How to Sand Inside and Outside Surfaces
Sanding is involved to some extent in the majority of painting projects. Its purpose is to get rid of irregularities; a uniformly flat wall holds paint better than one that’s covered in elevations and indentations.
Properly sanding a surface involves several stages of work. At first, the sander’s grit (the particle size distribution — that is, the texture of the tool’s sandpapery surface) should be on the rougher side. During the course of sanding, it’s important to switch to a finer grit in order to get the results you want. Making a coarse wall completely smooth requires a lot of work. If you’re not intent on perfection, you won’t have to put in quite as much energy.
Sanders and Other Tools
If you have a lot of sanding to do, a power sander will be your best friend. Random orbital sanders and disc sanders are both fine choices in general, but the former is gentler on delicate surfaces (e.g., redwood). On features like trim, a palm sander or trim sander is usually best.
Though power sanders are convenient, sanding always requires some manual work. You may be able to get to hard-to-reach corners using sandpaper or an abrasive sponge. These tools are also good for putting the finishing touches on spots you’ve already worked on with a power sander. It may seem superfluous, but doing a second round of sanding by hand can turn a fairly smooth surface into one that’s ideal for painting.
Sanding Indoor Surfaces
We may sound like a broken record, but it’s worth repeating: Prior to painting, you should make your indoor walls as smooth as possible. Where chipping or repair work has occurred, sand away elevated spots and edges. Dust that’s become trapped in a wall’s coating will be visible if you simply paint over it; instead, use sanding to get rid of it. On the other hand, if the surface is glossy, you may need to sand it until it’s coarse enough for new paint to adhere to.
Again, if you have a lot of square footage to sand, start with a power sander and go over the surface by hand afterwards. The grain should guide your sanding motion. Stained walls lend themselves to manual sanding, unless your goal is to take off the current stain in its entirety.
When you’re done sanding, use a vacuum to clean up the mess. Also, don’t forget to wipe the surface down with a tack cloth.
How to Handle Wood Trim That’s Already Painted
Finished trim presents special challenges from a sanding perspective. Sandpaper with a grit between 60 and 80 (or an abrasive sponge that’s medium fine) can help you take off brush strokes or previous coats of paint. Sanding itself can leave imperfections; these can be eliminated using 120 grit sandpaper or a finer sponge.
When wood is new, it’s best to use 120 grit sandpaper initially and follow up with the 150 grit variety. As usual, follow the grain of the wood, and be aware of elevated grain. Mill glaze, a protective coating applied to wood during the production process, is designed to be stain retardant. Unfortunately, it can also keep primer from sticking. Make sure to remove it all.
Sanding Outside Surfaces
Outdoor walls that are painted require power sanding. As mentioned previously, an orbital or disc sander is best for bigger portions of the exterior, while palm or trim sanders are made for a surface’s smaller features. Don’t be heavy handed in your work; as with pressure washing, it’s essential not to stop the machine in one place, because this can cause indentations.
Trim and Siding Made of Wood
If paint is peeling from an outside wall, it has to be scraped manually. Subsequently, a power sander can be used to eliminate pieces of loose paint and smooth any remaining edges. Paint applied thickly may require a rough sanding disc; 30 grit should suffice. A second round of sanding, using finer discs (60 grit, perhaps), will get rid of any marks you made during the first round.
Power sanders are harder to use than you might think. It’s all too easy to leave wavelike patterns in delicate wood surfaces. When in doubt, it’s always acceptable to employ fine sandpaper instead. It may not be as efficient, but it’s much more foolproof.
Sanding Masonite siding can be a real challenge. Use a power sander with a 60 grit disc (or finer) for this kind of work. The main difficulty Masonite presents is its fragility. Waves are hard to avoid, and Masonite that’s been around for a while has a tendency simply to break. As ever, make sure the sander is in constant motion.
Finished Doors and Windows
Power sanders send out waves of energy forceful enough to shatter glass. Thus, as you might imagine, it’s not a good idea to power sand windows. Do it manually instead: Scrape off residual caulk, putty, or paint, then use rough sandpaper to remove whatever the scraper didn’t. Remember to sand the wood surrounding windows, not the windows themselves, since they’re highly susceptible to scratching.
With finished doors, the process should begin with orbital sanding. An abrasive sponge can then be used to take paint out of corners the power sander couldn’t reach.
Stained Windows and Doors
Stained walls, trim, and other surfaces are sanded similarly regardless of whether they’re indoors or out. As usual, doors and windows require an extra dose of TLC; sand them manually with sandpaper and/or a sponge that’s on the less abrasive side. 180 grit is an appropriate abrasion level to get rid of brush marks and rough spots on paint that’s otherwise in good condition. If it isn’t, you may want to use 120 grit sandpaper to take off the top coating, then 180 grit to work on the stained wood underneath.
This line of products indicates abrasiveness via color coding. The sanding sponges start at 36 grit, which is extremely rough, to 320 grit, one of the least abrasive textures available. Most important, SandBlasters are efficient and stand up well to repeated use.