BPB Formula - Best Practice Guidelines

In order to obtain optimal results from our plasters, some basic usage guidelines should be respected. Technical data sheets exist with specific usage instructions for each BPB Formula product. The data sheets are available here.

It is important to respect the indicated plaster to water ratio and to accurately weigh the water and plaster. Variations in the plaster to water ratio have a direct influence on product characteristics:

Plaster is always added to water and never the contrary. We recommend using a clean recipient and clean tap water at a constant temperature, for mixing plaster. The plaster should be sprinkled slowly and evenly across the entire surface of the water. The time taken to do this will vary between 1 and 3 minutes depending on the size of the batch. If the plaster is sprinkled too quickly, dense and dry lumps can form that will not disappear during mixing.

The soaking time should vary between 1 and 2 minutes, depending on the size of the batch. Sufficient soaking ensures that each plaster crystal is surrounded by water, and that air bubbles can escape from the mixture. If plaster is not allowed to soak for long enough, air bubbles may remain in the finished plaster mould. Soaking for too long gives rise to a shorter setting time, earlier hardening and a grainy surface.

The mixture should be stirred vigorously with clean utensils which are free from set plaster, to obtain a homogeneous lump-free consistency. The optimum stirring time is dependent on the size of the batch and the dimensions of the stirring device. If plaster is not stirred for long enough it will not be evenly mixed, and if stirred for too long the mixture will become too thick, in both cases this has a negative effect on product characteristics. Longer stirring times generally lead to: greater strength, reduced absorption capacity and shorter setting time. Plaster which is vacuum- mixed has lower absorption capacity, reduced expansion, and increased strength.

Apply a specific lubricant or separating emulsion, in as fine a layer as possible using a brush. Wipe with a cloth afterwards to avoid remnants and structuring.

Incorrect or excessive use of lubricants may cause mildew, and lead to problems or defects during drying and lifting.

Plaster moulds must be carefully dried in order to achieve even and optimum physical characteristics. Ideal drying conditions are: 40-45C and 40% relative humidity. Dryers should record both temperature and relative humidity for effective mould drying.