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Plastering School

Lime Plasterers - Lime Plastering 13 Primary School Classroom Rochdale, Manchester

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

School Plasterers

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.

We had been involved with another school Rochdale Council trailed the lime plaster on in 2009. This trail proved successful eradicating the plaster problems.

A basic lime render or plaster can be made using the same ingredients and mixed in the same way as a pointing mortar. A coarse sand can still give a smooth finish suitable for most vernacular buildings although the mix should be slightly richer in lime than a standard pointing mix.. The mix will need to be slightly wetter than for pointing but it should be slightly stiffer than its modern cement or gypsum counterpart.

 

Damaged Plaster

The Gypsum based plaster with non breathable paint applied. This has 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.

We used a lime putty based lime plaster mixed with a pozzalan additive. Our plasterers applied 2 based coat & 1 lime skim coat.

Removing old plaster

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 sheeted the classrooms in the school with visqueen sheets. All the floor areas & fixtures also had to sheeted.

There is only one way to do it and that is the right way, is an often heard cry from craftsmen and specifies alike. However as our knowledge increases through analysis and investigation, it is apparent that there are as many 'right ways' as there are buildings with historic plaster work, particularly in pre-Victorian times.

 

Brickwork with plaster removed
Plastering in hydraulic lime mortar normally consists of two or three-coat work. Lime plaster made with feebly or moderately hydraulic lime and sand is the basis for this guide. This type of lime sets and hardens predominantly by an hydraulic set and re-absorption of Carbon Dioxide from the air. By its nature the drying and absorption process is slower than gypsum plasters, therefore lime plaster curing should not be hurried allowing approximately 3-5 days per coat depending on the hydraulic lime used.
Brickwork before plastering

The toilet area in the primary school. We removed the gypsum based plaster from the walls. Roof problems in areas had caused water ingress to the internal brick wall.

Our lime plasterers in Manchester have worked on listed buildings, churches & private houses. We generally apply a 3 coat lime plaster to brick walls. When lime plastering onto stone wall coats can go up to 6-7 coat depending on the substrate. It is only possible to apply 10mm - 12mm of lime plaster at any one time. The brick walls on this school had 3 coats of lime plaster applied.

Lime Plasterer applying lime plaster

Once all the existing gypsum had been removed we applied the first base coat of lime plaster. This plaster is a lime putty based. We had to remove the toilet cubical's & fix a ply cover over the toilets.

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.

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.

Lime Plastering

Lime Plasterer applying based coat lime plaster to brick wall in Rochdale, Manchester. 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. Small cracks appear on the pointing, water is allowed into the wall. This appears as damp on the internal walls, this will cause the plaster to de-bond from the substrate. There will also be a white powder forming on the surface of the plaster. Damp on old walls generally means there is a problem on the external walls. Old houses have been branded as damp and cold but this is manly due to water in the walls. Often when the walls are dry & breathing the building are warm.

Lime Plasterer

Most of the brick walls in the school had pillars and large windows. Our lime plasterers mould ed the base coat lime plaster around the pillars. The corners of the pillars had a 60mm chamfer to avoid damage. The corners were for formed with a wooden float.

On this photo our plasterer is applying the 2nd base coat to the brick pillar.

Base coat lime plaster

This shows the 2nd base coat applied to one of the main hall walls. You can see the original decorative wall tiles below the plaster. We used a aluminum scaffold tower to access the high level areas of the classrooms in the primary school.

The external brickwork of the school was re-pointed by a local Manchester brickwork contractor. The external brickwork of the school needed the cement base mortar removing. The brickwork contractor used a lime based mortar for re-pointing the brickwork.

Lime Plaster

Here is the 2nd base coat lime plaster to an old chimney breast. This chimney breast is now part of a classroom. The original gypsum based plaster has blown of the brickwork. This was due to roofing problems. The roof had missing slates & poor lead detailing. A local Manchester roofing contractor replaced the missing slates & repaired the leadwork.

At the top of the chimney breast wall there was a large amount of moisture in the brick wall. The lime plaster in this area took a while to set. The moisture in the wall due to the leaking roof had caused the plaster to blow & salts appear in the plaster surface.

Lime Plasterin toilet

Lime plaster applied in the school toilet area, this is the 1st base coat. Areas around the areas around the windows have had the plaster blow. As above the plaster had de-bonded from the substrate. We removed the existing gypsum plaster using small hammer drills.

In all the areas where we were plastering to existing plaster we had to marry the levels.

Lime Plaster in classroom
Here we have just applied the first based coat of lime plaster. This is a dubbing out coat to level the wall. Before our plasterers applied the second coat we remove some more of the gypsum based plaster.
Lime Plaster
Lime plasterers applying 2nd base coat lime plaster. Our plasterers used a scratching comb to score the base coat lime plaster.
Wood floating lime plaster

Wood floating a 2nd base coat lime plaster at Primary school in Rochdale, Manchester. Our plasterers are experts in the use of lime plaster we have applied 1000's of square meters of lime plaster in the past. We are applying lime plaster onto a brick background. This brickwork had to be dampened to allow the plaster to stick.

There is only a few contractors in Manchester with the skill set to apply a lime plaster. Many plastering contractors will say "lime plastering ya no probs" but a lot of the time it doesn't work.

Lime plastering pillar

We fixed stainless steel corner beads to the pillars and corners. The stainless steel corner beads wont rust when in contact with moisture. The stainless steel corner beads are bedded into the lime mortar in the 1st base coat lime plaster. We then apply the second base coat, leaving a small rise on the corner bead. When the top skim coat of lime plaster is applied this covers the stainless steel bead.

All the wooden floors had to be sheeted up with visqueen. This was to protect them from the lime plaster.

Lime plastering classroom

All the fixtures in the classrooms had also to be covered & protected. The damp in old buildings is mainly caused by water ingress into the wall front he external. This is caused by cement render or cement pointing on the external elevation.

It is important to rectify these external problem before applying the lime plaster. The cement render can be removed and replaced with a lime based render. The cement pointing can also be removed & replaced with lime pointing. This will prevent water ingress into the wall. Once the wall is dry the mould will not have any cold areas to settle on.

Lime Plastering Toilet

Top skim coat lime plaster in the toilet area. 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.

The skim coat lime plaster is mixed with a lime putty lime. Using the lime putty in lime plaster is the most breathable lime to use. If a NHL lime is used in the lime plaster say a NHL 5 breathable would be less.

Lime Plaster

Here we have toweled finished the lime plaster. The wall has also been re-pointed on the external elevation with a lime mortar. The wall before lime plastering was damp with moisture ingress from the external brick wall. We put on 3 coat of lime plaster in total. The base coat lime plaster and the float coat lime plaster had a synthetic fibre added to reinforce the lime plaster.

If the moisture from the external elevation had not been stopped the internal plaster would show signs of damp. The damp in the wall would not have damaged the lime plaster as it allowed the escape through the pores of the lime plaster. If a gypsum plaster had been using to "skim over" the existing plaster this would have de-bonded from the background.

Lime Plaster

Lime plaster in the boys toilets. We removed the existing plaster from the wall down to the tiles. Then primed the existing plaster which was the original lime plaster with a lime slurry. All the wall we re-plastered in this school had damaged plasterwork as they had been skimmed over with gypsum plaster.

The wall once we had finished the lime plaster was painted with a breathable paint.

Lime Plaster Manchester
Toilet wall from the picture above being skimmed with lime plaster. The cubicles have been reinstalled to the toilet area. The client was suitably pleased with the lime plastering work we did at the school. The school also approved the lime plasterwork. The school also decided to leave at section of the lime plaster unpainted to should the plaster finish.

 

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