen shows where the brush cut-in meets the rolled wall. What is that defect called and what causes it?

• a.Flashing, caused by the primer having been applied too thinly
• b.Burnishing, caused by cleaning the wall too soon after painting
• c.Picture framing, caused by the brushed film differing in thickness and texture✓
• d.Blocking, caused by two coated surfaces contacting before cure

Picture framing is the visible border where the brushed cut-in reads differently from the rolled field, and it is minimized by cutting and rolling wet into wet and rolling as close to the edge as the tool allows. Flashing from thin primer would show as blotches over patches rather than a border. Burnishing is a shiny scuffed spot from rubbing. Blocking is two painted surfaces sticking together.

A touch-up on a flat ceiling shows as a visible patch even though the paint came from the original can. What is the most likely cause?

• a.The paint separated in the can and changed color
• b.The touch-up was applied with a different tool and film thickness than the field✓
• c.The ceiling had not fully cured when the touch-up was applied
• d.The touch-up paint was applied at too low a temperature

Touch-up visibility comes mostly from a difference in application: a different nap, a different film thickness, or a brush against a rolled field changes how light reflects. Stirred paint from the same can matches in color. Cure state affects adhesion far more than appearance. Temperature affects film formation without producing a patch outline on its own.

A crew is rolling a south-facing stucco wall at 2 p.m. in July and lap marks appear within minutes. What is the practical fix?

• a.Move to the shaded elevations and return when it is cooler✓
• b.Add water to the paint until it stays open longer in the heat
• c.Switch to a longer nap so more material goes on at once
• d.Roll smaller sections while pressing harder on the roller

Hot surfaces flash the water out of latex before the next pass reaches the edge, and following the shade around the building is the standard field answer. Adding water beyond the label limit weakens the film and is a compliance risk. More material on a hot wall still skins over between passes. Pressing harder starves the cover and worsens the marks.

A dark stucco wall in full sun reads 130 degrees at the surface. What should the painter do?

• a.Wait until the surface temperature is within the stated range✓
• b.Spray a mist of water on the wall and paint immediately after
• c.Apply the coating at double thickness so it stays wet longer
• d.Add a retarder to the paint and continue coating in the sun

Products publish a maximum surface temperature because above it latex flashes rather than coalescing, so waiting for the wall to cool is the correct call. Wetting the wall puts water under the film. A double film on a hot substrate skins over the top and traps water beneath. Retarders help modestly but do not license working outside the stated range.

An exterior job is scheduled for a day when the afternoon is warm but the temperature falls sharply after sunset. What is the risk to a late-afternoon coat?

• a.The film will cure too quickly and lose its gloss overnight
• b.The film may not coalesce before the temperature drops✓
• c.The film will absorb dew and become permanently glossy
• d.The film will develop a stronger bond because it dries slowly

Latex needs time above its minimum film-formation temperature, and a coat applied late can be caught by falling temperature and condensation before it has coalesced, leaving a weak, spotty film. Cooling slows cure rather than accelerating it. Dew on an uncured latex causes surfactant streaks and dulling, not permanent gloss. Slow drying below the minimum temperature weakens the film rather than strengthening it.

On a cool morning the exterior siding is damp with dew although the sun is out. When can coating begin?

• a.After the surface has dried and warmed above the product's minimum temperature✓
• b.Immediately, because the coating will absorb the light surface moisture
• c.After wiping the siding with a dry rag to remove the visible moisture
• d.Immediately, if a solvent-borne primer is used instead of a waterborne one

Dew is a surface water film that breaks adhesion, so the wall must be genuinely dry and up to temperature before the first coat. Waterborne coatings do not absorb dew harmlessly. Wiping a whole elevation dry is impractical and leaves moisture in the substrate. Solvent-borne products are, if anything, less tolerant of a water film beneath them.

A two-component epoxy data sheet lists a maximum recoat time as well as a minimum. What happens if the second coat goes on after the maximum?

• a.The second coat will bond even better to the fully cured first coat
• b.The first coat must be completely removed and reapplied
• c.The maximum applies only to spray application, so brushing is unaffected
• d.The cured surface must be abraded, or the second coat may not bond✓

High-performance coatings bond chemically within a window, and after it closes the surface has to be mechanically abraded to create a mechanical key. A fully cured epoxy is harder to bond to, not easier. Removal is a costly overreaction when abrasion is what the data sheet calls for. Recoat windows apply regardless of application method.

A painter finishes bedroom doors on Friday and the owner closes them Saturday morning. On Monday the paint has pulled away where the door met the jamb. What happened?

• a.The film was applied too thinly and tore under its own tension
• b.The film blocked, since it was not cured enough to resist pressure✓
• c.The doors were painted in humidity that softened the enamel permanently
• d.The primer and finish were incompatible and separated at the edges

Blocking is the sticking of two coated surfaces pressed together before the film has cured, which is why enamels list a block-resistance time longer than the touch-dry time. A thin film does not tear from tension on its own. Humidity slows cure rather than permanently softening a properly formulated enamel. Incompatibility would show over the whole surface, not just at contact points.