Archive for November, 2012

Patchit & Bodgit Builders do more harm than good

Thursday, November 1st, 2012

Ugly cement mortar will damage the stone

A recent survey of a Grade II listed stone church yet again confirmed how advice from a builder can be fraught with problems.

They say “A little knowledge is a dangerous thing” and it certainly is!

Leaking gutter joints had been patched with an adhesive tape material. It may last a while if the rust has been well cleaned; but what chance of that?

The gutters had been repaired but the split rainwater pipes had been ignored!

Those issues are relatively minor; they can be easily remedied. And the gutters and pipes will need replacing in due course.

The greater sin was the ‘repointing’. The dark grey cement mortar, smeared all over the fine honey-coloured stonework is unsightly and has disfigured the walls. But worse than that, it will lead to accelerated deterioration of the stonework.

Mortar joints are designed to be ‘sacrificial’; they erode in preference to the stone. It’s much easier and cheaper to repoint a wall than to replace the stones.

Sandstone is relatively soft compared with clay bricks or concrete blocks, so a lime-sand mix is traditionally used; it’s weaker, permeable, lighter in colour and much more ‘forgiving’; small cracks in the joints will tend to heal themselves.

The strong cement mortar used is harder than the stone and the existing lime mortar; it is impermeable so moisture can be trapped behind it. Trapped water will freeze and shatter the stone. Salts in the trapped water can crystalize; the crystals will grow and force stone particles break-off – erosion.

Anyone can buy a van and be a builder; a Chartered Surveyor has many years of formal training in their specialism, and at Barlow & Associates we have many years of experience too.