This technical specification refers to the plastering of brick walls, walls made of hollow clay blocks or various concrete blocks and concrete walls in the interior.

1. Relevant standards

EN 13914-2 (2016) Design, preparation and application of external rendering and internal plastering - Part 2: Internal plastering

EN 998-1 (2016) Specification for mortar for masonry - Part 1: Rendering and plastering mortar

and other standards mentioned in these standards.

2. Material

The material should be declared according to mortar properties and/or application as General purpose mortar - GP (EN 998-1)

The material for plastering the walls should meet the following requirements:

- Compressive strength (EN 1015-11):

for plastering internal walls, that will be painted or covered with wallpaper, material should be declared as lime-cement mortar and classified at least as CS I.

for plastering internal walls, which will be cladded with ceramic or stone tiles, should be declared as cement mortar and classified at least as CS II.

- Water absorption by capillarity (EN 1015-18): there are no special requirements
- Thermal conductivity (EN 1745): there are no special requirements
- Reaction to fire (EN 13501-1): Class A1
- Durability on exposure to frost / thaw cycles: there are no special requirements
- Adhesive strength according to the test in EN 1015-12 should be not less than 0,25 N/mm2
- The coefficient of water vapour permeability µ (EN 1015-19): there are no special requirements 

- Flatness class (EN 13914-2) should be:
Level 1 for use in areas where finish is not critical
Level 2 to receive a textured wallpaper or a textured paint
Level 3 to receive a matt paint or smooth wallpaper
Level 4 to receive a semi-gloss paint and / or glancing illumination

Apart from cement and lime, which are already classified as materials with hazardous ingredients, the material must not contain other substances harmful to human health.

Before the start of work, contractor is obliged to submit manufacturer's certificates for all materials to the Supervisor for approval, through the Submittal process.

3. Workmanship

Before starting the work, the contractor should check whether the walls to be plastered are strong and clean, free from any film, such as dust, oil or paint, which could impair bond between plaster and substrate.

Before plastering, the contractor should check the flatness of the walls with a spirit level with a minimum length of 2 m, a rope and plumb bob. In case of larger deviations of 5 mm in height and length of the wall, further procedures should be agreed with the supervisor.

The contractor should double check that all installation works prior to plastering have been performed. Built-in doors, windows and other elements should be protected from damage.

The mortar mixture should be stored on the construction site in a dry place on pallets. The mortar mixing machine should be cleaned after previous work.

When working on plastering, in addition to the usual equipment, workers should wear protective glasses and gloves. The rooms in which work is done should be as well ventilated as possible.

All work should be performed strictly according to the instructions of the material manufacturer.

The walls should be plastered at full height, from the reinforced concrete floor slab to the ceiling slab.

The optimal temperature in the room where the works are performed should be between + 5ºC and + 25ºC. It is not allowed to heat the room due to the drying of the mortar.

The mortar should be prepared in a mixing plastering machine, by mixing the dry mixture with water. Brick or block walls to be prepared for plastering by pouring a spatterdash coat 2-3 mm thick. At higher temperatures, the walls should be moistened. Contact coating to be used for better adhesion for concrete walls. Vertical level strips should be placed on the walls, from the floor slab to the ceiling slab, at a distance slightly less than the length of the ruler. Angular level strips to be placed at the corners. If the plaster is applied in two layers, the second layer should be applied on the fresh first layer. After applying the second layer of plaster, the surface is to be levelled with an H-shaped aluminium ruler. A couple of hours after applying the second layer, the mortar should be finally levelled with a hand tool. The total thickness of the mortar should be 10 - 25mm. In case it is necessary to make a thicker layer, the plaster should be reinforced with mesh.

Flatness: Allowed maximum deviations of plastered surfaces in two meters is 3mm on surfaces covered with ceramic tiles, stone tiles or with textured wallpaper or a textured paint and 2mm on surfaces where the final coating is matt paint or smooth wallpaper.

If any installations need to be laid on plastered surfaces, after finishing plastering, they should be patched with the same mortar as the base mortar.

The time for drying the mortar and the beginning of the painting works is at least 10 days per cm of mortar thickness.

4. Supervision and measurement of works

After the material is delivered to the site, the supervisor should check whether the material is delivered in proper condition, it is packed and marked as required by this technical specification and whether it is properly stored.

Supervisor is obliged, before the beginning of the works, to check that the contractor has verified that the rooms are ready for plastering, visually check the condition of walls in the rooms and approve the commencement of works.

Supervisor is required to check the flatness of the plastered walls by the mason's bubble level, on random places (at least 25% of the walls). The results to be written in the contractor’s check lists. If major deviations occur, remedial measures approved by the supervisor should be applied.

Unless otherwise provided by the contract, executed works are calculated per m2 of plastered surface, the measures to be taken on the site. Openings in walls up to 3 m2 should not be subtracted from the total quantity and window reveals area should not be added. If the opening is 3 to 5 m2, area over 3 m2 should be substracted and window reveals area should not be added. If the opening is bigger than 5 m2, area of opening over 3m2 should be subtracted from the total quantity and window reveals area should be added.
In all cases, if windows reveals are wider than 20cm, then the area over 20cm should be calculated per m2 and added to the total amount.

February, 2021
Please note that the technical specifications on this web site are templates only, information provided should be carefully checked and aligned with your project needs.
Compressive strength at 28 days (EN 1015-1)
CS I - from 0,4 to 2,5 N/mm2
CS II - from 1,5 to 5,0 N/mm2
CS III - from 3,5 to 7,5 N/mm2
CS IV   ≥6 N/mm2
Mortars that contain organic materials in a fraction ≤1% (by mass or volume) are rated class A1, without requiring testing.
Contract documentation should specify if the final lighting of any surface is to fall at glancing angles (a critical lighting condition which exists when light hits a painted surface at an acute angle and casts shadows that highlight any surface irregularities). The contractor should be fully aware of any onerous lighting.
It happens that the contractor, because of the savings, suggests plastering the walls only 10 cm above the level of the suspended ceiling, which in my opinion should not be allowed.