Interior plaster: Types of plaster, quality levels and how to deal with defects

No more open cable ducts, no breakthroughs, and no markings on the walls. Smooth walls instead of raw masonry. Interior plastering marks the transition from shell construction to interior finishing. Mistakes are difficult to correct later. That’s why we looked into quality levels, types of plaster, and wall construction in depth beforehand.

Quality Levels for Plaster: Is Q2 Sufficient?

How smooth is smooth exactly? For interior plaster, quality levels indicate how even and uniform the wall surfaces are executed. For living spaces, Q2-Q4 are usually considered. Q2 is the standard for smoothed plaster surfaces and is often recommended for matte painted walls. The surcharge for Q3 would have been manageable for us, but we still decided on quality level Q2.

Our goal was clean, smooth walls without visible defects in everyday life. Q2 serves exactly this purpose and is sufficient for most living areas.

Overview of Quality Levels for Smoothed Plaster Surfaces

• Q1: Closed plaster surface
• Q2: suitable e.g. for:
  • Finishing coats, grain size >1.0 mm
  • Medium to coarsely textured wall coverings
  • Matte, filled paints/coatings (e.g., quartz-filled dispersion coatings) applied with a long-pile paint roller or textured roller
• Q3: suitable e.g. for:
  • Finishing coats, grain size ≤1.0 mm
  • Finely textured wall coverings, e.g., non-woven wallpaper (Vlies)
  • Matte, finely textured paints/coatings
• Q4: suitable for:
  • Smooth wall coverings and coatings with gloss, e.g., metal, vinyl, or silk wallpapers
  • Glazes or paints/coatings up to medium gloss
  • Filling and smoothing techniques

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The result surprised us positively. Even under grazing light, no significant irregularities can be seen with the naked eye. For our requirements, Q2 is perfectly sufficient.

The types of plaster used depended heavily on the substrate and the respective room.

Overview of Plaster Types and Wall Construction

There is no one-size-fits-all solution for interior plaster. The substrate and the use of the room determine which type of plaster is appropriate. Three different methods were used in our house.

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Concrete Walls: Adhesion Promoter and Lime-Cement Plaster

Concrete has a very smooth surface on which plaster does not adhere without preparation. Therefore, the plasterers first applied an organic adhesion promoter. This ensures that the subsequent plaster holds securely to the substrate. This was followed by a filled lime-cement plaster.

Sand-Lime Brick: Machine-Applied Plaster in Living Areas

The plasterers plastered the sand-lime brick walls with a single layer (12mm) of Knauf MP75 machine-applied interior plaster. For our living rooms, this was a simple and proven solution. The plaster ensures even surfaces, a calm wall appearance, and provides a good foundation for later painting.

Wet Rooms: Screeded Plaster

The bathrooms were plastered with a bathroom plaster as a "screeded plaster" using extended cement mortar, finished flat to accommodate tiles with tile adhesive. With the help of guide rails, the surfaces are precisely aligned. The result is even walls that significantly facilitate further construction.

Detail Work & Drywall: Windows, Wall Openings, and Ceiling Height

For the complete interior plaster, the plasterers must, of course, also close all remaining openings, connect window reveals flush with the wall, and adjust the ceiling height if necessary.

Wall Openings and Window Reveals

The plasterers closed all shafts for pipes and electrical lines with WEDI construction boards and plastered them. Afterward, they only had to plaster the window reveals. This created the foundation for the subsequent painting work.

Drywall in the Basement

In the basement, the shell construction in the bathroom has two different ceiling heights. This is necessary to ensure structural stability. Although the difference is only a few centimeters, the ceiling height should, of course, be a uniform 2.5 meters throughout the entire basement. To achieve this, the plasterer/drywaller suspended 6 m² of the ceiling area with drywall.

Inspection: Construction Defects in the Plastering Work?

Clean work, no damage, and nothing forgotten. The problem: more was done than agreed upon. The company commissioned for the interior plastering had attached cladding to the floor-to-ceiling windows and billed us for it. Completely without an order.

Annoying not only for us but also for the window installer, who was actually entitled to that work. Our architect and the site manager noticed this immediately, and together with both companies, we quickly found a solution. We are not paying for any of the costs resulting from this.

Such misunderstandings occur during house construction. It is important to identify them early and clarify them objectively. A pragmatic solution saves time and nerves.

How much does interior plaster cost in a new build? Prices at a glance