Lime Hemp Plaster (Hydraulic)

Preparing the mix

• A bell mixer is an ideal way to mix the lime hemp plaster. Place the dry plaster in the mixer and approximately 2/3rds of the water, for each 25 kg dry mix add approximately 10-14 litres of water. It should be left to turn for approximately 20-30 mins before adding any more water. Over mixing can cause air bubbles to become trapped in the mix, which will affect the final finish and might result in undue shrinkage of the plaster. The mix should be left turning long enough to achieve a suitable consistency.
• For the plaster to have more body and a feel similar to a fat lime hemp plaster then it should be allowed to steep over night once it has been mixed. It can then be ‘knocked-up’ again the following day. This will aid in the application onto ceilings.

Preparing the surface

• It is important that the hemp plaster is not applied to a damp wall as this can extend setting times dramatically especially during winter months. If in doubt please refer to manufacturer for guidance.
• There is usually no need for pre-wetting backgrounds (but please assess first) before applying lime hemp plasters as they hold more water than standard lime plasters. The suction created by differences in background moisture will help bond the lime hemp plaster to the background.
• If Celenit wood wool boards or wood-fibre boards are being used as the background, they do not require damping down. N.B. Do not put scrim or mesh directly onto the boards. Ensure that the background is clean and free from dust by brushing the surface.

Application of lime hemp plaster/render

• Lime hemp plaster is suitable for base coats, dubbing out and textured top coats.
• Unlike standard lime plasters, lime hemp plasters can be applied in single coats 15-25mm thick (thickness will depend on the substrate and application, see above, remember, the thicker the coat, the slower the drying).
• Lay on and trowel up with a steel trowel.
• Feather edge and soft brush the base coat to give a key then apply a top coat of fine lime hemp plaster at 6mm or 3mm of standard lime top coat plaster. Following good practice, this should be applied before the base coat is completely hard. Lightly mist the following day and lightly trowel or rub with a sponge float to achieve the desired finish.
• 10cm wide jute scrim should be trowelled into the base coat Lime Hemp Plaster at corners or at wall/ ceilings junctions. This will help counteract shrinkage in these areas.
• Finish with a limewash or breathable paint if required.

Application on ceilings

• For ceilings (heavy stress), onto 25mm CeWood wood wool boards, it is best to apply a 6mm coat of fine grade lime hemp plaster, then the render mesh can be trowelled in, followed by a 6mm top coat of fine grade lime hemp plaster or 3mm Finish Plaster.
• For ceilings (light stress) onto 25mm CeWood wood wool boards, apply 6mm coat (with no mesh) of the fine grade lime hemp plaster, followed by a 6mm coat of fine grade lime hemp plaster or 3mm Finish Plaster.