To properly finish drywall, you must first identify the right level of finish for the job, and this decision requires consideration of a variety of factors, including the location, layout, amount of lighting, planned paint or wall treatment, and even the number of windows. Each level builds on the previous levels, so a level five finish includes all the components of the previous levels and so forth.
Determining and Applying Levels of Finish
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Level Zero
The lowest level of finish requires no finish at all and no taping, joint compound or additional tools. This can be an acceptable option only if the drywall itself is temporary or while you are still determining the appropriate final finish level.
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Level One
This level offers a rough finish that is appropriate for areas out of public view, such as service areas in an industrial building.
While still largely unfinished, level one features some fire proofing and taping, though not necessarily up to full fire-resistant assembly requirements. You should apply joint compound and embed tape at all the joints and any interior angles, but it is not necessary to smooth these out as tool marks and unfinished edges are acceptable at this level. Apply wall-covering primer in any areas where you plan to use a wall covering.
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Level Two
This level is a good choice in areas where you are planning to cover the drywall with tile or in areas that are visible but where the client is not as concerned about the appearance, such as in a warehouse or garage.
In addition to applying tape and joint compound at the interior angles and joints, you must also smooth out the compound with a joint knife or trowel. You should plan to use joint compound to cover fastener heads and accessories. Some tool marks and edges in the finish are still acceptable at this level.
If you are painting, apply a single coat of a topcoat material to even out the surface, and then apply paint at a mil thickness, or approximately the thickness of a sheet of paper.] At this level, you are prioritizing cost and efficiency, so expect some visual inconsistencies in the paint finish that are out of your control.
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Level Three
This is a good level to consider if you are covering the drywall with a textured treatment with a medium to heavy texture or a heavy-grade wall covering.
This level calls for an additional coat of compound on the joint and angles, as well as on the fastener heads and accessories. At this level and higher, you should smooth out all tool marks and unfinished edges. To remove any marks, apply a damp sponge to smooth out the area or lightly sand it, taking care not to damage the facing paper on the drywall. Apply a final layer of drywall primer.
Before painting, you should apply two layers of the topcoat at approximately a mil thickness.
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Level Four
If you are using a lighter texture or wall covering or none at all, you can consider a level four finish but only with flat or enamel paints. Paints with more sheen, such as gloss or semi-gloss, are not a good fit with a level four finish as they can allow for joint photographing, or visible joint tape under the finished surface. When considering a level four finish, pay attention to areas with large uninterrupted walls, such as long hallways, and areas with many or large windows. These areas may require a higher level of finish to maintain a uniform look.
In addition to the previous layer, you should add another layer of joint compound over any flat joints, fastener heads and accessories. Besides the initial tape and joint compound on the corners and joints, this should give you two coats on the flat joints, one coat on the interior angles and three coats on fastener heads and accessories. Again, smooth out any tool marks and apply a drywall primer, though a drywall primer may not be necessary if you are applying some types of textured wall coverings. Check the manufacturer recommendations if you are not certain.
Before painting, apply a single layer of the topcoat over the drywall primer. Again, apply paint at about a mil thickness.
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Level Five
A level five finish requires the most time and expense, but it is also the highest quality and most forgiving. Use a level five finish in areas where strong lighting may increase the possibility of joint photographing and in areas where you plan to use a paint other than flat or enamel. Fiberglass mat drywall panels should generally receive a level five finish due to a naturally rougher texture than paper-covered drywall.
After applying all the joint compound required for level four, then apply a thin skim coat layer of compound or a surface primer designed for this stage. This coat should hide any small remaining variations in the surface texture of the drywall. Immediately skim off any excess compound, and smooth out any tool marks before applying the final drywall primer.
When painting, first apply two separate coats of topcoat over the layer of drywall primer. For best results, consider using a level-five gypsum board finish.
Keep in mind that level five requires the most layers, and therefore the most drying time, which can be an important factor to consider in colder or humid weather. Typically, you can expect 24 hours between joint compound coats, but plan on longer if the forecast calls for low temperatures or high humidity.