Rendering and Plasters Flashcards
Plaster
A wet mixed material usually applied on internal walls as a finish to provide a smooth, continious surface suited for direct decoration
Types of Plaster
- Lime
- Cement
- Casting
- Gypsum
- One Coat Gypsum
- Machine Applied Gypsum
Plaster Undercoats
- Retarded Hemihydrate
- Pre-mix Gypsum
- Bonding
- High Impact Undercoat
- Anhydrous gypsum
Rendering
Mix of a binder and fine aggregate with water and lime/plasticiser, applied to the external surface of walls
Render Requirements
- Strong key to the wall to avoid cracking during shrinkage
- A good render mix
- Well prepared surface of the wall before applying
Rendering Mix
Sand + cement + water
5:2:1
Steps to appplying rendering
- Clean and prepare surface wall
- Prepare walls that have openings
- Lay out tarpulin sheet for dust
- Fix guiding battens into place
- Apply first coat of rendering (5mm)
- Score the first coat before it drys
- Apply second coat (10mm)
- Float the layer and apply final finishes
Types of Rendering
- Cement
- Lime
- Clay
- Acrylic
- Silicone
- Single Coat
Surface Keys
Render Surface Preparations
- Masonry – Wall keyed12-15mm after first layer
- Wood – Metal lathing, wire mesh or expanded metal
- Concrete and other Denser materials – Hacked or use spatterdash
Rendering Finishes
- Spatter Dash
- Smooth float finish
- Scraped
- Textured finish
- Pebble dash/dry dash
- Rough cast/wet dash
- Tyrolean/machine applied finish
Machine Applied Finish
- 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
Roughcast/Wet Dash Finish
- Wet rendering finish is thrown ontop of undercoat by hand
- Gauge of the agtregate determines the texture
- Produces a rough texture for finish
Pebble Dash/Dry dash Finish
- Throwing dry pebbles, crushed stones or shingles into fresh rendering
- Lightly pressing the drydash into the rendering to ensure it sticks
Textured Finish
- Two coats applied normally
- 2nd Coat is scored by hand with wood comb, brushes, wire mesh, saw blades to create a texture
11mm, 8mm
Scraped Finish
- 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
Spatterdash
- 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
Smooth/Float Finish
- First coat is applied at 6mm/5mm
- 2nd Coat is applied at 8mm/10mm with trowel
- Finished by a wood float and sponged smooth
Density of Materials Affecting Rendering
- Soft, pourus require lean mix of lime and cement
- Denser ones require thicker/richer mix of lime and cement
Rendering Fucntional Purpose
Buildings on Coast and High Altitudes are ususally rendered to provide exrernal weatherproofing
