Eastwood’s ‘Shop Talk’, Episode 22: Kevin Tetz Talks Shop With Ryan Shand, Co-Host of Trucks & Truck TechClick Here To Read Full Post...
After you’ve sprayed your primer you might wonder what exactly to do next. Prep for paint can seem tricky at first but it’s not tough once you’ve got the proper steps down.
First you’ll need to prep your primer. How exactly you prep your project depends on which primer you’ve used, which products you’re using next, and your overall project goals. It’s important to note that paint prep is a widely debated topic and there are many ways to arrive at the same high quality result. The methods I’ll detail here are simply what I would consider the best balance between speed or effectiveness and high quality results.
Sanding scratches will be either straight or circular. Straight scratches don’t hide as well and may be seen in the final product if you don’t use the proper grit. Straight scratches come from block sanding and hand sanding in a back and forth motion. In my experience the best blocks to use for this process are Durablocks. They’re rigid enough to not bend when you’re trying to block a flat surface but they have some ‘give’ to them so that If you don’t have access to a DA (dual action) sander and you’ll be finishing your project with straight sanding scratches you’ll need to use a higher grit so that your color covers them better.
Using a DA sander creates random circular scratches that are effectively finer than the same grit paper when used to block sand. A DA sander is a very important tool to use in the prepping process because it allows you to create a surface that is rough enough to allow for proper mechanical adhesion yet hide those sanding scratches in a way that they won’t be able to be seen through the paint when you’re all finished.
Wet sanding offers a unique way to prep a panel that some people prefer over dry sanding. First, there is no dust to breathe in and we all understand the benefits of that. Wet sanding also allows you to work with finer grits more easily because the paper won’t clog with dust. The benefit there is that you can use those finer grits on a block and make straight scratches that will be easily covered by your sealer and color.
So what grit sand paper should you use? This is where each primer will be slightly different.
Prepping primer like our Contour Polyester Primer could go one of two ways. You could “finish” prep it in order to paint directly over it or you could treat it like body filler and simply block sand it flat and then prime over it with another material. If you’re going to be finishing it in order to paint directly over it you should use a combination of block sanding and DA sanding. You can rough out your work with 80, move to 180, 220, and then finish blocking with 320 grit. To get rid of those straight scratches you should DA sand with 400 grit. You could add another finer grit like 600 but in my experience 400 has proven itself to be fine enough to paint over with most materials. You should never wet sand polyester primer; it will absorb the moisture and could potentially cause issues down the road if it doesn’t completely evaporate before painting.
If you want to prep polyester primer in order to prime over it with another material, start block sanding with 80 to break it open and roughly knock the panel down flat and then do the majority of your blocking with 180 grit and finish with either 180 or 220 grit on a DA sander. This will give you the flat surface you need and avoid the extra work and time spent finishing with the finer grits. 2k Urethane Primer would be the next step from here.
When prepping 2K Urethane Primer it’s very similar to prepping polyester primer for paint except that you’ll skip the rougher grit steps. 320 grit is the best to use for dry block sanding 2K Urethane primer, it’s both rough enough to be able to sand quickly and fine enough to not need much more after you’re done. Once you’ve blocked your panels with 320 grit you should go over your work with 400 grit on a DA sander. Wet sanding 2K Urethane primer is best done with 400 to 600 grit wet/dry paper on a Durablock. Under most circumstances you will not need to DA sand over your work after wet sanding because wet sanding creates much finer scratches.
Wet sanding epoxy primer is usually the best way to prep it because epoxy has a tendency to clog paper when sanded dry. You would sand the same way as 2K Urethane Primer—400 to 600 grit wet.
Regardless of whether you’ve wet or dry sanded it’s always a good idea to go over your work with a gray or red scuff pad. This will ensure that you don’t have any areas left that are shiny. Everything must be scuffed or sanded in some way. The scuff pad makes it much easier to get into smaller areas where it might be difficult with a block or your DA sander.
After you’ve done your sanding and scuffing work, thoroughly blow off your entire project. You want to keep going over the entire thing with your blow gun until you see no more dust or debris. Pay close attention to corners, crevices, gaps in panels, door jambs, etc. Dirt and debris from prepping likes to hide everywhere. Even after taping everything up dust will always find a way to get into your paint work. After you’ve blown off all of the loose dust and dirt thoroughly wipe down all of your panels with PRE cleaner.
Let's start mixing it up!
At this point you’ll be ready to start thinking about mixing your paint. There are three components that come into play with nearly all top coats – the “solids” (color pigment or clear solids), activator, and reducer. It’s easiest to think about the solids and the activator as the main ingredients and the product instructions as the recipe. The instructions for each material will tell you exactly how much of each ingredient to add. The solids and activator are required items and the ratio is absolute. If you deviate from the instructions here your paint will not harden or dry correctly. The reducer would be most like salt or spices. Most recipes give a recommendation but how much you use is up to you, it’s all personal preference. Some people prefer to use reducer and some prefer to spray without it, the choice is yours.
Mixing ratios are easy to decode, take our Single Stage Urethane for example – the mixing ratio is 3:1. The first number in a mixing ratio always refers to the solids, in this case the color. The second number is the activator. Here we’ll have three parts paint to one part activator. Bring reducer into the picture (15% reduction for example) and the ratio would be written like this: 3:1:15%. That means that you’ll use three parts color, one part activator and then add reducer to equal 15% of the total volume of the first two components. 9 oz. of color : 3 oz. of activator : 1.8 oz reducer (which could be rounded to 2 oz. for easy mixing).
Once your paint is mixed you’ll need to strain it and pour it into your paint gun. Straining the material is a very important step If you don’t strain the paint there’s a good chance you could end up either clogging the gun with stray particles or metallic chunks that might not have broken up properly. If it doesn’t clog the gun it only has one other place to go – onto your fresh paint work. That means you’ll end up with unsightly chunks in your final product, some which can’t easily be sanded out. At very least you’ll create more work for yourself when you’re sanding and buffing later on.
Applying your color will be about the same whether you’re spraying basecoat or single stage. Remember that it’s always best to apply lighter coats of color and build up the coating gradually rather than load on heavy coats. You’ll need to focus on consistency and make sure that you have even color coverage. Making passes with a 75% overlap while holding the gun about 8” away from the surface is a good place to start. It will take some experience to learn just how fast you’ll want to go. There are very few absolutes when it comes to applying automotive paint, most of it comes down to personal preference and you’ll learn a lot as you go. Make sure to adhere to the recommended flash times between coats to avoid any issues. Your final coats of single stage will go on the same way you’d apply every coat of clear – medium to wet, watching for the material to flow out smoothly. If you plan on doing wet sanding and buffing to finish your project, spray three full coats of clear.
Here is a must-see video on HVLP spray gun set up and techniques for a professional finsh by my friend Kevin Tetz:
Fixing imperfections in your paint
When you’ve sprayed your final coats of single stage paint or clear coat you’ll probably see quite a few areas you’re not so happy with – runs, sags, drips, or most common – dirt nibs and orange peel. Don’t worry! It’s possible to correct most of these problems with sanding and buffing, no matter how bad they seem. First you’ll need to knock down the dirt and any runs or sags. Most of the time you’ll stick with 1500 grit paper for the dirt nibs and the larger orange peel. This will allow you to work quickly but without making scratches that are too deep. Once you’ve knocked down most of the dirt or peel, do the majority of your sanding with 2000 grit. To take care of the runs you could use one of our nib files or even a single edge razor blade. Carefully scrape the high spots on the runs or sags. It’s important to be patient with this step. Be sure to avoid cutting into the paint with the edges, just gently scrape away layers of the built up clear coat. When you’ve knocked down the run and brought it back down to the level of the surrounding clear, finish it up by wet sanding with 2000 grit.
If this is your first time painting a vehicle, then this is a must see, two-part video series on painting basics by Kevin Tetz:
When you’ve sanded out all of the imperfections you’ve found it’s time to buff. Use a rotary buffer like one from 3M or Dewalt with compound on a wool or foam compounding pad to do the majority of the work. It’s easiest to work on one small section at a time and do two or three passes with the buffer until you’ve removed all of the sanding scratches. Move on to polishing after you’ve made two or three passes with the compound. For the polishing steps you’ll use a clean foam polishing pad and machine polish. Make sure to set the buffer speed slower and keep the pad as flat to the panel as possible to avoid swirl marks.
Got paint chips to repair? Again, Kevin Tetz passes along all of his tips and tricks to fixing those pesky paint chips like they never happened:
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Eastwood’s ‘Shop Talk’, Episode 21: Kevin Tetz Talks Shop With Mark Lambert, Host of Classic Car Restoration for DIY NetworkClick Here To Read Full Post...
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