Research Bulletin 2000-5: Refinishing Plastic Parts

Research Bulletin 2000-5
Refinishing Plastic Parts:Sherwin-Williams (Updated)

Refinishing Plastic Parts,
General Information

Unprimed (Bare) Plastic

Caution:
The following “Sandable” and “Unsandable” recommendations are for bare plastic parts only.

Prior to following these recommendations, closely inspect the part to determine if the exterior has been primed. The color of OE applied primer can be similar to the color of the substrate. Look for signs of overspray on the backside of the part around edges, flanges, etc. In an inconspicuous area of the exterior, sand a small area and check for primer powdering.

Identification of Bare Plastic Substrates by Sanding

On the backside of the plastic part perform a sanding test. Clean a small area then sand using a DA finishing sander and P600 grit sandpaper. If the plastic substrate “powders”, the part must be thoroughly sanded following the “Sandable” plastic recommendations. If the plastic substrate does not powder but rather “gums” the paper, follow the “Unsandable” plastic recommendations.

Unsandable Plastic

Step 1: Clean all surfaces (inside and outside) thoroughly with SC155 Low VOC Plastic Surface Cleaner and a gold nylon scuffing pad.

Thoroughly rinse with clean water and wipe dry.

Step 2: Thoroughly scuff sand using a gold nylon scuff pad along with USP-90 Liquid Scuffing Gel, paying close attention to small grooves and depressions.

Thoroughly rinse off the scuffing gel with clean water and completely dry the surface.

Step 3: Thoroughly clean the plastic substrate with SC159 Plastic / Anti-Stat Cleaner and a gold nylon scuff pad. Dry excess material with a clean cloth and re-apply the SC159, followed by wiping the part dry with a clean cloth.

Tack surface to be painted with a clean tack cloth.

Step 4: Apply 1 medium coat of UPO7226 Clear or UPO7227 gray Plastic Adhesion promoter to the bare plastic substrate to be refinished, achieving no more than .2 - .4 mils of dry film thickness. Allow 10 minutes to flash.

Step 5: Apply Ultra 7000 basecoat with UH904 hardener. (1 oz of UH904 per RTS quart of basecoat)

Step 6: Apply Ultra 7000 clearcoat. (No flex additive is required in the following clearcoats: CC635, CC637, CC639, CC930, or CC940)

Sandable Plastic

Step 1: Clean all surfaces (inside and outside) thoroughly with SC155 Low VOC Plastic Surface Cleaner and a gold nylon scuffing pad.

Thoroughly rinse with clean water and wipe dry.

Step 2: Thoroughly clean the plastic substrate with SC159 Plastic / Anti-Stat Cleaner and a gold nylon scuff pad.

Dry excess material with a clean cloth.

Step 3: Sand thoroughly using P600, and/or a gray scuff pad and USP90 Liquid Scuffing gel.

Thoroughly rinse off the scuffing gel with clean water and completely dry the surface.

Step 4: Thoroughly clean the plastic substrate with SC159 Plastic / Anti-Stat Cleaner. and a gold nylon scuff pad. Dry with a clean cloth.

Tack surface to be painted with a clean tack cloth.

Step 5: Apply 1 medium coat of UPO7226 Clear or UPO7227 gray Plastic Adhesion promoter to the bare plastic substrate to be refinished, achieving no more than .2 - .4 mils of dry film thickness. Allow 10 minutes to flash.

Step 6: Apply Ultra 7000 basecoat with UH904 hardener. (1 oz of UH904 per RTS quart of basecoat)

Step 7: Apply Ultra 7000 clearcoat. (No flex additive is required in the following clearcoats: CC635, CC637, CC639, CC930, or CC940)

Although the above recommendations should be sufficient for most bare plastic substrates, refer to the Special Notes section below for additional technique tips for maximum performance on bare plastic substrates.

Special Notes:
Technique Tips For Maximum Performance on Bare Plastics

When cleaning a part, always clean all sides, including the back, to avoid transferring contaminants to the outside during handling or set-up.

For unsandable plastics, Gray, and especially Red, scuff pads have been shown to severely scratch some bare plastic parts to the point of telescoping sand scratches in the final finish. The gold scuff pad eliminates this problem, while providing adequate cleaning of the surface. Pay special attention to cleaning all edges, grooves and feature lines.

USP-90 Scuffing Gel can be used to enhance the effectiveness of the white scuff pad.

Use a stiff bristle brush or an appropriate scuff pad and liquid scuffing gel for textured surfaces.

Tempering of bare plastic parts is optional, but may be beneficial when topcoat adhesion is compromised by imbedded mold release agents.

If a part primed with UPO-7226/7227 sets overnight, use only clean water to wash any dust off prior to refinishing with hardened basecoat and clearcoat. Do not use wax and grease removers.

When refinishing with basecoat/clearcoat hardener must be used in the basecoat color at the ratio of 16:16:1. (UH-60, UH-70, UH-80, or UH904 hardener may be used)

No flex additive is required in the following clearcoats: CC-635, CC-637, CC-639, CC930 or CC940.

Urethane Sealers S56/S57/S58 or S59 must use a flex additive. S61 transparent Adhesion promoter must use flex additive. S65 Basecoat Transparent must be used 2K only. PSE4600/4601 Epoxy requires no flex additive. P30 SpectraPrime surfacer/sealer requires no flex additive. P47 must use flex additive.

Primed Plastic Parts

Check primed parts for solubility by pressing a solvent saturated towel on the surface (small area) on a feature line, where the primer is thinnest and hold for 30 seconds.

If the primer is soluble:

Step 1: Remove the primer.

Step 2: Follow recommendations listed on previous page for Un-Primed (Bare) Plastic.

If the primer is insoluble:

Step 1: Clean part on all sides with SC155 Low VOC Surface Cleaner.

Step 2: Scuff sand using a gray scuff pad and USP-90 Liquid Scuffing Agent giving special attention to small grooves and depressions.

Step 3: Thoroughly rinse off the scuffing agent with clean water and completely dry the surface.

Step 4: Reclean the surface with SC159 Plastic Cleaner / Anti-stat.

Step 5: Apply flexed S56/S57/S58 or S59 Color Seal, flexed S61 Transparent Adhesion Promoter, S65 Basecoat Transparent 2K Adhesion Promoter, SpectraPrime Sealer, or PSE-4600/4601 4.6 Epoxy.

Step 6: Apply basecoat with any Ultra (UH) hardener (1oz per sprayable quart)

Step 7: Apply clearcoat as recommended. No flex additive is required in the following clearcoats: CC-635, CC-637, CC-639, CC930, or CC940.

Original Finish Plastic Parts (in sound condition)

Step 1: Clean part with SC155 Low V.O.C. Surface Cleaner.