1. Prepare background surfaces and plaster materials

2. Develop an understanding of different types of suction on backgrounds, as well as the mechanical key they will have

3. Aims: Objectives: Prepare backgrounds
Introduction
Aims:
To understand the different backgrounds to which plaster is applied
Objectives:
To know and recognise different backgrounds
To know how to prepare different backgrounds

4. A background is any surface which plaster / render can be applied to
Prepare backgrounds
What is a background?
A background is any surface which plaster / render can be applied to
Examples:
Brickwork
Blockwork
Concrete
No background, no plastering

5. Can you answer the following?
Prepare backgrounds
Introduction
Can you answer the following?
What is suction?
How can suction be controlled?
How can suction be created?
What is a mechanical key?
What is a bonding agent?

6. Prepare backgrounds Backgrounds This is called SUCTION Question:
If a background is porous, it will absorb water like a sponge.
If a background is dense, it will absorb little or no water
This is called SUCTION
The more water the background absorbs, the higher the suction rating.
The less water a background absorbs, the lower the suction rating.
Question:
What affect will this have on the plaster applied?

7. Backgrounds Prepare backgrounds
Gypsum plasters rely on retaining some of the water used to mix them until the setting process is complete, if too much of the water is absorbed by the background the plaster will shrink and crack and lose adhesion with the background causing bond failure.
Suction needs to be controlled.
How can you tell if a background is HIGH, MEDIUM or LOW SUCTION?

8. Suction Try it! Prepare backgrounds
To establish how much suction a background has is quite simple.
It’s as simple as splashing some water onto the background and watching how quickly the water is absorbed. The quicker the water is absorbed the higher the suction.
Over time and with practice this will become quite a good indicator to you has to how much suction a background has.
Try it!

9. High suction backgrounds
Prepare backgrounds
Background preparation
High suction
backgrounds
High suction backgrounds
Bonding agents are used to seal the background and control the suction to leave a surface suitable for plastering.
The most widely used are PVA, Thistle Gypprime and SBR. It is vital that the manufactures instructions are followed when using these products to avoid problems in the future.
Easily applied using a roller.
Thermalite Blocks
Porous Bricks

10. Low suction backgrounds
Prepare backgrounds
Background preparation
Low suction backgrounds
Because plaster relies on some suction and in most cases some form of key this type of background needs the most treatment.
Dependent on the type of background (tile, concrete) the easiest treatment is to coat the surface with a bonding agent such as Thistle Bond-It, which creates a key and creates an even suction throughout the background.

11. Prepare backgrounds
Background preparation
Different backgrounds require different treatments before we can apply any plaster.
Treatments vary from:
Damping down
Bonding agents
Scratch coats
Hacking
Raking out of joints

12. Creating key Hacking Racking out joints Prepare backgrounds
Background preparation
Creating key
Mechanical key
Hacking
This can be done using mechanical or manual means and is done to provide a key for the plaster to bond to low suction background
Racking out joints
Again this can be done both mechanically or manually

13. Creating key Scratch coats Bonding agent Prepare backgrounds
Background preparation
Creating key
Mechanical key
Scratch coats
Applied using various materials depending on circumstances, can be used to create key, suction or to even out suction especially on composite backgrounds.
Bonding agent
Bonding agents are easily applied using a roller, and are used to seal the surface and with some bonding agents to create key as well

14. Creating key Expanded metal lath Prepare backgrounds Mechanical key
Background preparation
Creating key
Mechanical key
Expanded metal lath
Can be used to create key on timber lintels or timber wall plates, and is very useful to overcome situations involving composite backgrounds.

15. Creating key Prepare backgrounds Natural key
Background preparation
Creating key
Natural key
Is the open texture found on some backgrounds such as breeze block and some brickwork.

16. You should now be able to answer the following:
Prepare backgrounds
Conclusion
You should now be able to answer the following:
What is suction?
How can suction be controlled?
How can suction be created?
What is a mechanical key?
What is a bonding agent?

17. THANK YOU