Paints in powdered form require the addition of a liquid to prepare them for use. The manufacturer's directions as to the amount of oil, varnish, water, or other vehicle required should be followed. You scuff up existing paint for two reasons. First, you want to get rid of any oil, grease or dirt trapped in the top layer of paint. This is the stuff that cleaners and degreasers can't get off. The second reason to scuff is to set up a physical bond for the new primer and paint to adhere to. You want to give the old paint some tooth so the new sticks better. Also, when checking the paint, be realistic and don't ignore areas just for the sake of convenience. It will cost you more in time and money later. Typically if one area of the paint is cracked or peeling, then the paint on the entire car is suspect. Maybe the rest of the car just hasn't quite reached that point of decay, but it will shortly. So if you only fix areas that look bad, you'll likely find that you wasted a paint job when the other areas start to crack or peel in a year or two.
You can tell when the bucket of paint is getting low when the airless starts pumping really loud and doesn't stop. Simply tip the nearly empty bucket of paint, at an angle so that the mesh filter is covered and wait for the airless to catch up and stop pumping. Sometimes it's just easier to just to replace the bucket of paint with the new one and when that starts going down, pour the excess from the old bucket into the new one. Now that you have primed the airless, make sure that there isn't a tip in the gun of the airless and bring it over to the empty bucket. Since there is typically cleaning solution in the hose leading to the gun it is a good idea to spray that out until you see thick paint coming out. Once you have thick paint coming out you may put your tip back in. Remember that the tip will have an arrow on one side of the handle that shows which direction it must be in, in order to spray. Tools, there is a wide variety of brushes and rollers to choose from, it is critical to select quality tools and maintain them. We will discuss brushes first, I use and recommend only Purdy brand brushes, they will give you the best results in terms of coverage and make the project go much easier and quicker. A Purdy brush is a little more expensive but if kept clean promptly after each use and stored properly, it will last for years and many projects. Most any other brushes out there, especially the cheap ones, are made of far inferior hair and I liken them to using a hand (or whisk) broom to paint with. Using lower quality tools will only frustrate you and lead you to assume that you are incapable of painting. You are capable! and the proper tools, materials, and advise are all you need. If your painting project will be on going for a couple of days, you can wet the brush with paint, wrap the brush up in a plastic sandwich bag and tape the plastic bag to the handle above the metal ferrule. Sealing it up will keep it from drying out, storing it flat will maintain the shape and permit you to use it for a couple of days without cleaning it. Because, after a couple of days or if it has had extended use on a hot day, it will loose its shape and start to collect a lot of dried paint on the hair, you should clean it with warm water and a wire brush. Once you have ran some water through the brush hair, the wire brush will then be used to remove the dried paint from the hair. Always run the wire brush down the entire length of the hair and never across it, to prevent crimping and damaging the hair. After you get the brush clean, spin it between your two hands, shedding as much water as possible from it. Then, using the wire brush again, comb the hair, shape/style the hair with your hands and lay it flat to dry. Once dry, if you will not be using the paint brush again soon, protect it by storing it in the paper shuck/cover that it came in and it will be like new the next time you use it. Our next step is mixing the oil paint. DO NOT SKIP THIS STEP. Obviously you will need to buy some paint thinner, but the most important product you will need is Penetrol $12. Take a plastic quart cup that you will be painting out of and fill it up about three quarters with paint. Now mix in a couple of tablespoons of Penetrol and the slightest amount of thinner. Mix it up with a stick real good and you are ready to go. Why Penetrol? This product is the key to a fantastic looking job. Penetrol will not only smooth out the finish it will extend the time (usually about 20 minutes) before the paint starts to get sticky. This will allow you to apply a glass like finish and eliminate brush marks. We are going to apply two coats here as well so don't glob on the paint. When you are painting the door frames get used to the paint and watch your drips. After about ten minutes or so you will get used to how the paint flows and how damn good your finish looks. Allow to dry overnight before apply second coat. Tip: after you apply the second coat remove the tape and don't allow to dry first. You will get a little paint on your hands from the tape, but deal with it. By removing the tape now you will ensure crisp lines. In some case when you allow the second coat to dry you will pull a bit of the oil paint off. It is not common, but in my opinion why take the chance.