Inside Corners, Outside Corners, and Fastener Dimples

Why Corners and Dimples Matter

Corners and fastener dimples are the most visible indicators of a finisher's skill. A crowned outside corner bead or a raised dimple will telegraph through every coat of paint. Getting these surfaces flush — not just covered — is the standard every inspector and painter will judge you against. This lesson covers the three tasks you will repeat on every drywall job: inside corners, outside corners, and fastener dimples.

Safety Before You Start

Wear safety glasses whenever you are cutting or crimping metal corner bead — cut edges are sharp and fragments can fly. Fit an N95 respirator before mixing or working with joint compound; even pre-mixed compound releases fine particles during sanding and heavy wiping. Wear work gloves when handling metal bead. Keep your work area clear of cords and compound buckets to prevent trips. If you are using a staple gun, keep fingers clear of the nose and treat it as a tool capable of serious puncture injury.

Inside Corners

An inside corner is the 90-degree junction where two walls meet, or a wall meets a ceiling. Paper tape is the correct reinforcement here — fiberglass mesh tape is not recommended for inside corners because it is harder to bed flat into a tight angle and is more likely to crack.

Step 1 — Apply compound to both faces. Load a 6-inch knife and apply a thin, even coat of all-purpose or taping compound to each face of the corner. Cover roughly 3 to 4 inches out from the corner on each side. The compound should be wet enough to bond the tape but not so thick that it oozes out and creates buildup.

Step 2 — Fold and press the tape. Tear or cut paper tape to length. Fold it lengthwise along the pre-creased center line. Press the folded tape into the wet compound, starting at the top and working down, keeping it centered in the corner.

Step 3 — Bed with a corner knife or a 6-inch knife. An angle corner knife lets you press and smooth both faces simultaneously. If you use a flat knife instead, wipe one face flat first, then the other. Either way, the goal is to embed the tape fully so no bubbles or dry spots remain, while keeping each face of tape flat against the wall — no wrinkles, no lifted edges.

Step 4 — Wipe each face flush. Remove excess compound with a light finishing stroke. The tape surface should be smooth and level with the surrounding board face. Check with a raking light held low and parallel to the wall; any ridges will cast a shadow and must be knocked down before the coat dries.

Outside Corners

An outside corner is exposed and takes physical abuse from carts, furniture, and traffic. It requires rigid reinforcement: metal corner bead (galvanized steel) or vinyl corner bead.

Bead selection. Metal bead is the traditional choice and handles impact well. Vinyl bead is flexible, resists rust, and is common in humid environments. Follow the project specification or local practice.

Installing metal bead. Cut the bead to length with tin snips. Position it over the corner so the nose — the raised ridge running down the center — sits at or just below the plane of the finished wall surface. Secure it with a corner crimper every 6 to 8 inches or with a staple gun, following the manufacturer's direction and local practice. The bead must be straight and tight against the board on both flanges with no gaps.

First coat of compound. Use a 10-inch knife. Apply compound on one face, starting at the bead nose and feathering out 4 to 5 inches onto the wall. Then do the other face. The nose of the bead acts as a screed — your knife rides along it. Do not pile compound on top of the nose; the goal is to bring the surrounding wall surface up level with the nose, not to bury the nose.

Check for crown. Lay a 48-inch straightedge across the corner, spanning from wall to wall. If the straightedge rocks, compound has built up over the bead nose and you have a crown. Scrape it back before it dries. Pass means the straightedge lies flat — the bead nose is flush or very slightly recessed, never proud.

Fastener Dimples

Every screw or nail driven into drywall must be set just below the surface — creating a small dimple — without breaking the paper face. If the fastener is set correctly, you have a clean recess to fill. If the paper is torn, the fastener must be reset or an additional fastener driven nearby.

Filling the dimple — first coat. Load a 6-inch knife with a small amount of compound. Draw the knife across the dimple at a slight angle, packing compound into the recess. Immediately wipe across the other direction to level it. Two strokes is the target. The compound should be flush with the board face — not crowned above it.

Avoid compound buildup. Crowning is the most common error. If you apply too much compound, it cures proud of the surface and must be sanded or scraped back. A raking light will reveal crowns instantly. Check your work before moving to the next dimple.

One coat is not enough — but one coat is today's goal. Dimples typically require two or three thin coats as compound shrinks as it dries. Today you are applying and evaluating the first coat only. Each subsequent coat will be applied after the previous one is fully dry.

Using a Raking Light

A raking light — a work light held close to and nearly parallel with the wall surface — is the finisher's best quality-control tool. Use it after every coat to catch ridges, crowns, voids, and tape edges before the compound dries. Develop the habit now.