Scratch Builds: Prepping: From Start to Finish

Discussion in 'Tutorials and How Tos' started by Wikkid, Feb 7, 2012.

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  1. Wikkid

    Wikkid Semi-retired customizer

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    This is a step by step process I use to ready my projects for primer sealers. Then again for paintwork, I'm an auto body tech by trade and this is also the method used to prep plastic car panels for topcoats.

    I use a solvent based wax and grease remover on raw plastic parts. It's quite strong and can be absorbed into your skin, so wear disposable gloves. There is also a water based degreaser that is slower but just as effective. I never use a solvent based degreaser on styrene plastic as it warps and re-flows the plastic:

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    I sprayed the Seeker base panels down in solvent based Rre-Kleeno and let it sit for a few minutes to dig away at the mold release agents. Then, I just scrub it off with a paper towel. Is it this easy? Yes, it is. The alternate method is to soak your parts in soap and water, and scrub the panels with a tooth brush:

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    To scuff, I use 3M Scotch-Brite pads. They come in varying coarseness. The red is equivalent to 320 grit; the gray: 1000. To prep for a sealer/primer stage, I use the red:

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    All you have to do is rub the stuff around on the project. There’s o need to put pressure on it, as it cuts quite fast and evenly:

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    Here's a side by side of a prepped and unprepped panel. You’re just looking to take the shine off the part:

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    This is a prep pen. It comes with refillable ends that are made up of fiberglass hairs:

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    To use it, just run it through all the odd shaped areas that the Scotch-Brite pad can't reach:

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    The same rules apply on styrene figures:

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    This is how I do my first stage primer using spray bomb. Be sure to mask off areas that have close tolerances as you don't want to get too much paint applied to these areas.

    Shape the can well until the balls have freed up and are rattling freely. You also need to do a spray out on a piece of paper to release any unmixed solvents caught in the system and to free up the spray pattern:

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    Shown here is the distance between the project and your rattle can. If you're too close, you may end up getting a run or even worse, solvent popping. Be sure to let each coat dry thoroughly before applying the next:

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    In the event you have to prime a body-worked area but don't want to spray the whole panel to avoid losing details, you can back-mask an edge as shown at the end of the red line. Back-masking keeps the primer from forming a hard edge making it easy to sand out without leaving a line:

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    If you plan to glue panels together after it's been painted, be sure to mask those areas as well. Glue tends to muck up most primers by reactivating it. Hell, it doesn't even stick to a two-part primer:

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    Let it dry for a day or two. I then go in and check for any and all imperfections and fix those. I then re-sand everything using 320 sandpaper:

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    Everything is then remasked for an activated high build primer (high build primers should ONLY be applied to panels that won't rub other surfaces):

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    I let my high build primer set up for a couple days. Being that I used a white primer, I grab a can of black spray bomb and . . . .

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    . . . . lightly pepper the surface. This is called tracer coat. It's meant to highlight imperfections as you do your final wet sand:

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    Grab some 600 wet sand paper and a bucket filled with warm water:

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    Tear your paper right in two and fold it into three pieces:

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    . . . . and again like so. Folding it like this makes it nice and stiff so it doesn't hook and pile up on you:

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    When wet sanding, it's best to sand across your fingers as shown with the red line. If you go along the fingers, you risk sanding grooves into your project:

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    What’s shown here is very important. You want the whole panel to be pure white. The tracer coat highlights your low spots. Keep sanding flat until it's gone WITHOUT digging the tracer coat out as it that would defeat its purpose:

    [​IMG]

    Once the whole thing is white again, dry to parts off and you're ready for paint.
     

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