Castleton School, Rochdale Manchester

Cracked & bubbled plaster

On this project in Rochdale, Manchester our team of Specialist Lime Plasterers were required to apply a 3 coat lime plaster to classrooms suffering from damp & water ingress. We were sub-contracting for a Manchester based building company, Tomax Building Contractors.
The contract was carried out in the school summer holidays in 2012. Our Restoration Lime Plasterers had only 6 weeks to complete the works. Past Plastering Contractors had used a Gypsum skim coat & bond based coat. These non breathable plasters had caused the plaster to blister & blow.
The local contractors had fixed timber panels to cover up the damage plaster work caused by the gypsum based plasters. Many of the angle bead in the school had rusted and stained the plaster. The salts in the gypsum plaster mixed with moisture in the wall causes the angle bead to decay.
The Gypsum based plaster combined with a non breathable paint, caused the plaster to crack & become detached from the substrate. All the areas to be Lime Plastered were identified by the local authority. Our plastering team did discover more areas that required lime plastering when prepping area for painting.

Applying first coat of lime plaster to smooth out the wall

We used a lime putty based lime plaster mixed with a pozzalan additive. Our plasterers applied 2 based coat & 1 lime skim coat.
The existing gypsum plaster was removed from the brickwork. Some of the plaster on the walls detached very easily & other areas were more difficult. Our plasterers covered the classrooms in the school with visqueen sheets. All the floor areas & fixtures also had to sheeted.
Once all the existing gypsum had been removed our team applied a base coat to build up and smooth out the wall, followed by a 2nd coat and final Skim Coat . The plaster used was lime putty based.
A lot of the buildings around Rochdale & Manchester are pre 1919. These buildings are often built in solid wall construction, this means there is no cavity. Any moisture or damp in the walls can travel through the wall to the internal elevation.  Most of the stone walls & brick walls around Manchester have been pointed with cement based mortar. The cement mortar does not allow the wall to breathe. With a lime pointing on the external brickwork and a lime plaster internally the solid walls can breathe. Any moisture in the solid wall will be evaporated through the lime.

When our skilled lime plasterers are using the top coat or skim coat lime plaster we can either trowel finish or sponge finish. Trowel finishing lime plaster is normally done for ornate or high class plaster work. Sponge finish is normally undertaken in the likes of cottages and farm houses. On this project we used a skim coat mixed with a very fine sand.

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