Plaster

Burnley College Plastering Diploma Level 2

Internal solid plastering • • • • •

Internal plastering covers walls and ceilings, prior to decoration. A variety of materials can be used to provide a sound, flat, smooth surface for decoration. Sometimes, decoration is needed. Plastering provides sound and thermal insulation. It also improves levels of hygiene, allowing for wiping down.

Burnley College Plastering Diploma Level 2

History of plastering • •

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Plaster is at least 4,000 years old. It was used by the Egyptians (in the pyramids) and the Greeks (who produced plasterwork in 500 BC). The Romans introduced plastering to England. Henry III admired the whiteness and fineness of gypsum (‘Plaster of Paris’), so he brought it to England. Plasterers were formed into a guild (a company) which was granted a charter by Henry VII.

Decorative ceiling and frieze

Burnley College Plastering Diploma Level 2

Examples of some tools and equipment used for internal plastering • • • • • • • • • •

Hawk Trowel Floats Spirit level Gauging trowel Spot board and stand Floating rules Mixing equipment Internal angle trowels Other tools and equipment required

Two sizes of plastering trowel

Burnley College Plastering Diploma Level 2

Preparation of background • •

What is adhesion? What is suction and how does it improve or hinder a plasterer?

Block work toothed into facing brickwork

Types of background 1. Normal clay bricks or blocks 2. Dense clay brickwork, blockwork, calcium silicate blocks, concrete blocks 3. Dense concrete, engineering bricks 4. Painted brickwork, glazed tiles, glazed brickwork

Burnley College Plastering Diploma Level 2 Surface key is it good , Preparation moderate or poor required prior to Good key: • if joints are raked out • keyed blocks • when keyed bricks are used Moderate key: • flush brickwork or blockwork Poor key: • flush brickwork or blockwork • unless surface has been keyed in manufacture

plastering • Brush and damp down according to suction. • Rake out soft joints in old brickwork. • Test suction if poor and apply spatterdash coat. • Mechanical key, hand key or spatterdash coat. • Test with bonding agent (PVA).

Burnley College Plastering Diploma Level 2

Types of background in British Standard 5262 • • • • •

Dense, strong and smooth materials Moderately strong, porous materials Moderately weak, porous materials No fines concrete Composite backgrounds

Burnley College Plastering Diploma Level 2

Forming a key • • • • •

Purpose of a key Forming a mechanical key Forming a spatterdash coat Using liquid PVA or EVA for forming a key Forming a key by hacking the surface

Burnley College Plastering Diploma Level 2

Preparation checklist • • • • • • • •

Brush down background to clean it. Remove mortar snots from joints, internal and external angles. Make a key (if needed) to background. Test background for suction; treat if necessary. Place drop boards at bottom of wall to catch falling materials and keep floor cleaner. Fix EML to timber wall and soleplates as necessary. Fix angle beads. Set up spot board and stand; wet in the board.

Burnley College Plastering Diploma Level 2

What is contained in a specification? • • • •

Type of material Number of coats Thickness of plaster Standard of work

Burnley College Plastering Diploma Level 2

Materials used in plastering • • • •

Sand Lime Cement Plaster

Burnley College Plastering Diploma Level 2

Sand • • • • • •

Types and sources of sand What is meant by a well-graded sand? What is the purpose of sand? The effects of bulking Performing a simple site test for sand What is silt and how does it affect Sand contained in a sand bay with protective covering sheet plastering sand?

Burnley College Plastering Diploma Level 2

Faults with poor quality sand Symptom

Result

Possible causes

Delayed set or total failure

Weakness, shrinkage, cracking, delayed expansion

Too much clay

Very slow set of gauged lime mortar

Delay in build

Too much clay, animal or vegetable matter (e.g. leaves)

Low finished strength or mortar

Poor sticking of backing coats

Too much sand; too much clay

Efflorescence, dampness and rusting of metalwork

Unsightly appearance, damage to brickwork

Too much salt

Poor workability

Poor stickability

Badly graded sand

Rust-coloured staining

Lots of expansion

Too much iron impurity

Blowing of plasters and rendering

Bond failure

Clay balls or coal particles

Burnley College Plastering Diploma Level 2

Lime • • • • •

Manufacture of lime Types of lime Hydrated lime Hydraulic lime Purpose of lime in a plastering mix

A lime works

Burnley College Plastering Diploma Level 2

Ordinary Portland cement • • • • •

Raw materials of OPC Manufacture of cement Hardening and curing of cement Other types of cement Lightweight cement-based materials

Burnley College Plastering Diploma Level 2

Plaster • • • • •

Chemical formula of plaster CaSO4 2H2O Setting of plaster Types of plaster and their uses Storage of plaster and effects of poorly stored plaster Method of mixing different types of plaster

Burnley College Plastering Diploma Level 2

Additives • • • • • •

Expanded Perlite Vermiculite Coloured pigments Plasticiser Waterproofers Hardeners

Burnley College Plastering Diploma Level 2

Proportioning and gauging plastering materials • • • • • •

Method of gauging materials Traditional cement, lime, sand mixes Mixing in a trough Mixing in a bucket or drum Mixing by cement mixer Mixing by hand

Mixing of lightweight plaster in a trough, using a larry/rake. Work station set up.

Burnley College Plastering Diploma Level 2

Plaster coats – method of work • • • • •

One-coat work Two-coat work Three-coat work Dubbing-out coat Render coat

Application of lightweight plaster

Burnley College Plastering Diploma Level 2

Forming box or broad screed • • • • •

The purpose of screeds The method of forming screeds, horizontally and vertically Method of ruling off screeds Filling in between screeds Method of forming a key between plaster coats

Ruling in a vertical screed

Burnley College Plastering Diploma Level 2

Dot and screed or plumb and dot • •

Use of the dot and screed or plumb and dot system Method of forming dot and screed and plumb and dot systems Ruling in from horizontal screeds

Use of a plumb bob and gauge

Plaster dot

Plumbing in horizontal screeds

Burnley College Plastering Diploma Level 2

Setting coat • • • • •

Method of forming a finishing coat depends on background Finishing coat should not be stronger than backing coat Purpose of a finishing coat Method of forming a finishing coat to a floated background The setting system; trowel, trowel, and trowel, float, trowel A bucket of mixed finishing plaster

Burnley College Plastering Diploma Level 2

Setting coat to a plasterboard ceiling: applying reinforcement • •

Types of reinforcement of plasterboard joints Application of reinforcement Position of reinforcement to a ceiling

Burnley College Plastering Diploma Level 2

Plastering a ceiling or wall on plasterboard in one coat system Applying a finishing coat to a ceiling

Applying a finishing coat to a partition

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1st coat lay between reinforcement 2nd coat laid over whole ceiling Always work leaving behind finished work Trowel up leaving a finished matt surface

Burnley College Plastering Diploma Level 2

Beads (metal and plastic trims) • • • •

Purpose of beads Types of beads available Method of fixing of angle beads Standards required for the fixing of beads

Fixing and levelling in an angle bead

Burnley College Plastering Diploma Level 2

Forming window openings, reveals and attached piers • • • •

Method of fixing beads around windows Using timber rules around window openings Forming reveals to window openings using reveal gauge Forming returns and corners to attached piers

Burnley College Plastering Diploma Level 2

Forming attached piers (1) • •

What is an attached pier? Back wall floated flat and keyed

Looking down onto an attached pier An attached pier

Burnley College Plastering Diploma Level 2

Attached and independent piers (2) • • • • • •

Fix angle beads or timber rules plumb and straight Check at top, middle, bottom, for equal measurement on face When using angle beads check for squareness at top, middle and bottom Float and set face and returns when using beads When using rules float face, return rules onto face. Float and set returns Return rules back onto return and set face

Burnley College Plastering Diploma Level 2

Lining in attached piers Method of lining in face of pier •

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Angle beads fixed at the two ends String through line Place a nail or piece of timber between string and nosing of two end angle beads Fix intermediate angle beads checking for plumb and straightness Check that nosing of bead does not fail on the string

Lining through a row of attached piers

Burnley College Plastering Diploma Level 2

Independent piers • • • • •

Lay floating rule on floor thickness of floating from face of pier Mark along rule with a pencil Using building square against rule mark floor Continue around pier Place nosing of bead on intersection of lines

Setting out and squaring in an independent pier

Burnley College Plastering Diploma Level 2

Floating and setting coat to a ceiling • • •

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Set up a datum line Position of dots on ceiling by using the building square Positioning and ruling in screeds using dots on ceiling Float up ceiling off of screeds Form a finishing coat to ceiling Setting out of dots to a ceiling

Burnley College Plastering Diploma Level 2

Floating a beam • • • • •

Fix and line through beads Check squareness of side checks of beam Check measurement of soffit of beam Position of screeds and ruling in Method of finishing beam Worm’s eye view of a ceiling beam

Burnley College Plastering Diploma Level 2

Method of patching a ceiling • •

Method of forming repairs to a wood lath ceiling Method of forming repairs to a plasterboard ceiling

Burnley College Plastering Diploma Level 2

Making good to a wall 1. 2. 3. 4. 5. 6. 7. 8.

Brush down damaged area; remove dust. Rake out mortar joints to form key. Remove plaster to form undercut under existing plaster. Wet in background area and undercut, or coat with PVA adhesive. When PVA is tacky, add plastering material to repair. Rule in floating coat, then key to receive finishing coat. When plaster set, cut back floating – especially around edges of repair. Wet in surrounding area and add finishing coat.