kpcrash Posted November 10, 2008 Report Share Posted November 10, 2008 How to sand a finish - by kpcrash First, it is important to understand a few basic things. This is not the all-knowing, end all of sanding techniques - merely what I feel is a good place for beginners to read about what's necessary (tools) to be able to make your finish look incredible using the minimum in expense. There are several ways to do this with more advanced techniques and equipment, but if you're just starting out - follow along below and you should have more than adequate results. 1. The tools needed? Your hands - they are very important for this Sandpaper of the following description: Regular 400 Grit Dry, Wet/Dry sandpaper in 400,600,800,1000,1200,1500,2000 grits. (More about this below) Water A little soap A damp rag A clean dry lint free cloth A small spray (spritz) bottle that has never been used for anything else - especially a household cleaner. A sanding block 2. About Sandpaper: Sandpaper works by making tiny cuts in the material it is rubbed against to remove minor amounts at a time - otherwise you could do this with a knife All sandpaper has an abrasive glued to a paper material. Wet/Dry sandpaper uses a paper and adhesive that keeps the abrasive attached and the paper solid even when completely soaked in water. The higher the grit number, the finer the sanding - hence starting this process at 400 grit. Anything rougher would gouge the finish too deeply and there are times when 400 is too much it depends on the level of "orange peel" you have. 3. Setting up At this point, you should already have any color coats on your guitar and depending on clear coat type, several coats. For this specific example, I'm using Rustoleum Painter's Touch Clear Gloss (Acrylic Lacquer) out of a rattlecan. So I've taken a small container and filled about 2/3 of the way with warm water and a few drops of dish soap (Ivory). Next, I put 2 1/4 sheet pieces of each grade of wet/dry into the container to soak overnight. Why? IMHO, it holds water better that way. The paper absorbs just a bit and becomes very easy to work with. Also make sure you have a clean work area. A small speck of grit, dog hair, etc. can cause a deep scratch you just don't want to deal with. Hence the lint free towel, as you'll be wiping this down frequently to make sure no grit gets left behind. 4. What does sanding until all the clear spots are gone mean? When you spray with a rattlecan, or other sometimes, the finish is not perfectly flat. It has little pits and groves or is just generally "bumpy" in a way that can resemble "orange peel". Sanding until all the clear or shiny spots are gone means sanding down the finish until you can't see them anymore such as shown below. When sanding your finish - make sure you go with the grain and use a block. Sure this can be done with a machine, but often leaves swirls or "fish scales" that make it not worth it. Also if you're new to finishing, using a machine makes it too easy to sand through the finish. Using a machine also makes it impossible for to "feel" the finish as you're sanding. 5. So, enough talk, what does it look like? This has been the hardest part to learn. Here is what the various stages may look like as you sand from 400-2000 and final "buffing" (discussed later) First, use dry regular 400 grit to get the finish as level as possible (meaning, no shiny spots). DON'T USE HEAVY PRESSURE - let the sandpaper work. Then hit it with 400 wet/dry... guess where we're going from here... Sanding is again, always done with the grain and in as long a stroke as possible. If you have problems with the horns, a little piece of PVC pipe can be quite a help. The reason for each of these grits that what we're doing is making the groves (or sanding marks) smaller and smaller. Your goal is to make the finish look like a nice satin finish with lines so small you can barely (if at all) see them. Use the spray bottle to make sure things stay lubed up. After giving the guitar a good once over with the sandpaper, make sure to use the damp cloth to wipe it down, then use the dry towel to wipe it down again. 6. How do I know that I've sanded enough with one grit? You will come to know the feel associated with when the sandpaper isn't really doing anything anymore - until then... You'll sand an area a few times, wipe it down, dry it off and look. It should look very smooth. Any lines should be quite light, but visible. Again, the lines should be fading more and more as you increase grit. As you get close to done, you'll start to notice a definite sheen, see below: You should have a nice "flat" finish with no real noticeable lines or what looks like a satin finish with an extremely fine brushed look. 7. Ok, I'm there - what next? This is an area of personal preference as well. Some like to hand rub various creams/polishes - I like my buffer . For this step, I use the following: A 9" buffer (regular electric car buffer), Maguier's #9 and ScratchX, and 3 different pads - an applicator (thin gauze like), an applicator/remover (terrycloth) and a finishing buffer pad. Starting with Mag. #9 on the applicator, give the entire unit a good once over. You'll quickly start to see the shine come through. Make sure to keep the spritz bottle close by here as well to keep extra water going as these products use self-reducing grit (it breaks down while being used). Wipe down with clean damp rag, then wipe off with lint-free dry towel and move to ScratchX on applicator/remover, then final buff. As for horns, I do them by hand, sometimes using a flannel buffing wheel to expedite for something that looks similar to the below: For this, held up to the television to get a good shot of how reflective the image is. The clearer the finish, the better the reflectivity (we can discuss physics later). Hope this helps out - one more thing - What if I sand through? You need to finish sanding to get a level surface and refinish. Keep in mind that edges are damn easy to sand through and correcting this has just as much to do with painting technique as sanding technique. Personally, I do edges by hand, with no block. Quote Link to comment Share on other sites More sharing options...
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