Q1, Q2, Q3 or Q4: which drywall finish level your project actually needs

The finish levels Q1 to Q4 are not an Estonian national standard. The Knauf Estonia material says so outright: the quality levels Q1 to Q4 for finishing plasterboard surfaces were developed by Eurogypsum, the European gypsum industry association, together with UEEP, the union of finishing contractors. It is a joint system of manufacturers and finishers, not a regulation.

The practical consequence is simple. No Estonian legal act known to us says that a corridor wall has to be Q3. The level is set by whoever writes the works description: the designer, the cost consultant on the client side, or the main contractor's scope text. If nobody writes it, the level does not exist in the contract, and what applies instead is the chapter below on a contract that names no level.

Knauf recommends exactly this to whoever drafts the contract. The manufacturer page states that in order to avoid disagreement between client and contractor over the end result, it is sensible to set the quality requirements precisely through surface quality levels. That is advice about contract text, not an installation instruction for the tradesman.

The same page adds the other half, the half a scope is usually missing: finishing contracts and works descriptions define the properties of the surface to be finished and its quality level. Properties and level are two separate lines. The level alone does not say what goes on top of the surface, and that is exactly what decides whether the level was chosen correctly at all.

Each level contains the one below it. What follows tracks the definitions on the Knauf Estonia filler page.

Q1 is the technically necessary level. Board joints are filled with compound and, where needed, joint tape, and visible screw heads are covered with compound. No optical requirements for smoothness or appearance apply to a Q1 surface. Q1 suits a surface that will be covered with ceramic or decorative tile, and it serves as the base for the next coat.

Q2 is standard filling. On top of Q1 comes a second coat, applied so that the transition from one board to the next is smooth; the same requirement covers fixings, internal and external corners and the edges of movement joints. Q2 suits matt paints, coarser-textured wall coverings and decorative renders with a grain above 1 mm. No tool marks and no compound residue may be left on the surface.

Q3 is standard filling plus wide filling over the joint zones and a thin skim across the whole board face that fills the pores. The levelled surface is sanded as required. Q3 suits thin wall coverings, matt paints and decorative renders with a grain up to 1 mm.

Q4 is a full skim. The joints and the entire board face are covered with an even 1 to 3 mm coat of compound and, where required, the sanded and dried surface receives one further thin coat. Q4 is the flattest level and suits smooth and glossy wall coverings, mid-sheen paints and decorative finishing compounds.

The name of the room is not the basis for choosing a level, it is shorthand. The manufacturer ties the level to the finishing material: to what goes on top of the compound and how much light that surface throws back. A room-type table works only when every row carries with it the finish the level was meant for. Without that, the table is an opinion.

Two rules override the table. First: where the surface will be covered with ceramic tile, the Knauf instruction is to fill the joints only, and to avoid sanding and filling beyond the joint zone. A higher level here is money that disappears under the tile. Second: on a multi-layer construction with a fire resistance requirement, the joints of the lower board layers must also be filled with compound, without joint tape and without covering the screws. That work is not part of the level of the visible surface and belongs in the scope as a separate line.

The third factor is light, and it outweighs room type often enough to have earned its own chapter.

Raking light is what exposes the difference. Compound shrinks as it dries, so a flat surface covered evenly with fresh compound pulls into a shallow hollow over the joint. In direct light it is invisible; in sharp raking light the eye reads the hollow as a shadow. Knauf describes this mechanism explicitly at Q2 and states that Q3 reduces the strength and extent of the shadowed areas rather than removing them.

At Q4 the message is blunter still. According to Knauf, filled surfaces that are completely even and free of shadow under light falling from the side are not technically achievable. Which means a shadow-free wall is not an enforceable contract requirement at any level. What is enforceable is the level, the finishing material, and the lighting under which the surface is accepted.

The same page adds a warning that gets ignored on site constantly: where a surface was levelled under LED work lighting alone, with no account taken of daylight, visual differences caused by light and shadow may appear later. Knauf recommends dealing with the lighting question during the filling works and, where necessary, adjusting the choice of the planned raking light source or the direction of its beam.

For the scope that means three lines: which finish goes on the surface, what its sheen is, and under which light handover takes place. A wall-washer or a floor-to-ceiling window makes a corridor a Q4 case even when the room-type table says Q3. And the other way round: an interior in matt paint with no raking light does not need Q4 in order to be sound.

When the contract names no level, the gap does not stay empty. Clause 4.9.1 of the general conditions of building contracts ETU 2013 states that where the contract sets no more specific quality requirements and none follow from legislation either, the contractor shall carry out the works, having regard to the circumstances, to at least average quality, and shall follow good building practice.

Average quality is not a number. The subcontractor prices it as Q2, because that is the market default. The designer on the client side had a Q3 surface in mind, because there is a wall-washer on that wall. Neither is lying and neither knows the assumption of the other. The difference surfaces at handover, under the client's own light, once the surface is already painted.

From there the ETU 2013 machinery is formal. Clause 4.9.5 gives the client five working days from discovery to give notice of non-conformity, allowing a reasonable period for remedy. Clause 4.9.7 states that in a dispute over quality or quantities the parties shall arrange control measurements or tests within five working days at the latest, in the presence of the representatives of both parties; unless agreed otherwise the contractor arranges them and gives three working days of notice.

But a control measurement cannot agree a level that was never agreed. It can only compare the surface against what the contract says. If the contract says filling and painting, then at least average quality is what gets measured, and the dispute ends not in a measurement but in a negotiation where both sides hold a defensible position.

The cost is asymmetric. Raising the level after painting is not a repair but a new cycle: priming, filling, sanding and repainting across the whole surface group. A patch repair shows up under exactly the light that found the defect, so a partial solution does not technically exist.

Novashop settles this on the contract side, not on site. The level is fixed in the scope before the first coat, surface group by surface group, together with the finishing material and the handover lighting. The quote is fixed and the contract written, work starts with no advance payment, and the filling stage is accepted against a checklist before the painter starts. A change of level is then a visible variation rather than a difference of opinion discovered at handover.

A higher level is not the same work done better. It is more coats, more drying and more sanding passes. Q1 to Q2 adds a second coat over the joints and the fixings. Q2 to Q3 adds wide joint filling and a thin skim across the whole board face. Q3 to Q4 adds a 1 to 3 mm skim and, where required, one more thin coat after sanding.

Every coat has to dry before the next one. Knauf notes separately that the drying time of ready-mixed dispersion compounds is governed by the temperature and humidity of both the surrounding air and the substrate, and that the temperature and humidity conditions on site affect the final quality of the work. Drying is calendar time. It is not accelerated by putting more people against the wall.

Priming falls in between. Knauf recommends priming the surface to be filled in order to even out the different absorbency of board and compound and to secure adhesion, and adds that to avoid disagreement it is sensible for the necessary prior priming to be done by the same party that does the filling. In the program that means the primer is a line of its own, not the painter's first day.

The third effect is dust and sequence. Sanding does not run in parallel with many other trades in the same zone. The higher the level, the more times the zone has to be closed to others, and the more the completion date depends on sequence rather than speed. A change of level therefore always travels with a change to the program, and it belongs in the milestone matrix before the fact, not after.

Tenders become comparable when every bidder prices the same surface to the same level. The seven lines below are the scope language that achieves it. They belong in the works description, not in a covering letter and not in the minutes of a site meeting.

With those seven lines you can lay three tenders side by side and see why one is cheaper. Without them, the cheapest tender is usually cheaper for one reason: it priced a lower level, and the difference comes back at handover, where somebody else pays it.