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TRANSCRIPT
Level 1 Diploma in Plastering
© 2013 City and Guilds of London Institute. All rights reserved.
1 of 14
PowerPoint presentation
Prepare backgrounds
Unit 122: Apply scratch coats to internal
backgrounds
Level 1 Diploma in Plastering
© 2013 City and Guilds of London Institute. All rights reserved.
2 of 14
Preparation of backgrounds
‘Before anything else, preparation is
the key to success’
Alexander Graham Bell
Level 1 Diploma in Plastering
© 2013 City and Guilds of London Institute. All rights reserved.
3 of 14
Prepare backgrounds
The previous statement was made by the man who invented the
telephone but can be applied to every plastering task.
The correct preparation of any
background is making sure that there
is a good bond between the
background and scratch coat. It is
arguably the most important part of
any plastering job and will certainly
extend the lifespan of the finished wall
or ceiling. If the preparation is poor,
the material will most certainly sheet
away from the background, leading to
cracks and possibly areas of the
plasterwork coming away from the
background.
Level 1 Diploma in Plastering
© 2013 City and Guilds of London Institute. All rights reserved.
4 of 14
Background preparation
• The preparation starts with assessing the background to determine
the action to be taken.
• For example, if old plasterwork was perished, it would be removed
and the background would be brushed down and damped down
ready to receive the material.
• At the damping down stage, a bonding agent such as polyvinyl
alcohol (PVA) or styrene butadiene (SBR) can be used in order to
help to control the suction. You would not use a bonding agent if the
material being used is a lime/sand mortar.
• PVA and SBR form a barrier and help to control suction and allow
the materials to cure at the correct setting times.
• Traditional work which requires lime to be used as the main binder
will need to ‘breath’ and therefore no bonding agents such as PVA
and SBR should be used.
Level 1 Diploma in Plastering
© 2013 City and Guilds of London Institute. All rights reserved.
5 of 14
Identify the background
What type of background is this and what type of
preparation would be required before a scratch coat was
applied?
Level 1 Diploma in Plastering
© 2013 City and Guilds of London Institute. All rights reserved.
6 of 14
Identify the background
What type of background is this and what type of
preparation would be required before a scratch coat was
applied?
Level 1 Diploma in Plastering
© 2013 City and Guilds of London Institute. All rights reserved.
7 of 14
Identify the background
What type of background is this and what type of
preparation would be required before a scratch coat was
applied?
Level 1 Diploma in Plastering
© 2013 City and Guilds of London Institute. All rights reserved.
8 of 14
Examples of different types of backgrounds
Low suction – An example of a low suction background would be a
Stafford blue engineering brick (slide 5 pic). This type of background
would require expanding metal lath (EML), spatterdash or a modern
bonding agent applied to the wall before the scratch coat is applied.
Medium suction – A common clay brick used on internal party walls is
an example of a medium suction background (slide 6 pic). This type of
background would require brushing and damping down. A key could be
created by raking out the brickwork; however, a brush down to remove
heavy debris and a light dampening with a water spray should be
sufficient.
High suction – An example of a high suction background would be a
modern aerated lightweight block (slide 7 pic). These blocks have
excellent thermal properties due to their porous nature but are not as
strong as the backgrounds listed above. A 5:1 water to PVA mix could
be applied before the scratch coat in order to control the suction.
Level 1 Diploma in Plastering
© 2013 City and Guilds of London Institute. All rights reserved.
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Tools and equipment required for preparation
• Hard bristle brush/soft brush
• Shovel
• Wheelbarrow
• Water spray
• Chisels
• Feather edge
• Spirit level
• Claw hammer/lath hammer/scutch hammer
• Hop-ups/platforms for working at height
• Plumb line/string line
Level 1 Diploma in Plastering
© 2013 City and Guilds of London Institute. All rights reserved.
10 of 14
Identify the following tools and equipment
Image courtesy of www.axminster.co.uk. Reproduced with permission.
Level 1 Diploma in Plastering
© 2013 City and Guilds of London Institute. All rights reserved.
11 of 14
Identify the following tools and equipment
Image courtesy of www.axminster.co.uk. Reproduced with permission.
Level 1 Diploma in Plastering
© 2013 City and Guilds of London Institute. All rights reserved.
12 of 14
Identify the following tools and equipment