Rendering and Plasters

Question 1

Plaster

Answer 1

A wet mixed material usually applied on internal walls as a finish to provide a smooth, continious surface suited for direct decoration

Question 2

Types of Plaster

Answer 2

1. Lime
2. Cement
3. Casting
4. Gypsum
5. One Coat Gypsum
6. Machine Applied Gypsum

Question 3

Plaster Undercoats

Answer 3

1. Retarded Hemihydrate
2. Pre-mix Gypsum
3. Bonding
4. High Impact Undercoat
5. Anhydrous gypsum

Question 4

Rendering

Answer 4

Mix of a binder and fine aggregate with water and lime/plasticiser, applied to the external surface of walls

Question 5

Render Requirements

Answer 5

• Strong key to the wall to avoid cracking during shrinkage
• A good render mix
• Well prepared surface of the wall before applying

Question 6

Rendering Mix

Answer 6

Sand + cement + water

5:2:1

Question 7

Steps to appplying rendering

Answer 7

1. Clean and prepare surface wall
2. Prepare walls that have openings
3. Lay out tarpulin sheet for dust
4. Fix guiding battens into place
5. Apply first coat of rendering (5mm)
6. Score the first coat before it drys
7. Apply second coat (10mm)
8. Float the layer and apply final finishes

Question 8

Types of Rendering

Answer 8

• Cement
• Lime
• Clay
• Acrylic
• Silicone
• Single Coat

Question 9

Surface Keys

Render Surface Preparations

Answer 9

• Masonry – Wall keyed12-15mm after first layer
• Wood – Metal lathing, wire mesh or expanded metal
• Concrete and other Denser materials – Hacked or use spatterdash

Question 10

Rendering Finishes

Answer 10

1. Spatter Dash
2. Smooth float finish
3. Scraped
4. Textured finish
5. Pebble dash/dry dash
6. Rough cast/wet dash
7. Tyrolean/machine applied finish

Question 11

Machine Applied Finish

Answer 11

• Texture of the finish is determined by the gauge of the aggregate uused in the wet dash finish
• Colour may be introduced to produce a tyrolean finish

Question 12

Roughcast/Wet Dash Finish

Answer 12

• Wet rendering finish is thrown ontop of undercoat by hand
• Gauge of the agtregate determines the texture
• Produces a rough texture for finish

Question 13

Pebble Dash/Dry dash Finish

Answer 13

• Throwing dry pebbles, crushed stones or shingles into fresh rendering
• Lightly pressing the drydash into the rendering to ensure it sticks

Question 14

Textured Finish

Answer 14

• Two coats applied normally
• 2nd Coat is scored by hand with wood comb, brushes, wire mesh, saw blades to create a texture

11mm, 8mm

Question 15

Scraped Finish

Answer 15

• Two coats are applied and smooth finished
• The top coat is scraped away of 2mm with a straight edge saw or a saw blade
• Produces a course texture

Question 16

Spatterdash

Answer 16

• Usually applied to denser walls
• Cement + Sand 1:2
• Shot onto the surface and left to harden
• Provides a suitable surface for noemal rendering

Brick, in-situ cast concrete

Question 17

Smooth/Float Finish

Answer 17

• First coat is applied at 6mm/5mm
• 2nd Coat is applied at 8mm/10mm with trowel
• Finished by a wood float and sponged smooth

Question 18

Density of Materials Affecting Rendering

Answer 18

• Soft, pourus require lean mix of lime and cement
• Denser ones require thicker/richer mix of lime and cement

Question 19

Rendering Fucntional Purpose

Answer 19

Buildings on Coast and High Altitudes are ususally rendered to provide exrernal weatherproofing