Nov 29, 2016

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Lime Plastering Advice For Contractors

the guild logoWhether you’re a contractor required to procure in this service or an interior decorator needing to understand the nuts and bolts of the different terms. Here’s my lime plastering tips and advice you must think of before engaging on a lime plastering job. I worked with a couple of specialists over the years on Lime projects, including a good friend of mine Noel Dunn. Noel is a very skilled plasterer in Manchester and a long time member of the Guild of Craftsmen. He kindly lent a hand putting this article together and is happy to field any queries you might have if you have an upcoming project. Or if you need a hand with a project in the North West Noel and his team are great to have on the team!


Considerations When Lime Plastering

Previous drawings – If you want to replicate or restore a period look, it is useful to seek drawings from archives or deeds.

Budget – The above mentioned directly has an effect on this as detailed work will need a higher budget.

Deadline to completion – Look ahead in order that you/your customer can work it proficiently into your timetable.

Challenges to work around? Think about access, previous damage that we may want to know about.

Timing of project – Perhaps you will need to avoid factors such as risk of frost damage (resulting from ice crystals forming within the lime mortar).

Requirements – Decide if you should replace or repair.

Buildings HeritageGrade-listed buildings might have strict rules to abide to. If a building is considered to be of special architectural or historic interest it will be included in a list of such buildings.

Preparing the wall for rendering

lime rendering applicationFor stone and brick any hollow or decayed render should be hacked off and any loose pointing must be raked out and replaced ahead of rendering. Brush the wall to remove loose material. Do not rake out pointing to provide a key. Do not use plastering bead on corners as this gives a modern appearance. Do not use chicken wire or metal lath to form a key as it can cause stress in the render due to differential thermal movements and can lead to large-scale failure, specially when it rusts.

For plastering onto existing wooden laths be sure they are solidly fixed and free from lumps of old plaster. New laths should preferably be riven oak or chestnut. Sawn laths are low quality because they are smoother and weaker than those split over the natural grain of the wood. Laths should be fixed so the distance between them is roughly 8-10mm. This allows the correct amount of space for the plaster to be pushed between the laths and flop over to form a key. Do not apply preservative treatments to either old or new laths as they could add harmful salts into the plasterwork. Metal lath is sometimes employed internally rather than timber laths because it is quicker to fix and less expensive, but it is harder to plaster onto as it’s slippery and the sharp edges may cut into and weaken the plaster key. Plenty of hair in the mix is critical.

For masonry, adequately wet the wall with clean water using a hose-pipe . The more porous the background the more water is going to be required. Let the water to soak in a bit then spray again, and repeat until the surface layers of the wall are extensively damp. Brush the wall to remove loose material. Do not rake out pointing to provide a key.

Do look out for further job tips and advice on lime plaster and lime render coming out on the blog during the next few months.

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