SKIMMING AND PAINTING OF WALLS AND CEILINGS
1. Relevant standards
EN 13300 (2009) Paints and varnishes - Water-borne coating materials and coating systems for interior walls and ceilings - Classification
EN ISO 11998 (2006) Paints and varnishes - Determination of wet-scrub resistance and cleanability of coatings
EN ISO 2813 (2014) Paints and varnishes - Determination of gloss value at 20°, 60° and 85°
EN 21524 (1991) Paints and varnishes - Determination of fineness of grind
ISO 787-7 (2009) General methods of test for pigments and extenders - Part 7: Determination of residue on sieve - Water method - Manual procedure
This Technical Specification refers to water-based coating materials for substrate preparation (primers), skimming and painting of plastered walls and ceilings or gypsum board surfaces. All these materials should be mutually compatible, which should be confirmed by the manufacturers of materials.
The products must be free of any harmful substances, components containing heavy metals such as lead, mercury or chrome and must not contain toxic solvents. The products must have a complete Safety Data Sheet and all the carcinogenesis compounds and Volatile Organic Compounds emitted by the product must be measured. The maximum VOC content, in a ready to use condition, should be less then 30g/l.
Dillution of all materials must be with clean water, free from harmful substances.
Paint must be machine tinted, tinting paint on the site is not allowed.
Unless otherwise provided by the design, paint should be classified by gloss (according to EN ISO 2813) as matt or dead-matt.
The paint structure, classified by largest grain size (in accordance with EN 21524), should be "fine" (grain size up to 100 µm).
The coating system (primer - skimming - paint layer) should form a vapor permeable structure.
The paint should be stable and resistant to fading when exposed to light.
Applied materials must be such that during the exploitation of the building, it is possible to re-paint the surface (at least) with the same material.
Painted surfaces should be resistant to "wet scrubbing" (in accordance with EN ISO 11998) as follows:
- At least class 2 for the walls of the area where there is a greater possibility of dirt, such as halls, stairs, cafes, etc. or
- At least class 3 for walls of rooms where there is less risk of damping, such as rooms, offices, etc. and
- At least class 4 for ceilings of rooms.
Contractor is to submit manual for maintenance and cleaning.
All materials should be approved through the Submittal process.
Material delivered on the site should be in original packaging that legibly show name of the manufacturer and product name, date of manufacture, manufacturer's directions including any warnings and special precautions, the content of the harmful substances (VOC). Unless otherwise stated in the manufacturer's instructions, the material must be stored in a ventilated room at a temperature of 7° C to 30° C.
Plastered surfaces and decorative gypsum elements shall be allowed to cure at least 30 days before the start of the painting works. The maximum permissible humidity of the mortar should be in accordance with the instructions of the manufacturer of the material for painting works.
The preparation of surfaces for painting works includes the removal of metal parts, screws, anchors, and the like. Surfaces should be cleaned of dust and other dirt, such as oil, grease, rust, cement mortar and the like. All minor damages, cracks, holes, should be repaired. Parts of plastered surfaces with surface irregularities or old coatings that are not solid, soft, weak, cracked or frozen mortars, should be removed by an appropriate method, such as scraping, washing, grinding and the like.
All electrical fittings, lighting fixtures, HVAC accessories etc. should be dismantled before the start of the work by workmen skilled in the trades involved, and after the completion of painting should be reinstalled. Protect from paint all surfaces that are not subject to painting, by paper, foil and / or crepe tape.
Surfaces soiled by coating materials should be restored to original condition after the works.
The flatness of the walls should be checked by mason's bubble level (minimum length of 2,0 m). Allowed unevenness is maximum +/- 2mm in length of 2m.
The Contractor's responsible person has to keep records about the dates of application of each layer individually: primers, skimming layer and final layer of paint, for each room.
Painting work should be carried out at temperatures higher than 10 °C and less than 32 °C (with relative humidity not exceeding 80%), unless otherwise specified by the manufacturer's instructions or permitted by the Supervisor.
The drying time between coats should be as recommended by the coating manufacturer, to enable thorough drying, but not to present topcoat adhesion problems. Each coat should be in specified condition to receive next coat.
The joints of different materials or two gypsum boards should be reinforced with fiberglass tapes, minimum 5 cm wide, which are placed in the first skim layer, 1 mm thick. Tapes can be embedded in two ways; to drown in a fresh layer of skim, or to glue on the skimmed surface. In both cases, another layer of skim is applied, so that the system skim-tape-skim are formed. The tapes should be vapour permeable. Self-adhesive tapes are used to reinforce the joints of gypsum boards.
External corners to be protected with aluminium angular profiles.
Skimming mass should be applied manually or mechanically. The thickness of mass is to be equal everywhere (2-3 mm) and free of unevenness and lines from the ends of the float trowel. When the walls have dried, surfaces should be sand with sandpaper (manually or mechanically). A second layer should be slightly thinner than the previous one. When the second layer is dried, repeat the sanding process. If the flatness of surface is not satisfactory, apply a third layer that is slightly thinner than the previous one. After the final layer has dried, the surface should be slightly sanded with fine sandpaper.
For each paint application technique and colour, a sample mock-up (minimum dimensions 1,0x1,0m) should be made and ensure the approval of the Supervisor. Once approved the mock-up samples shall be used as a standard of workmanship for installation within the project.
Unless otherwise specified or recommended by the manufacturer, paint should be applied in at least two layers, by microfiber roller (brushes to be used if necessary only) or spray gun.
Each coat of paint should be applied so dry film shall be of uniform thickness and free from drops, waves, brush marks, and variations in colour and texture. Special attention should be given to ensure that all edges and corners receive a film thickness equal to that of adjacent painted surfaces.
Erection, use and dismantling of the scaffold with a working platform up to a height of 2.0m, repair of minor surface irregularities (screw holes and the like) and preparation of samples mock-up are not charged separately.
Waste of materials must not be thrown into sanitary drains.
4. Supervision and measurement of works
After the material is delivered to the site, the Supervisor should check whether the material is delivered undamaged, it is packed and marked as required by this technical specification and whether it is properly stored.
Supervision is obliged, before the beginning of the works, to check that the Contractor has verified that the rooms are ready for painting works, visually check the condition of walls and ceilings in the rooms and approve the commencement of works.
Supervisor is required to check the flatness of the walls before the beginning of the skimming works, by the mason's bubble level, on random places (at least 10% of the walls). The results to be written in the Contractor’s check lists. In the same way, the skimmed walls should be checked before the start of painting.
When the Supervisor is not sure that the plastered substrate is sufficiently dried, he should require the Contractor to measure the moisture content of the substrate, before approving the start of the execution of the painting works.
During the execution of the works, Supervisor is obliged, on daily basis, to visually check the premises where the painting works are performed and whether the Check lists are properly filled by Responsible person of Contractor.
Unless otherwise provided by the contract:
Executed works are calculated per sqm of painted surface or per piece, the measures are taken on the spot. Openings in walls sizes up to 3 m2 shall not be subtracted from the total quantity. If the opening is greater than 3 sqm, area of opening should be subtracted from the total quantity and 3 sqm should be added. As openings are considered windows, doors, built-in cabinets and the like.
For works calculated per a piece, with the indicated dimensions, a deviation of up to +/- 5 cm from one measure specified in the description is not taken into consideration. For greater deviations (at least one dimension), the price of the pieces changes proportionally in relation to the change in the painted area.
Works in rooms higher than 4 meters are calculated separately.
The lateral surfaces of the beams, stairs, niches and the like, are calculated per sqm.
The height of the walls is measured from the floor or upper edge of the base to the upper edge of the wall. If the base is made of other material or is made in another painting technique, 20% of the height of the base is added to the height of the wall. If the height of the base, made of another material, is less than 25 cm, then the height of the wall is measured from the floor to the upper limit of the wall.
Water based paints are sold in the market with a variety of commercial names, such as latex paints, acrylic paint, dispersion paint, etc.
Classification by gloss (EN ISO 2813):
- mid sheen
Glossy surfaces are more resistant to washing then matt surfaces, but they emphasize all the unevenness on the surfaces. Paints with matt surfaces can also be resistant to washing.
Directive 2004/42/EC of the European Parliament and of the Council of 21 April 2004 on the limitation of emissions of volatile organic compounds due to the use of organic solvents in decorative paints and varnishes and vehicle refinishing products and amending Directive 1999/13/EC ("the Paints Directive") aims to prevent the negative environmental effects of emissions of volatile organic compounds (VOC) from decorative paints and vehicle refinishing products.
Classification by largest grain size (EN 21524 or ISO 787-7):
- fine (grain size up to 100µm)
- medium (grain size up to 300µm)
- coarse (grain size up to 1500µm)
- very coarse (grain size up to 1500µm)
Wet scrub resistance (EN ISO 11998) classification:
- Class 1 (<5µm (loss of thickness of the coat) at 200 scrubs)
- Class 2 (=5µm and <20µm at 200 scrubs)
- Class 3 (=20µm and <70µm at 200 scrubs)
- Class 4 (<70µm at 40 scrubs)
- Class 5 (=70µm pri 40 scrubs).
Note: It can only be measured on coatings of largest grain size (granularity) smaller than 100µm.