Lesson 16. Defect Correction: Methods of Elimination

In the previous lesson, we discussed that when evaluating wall preparation quality according to the Q1–Q4 system, certain indicators may correspond to a lower level due to defects — either left during preparation or appearing after completion. We also examined when full wall treatment is required to achieve the desired quality, and when spot repair is sufficient.

In this lesson, you will learn which surface defects most often occur during decorative work and how to properly perform defect correction. We begin with areas where hidden problems most frequently appear. These can spoil even a well‑prepared surface and complicate work with decorative plaster.

Typical Problem Areas

Special attention should be paid to corners, joints with floor and ceiling, and narrow zones inside niches. These areas are harder to prepare because tool control is limited, so defects often remain. When decorative plaster is applied, such flaws become especially noticeable.

Central wall zones, by contrast, are usually prepared better: the craftsman can stand comfortably, control tools easily, and work without restrictions. This principle applies both to preparation and to applying the decorative finish.

If difficult areas were poorly prepared and defects left uncorrected, applying decorative material without masking properties will highlight them and reduce the overall aesthetic quality.

Types of Defects

All surface defects can be divided into two groups: protrusions and depressions. Defect correction means reducing protrusions and filling depressions.

Eliminating Protrusions

Protrusions — ridges of plaster or putty, small bumps — are removed with abrasives. Use P180 or P240 to reduce height, then smooth with P320. Work carefully: pressure should be applied directly to the defect to avoid removing surrounding material. A sanding block is used to hold the paper.

Extra care is needed before applying thin‑layer decorative materials. If sanding creates a depression, it must be filled with putty. Corners and tight areas require delicate handling to avoid damaging adjacent surfaces.

Since putties vary in hardness, test how easily the material sands. If hard, increase pressure or use coarser grit; if soft, reduce pressure and use finer grit. Very small protrusions can be trimmed with a utility knife.

After correction, re‑priming the entire wall is unnecessary — only the treated area should be primed.

Eliminating Depressions

Depressions include scratches, chips, and holes. They are filled with non‑shrinking putty. Before filling, prime with strengthening or deep‑penetration primer.

Non‑shrinking putty can be replaced with white acrylic wood filler for small defects (1–3 mm deep). These materials are sold in small volumes, convenient for local repairs.

Apply putty with a spatula, filling flush with the wall surface. Non‑shrinking putty does not sink after drying. Standard putties shrink, so they must be applied with a slight excess.
For deeper defects (3–5 mm), use plaster or several layers of putty, allowing each layer to dry. After filling, sand tool marks and prime the area.

Cracks

Cracks are a separate type of depression. On drywall bases, they usually appear at sheet joints due to storage issues, humidity problems, base deformation, weak profiles, or poor joint treatment.

Correction requires cutting open the joint and re‑filling with reinforcing tape. Screws fixing sheets to guide profiles may be removed to reduce rigidity. Check that compensation gaps at ceiling and floor are present.

Decorators do not perform such structural corrections — they explain the issue to the client and recommend re‑work by specialists.

On plaster bases, micro‑cracks resembling spiderwebs often result from poor technology: wrong priming, unsuitable temperature, lack of mesh, or bad mix. If the surface is still solid, it can be reinforced with fiberglass fleece or mesh. But decorative materials must not be applied directly over cracks.

Small cracks (~1 mm wide) caused by building settlement can be corrected by the decorator: cut open with a knife (5–10 mm wide), prime, and fill like any depression. In corners, acrylic sealant can be used for elasticity.

Large cracks, or those indicating plaster detachment, require full re‑work by specialists.

Conclusion

In this lesson, we examined how to eliminate minor wall defects. These skills will be useful repeatedly, helping you work faster and maintain quality.
In the next lesson, we will explore how Q1–Q4 preparation levels interact with decorative materials.