Producing Plaster Components

   Casting a flood

mould

Producing Plaster Components

• For this presentation you are required to take notes for your records

Ten thing you should know about Producing Plaster Components

  1 A release agent is used to allow the cast to be removed

 2 Plaster is applied to moulds using a splash brush

3 Flood mould are used to cast repeat pieces of work

4 Reinforcement in plaster casts from flood moulds is comprised of canvas hessian

 5 The type of plaster used for casting is Class A

 

Ten thing you should know about Producing Plaster Components

• 6 When casting in plaster the two coats are know as firstings and seconds

• 7 The reinforcement in plaster casts is placed in the second coat

• 8 Lath reinforcement in plaster casts run parallel to the strike offs

• 9 Timber bearers for a plain faced cast should be at least 30mm x 30mm

• 10 Shellac is used as a sealant

A selection of materials used for producing plaster components

 • Shellac is a painter’s knotting or button polish

• Plasterers mix it with meths to thin it down

• Shellac is an all-natural resin secreted by the female lac bug to form a cocoon, on trees in the forests of India and Thailand

• Shellac is used to seal the surface of the mould and prevents water from other coats been dried out

• Apply 3 thin coats to the plaster surface to give a polish

• Shellac is also used on bench surfaces

Lac (Laccifer Lacca) are scale insects (insects that attach themselves in great numbers to plants and trees) which drain the sap from the bark of their

host tree, allowing them to secrete lac resin which is scraped off and manufactured into shellac. Around 300,000 insects are used to produce 1kg

of lac resin

6

Alum

• This is an accelerator used in casting.

• Why do you think you would use this?

7

Grease/release agent/Raw Linseed Oil• Raw Linseed Oil• Raw Linseed Oil 500ml

Bottle. Has many uses and works well as a releasing agent on fibreglass or sealed plaster moulds.

• (Tallow)Used to prevent the plaster from sticking to the bench, and also helps with the running of the mould along the bench.

• Made from animal Fat

8

A selection of materials used for producing plaster components

• Tri-sodium citrate (sodium citrate) is a very potent retarder to plaster setting time.

• Just a pinch of it added to the gauging water prior to adding the plaster will retard the set for several minutes

•  Fine Casting plaster is probably the most common plaster for fibrous work

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A selection of moulding tools used for producing plaster components

 

• Small tool ideal for moulding

• Joint rule mainly used for mitre work, also used for bench work

 

A selection of moulding tools used for producing plaster components

• Spring steel busks ideal for scraping shaping and filling plasters

•  A good bowl for bench work with plaster. Flexible crack resistant black polythene

•  

The materials required to cast a flood mould

 

Hessian

Mixing Bowls

Scissors

Rule

Class A Casting Plaster

Latex Gloves

Flood Mould used for the plaster cast

Casting a flood mould

Using a gloved hand , the casting plaster is mixed in a bowl of clean cold water

Question which piece of P.P.E is missing

Answer

Dust Mask

Casting a flood mouldOnce mixed to a creamy consistency the plaster is poured into the centre of a clean flood mould , making sure that all the mould is covered.

This is called the firstings.

Casting a flood mould

The flood mould is carefully vibrated to remove any air pockets and making sure that all the enrichments are fully covered

Casting a flood mould

Canvas Hessian is now laid onto the cast this will provide reinforcement, and give the plaster cast strength

Casting a flood mould

The plaster cast is now ready for the second pour (seconds).

Casting a flood mould

Once it is poured, it can be ruled of to produce a flat, and true surface

that ca be fixed to a ceiling once set

and dried.

Casting a flood mould• When the plaster cast is finished

it is then left until it has set and all the heat given off while setting has died away.

•  The cast is placed at the edge of the bench , and slowly the fence of the mould is removed from the cast. 

• Continue all the way around the flood mould until the plaster cast is free.

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Casting a flood mould

The flood mould is now turned over and removed from the plaster cast

Once the cast the been removed from the flood mould , make a check for any imperfections, then store in a clean and dry location until fully dried

Clean the flood mould ready for making another cast