Backgrounds and plaster Prepare background surfaces and plaster materials

Understand the range of plasters and the backgrounds they are used on

Backgrounds and plaster Aims and objectives Aims: To match plaster to a suitable background Objectives: To recognise different plasters suitability to backgrounds

Backgrounds and plaster Introduction What do you know? What backing plaster is suitable for high suction backgrounds? What backing plaster is suitable for low suction backgrounds? How do we judge the properties of a background? How many backing coats can you name? How do we finish backing coats?

Backgrounds and plaster Aerated concrete block (Aircrete) Suitable for: General build walls Likely locations Cavity walls Solid walls Partitions and separating walls Key: Good mechanical key (very good if scratched) Suction: High to very high

Backgrounds and plaster Common bricks / Facing bricks Suitable for: Exterior walls and facings of buildings Likely locations External walls (aesthetic reasons) Internal walls (in older buildings) Key: Good to medium Suction: High

Backgrounds and plaster Medium density bricks Suitable for: General build and residential walls Majority of standard applications Block and beam flooring Likely locations Inner leaf of cavity walls when used with secondary insulation Separating or partition walls Infill blocks in beam and block flooring systems External walls (rendered or clad) Key: Good to very good Suction: Medium to high

Backgrounds and plaster Cast in situ and pre-cast concrete Likely locations Commercial sector High rise Pre-cast stairs and lift shafts Soffits Key: Typically poor but can vary Suction: Medium to low

Backgrounds and plaster Plasterboard and Glasroc F MULTIBOARD Suitable for: Internal wall linings / ceilings Curved wall / ceilings Pre-cast stairs and lift shafts Soffits Key: Medium to low Suction: Medium to low

Backgrounds and plaster Painted and tiled surfaces Likely locations Bathrooms, kitchens, etc Key: No mechanical key. No chemical key Suction: Very limited (painted) to zero (tiles)

Backgrounds and plaster Engineering bricks Suitable for: Denser and stronger than ordinary facing bricks Two classifications, Class A and B Based on minimum compressive strength and maximum water absorption Class B: Red in colour, smooth in texture. Account for the majority of the market. Among the cheapest bricks in the construction industry Class A: Blue/grey in colour, smooth in texture. Increasingly being used for facing due to their colour, quality and distinctive appearance

Backgrounds and plaster Engineering bricks Likely locations Where strength and low levels of water absorption are paramount Retaining walls Groundworks Key: Medium (if joints are raked) to poor Suction: Low to medium

Backgrounds and plaster Dense blocks Suitable for: Dense concrete blocks that can be used in virtually any part of the project in normal conditions Characteristics Excellent sound insulation High strength makes them especially applicable to partition and separating walls Block and beam flooring

Backgrounds and plaster Dense blocks Likely locations Partition and separating walls External cavity or solid walls Load bearing and non-load bearing walls Foundation walls below DPC Fire resistant walls Key: Good to medium Suction: Medium to high

Backgrounds and plaster Metal lathing Introduction Used to provide a mechanical key to a substrate Suitable for: Non-consolidated backgrounds (dusty) Variable backgrounds (on the same wall) Smooth To provide intricate detailing

Backgrounds and plaster Metal lathing Likely locations Bridging gaps in walls Bridging columns To aid extreme thickness backing coats on very uneven walls Key: Good mechanical key. No chemical key Suction: Zero

Backgrounds and plaster Composite rounds These backgrounds containing different materials are often a source of cracking or loss of adhesion. Concrete or timber lintels over doorways and windows can cause trouble unless treated. A composite background can be made up of any of the bricks and blocks covered in the slides.

Backgrounds and plaster Conclusion You should now have the knowledge to complete the following: What backing plaster is suitable for high suction backgrounds? What backing plaster is suitable for low suction backgrounds? How do we judge the properties of a background? How many backing coat plasters can you name? How do we finish backing coats?

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