Plaster has a shelf life, if the plaster is used after its life is over you will not get the finish your after and spreading the plaster can be harder as it sets to quick, which will also course the plaster to crack at the joints.
Never add water to plaster that's already gone off or even more plaster powder then water, this will weeken the mix and results will not be great.
While storing plaster try to make sure its its in a warm dry place, plaster attracts moisture which will make the powder lumpy if stored in damp/cold conditions and can even make it set while in the bag.
Plastering - Types of Plaster
There is a range of plaster products available in bag form and knowing which one is right for you can be confusing, in this page we will explain what each different back is used for, the consistency to mix to and how much each bag will cover.
Plaster is a natural product of Gypsum, its adopted to be used in many different situations. Depending on where the Gypsum was mined is what determines its final colour.
There is also ways to mix other materials to use instead of plaster - See Render.
For help on plastering why not visit our other pages on plastering.
Sand & Cement - Typically used as a cheap but strong undercoat, when mixed with a waterproofer admix product this can be used externally. only to be used on masonry backgrounds
Applied using a towel/float up to 50mm thick beads (2inch) normally only applied in 12mm beads.
MIXING - 5 or 6 parts soft sand to one part Cement, ideally mixed in a drum mixer to the consistency of thick milkshake.
- One Coat Products
Universal One Coat - Typical use is for a quick solution where a perfect finish isn't required.
Can be applied using plastering tools and machines, direct on to al sorts of backgrounds (brick, existing plaster, blocks etc). It can spread in beads up to 50mm (2 inch) per coat.
MIXING - simply mix the plaster with water until its consistency is around a little thicker then melted ice cream, thicker if your applying it quite thick.
The average bag of 25kg will cover 2.5sq/m of wall at a 13mm (1/2 inch) bead (thickness is maintained).
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Universal One Coat - Typical use is where you require to apply plaster via a machine.
MIXING - To the consistency of thick melted ice cream.
Coverage with a 25kg is on average 2sq/m using a 13mm bead (1/2 inch)
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- Undercoat Products
Bonding Coat - Typically used when a good solid bond is required between background (what the plaster is to stick to) and final coat or where the background isn't going to provide enough grip to hold the final plaster.
You would normally use bonding coat under Hardwall or finishing plaster using a thin coat, you can use bonding coat for up to 50mm (2 inch) but not in large areas.
MIXING - to the consistency of thick melted ice cream.
The average bag of 25kg will cover around 3sq/m at an 11mm bead
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Hardwall - Typically Used instead of a render, NOT to be used where there is damp or the background is high suction (Wall soaks up the water fast).
If you have more then 11mm (1/2 inch) to build up the use render first then Hardwall then finish coat.
MIXING - to the consistency of Blended Fruit.
A 25kg bag will cover on average 3sq/m with a 11mm bead.
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Tough Coat - Typically Used where you need a very hard finish like where kids are likely to play and hit the walls with toys or even where wheelchairs maybe passing alot (NOT to be used externally).
You would bond coat if needed, then apply Touch coat then finish coat.
MIXING - to the consistency of thick melted ice cream.
The average bag of 25kg will cover 3.25sq/m using a bead of 11mm (1/2 inch)
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Browning - Typically used on new block work instead of a render mix, you should have a keyed service (grooved and other stuff the plaster can grip to)
A Multi finish Finish coat should be used after.
MIXING - To the consistency of melted ice cream.
An Average bag of 25kg will cover 3.75sq/m at a 11mm bead (1/2inch)
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Dri-Coat - Typically used where the wall has been treaded for damp, you would build up using this product (bonding first if required) then a finish coat.
This stuff is different due to protection against damp.
MIXING - To the consistency of Whipped Fruit.
Average Coverage is 3.25sq/m using a 11mm bead (1/2 inch)
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X-Ray - ONLY FOR PROFESSIONAL USE - Used in X-Ray rooms as this will help stop the x-rays penetrating the walls, Its mixed quite thick and will only cover around 1sq/m per bag.
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Limelite Renovating plaster - Used where injection damp proofing has been applied, its like Dri-coat but uses lime instead.
Trowelled on up to 12mm thick (1/2 inch), takes 24 hours to go off so if a skim coat is required should be done on the next day.
MIXING - to the consistency of melted ice cream.
An average bag of 25kg would cover 3.75sq/m at a 11mm bead (1/2 inch).
- Finish Coat Products
Multi-Finish - Typically use for Skim Coats.
Very versatile and can be used in just about all applications even without and undercoat in some cases but not to a great thickness.
Great for small patching jobs and skim coating over undercoats or plasterboards, perfect for getting flat smooth finishes.
MIXING - To the consistency of melted Ice Cream, to test this you can put a stick upright in the middle and it should JUST ONLY stay upright.
One Bag of 25kg will cover on average 10sq/m at a 2mm skim bead.
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Board Finish - RECOMMENDED - Typical use is as a skim coat over plasterboard, works just as well over undercoats.
Easier to work then multi-finish.
MIXING - To the consistency of melted ice cream.
a 25kg bag will cover on average 10sq/m with a 2mm bead.
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Plaster Of Paris - Gypsum mined in france, used for more ornamental plaster works like Coving, Cornices and Ceiling roses, its typical use would be to repair ornamental work already in place.
Small tools including your own fingers would be used to apply this, in a domestic situation you would be applying to into cracks or as lumps to repair sections.
No more then a 5kg bag will be required for most jobs, this sets very fast only 20 minutes working time and 25 minutes till its set.
MIXING - to the consistency of melted ice cream, its recommended that you only mix little bits at a time as the working time is so short your likely to finish of one part and the mix is to hard to work into the next part.
Coverage will depend on what repairs your doing.
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