1. Spokane Community College
Finishes
Materials & Guns
Spokane Community College
Airframe

2. Paint types Synthetic enamels Common for cars
Good gloss and do not require rubbing out
Chemical resistance is nominal and not very abrasion resistant
APPLICATION Thin to viscosity
Light mist coat
Full wet cross coat
Mask and tape within 48 hours
Acrylic Lacquer
Production line aircraft
Touchy to apply
APPLICATION
Primed with 2 part wash primer and once essentially dry –
Sprayed with acrylic lacquer
Light tack coat
Three –minimum – cross coats
Use many thin coats as opposed to heavy coat – will orange peel
Final gloss coat – one part retarder to three parts thinner – flows out better
Polyurethane
Most durable and best look
Wet look
Chemical Resistant
Twice as many solids as acrylic
Slow flowing resins – flow out better
Primer – use proper matched to the paint – critical component of the system
Mix polyurethane and catalyst – let stand before application (15 to 30 minutes)
Stir in reducer – use viscosity cup – dip in paint, time the stream, first break flowing out of the hole is the viscosity measure
Adjust reducer accordingly
Spray VERY LIGHT tack coat
Thinner evaporates – heavy wet cross coat – BEWARE – easily sprayed on too thick
Continues to flow after application – take several days to stop flowing
Can tape within 5 hours but best to wait 24 hours
Six to eight hours pot life
Do not let dry in the gun
Acrylic Urethanes
Advantage of acrylic and urethane
Easy to apply
Same characteristics of urethane
Usually clear coat

3. Finishing Materials
Choosing materials is an issue of performance, then preferences than need.
PRIMERS
Metal prime bonds metal and top coats
Zinc chromate – preferred in the past
Now matching epoxy primers to the paint
Wash primer
Cures quickly
Acrylic or enamel topcoats directly over after as little as ½ hour but no more than eight hours before finish - Industrial aircraft and sea planes then need a coat of epoxy primer
Three component
One part acid– if cannot final coat within 8 hours, apply another coat omitting the acid also when applying over fiberglass or plastic.
Four parts thinner up to eight as required
Four parts primer
Apply thin coat – will not hide the surface but will cast a hew
MUST HAVE SUFFICENT MOISTURE IN THE AIR – Use comparison between wet and dry bulb temp to find proper humidity according to the chart given –
WET BULB – wrap damp cotton wick around the bulb of one and spray with air from spray gun – compare the readings and use the chart
If there is not enough water in the air – in some cases you can add water to the thinner – at least in the case of wash primer

4. Special Finishes and Finishing Products
High visibility
Wrinkle Finish
Flat black lacquer
Wing walk compound
Acid proof paint
Float bottom compound
Fuel tank sealer
Seam paste
High visibility
Vivid color finishes
Used for select areas on aircraft
Transparent finish over white reflective base coat
Wrinkle finishes
Rough treatment areas – best method is baked once applied
Flat black lacquer
Non reflective for instrument panels, glare shields and props
Spray thin so they do not gloss in areas
Wing walk compound
Sand in enamel material
Brush or putty knife
Acid proof paint
Battery boxes – essentially tar – treat with Alodine before application
Float bottom compound
Similar to acid proof paint – may add aluminum powder to give aluminum finish
Fuel tank sealer – Sloshing compound – I DON’T LIKE!
Seam Paste - chromate material for joints in seaplane hulls, floats, fuel tanks – PRO SEAL – will not harden

5. Special Finishes and Finishing Products - Continued
Engine enamel
Heat resistant aluminum paint
Rot inhibiting sealer
Spar varnish
Tube oil
Thinners and reducers
Rejuvenator
Spot putty and sanding surfacer
Engine enamels – color fast under heat except Lycoming grey and Continental gold
Heat resistant aluminum paint – Exhaust system s and heater shrouds – high aluminum content – 1,200 degrees
Rot inhibiting sealer – alkyd resin and fungicidal materials – treat before varnish
Spar varnish – pheonlic modified varnish – cures by oxidation
Tube oil – raw linseed oil – protects the inside of tubular structures – VERY FLAMMABLE
Thinners and reducers – Use only what is recommended by the manufacturer
Butyrate dope thinner can be used with nitrite dope, nitrite can not be used with butyrate
Retarders – thinner that dries slowly
Anti blush thinner – between regular thinner and retarder – still slows drying process
Acetone – universal solvent and cleaner
Rejuvenator – softens dope and flows the cracks back together
Spot putty and sanding surfacer – fill surface irregularities

6. Viscosity and measuring
Agitate paint before mixing – do not use electric drill and paddle
Measure viscosity with viscosity cup
Impart thinner as required to achieve proper viscosity

7. Spray gun adjustment Suction cup vent hole must be open
Adjust air regulator to achieve proper pressure at the gun WHILE THE AIR IS FLOWING
“The amount that the air valve is open determines the shape of the spray pattern. When there is no airflow through the wing ports, the pattern is round and as the airflow increases, the pattern flattens out.”

8. Spray Gun Operation
Pulling the trigger allows air to flow out of the center hole in the air cap
Continuing to pull back on the trigger moves the fluid needle back so that material can be pulled up and sprayed out with the air
As the fluid exits, it atomizes
Adjusting the wing port adjustment valve – allows air to flow out of the holes in the wing ports. Air blows against the stream of material and determines the spray pattern
Desired is a uniform fan shaped pattern with the fan perpendicular to the wing ports
If the pattern is heavy on the top or the bottom – some of the holes may be plugged or reduced

9. HVLP guns and other systems
HVLP – Lower paint velocity
Set at psi gun
Greater application control
Environmentally friendly
Less overspray
Electrostatic system
Minimum overspray
Metal and some wood only
Attracted electrically to the grounded work piece
75% transference rate
Buildup in curves and small cavities
Also rubber, ceramic and glass cannot be grounded and will not attract paint
Powder Coating
Ferrous material application only
Tough material – good holding characteristics – Heat resistant
Must be baked
Dry look

10. Spray gun styles Read the instructions to the gun and follow
Suction guns – Low pressure across draws paint from canister
Hole in canister allows low pressure draw
Pushes the paint across the into the needle valve
Pressure guns
Fluid is delivered to the gun under slight positive pressure
Slide

11. Pressure pots Pressure pots - large volume application
Air pressurizes paint to gun
Often include mixer
Airless guns – High fluid velocity – small nozzle
Paint is atomized by high velocity
Large volume of painting in short period of time

12. Respirators and Masks
Respirators - Do not use dust respirators – remove particles
Charcoal – O.K. for limited application
Air flow respirator – much preferred – also protects eyes

13. Spray pattern
Too heavy in the center – too thick material or too much material
Close the fluid valve – if not – thin the material
If the spray pattern slits or is too thin in the middle - too much air through the wing ports – close the spreader adjustment
Jerky /intermittent spray – air leak or too little material in the cup
Bananana shape – wing port plugged – clean out
Too much overspray – too much pressure

14. Proper gun operation Runs and sags – too close or too concentrated
Hold parallel
Start air stream before application
Keep open until complete pass
Cut in corners and edges first

15. Gun orientation Read slide Sequence
Overspray should land on the unpainted surface
Paint
Flap and aileron wells
Wing tips
Leading and trailing edges
Landing gear
Wheel wells
Control horns and hinges
All the difficult spots
THEN
Bottom of the airplane
Bottom of the wings – root to tip
Horizontal surfaces
Then top surfaces = overspray to the non painted surfaces
DON’T FORGET TO CHECK CONTROL SURFACES FOR BALANCE

16. Spray Overlap
Spray pattern inches
Overlap by 2/3
Move parallel

17. Cleaning the gun
Clean all passages
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