Dry Sanding. Wet sanding with a sponge is ideal for small patches and tight corners since it's easier to work a sanding sponge into those areas. Wet sanding also creates less dust, making it easier to clean up after the job is done. However, this method tends to result in finish that is less smooth than dry sanding.
Wet sanding an entire patch can make the patching look blocky. Dry sanding opens the pours of the plaster, and then your primer/flat paint lays on that real nice and smooth since there is a tooth for it to grab. Wet sanding over smooths the surface and makes the patching more noticeable, even when primed and painted.
Wet sanding is renowned for its ability to deliver a smoother finish on surfaces. The water acts as a lubricant that helps the abrasive material glide more smoothly over the surface, reducing the risk of leaving scratch marks that are often more apparent with dry sanding.
Use semi-coarse sandpaper of 100 of 120 grit to sand down the rough areas or dried compound, then continue with 150 grit to smooth the areas further.
Over Sanding
Perhaps the #1 mistake is to over-sand the joint, which can damage the drywall. If this happens, you'll need to apply a fresh coat of joint compound and start again… carefully.
You should do a little bit of sanding between adding coats of mud. Knock down any ridges or significantly imperfect areas through sanding, which should help you apply the next coat of mud smoothly. If your first coat of mud is pretty smooth after it dries, a quick sanding is all you'll need.
Pre-Mixed Joint Compound: Typically, pre-mixed joint compound takes about 24 hours for the first coat to dry, and an additional 24 hours for each subsequent coat. In ideal conditions, it can be ready for sanding and painting within 48 hours.
One of the most effective methods for minimizing dust during drywall sanding is wet sanding. It involves using a damp sponge or sanding screen along with a bucket of water. Dip the sponge or screen into the water, wring out any excess, and then sand the drywall surface.
Once you develop good techniques, you don't need to do anything other than scrap the joints with a dry drywall knife and wipe the drywall down before painting. To get to this point, you have to put three coats of drywall compound down. You use a larger drywall knife for each coat.
Cons of wet sanding
The presence of water or a liquid lubricant extends the drying time of the surface, which may increase the overall project duration. Additionally, wet sanding is not suitable for all materials or applications. Some materials may absorb water, causing swelling or damage.
Because wet sanding is a finishing process, you'll likely use high-grit sandpaper, from 1000 grit to 3000 grit and above. Compare this to dry sanding, which typically begins with 600- or 800-grit sandpaper. It's best to use a backing pad when wet sanding to achieve a uniform finish.
Fill a bucket with water and add a small amount of automotive soap. This will provide the lubricant for the sandpaper to prevent it from burning the paint when force is applied.
If your mud is too thin, you run the risk of leaving water rings on the drywall. Often, the mud will hit the wall and flatten out if it doesn't have enough elasticity. However, if your mud is too thick it could clog your hopper and create an undesired effect on the drywall.
Sand Taped and Mudded Drywall
After your third coat of mud has dried completely, it's time to sand and smooth the wall with 120-grit sandpaper. Although you can do this by hand, consider using a drywall pole sander to make the job easier.
The ideal environmental condi- tions for drying joint compound are a temperature range of 65 degrees to 80 degrees Fahrenheit and a relative humidity between 20 to 40 percent.
Wet sanding also creates less dust, making it easier to clean up after the job is done. However, this method tends to result in finish that is less smooth than dry sanding. Dry sanding offers a more even and smooth finish. This is a great option for covering larger surface areas and whole walls in bigger rooms.
When painting or installing drywall in closed spaces, an HVAC system will not dry the materials or remove excess moisture from the air adequately. Moreover, the use of an HVAC system for construction drying purposes results in energy losses and unnecessary wear that could void its warranty.
Use a push-pull motion with a pole sander or hand sander to apply pressure along seams, nail and screw patterns and even pressure. To smooth out rough areas, use semi-coarse paper of 100 or 120 grit. Next, add 150 grit. For finishing drywall sanding, use sheets of sandpaper.
Good air flow also helps speed things up. To dry mud quicker, pros use fans for better air circulation. Some also use heaters to warm up the room.
Too much sanding will cause damage to the paper face on the drywall.
Any skim coat or the outer edges of feather coats will dry within 15 to 20 minutes. Properly installing drywall requires not just effort but also plenty of time, particularly when it comes to drying time for each coat of drywall mud. For a better paint job, avoid pushing drywall mud times.
If you notice a lot of bumps or uneven surfaces, then it's likely due to improper drywall finishing. Keep in mind, some roughness near lower levels of the finish might be acceptable, but be sure to pay close attention to corners and edges as these areas can especially appear to be uneven.