Cellulose synthetic (half-hour. 1 Rub down damaged area with P180 grade

enamel): local repair

1 Rub down damaged area with P180 grade

paper (wet) to obtain a feather edge. Wet flat

surrounding paintwork with P400–P600 grade

paper. Alternatively, dry sand with a dualacting

sanding tool using P80–P150 grade

paper.

2 Treat exposed metal with phosphating solution.

Automotive finishing and refinishing 605

3 Apply thin coat of etch primer to bare metal

only; alternatively, spray one coat of primer

surfacer directly on to bare metal, thinned 1:1.

4 Fill up defects with cellulose stopper in thin

layers.

5 Wet flat stopper with 320–360 grade paper.

6 Spray sufficient coats of primer surfacer or

filler (thinned 1:1) at 3 bars (45 psi) to bring

repair up to level of surrounding surface.

7 Wet flat with P600 grade paper.

8 Burnish surrounding area with rubbing compound

and a damp cloth to ensure a good

colour match and better blending in.

9 Tack off.

10 Spray colour coats, thinned 1:1 to a viscosity of

19–23 seconds, at a pressure of 3 bars (45 psi).

Spray several coats lightly until a good colour

match is achieved. Allow to dry hard.

11 Wet flat with P800 grade paper, dry off and

tack off.

12 Overspray the repair with a mixture of 75 per

cent thinner, 25 per cent colour, carrying the

spraying beyond the edge of the repair to

obtain a soft blend.

13 Allow to dry hard (preferably overnight) and

wet flat with P200 grade paper.

14 Burnish and polish.

Any masking off that may be required should be

done between stages 2 and 3. A coat of sealer may

be applied just prior to the colour coats to provide

better hold-out, thus obtaining a smoother finish.

Synthetic resin primers have not been included in

this process as they have a tendency to peel back

from the edges when rubbing down takes place.

Overspray from the spray gun can create unnecessary

work when carrying out local paint repairs,

but this can be restricted by using a narrower fan

pattern than that used for spraying a whole panel.

When this is done, a higher volume of paint will be

applied, increasing the risk of runs, and so the fluid

needle adjusting screw should be turned to the

right until a satisfactory volume of paint issues

from the fluidnozzle.

Occasionally the spray painter may be called

upon to repaint a motor car on which the paintwork

is in excellent condition, the customer simply

desiring a change of colour. In this case he may

only require to wet flat the surface with P600 grade

paper using a weak solution of water miscible

cleaning solution to remove any wax polish. Then

following thorough drying off and masking up,

three coats of half-hour enamel will produce quite

a good finish which can be further improved by

flatting, burnishing and polishing.

Acrylic lacquer

Though cellulose synthetic finishes are best left to

dry in their own time to obtain best results, acrylic

lacquer can be force dried without damage to the

paint film, with a consequent speeding up of the

process. This can be done with infrared lamps or in a

heated booth (though not in excess of 50 °C). The

filler materials possess better build and flowout than

the cellulose-based materials, thus providing better

surfaces for the finishing coats. The spraying viscosity

of the finishing enamel is more critical than the

half-hour enamel, and only the thinner recommended

by the paint manufacturer must be used. Solvent

evaporation from the wet paint film is governed to

some extent by the workroom temperature, and

should this be below 15 °C a special quick repair

thinner should be used. This thinner evaporates very

quickly but tends to produce a low gloss which will

require burnishing and polishing. However, should

the ambient temperature be 15 °C or above, a good

hard glossy finish can be obtained straight from the

gun which does not require polishing. As acrylic

primer fillers have good adhesion properties the use

of etch primer, though recommended, is not essential

provided that the metal substrate has been properly

prepared and treated with a phosphating solution.

17.14.6 Acrylic lacquer: complete respray

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