Level 1 Diploma in Plastering

© 2013 City and Guilds of London Institute. All rights reserved.

PowerPoint

presentation

Methods of providing a key to backgrounds

Unit 121: Prepare background surfaces and mix

plastering materials

Level 1 Diploma in Plastering

© 2013 City and Guilds of London Institute. All rights reserved.

Assessment criteria

1.5 describe the importance of forming a key and using

bonding agents to background surfaces

2.5 provide key and bonding agents to backgrounds

surfaces

Level 1 Diploma in Plastering

© 2013 City and Guilds of London Institute. All rights reserved.

Forming a key means

creating a rough surface to

improve its adhesion.

Forming a key for plaster

is one of the most

important jobs a plasterer

can do. Failing to provide

a key will result in bond

failure and the plaster

falling off the wall.

Forming a key

Level 1 Diploma in Plastering

© 2013 City and Guilds of London Institute. All rights reserved.

Skutch hammer

This hammer can be used to apply a

key to smooth background such as

dense concrete.

Mechanical stripping tools

You can also provide a key using

attachments for a 110V stripping tool.

Mechanical key

www.youtube.com/watch?v=EzWd40dIrYI

Level 1 Diploma in Plastering

© 2013 City and Guilds of London Institute. All rights reserved.

Raking out joints

This process means that

you cut out a recess in

the brickwork mortar

joint. When you have

raked all the joints, you

can plaster the wall; the

plaster grips in the

raked-out joint.

Mechanical key

Level 1 Diploma in Plastering

© 2013 City and Guilds of London Institute. All rights reserved.

Raking out joints

This can be done by hand using a pick hammer or by

using a hand-held 110v grinder. There are also

specialist tools on the market made solely for the

purpose of raking out.

Mechanical key

www.youtube.com/watch?v=OHBPl5TqJsk

Level 1 Diploma in Plastering

© 2013 City and Guilds of London Institute. All rights reserved.

Spatterdash/slurry/stipple

coats

A coat used on dense

backgrounds to form a key.

This helps the plaster to

bond to the wall.

Chemical bonding agents

Level 1 Diploma in Plastering

© 2013 City and Guilds of London Institute. All rights reserved.

Polyvinyl acetate

Commonly referred to as PVA,

this is applied by a roller or

brush and is mixed 1 part PVA

to 5 parts water.

PVA must be tacky when

applying plaster; it seals the

background giving even

suction and helps plaster to

adhere to the wall/ceiling.

Chemical bonding agents

www.specifinder.com/brochures/3013_pdf6.pdf

Level 1 Diploma in Plastering

© 2013 City and Guilds of London Institute. All rights reserved.

PVA

Can be used on a variety of backgrounds, including:

• old plastered walls

• Thermalite blocks

• textured coatings

• painted surfaces.

Note: the more porous the surface, the more PVA you

will have to apply in order to kill the suction.

Chemical bonding agents

Level 1 Diploma in Plastering

© 2013 City and Guilds of London Institute. All rights reserved.

ThistleBond-it

High quality bonding agent

especially made for the

plastering industry.

• Apply with a roller or

brush

• Green in colour so you

can see missed spots

• Has a grit added so

plaster adherers

• Plaster 24 hours after

application

Chemical bonding agents

Level 1 Diploma in Plastering

© 2013 City and Guilds of London Institute. All rights reserved.

ThistleBond-it

Can be applied on:

• dense smooth surfaces

• painted surfaces

• stone.

ThistleBond-it is the most practical

background treatment on the

market, as it eliminates any suction

problems you may find.

Chemical bonding agents

www.british-gypsum.com/products/ThistleBond-it

Level 1 Diploma in Plastering

© 2013 City and Guilds of London Institute. All rights reserved.

Any questions?