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Level 1 Diploma in Plastering
© 2013 City and Guilds of London Institute. All rights reserved.
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presentationMixing plaster materials
Unit 121: Prepare background surfaces and mix
plastering materials

Assessment criteria
3.1 identify different types of plastering materials
3.2 state the requirements for mixing plastering materials
3.3 identify different types of equipment and tools used for mixing plastering
materials
4.1 select plastering materials
4.2 select the tools and equipment to gauge and mix plastering materials
4.3 set up the mixing area
4.4 use correct access equipment
4.5 follow current environmental and current health and safety regulations.
5.1 state the different methods of mixing plastering materials
5.2 identify the potential hazards when mixing plastering materials
5.3 identify control measures when mixing plastering materials
5.4 state effects relating to incorrect gauging and mixing of plastering materials
5.5 state the equipment for protecting the work and surrounding area.
6.1 mix proportions of materials to given specifications
6.2 report problems when mixing plaster materials to the relevant personnel
6.3 use correct access equipment
6.4 follow current environmental and current health and safety regulations

The following PPE should always be worn when mixing plasters:
Gloves Safety glasses Dust mask
Plaster should also be mixed in a well-ventilated area.
PPE

• Prior to mixing any plaster there must be a
continuous supply of clean drinking water with which
to mix the powder.
• Also, any services such as 110V power supply for
mechanical whisks must be present.
• Any electrical equipment must comply with PUWER
(Provision and Use of Work Equipment
Regulations 1998).
www.hse.gov.uk/work-equipment-machinery/puwer.htm
Mixing area: water and services

Note: dirty water will result in a flash
set. This means that the plaster will
set suddenly, not gradually, and
create a weaker finish.
Water

Control of Substances Hazardous to Health (COSHH) is the law
that requires employers to control substances that are hazardous
to health. You can prevent or reduce workers’ exposure to
hazardous substances by:
• finding out what the health hazards are
• deciding how to prevent harm to health (risk assessment)
• providing control measures to reduce harm to health
• making sure these measures are used
• keeping all control measures in good working order
• providing information, instruction and training for employees
and others
• providing monitoring and health surveillance in appropriate
cases
• planning for emergencies.
COSHH and risk assessments

Materials that you may use when creating a
background for finish plaster include:
• sand
• cement
• lime
• pre-mixed lightweight plasters
• additives (waterproofer, plasticiser, etc).
Backing plasters

Bonding grade backing plasters
Suitable to apply on to:
• smooth concrete
• plasterboard
• EML
• engineering brick
• textured coatings.
Backing plasters
www.british-gypsum.com/~/media/Files/British-Gypsum/Data-Sheets/PDS-Thistle-Bonding-Coat.pdf

Browning grade backing plasters
• common brick
• concrete brick (raked joints)
• lightweight breeze blocks
• dense breeze blocks.
Backing plasters
www.british-gypsum.com/~/media/Files/British-Gypsum/Data-Sheets/PDS-Thistle-Browning.pdf

Hardwall grade backing
plasters
• common brick
• concrete block (raked joints)
• breeze block
• no-fines concrete.
Backing plasters
www.british-gypsum.com/~/media/Files/British-Gypsum/Data-Sheets/PDS-Thistle-Hardwall.pdf

Drag or larry used to mix
backing plaster in a mixing bath.
Mixing bath or trough used to
mix backing plaster.
Traditional methods for mixing backing plasters

Modern plasterers now mix
backing plaster using a 110V
mechanical whisk. These
whisks are designed to mix
plaster faster than traditional
methods.
WARNING! Over-mixing will
result in the plaster setting
faster, thus giving you less time
to apply and rule flat.
Mixing backing plasters

Using a whisk to mix backing
plaster means that you need a
round vessel. Plasterers
commonly use flexi buckets;
these tubs are excellent for
mixing large amounts of
backing plaster and they are
easy to clean.

Backing plasters should be mixed to a semi-stiff
creamy consistency to allow application to the wall
and ruling in.
Under-mixing will result in a lumpy mix with unmixed
powder, thus making the plaster difficult to apply and
rule.

Multi grade finish plasters
Can be used on the following
backgrounds:
• Browning grade backing
plasters
• Bonding grade backing
plasters
• plasterboard
• bonding agents, eg PVA.
Finish plasters
www.british-gypsum.com/~/media/Files/British-Gypsum/Data-Sheets/PDS-Thistle-Multi-Finish.pdf

Board Finish grade plasters
Can be applied to the following
backgrounds:
• plasterboard
• bonding agents, eg
ThistleBond-it.
Finish plasters
www.british-gypsum.com/~/media/Files/British-Gypsum/Data-Sheets/PDS-Thistle-Board-Finish.pdf

Durafinish grade plasters
backgrounds:
• Browning grade backing
plasters
• Bonding grade backing
plasters
• Hardwall grade backing
plasters
• plasterboard.
Finish plasters
www.british-gypsum.com/~/media/Files/British-Gypsum/Data-Sheets/PDS-Thistle-Durafinish.pdf

Spray Finish plasters
backgrounds:
• plasterboard
• bonding agents, eg PVA and
ThistleBond-it.
Finish plasters
www.british-gypsum.com/~/media/Files/British-Gypsum/Data-Sheets/PDS-Thistle-Spray-Finish.pdf

How to set up and use a spray finish machine:
www.british-gypsum.com/products/Thistle-Spray-Finish
Spray finish machines

Plaster mixing wheel
• Commonly known as a
posser or podger
• Used to mix finish by hand –
a very physical task
Finish bucket
• Especially designed to mix
one 25kg bag of finish
Traditional methods of mixing finish plaster

Plaster whisk
The whisk used to mix backing
plaster can also be used to mix
finish plasters.
Again, as was the case for
backing plaster, over-whisking
can result in the mix setting
faster.

When mixing finish plaster, it
should be creamy and stiff
enough to sit on the hawk.
If skimming ceilings, it should
be mixed a little thicker to avoid
plaster splashes from above
when applying.

Any questions?

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