On another site I'm on a member wrote this up in 2003 for prepping plastic for paint.
This topic is about painting plastic parts for you interior or exterior I thought that I would post this up for those of you that would like to try painting your parts or have thought about having someone else paint your parts and wanted to obtain that smoothed an painted to match look. You know the kind.
Here is my advice:
(A) Don't trust any bodyshop to prepare them for ya unless they are a custom shop that has extensive knowledge of fabricating and customizing show cars and plastic smoothing techniques because most mom & pop shops only intent is to get the job done a.s.a.p and because of that they may not clean, sand and prep them as good as it should, so I will explain ways you can guarantee that what ever paint is sprayed it will stick even if you have them paint it.
(B) If you spray it your self, the types of spray paint that you can buy over the counter is the one's in the can but remember you will never find paints to match the color coded paints of your car unless you order them on-line or you know a paint shop (Jobber) that will mix to code and sells them in a aerosol application. Even then sometimes you cannot predict by how much pressure the aerosol spray lays out the paint when it hits the surface causing the paint not to flow and gloss especially if it is a solid color. Today most can spray applications have a clear paint that you can spray over the color for more shine and gloss.
You do have 2 choices, try painting it yourself using spray can paints or have a pro paint it for ya using automotive paints. There is 3 draw backs to using aerosol spray paints. A. You can't always find a place to order or mix the paint in that application to your exact color code. B. It will not flow and gloss like automotive paints will. C. It is not as durable and long lasting as automotive paints, some brands are better then others for your particular application.
The most important thing to do before any painting is involved is preparation, and in this case we are talking about any plastic part that is hard and not easily bendable like dash parts, outside mirrors, cowls, fiberglass parts bumper valances & covers ect.... Either way you go as far as spray can VS pro automotive paints the preparation is the same and depends on the particular part and application.
I do not recommend spray can paints for any exterior part PERIOD! Not saying you can't I am just saying it is not as durable and in most cases do not have the depth and shine as pro paints.
I DO NOT BELIEVE IN PAINTS THAT SAY YOU DON'T HAVE TO SAND THE PART (For the Krylon Fusion users). I don't have time to do it over again, so I sand everything. Besides, I don't use spray can paints at all.
Pre-clean all part first, scrub wash the part with a prep clean soap you can buy at your local paint and body supply store with a mild scuff pad and water. This will remove oil, dirt, amoral or any interior dressings and let dry prior to any sanding, if this is not done and you sand without cleaning the oily residues will remain in the dust particles on the surface of your part.
Here is what I do.
1. For soft and rubbery parts re: lower bumper valances, interior grab handles etc… Buy some good mechanics hand soap (The kind with the grit in it) and some double ott #00 steal wool pads, the larger the pad the better. Using a lot of water get the part completely wet and taking the steal wool and dipping it in the hand soap scrub the part very thoughly and make sure to get every crevice and corner. Rinse well and let dry in the sun, after drying you can see any spots that you may have missed and re-do scrubbing with the materials and let dry again and check. The hand soap and steal wool serves 2 purposes the hand soap washes and get's all grime, oil, dirt & bugs off the parts and rinses well while sanding the surface very fine without damaging or fraying the plastic, and the steal wool does exactly the same assuring fine sanding of the surface. This method works well with OEM textured valances and interior plastic parts.
Once you see that every nook and cranny has been scrubbed and sanded, once rinsed and dried it will look hazy and dull and is ready for primer.
For hard plastic parts:-
A lot of our Ford plastic parts that have texture have different characteristics compounds in the plastics where you can sand the texture off with 80 grit sandpaper. For example: Back window surrounds, 3rd brake light housing seat plastic surrounds ect..., where the plastic of a lower OEM valance are soft. The harder plastics can be sanded with 80 grit where as the soft plastics will fray this is where you would use the steal wool & soap method only on the soft plastic parts.
If you choose to sand the harder plastics with 80 grit, sand down the texture till flat (Test first a small spot) then sand with 150 and 220 and primer with flexible primer as usual. spray a mist of black can spray paint to mist on a check coat & Let dry overnight . Wet sand after a day or so with 400 grit wet/dry sandpaper using water at all times to rinse off residue and make sanding easier. Sand till all the black check coat sands off but try to be careful not to sand through the primer back down to the plastic as you will have to re-primer that spot being careful of sharp edges and corners. let dry and paint as usual.
EXTRA NOTE: On interior hard plastic parts you can use the bulldog spraycans of flexible primers but DO NOT use the professional version of bulldog on dash parts as per the instructions, the interiors get hot during the summer seasons and the bulldog that is bought at your local paint jobbers do something weird. It is best to just primer your parts after sanding directly with the bulldog mixed with the primer instead of spraying the bulldog straight as directed on the container. The instructions say's to spray 2-3 coats on bare or freshly sanded plastic parts. During extreme heat in the interior of a vehicle the bulldog liquefies and bubbles under the primers causing a extreme mess and lifting of the primer/paint away from the part. I have found out that the professional version of Bulldog works best on exterior parts when sprayed by itself as instructed on urethane bumpers and all urethane parts/aftermarket plastics etc.....
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On new flat (No texture) urethane bumper, valances and all aftermarket urethane parts you should use 400 grit wet/dry sandpaper using water. Use the same procedures by rinsing and letting it dry to see where you missed spots. In very tight corners you can use the steal wool and hand soap as well.
(2) At this stage if you want to paint it yourself you will need a few things that can be bought at Autozone & Pep boys and some automotive paint stores. They have a special flexible primer promoter at $5 a can and depending on how many parts you have you may need 3-4 cans. The same with the primers of the same brand but make sure they say flexible primers for plastic parts. Spray the promoter first as directed let dry 2-3 minutes on the last coat and then it's ready for the primer as it needs to be sprayed wet on wet so don’t wait long after the last coat of promoter to start spraying your primer otherwise you will have to sand the surface before applying your first coat of primer. Sweep side to side slightly overlapping the prior coats edge and don't stop in one spot without releasing the spray button for it will build up and run. Anything you don't use you can return for a refund (Unused can).
After your primers are dry (Preferably over night) If your going to allow the texture on your OEM parts to show through then your need not sand it smooth, purchase a scuff pad (resembles a scouring dish pad) but it's made to scuff paints and primers There is red and gray, I prefer the gray because it sands lighter then the red. After scuffing the surface trying not to scuff through the primer and watch out for the edges otherwise you can sand through and you'd have to re-primer in those spots, wash it down with water to rinse all dust, dirts, hairs, etc…... and let dry. Try not to touch the paintable surface with your fingers because you have natural oils on your hands that will ruin your paints and paints have a tendency to separate from an oily spots, they call fish eye's
If you are going for a flat smooth finish with no textures showing through you should spray a check coat first, this is a technique that helps you wet sand your part completely by visually seeing a change. Get a can of any black spray paint and spray a mist layer of paint from 9-15 inches away from your part and spray mist layers all around the primered part till you see thousands of tiny spots on the surface. Let the check coat dry for a few hours in the sun then when it doesn’t feel sticky and feels dry your ready to sand the primered surface, sand with wet/dry 400 grit sand paper using water at all times. You will see the check coat being sanded and will rinse off with the water letting you know that the surface is completely sanded in that area. Any left over spots of the check coat will indicate that area or spot has not been sanded, once all the check coat seems gone this will indicate a completely sanded surface, this will also show you low spots that may need to be repaired or re-primered to build up that low spot or deep scratch. This same technique spraying a check coat is used in bodywork repairs after primering to assure a smooth flat surface before top coating (Painting). After sanding rinse with water and let dry to see how far you have sanded and repeat if necessary. . Additional coats of primer is necessary to build up the surface to hide the texture and sand scratches, if you sand through then repeat with a check coat and sand again after drying.
Up-date 9/6/04: For semi professional painters that have the equipment and experience, I have always used Bulldog Flex/tiecoat/Flex additive in all of my primers, paints and sometimes the clearcoats for added flexibility but according to the instructions for these types of modifications especially on interior plastic parts I do not recommend spraying pre-coats of the Bulldog on the freshly sanded surfaces as I had instructed above in the topic "Extra Note"
What is important to note here is that especially flexible parts must be sanded smooth and flat not to rely on the use of the primer build up technique to hide the texture as it will not matter how much flex additive you put into your primer mixture it is bound to crack from the slightest bend. So the trick here is to assure a flat sanded surface first and make sure the frayed plastic hairs are to it's minimum applying only 1-3 coats of primer, so when you apply your check coat and wet sand with 400 grit or above you end up with a thin coat of primer on the surface minimizing the chance of cracking due to excessive layers of primer build up.
All right now everything is prepped________________________________________-
An you are ready for painting, Make sure that where you are painting there is no wind present to blow dust in your paint job and if you are painting outside in the drive way, water down the driveway/garage to keep the dust and lint down. Best weather conditions to spray would be around 65-75 degrees. This description is for those who do not have professional equipment for spraying pro auto paints.
Spray can paints can be hard to obtain the kinds of results that make the paints gloss, you must make sure that you start off with a couple of light even coat, let dry tack dry according to the instructions and do a wetter even coat. Let tack dry and follow with a 2 or 3 very wet coat and make sure to make it even coats all around or enough for even coverage. For a shinier finish on solid or metallic colors you should also follow with a clear coat. 2 light coats followed by 1 wet coat letting tack dry according to the instructions between coats. followed by the last wet coat as desired.
FINAL NOTE: If you have a pro paint it be sure to prepare it as instructed above to insure that what ever paints they spray it will stick. You do not at this point have to purchase any paints or primers they will do that. But make sure to mention that you want flex additives added to the primers, and all paint stages to be sprayed on your parts and get it in writing. This will help in your warranty and protect you from having them (The paint shop) deny your claim.
