Lesson 15. Base Defects and Their Features

In the previous lesson, we completed the study of methods for preparing rough walls up to Q1–Q4 levels. You now know which materials and techniques can improve the surface: from minimally prepared (Q1), suitable only for simple decorative finishes, to perfectly smooth (Q4), capable of highlighting the aesthetics of even the most demanding glossy thin‑layer coating.

With this general knowledge of flatness and smoothness criteria, and understanding which defects are permissible at each level, we can now move to a more detailed examination in the context of decorative plaster.

In this lesson, we will dive deeper into the Q1–Q4 preparation system and analyze the concept of defect correction. Our goal is to form a clear understanding of when it is necessary and why it is important to master this skill.

For a craftsman, studying the Q1–Q4 quality system means developing a professional view of this classification. It is not only about clear criteria and permissible defects at each level, but also about understanding what they represent.

Key Principles

The most important point: a surface does not have to fully meet all requirements of a given level (Q1–Q4) to be classified as such. In practice, one wall often combines features of different levels, and classification is always determined by the lowest level present.
If a wall is declared as prepared to Q3, this means the entire surface meets Q3 criteria. It is unacceptable for the central part to meet Q3 while, for example, the upper corner only meets Q2. Quality must be consistent across the whole plane, otherwise the work is considered at the lower level.

Example:

• Vertical deviation: no more than 1 mm per 2 m
• No visible defects: dents, scratches, gouges, tool marks
• Side‑light shadows: present
• Sanding scratches: up to 0.3 mm deep
• Local ridges of plaster: up to 2 mm high

Here, most of the surface corresponds to Q3, but the presence of ridges already disqualifies it from Q3 and automatically assigns it to Q1. As a result, the entire wall is evaluated at Q1. This drastically limits the choice of decorative materials: instead of almost any finish, including thin‑layer coatings, only thick‑layer options remain.
Defect Correction vs. Full Rework

Defect correction does not mean repeating the entire Q1–Q4 preparation process. It does not include applying plaster or putty over the whole wall, nor leveling large areas to fix vertical deviations. Defect correction refers only to localized fixes of individual flaws without redoing the entire surface.

In practice, spot repairs are done when:

• Small flaws remain after preparation (scratches, chips, ridges of putty — no more than 1–2 per m²).
• Defects appear later (moving furniture, tools, or during adjacent work).

If defects exceed 1–2 per m², this is no longer defect correction but requires full re‑puttying or sanding of the surface.

Communication with Clients

In such cases, it is important to explain the issue to the client and agree that major corrections should be done by the specialists who prepared the wall. For old walls where the client does not know who did the preparation, you must clarify what result is needed for the chosen finish, what exactly should be done, and what requirements to set for workers. You may also recommend trusted specialists.

If the client is unwilling to invest in extra work, suggest alternative decorative materials that will look harmonious with the current preparation level.

Professional Skills

Defect correction is a natural part of a decorator’s work. It is important not only to identify flaws but also to know how to fix them. Even on surfaces that appear smooth, defects may be hidden: deep scratches, fine grooves from abrasives, chipped corners, dowel holes, rough traces of patched chases or sockets, ridges of putty, bumps, cracks.
Most of these are visible immediately, but some appear only during work — for example, after priming, which highlights unevenness, or during painting when creating a background for decorative material.

The ability to quickly fix small defects saves time and avoids unnecessary delays. A couple of chips or scratches should not stop work or force waiting for another specialist. The ability to correct them promptly maintains workflow, demonstrates professionalism, and ensures a high‑quality final result.

Next Step

In the next lesson, we will examine the most common defects encountered in practice and learn how to eliminate them easily and independently.