1. Chapter 14 Vehicle Surface Preparation

2. Objectives Prepare a vehicle for painting/refinishing Properly clean a vehicle using soap, water, air pressure, and a wax-grease remover Evaluate the condition of the vehicle’s paint Describe methods for removing the damaged paint if needed

3. Objectives (continued) Properly prepare and treat bare metal surfaces Correctly sand and featheredge surfaces Apply an undercoat Mask a vehicle properly

4. Introduction Vehicle preparation involves all final steps prior to painting/refinishing Foolish to apply any kind of finish to a surface that is not properly prepared Even if original finish is in good condition, it should be lightly sanded after washing If paint surface is in poor condition, paint should be removed down to bare metal –Provides a good foundation for new finish

5. Vehicle Cleaning Vehicle should be washed before bringing it into shop area Wet whole vehicle with a water hose, concentrating water flow onto trim pieces, around windows, door jambs, and wheel wells Scrub all surfaces with detergent and water, rinse the vehicle and let it dry completely Paint will not adhere to a waxy surface, so all surfaces must be cleaned with a prepainting cleaning agent

6. Surface Evaluation Surface evaluation is a close inspection of paint to determine its condition Look for signs of paint film breakdown, paying close attention to gloss level Do a paint adhesion check by sanding through a small area of the old finish –If you can’t featheredge it, it must be removed Preexisting damage includes cracking, scratches, acid rain, and industrial fallout

7. Surface Evaluation (continued) Acid rain may etch craters into paint film Industrial fallout appears as black or brown spots or rust-colored rings on paint surface Hard water spotting damage leaves a round white ring on paint surface UV radiation damage causes discoloration, cracking, checking, dulling and yellowing Paint is removed from metal surfaces by chemical stripping, abrasive blasting, or sanding

8. Chemical Stripping Chemical stripping is often used to strip large areas of paint, and areas where a power sander cannot reach Mask off area to ensure remover does not dissolve paint not meant to be stripped Lightly sand area before applying stripper Allow paint remover to stand until finish is softened Be sure to rinse off any residue that remains

9. (B) Use a scraper to remove softened paint before sanding. Figure 14-3. Here a technician is using a chemical paint stripper. (A) Apply chemical stripper with a paint brush while wearing protective gloves and goggles.

10. Blasting Paint Abrasive blasting involves using air pressure, a blasting gun, and an abrasive to remove paint Blasting will quickly reveal hidden rust that can result in scaling or other refinishing problems Blasting makes hard-to-reach areas accessible Sand or hard media blasting is not recommended for large flat panels that can warp Plastic stripping media will remove paint from almost any surface without damage

11. Removing Paint Machine grinding is suitable for small flat areas or gently curved areas Start with a No. 40 grit paper on a soft backing pad, and hold face of pad at an angle Work back and forth evenly over area to remove bulk of finish down to metal Follow with a No. 80 grit paper, and then a No. 180 grit paper Go over entire area to be repaired

12. Bare Metal Treatment Proper bare metal treatment prepares metal for primer and can inhibit erosion Self-etching primers etch bare metal to improve paint adhesion and rust resistance Self-etching primers work best on lightly sanded surfaces

13. Preparing Metal Replacement Parts Many manufacturers prime replacement panels to protect metal against rust, but not necessarily to provide a basis for a paint system Clean new part with wax and grease remover, and examine part for scratches Sand imperfections but do not remove coating Scuff sand the entire panel, and apply primer Clean e-coated panels with a solvent, and treat panels with a metal conditioner

14. Sanding/Featheredging Sanding prepares surface by tapering sharp edges in paint, removing loose pieces, and improving adhesion by scuffing surface Open coat sandpaper is good for sanding softer materials such as old paint, and body filler Closed coat sandpaper provides a finer finish Grit sizes vary from coarse to microfine grades – select finest grit that will do the job Power sanding uses air sander to begin smoothing

15. Types of Sanding Bare metal sanding smoothes rough metal surfaces –Use No. 80 grit to level out burrs, nibs, scratches Paint sanding is needed when finish is in poor shape, and to level primed areas –Block sanding is recommended Block sanding is simple back-and-forth action with sandpaper mounted on a blocking tool –Often used on flat surfaces –Do not sand in a circular motion

16. Figure 14-7. Dry block sanding works well when using smoothing sandpapers. Block sanding will quickly level body filler and feather it accurately. Never sand flat surfaces by hand or with your fingers without using a block.

17. Types of Sanding (continued) Dry sand with coarser nonwaterproof sandpaper, without using water Wet sand with finer waterproof sandpaper, using water to flush away particles Wet sanding reduces paper clogging Wax and silicone can penetrate beneath the surface, you might want to add wax and grease remover or soap to the water when wet sanding

18. Scuff Pads Scuff padding is done with a nylon pad on hard- to-reach areas to clean and scuff surface Paint scuffing makes new paint bond properly Scuff with find sandpaper or scuff pad, wet or dry Scuff pad can be placed over a sanding block on flat surfaces, or hand-held on curved areas

19. Featheredging If a new coat of paint is applied over a broken area, broken area must be featheredged Featheredged means the sharp edge of broken paint is gradually tapered down by sanding Bare metal areas are filled with a primer and entire area is sanded smooth and level Start by positioning sanding disc flat against work surface After leveling rough paint edges, lay sander flat on panel, finish tapering in a crosscutting pattern

20. Priming Systems Primer-surfacers provide priming and filling in one step Apply primer-sealers to prevent solvents in paint from being absorbed by the primer-surfacer Sealers improve adhesion between old and new finishes –Necessary between an enamel and a lacquer After sanding, if fine scratches still appear, another primecoat might be required

21. Using Spot Putty Glazing or spot putty fills small scratches and pinholes after priming Two-part putties come with two ingredients that must be mixed to start curing process To apply two-part spot putty, mix ingredients, then use a rubber squeegee to apply material to small scratch Allow putty to cure until hard, then dry sand area Clean surface, and reapply primer

22. Using a Guide Coat Guide coat is a very thin coat of powder or primer that shows high and low spots Spray or dust a light coat over repair area Sanding reveals high and low spots by contrasting guide coat color with material underneath When surface is flat and ready for painting, guide coat will sand off evenly Scuff areas where old finish is in good condition to improve adhesion

23. Masking Masking keeps paint mist from contacting areas other than those to be refinished Overspray from two-component-type paints cannot be removed with a thinner or solvent Masking paper is a roll of paper designed to cover parts of a vehicle –Heat resistant, good wet strength, freedom from loose fibers, resistant to solvent penetration Masking plastic comes in large sheets for covering large areas of vehicle

24. Figure 14-16. When using masking tape, pull lightly on the tape with one hand without stretching the tape. Moving the hand up or down will control the direction of the tape application. The other hand is used to press the tape down securely on the surface. Note the use of masking paper over the taillight assembly.

25. Masking (continued) Masking foam or masking rope is a self-stick foam rubber cord for masking behind panels Masking tape is sticky paper tape designed to cover small parts and to hold masking paper Refinishing masking tape should not be confused with tape for home use Fine line masking tape is a very thin, tape used to produce a better paint part edge Masking covers are specially shaped cloth covers for masking specific parts

26. Figure 14-18. Note how a technician has applied fine line masking tape first and has then gone over it with conventional masking tape. This will let you have better control of fine line tape application for more accurate masking. Always check sharply curved masked areas for leaks. When the tape is curved, it can lift up and allow overspray to go under the tape.

27. Masking Procedures If a part can be removed easily this is better than trying to mask around it Removal of trim and moldings is more often necessary when using a base/clear system Vehicle should be cleaned and detailed before and after masking Cold and damp environments may prevent masking tape from sticking Before masking glass areas, remove accessories such as wiper blades

28. Masking Procedures (continued) Overspray results when you do not seal area and paint gets on uncovered area Use fine line tape to protect existing pinstripes from overspray Double masking uses two layers of masking paper to prevent bleed-through or finish-dulling from solvents Reverse masking requires folding masking paper back over tape –Often used during spot repairs

29. Figure 14-20. Reverse masking will help blend a repair area. Overspray will hit the folded-over paper and blend more smoothly into the old paint.

30. Liquid Masking Material Liquid masking material seals vehicle to protect undamaged panels and parts from overspray Use liquid masking on areas where masking is difficult to apply, such as wheel wells Masking liquid comes in a large ready-to-spray drum, and is sprayed on vehicle Masking liquid can be washed off with soap and water after paint has cured

31. Summary Vehicle preparation involves all final steps prior to painting, including cleaning, sanding, stripping, masking, priming, and related tasks Open coat sandpaper is good for sanding softer materials such as paint, body filler, plastic and aluminum Closed coat sandpaper generally provides a finer finish and is commonly used in wet sanding

32. Summary (continued) Masking keeps paint mist from contacting areas other than those to be refinished or painted Some masking materials include masking paper and tape, masking foam, plastic sheeting, cloth, plastic covers, and liquid masking material