Internal Finishes
Overall Considerations
Whatever the background, the choice between the use of a lightweight or a dense plaster will depend, amongst other factors, on whether a gypsum or cement based system is to be used.
Most types of plaster can be applied to ecobrick. Differential movement between plaster and background, as with relative movement between two dissimilar coats, can cause cracking or loss of adhesion and it should be remembered that the thermal expansion of gypsum plaster is greater than that of most backgrounds.
Preparation
Under normal conditions ecobrick can be classified as having moderate suction and the only preparation necessary is that of following normal good practice. The wall should be cleaned of any dust, loose particles and contamination which may have occurred during construction. In extreme cases of bad site storage or wet conditions bricks must be allowed to dry out prior to coating. An acceptable level is below 20% by weight.
Application
In dry conditions it may be necessary to dampen the wall using a stock brush or fine spray immediately before plastering to balance the blocks initial suction. This should be a controlled operation carried out over relatively small areas and only until the bricks take on a darker shade. Excessive wetting of the wall must be avoided.
Adequate time should be allowed for each coat to dry out before the application of the next coat, and must not be allowed to dry out too quickly.
Mixes
Base Coat Renders
Cement Based: 1:1:6 Cement/Lime/Plastering Sand.
Lime Based: 1:2:9 Cement/Lime/Plastering Sand
Proprietary Lime/Gypsum Based plasters. Manufacturers should be consulted on application procedures.
Portland cement and gypsum plasters should never be used in the same mix nor allowed to contaminate each other at any stage of the mixing or gauging of materials.
Gypsum plasters have a limited storage life under normal conditions.
Finish Coat Plaster Mixes
- Gypsum/Lime plasters
- Textured paints
All mix ratios are by volume.
Thickness of Plaster
Total thickness:
- Single coat systems: 10-13mm
- Double coat systems: 13mm
The above figures are exclusive of any flushing which may be necessary where walls have been constructed out of plumb or alignment or where architectural features require localised thickening of the plaster finish.
Dry Lining
The two methods generally used for the installation of plaster boards are:
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Direct Bonding
Plaster boards can be fixed directly to ecobrick using either plasterboard adhesive or deep threaded screws. Screws should be spaced as per plaster board manufacturer's recommendations.
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Battening
Timbers should be spaced at the centres specified by the board manufacturer. Fixing of the battens to the brickwork should be in accordance with the guidance given in the Attachment of Fixings section of this Handbook.
