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Take great care when you build a new boundary wall.

I have a confession to make. I don't enjoy the `make over' programmes that have burst on to our televisions in the last few years. It's probably because I see them as tarting up, rather than getting to grips with rejuvenating the building.

I will say one thing, it has created considerable interest in upgrading of properties. The overall effect of the programmes can be seen in the major changes in appearance of many properties over the last few years and in many instances, this is a change for the better.

One aspect I particularly like is where property owners are replacing previous brick boundary walls and setting wrought iron railings on top, the way they were before the Second World War. During the war iron railing and gates were removed and used for scrap to help the war effort. For 50 years after the war, very few of these railings were ever replaced.

Now we see an upsurge in new walls replacing the old dilapidated boundary walls with new ornate railings, setting off the house behind.

Unfortunate, many of the walls that are being built now are giving rise to problems shortly after they are constructed. Maybe its because we haven't much recent history of building boundary walls. We must remember, boundary walls are exposed to all of the weather elements. They are saturated by rainfall, dried out by drying winds and the winter frosts will cause any water that is lingering in the wall to expand and damage the bricks or mortar. Therefore it is very important to get the design of the wall right.

The first decision is what type of brick to use. The bricks in boundary walls should have a low level of absorption. The brick supplier will specify the absorption rate, therefore the contractor should be able to show you the variety of low absorption bricks that are available on the market.

Next the bricks should have a low sulphate content. Depending upon the quarry where the clay is excavated to form the brick, will be the amount of sulphates that are embedded in the brick. Bricks used in relatively dry areas will not suffer from sulphate problems, but bricks that are used in walls that are easily saturated can suffer from sulphate problems, if sulphate content of the bricks, or even the mortar that is used, is above normal levels.

The design of a boundary wall should prevent rainwater soaking down from the top into the bricks beneath. The simplest method is to use a dense concrete coping stone set on top of the wall with a damp proof course beneath it. The coping stone should project some 25-40mm each side of the wall so that any rainwater is shed clear of the bricks beneath.

The new metal railings need to be carefully protected from rusting, not just in the areas you can see, but also in the parts that are embedded into the wall. The railings are best held into position with lead wool that is tightly compacted around the post and into the hole in the wall, to tightly grip the rail. By using lead, you are able to protect the wrought iron from rusting.

I don't recommend fitting a damp proof course at the bottom of the wall, mainly because it weakens the brickwork and makes it easier for the wall to be pushed over. If you are in a damp area, it is better to use a heavyweight dense brick for the bottom two layers, with a dense waterproof mortar. This will prevent the water rising up the wall and keep the brickwork sound.

Building a boundary wall with a normal facing brick and without adequate protection at the top and bottom from the effects of water, can result in a multitude of problems. The first is the problem of frost on any water that has soaked into the wall. This causes cracking of the bricks and the mortar, eventually it will lead to instability.

Sulphates embedded in the brickwork react with any water penetration causing expansion in the mortar joints. As the mortar joints expand so the wall twists and distorts, almost to the point of overturning. The right type of brick and a reduction of exposure to rainfall should overcome the problem.

A more common problem with boundary walls is that of white efflorescent salts. These naturally occurring chemicals either originate in the bricks themselves, from the mortar, or even from atmospheric pollution. Again, rainwater mobilises these salts and as the wall dries out so they crystallise on the surface of the bricks. The salts on the surface are quite harmless, but do disfigure the face of the wall. You need to brush off the salts as they appear, because if you let them set, they become quite hard and you need to attack them with a wire brush.

There are times, when the efflorescent salts crystallise below the surface of the brick. Technically, this is called crypto-efflorescence. The crystallised salts cause the face of the brick to break away. This delamination or spalling of the bricks is most unsightly. Particularly so if the brick is a facing brick with an attractive surface to match the rest of the building.

The good news about efflorescence is once you have brushed it off, it will not come back. Eventually, all of the salts migrate to the surface of the wall and that will be the end of it. You do however, have to keep brushing the wall down to stop the salts being washed back into the brickwork by rainfall.

* Peter W Fall is the Senior Partner of Peter Fall Cowie, Chartered Building Surveyors. The company can be contacted on (0191) 232- 7733. To request back copies of the House Doctor articles, visit
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2003 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Features
Publication:The Journal (Newcastle, England)
Date:Aug 9, 2003
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