Table of contents:
- Leaflet as a basis
- It is important to ensure that there is no detachment on plasterboard
- Checks before coating to prevent detachment on plasterboard
On drywall, there are always complaints due to partial detachment of the coating from the substrate. But where does this phenomenon come from and how can you be sure that you have a load-bearing surface and that there are no detachments on plasterboard?
Authors: Markus Grabenschröer and Daniel Christoffers | Photos: Caparol
Gypsum (cardboard) slabs and gypsum fillers have become an integral part of drywall construction. Today they are used in almost every private and public new building. In practice, the combination of wall structure and joint filler has proven itself, however, there are always complaints that are subject to discussion due to partial detachment of the coating from the substrate. The detachments on plasterboard are often only found when property developers want the functionality of the paint to be checked by a specialist or an expert, or when tenants want to color the areas. In both cases, an adhesive tape is used, which peels off with the plaster spatula after the paint has been removed. The problem is not new and was already communicated and examined in detail in 2012. The topic is currently being discussed again. For this reason, the following guideline or this test method was developed on the basis of the available knowledge in order to counter increasing uncertainty in the market.
Leaflet as a basis
In leaflet 1 “Construction site conditions for dry construction work with gypsum board systems”, the Federal Association of the Gypsum Industry points out the following important points for the craftsman:
- In general, adequate ventilation must be provided.
- For filling, the room temperature must not fall below +10 ° C (DIN 18181).
- Rapid, shock-like heating-up of the rooms should be avoided, otherwise tension cracks may occur as a result of changes in length and breakdown, this applies particularly to winter construction.
- Avoid blowing directly on the gypsum (cardboard) and gypsum fibreboard with hot or warm air. Extremely fast drying when starting ventilation and air conditioning systems without a humidifier or when using construction dryers should also be avoided.
- Many years of experience have shown that for the processing of gypsum (cardboard) and gypsum fibreboard, the favorable climate range is between 40 and 80% relative air humidity and above a room temperature of +5 ° C.
It is important to ensure that there is no detachment on plasterboard
A sufficient amount of water must be available during the setting process so that the plaster hardens properly. If one of the points mentioned below is not observed, the load-bearing capacity of the gypsum filler cannot be guaranteed.
- Substrate: In the case of strongly absorbent substrates, the gypsum filler / plaster mortar is deprived of the absolutely necessary water deposit for crystallization from the hemihydrate to the dihydrate; sufficient strength is not achieved.
- Processing: Gypsum plastering with the required amount of water is to be carried out according to the technical data sheet. Cut edges must be primed beforehand. The processing temperatures mentioned above must be observed during processing. Already stiffened material must not be mixed with water or with other gypsum powder.
- Layer thickness: If the gypsum filler is applied too thinly (less than 500 μm or 0.5 mm), the necessary water is removed too quickly (through the substrate and / or the air). The crystallization is disturbed or does not take place. This keeps the plaster slightly water-soluble after drying.
Checks before coating to prevent detachment on plasterboard
To ensure that the surface has hardened properly, an underground test is essential. Before coating with interior paints, the gypsum filler must be checked for its load-bearing capacity. This can be done with layer thicknesses over one millimeter by gentle pressure with a hard object. If the surface is easily damaged or if flaking occurs during this process, the strength is impaired. In the case of layer thicknesses below one millimeter, testing is carried out by wetting with water. If the gypsum filler can be dissolved with water immediately after wetting and a soft, greasy film forms (finger test), this indicates an insufficient crystallization or hardening of the plaster. If there is insufficient strength, a suitable primer must be applied.
The success of the individual measures is to be checked by a sample area on the object. When gluing wallpaper and other wall coverings in connection with pasty wall fillers, the manufacturer's instructions must be observed. If necessary, contact the technical advisory service for further important information. According to VOB Part B § 4 No. 3, the contractor (craftsman) is responsible for the general assessment and inspection of the subsurface. If the contractor detects a defect, this has an obligation to notify the client. Appropriate formulations from BFS Leaflet No. 20 "Assessment of the subsurface" can be used for this.