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Level 3 Diploma in Plastering

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Applying plastering materials to detailed interiors

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Unit 312: Applying plastering materials to detailed interiors



Assessment criteria1.1 Explain the purpose of detailed specification.

1.2 Describe the different types of detailed drawings.

1.3 Explain the purpose of schedules for internal plastering materials.



Internal plasteringThis session looks at the contract documents that relate to internal plastering:

• Types of drawings.

• Specification, schedules and manufacturers’ information.

• Planning work.

The application of plastering procedures that includes types and preparation of backgrounds, including problems associated with internal plastering surfaces.



Applying internal plastering materials to detailed interiorsInternal plastering can be classed as one, two and three coat plasterwork applied to wall and ceiling surface areas.

One coat work is generally classed as applying setting or finishing coats to plasterboard surfaces that are flat and true.

Two coat work is classed as applying a floating coat and setting coat to masonry backgrounds that are reasonably straight. Uneven plasterboards would also require two coat work.

Three coat work would be suited to more uneven backgrounds that require a scratch coat or pricking up coats that are applied to EML or timber lath backgrounds. However, severely uneven backgrounds, such as stone, may require dubbing out coats to first fill out the joints.



Selecting performance plastersTraditional and modern solid plasters are commonly used in the building industry, whether they are used to obtain a high class surface in new buildings or used in renovation or conservation projects.

Applying plaster to surfaces can also perform fireproofing, soundproofing, waterproofing or increase thermal values.

Every background will be different in character and may require some type of preparation before plaster application. Different types of background will also dictate the amount of plaster that needs to be applied to its surface, to bring it out to the required standard.

The selection of appropriate plastering materials will depend on:

Architect’s design, manufacturers’ instructions, client requirements, cost, expected performance, environment, and finish quality.



DrawingsBlock plans and site plans provide information on the allotment of plots and their surrounding areas, which are useful for arranging access for deliveries and storage of materials.

• Scale of block plan 1:1250

• Scale of site plan 1:500 and 1:200



DrawingsFloor plans provide information and measurements for room layouts and walls, with the position of openings.

These can be used to work out quantities and costings for labour and plastering materials.

Doc.elevenworks.com



DrawingsReflective ceiling plans show the background structure – such as timber joists and steel easy joists – and soffit beams, such as precast concrete block and beams.



DrawingsDetail drawings show cross sections that identify the types of materials and their position.

Scale 1:200, 1:100, 1:50, 1:10, 1:5 and 1:1



Component drawingDetailed image of a component showing how EML is fixed by tying steel wire to metal furrings.



Detailed specifications Specifications are usually prepared by the architect and accompany the drawings. They provide precise detailed information on the plastering products that are to be used for the work. • Specific plastering materials, which will include the make or

manufacturer.• Types and size of beading and fixings.• Background information, preparation and treatment, if required.• Number of plaster applications, thickness and ratios of mixes.• Type of additives and reinforcements.• Standards and accuracy of workmanship expected.

Specifications should also be referred to when ordering materials.



Manufacturers’ information sheetsBefore using plastering materials and products you need to familiarise yourself with the manufacturers’ guidelines and data sheets. These documents are designed to provide specific information on how to prepare and install the product during installation.

Not only will they provide installation instructions they will also list manual handling, storage, associated hazards, possible exposure and toxology, and first aid procedures relating to the use of specific materials.

Following manufacturers’ instructions and guidelines will ensure the warranty of the product applied or installed.



SchedulesSchedules will provide information on repeated materials that may be required for larger contracts, such as multiple housing estates that have the same or similar design.

A typical internal plastering schedule may include the following:

• Types and number of performance plasterboard and fixings.

• Types and number of EML or rib lath and fixings.

• Types and number of different beading and fixings.

• Types and number of undercoat and top coat plasters.



Planning work schedulesBefore the work starts careful planning will need to be put in place to schedule labour and materials to coincide with the work programme. This will ensure timescales and budgets for the contract are met.

Specified materials will need to be pre-ordered and delivered in line with set work activities to ensure the continuation of work and avoid plastering materials becoming unused for long periods and passing their shelf life and therefore becoming unusable.

Suitable storage areas for materials and access will need to be identified, including mixing areas, which will need to include services such as water and electricity.

Risk assessments and method statements will need to be produced to ensure safe working and eliminate unforeseen accidents and possible injuries within the working environment.



Compatibility of plasterComplying to specifications and manufacturers’ instructions when mixing and applying the plaster will ensure that the plaster adheres to the background surface.

• The plaster must never be stronger than the background and this must be the same for subsequent coats.

• Key, suction and strength are key to establishing good adhesion –knowing this will help you understand how to prepare backgrounds.

• However, if the properties of the background are weak and have poor adhesion, you will need to prepare the background.

• Applying a bonding slurry improves adhesion on poor surfaces.

• Fixing EML can increase strength and reinforce the surface.



Preparing backgrounds for plastering• Solid block and brick

• Stone and slate

• Composite

• Concrete

• Plasterboard

• Expanded metal lath or rib lath

• Timber laths

• Timber sheeting or wall plates

• Steel



Procedure for applying traditional and premixed plasters

Background Application Type of plaster

Brick or block Float and set ?

Stone and slate Dubbing out, scratch, float and set ?

Composite Pricking up, float and set ?

Concrete Scratch, float and set ?

PlasterboardUneven plasterboard

Setting coatFill out and set

?

EML or rib lath Pricking up, float and set ?

Timber laths Pricking up, float and set ?

Timber sheet or wall plate

Pricking up, float and set ?

Metal furrings and encasements

Setting coat ?



Faults in plasteringFaults Appearance on surfaceWidespread cracksHairline cracks Crazing cracks

Structure movementHigh percentage of shrinkage in the plaster mixApplying plaster on high-suction backgrounds

Blistering or bubbling Trapped air in backgrounds, applying setting plaster over damp surfaces.

Sweat out Trapped moisture in the applied plaster Bond failure on solid surfaces and plasterboard

Set plaster becoming loose and failingPlaster shelling

Mould growth Black fungal stains on the surface of plasterEfflorescence Crystalline deposit of salts bleeding through the wallGrinning Minor pattern staining from the devil float or plasterboard

joints showing in the setting coat Flash set Accelerated setting

Plaster/plasterboard deteriorate Plaster material crumbling in damp conditions



Solutions to faultsFaults Remedy/solution Widespread cracksHairline cracks Crazing cracks

Mechanically fix EML over cracks to reinforceAvoid using strong cement mixes, poor gaugingCheck suction on backgrounds and control

Blistering or bubbling Ensure the background has dried sufficiently and trowel surface as the plaster sets – avoid over trowelling

Sweat out Allow sufficient drying of subsequent coats to eliminate trapped moisture

Bond failure on solid surfaces and plasterboard

Prepare by scabbing or use of bonding adhesivesRemove dust from surface and check paper on surface

Mould growth Adequate ventilation required; reduce condensationEfflorescence Treat damp, use salt inhibitor, use breathable plaster, correct

sandGrinning Don’t key surfaces too deeply; apply thicker coatsFlash set Check date on bags, check for lumps in plaster

Plaster/plasterboard deteriorate Avoid moisture contact on surface



Any questions?

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