Damage caused to stone and brick walls by Cement Pointing
One of the major causes of damp in old houses is linked to the use of cement strap pointing. This became popular in the late 1960's and 1970's, when every builder was going around offering to 'repoint your walls and make them look nice'. A solid brick or stone wall, built with lime mortar, needs to breathe. It loses its moisture content through the mortar joints. If this breathability is blocked, through the use of cement, the wall immediately starts to get wet. Water is trapped, and the only way it can get out is via the brick or stone. In winter, the damp brickwork then freezes, and the familiar rotting and spalling bricks or stone start to appear. Cement pointing is responsible for dreadful damage to thousands of walls all over the country. At the same time as trapping water, it forces water into the wall - where it emerges inside - blowing plasterwork, and creating the usual symptoms of 'rising damp' - which of course, it is not! The 'timber and damp surveyor' will try to sell you yet another injected damp course, which you don't need - to prevent a problem which doesn't exist. If you have cement pointing to an old wall - the simple solution to any damp problems is to get rid of the cement. Usually, this will be all that is needed. Builders rarely if ever re-point properly, and the strap pointing usually falls off quite easily. Underneath, you will find nice, solid lime mortar that isn't damaged. If the mortar is very badly eroded, or has cracks and holes in it, then you may want to re-point using hydraulic lime mortar.
Investigate the claims made by the damp companies and building companies that you invite to 're-point' your stone or brick wall. You will be very surprised if any of them recommend using lime - most of them will want to use cement, and many of them will blame the damp problems you may be experiencing on 'rising damp' - which of course by now we know it isn't, and never was. These people just won't get the message that the solutions are so simple and cheap, that if everyone DID get the message, the timber and damp surveyors, and the chemical companies that employ them, would be out of a job. Quite often they will try to persuade you that the wall is badly damaged and needs to be 'Rendered in a Waterproof coating'. This is complete rubbish - and will destroy the wall. NEVER allow anyone to use a cement or waterproof render on any wall.
Repointing of old walls must be done using a mortar that is softer than the material we are pointing - this gives the wall the best chance of breathing. Generally, a very soft old red brick, or a crumbly sandstone or soft limestone would need what we call an NHL 2.5 hydraulic lime mortar to point it with. The joints are raked out to a depth which is equivalent to twice the width of the mortar joint - it's important to make sure that we have a good depth of mortar in the joint. We show you how to do this on the lime pages of the site if you need to do it yourself - it's not hard, and a good way to spend a summers day - I tell my clients to grab a few cans of beer and a chip hammer, and just chip away and have fun - it shouldn't become a chore. A 'beer o'clock job' as we used to say in Australia!