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Dutch teach bricklayers to think thin

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The advantages of thin-bed masonry and glue mortar have revolutionised architecture on the Continent, writes Els Bleus

A little more than 10 years ago, a new technique of using bricks was developed in the Netherlands. The intention was to develop a new kind of brick architecture and to make bricklaying easier, less demanding and less of a strain for the bricklayer.

On the Continent, thin-bed masonry is becoming increasingly popular. It is being used in the commercial sector as well as in the housing one. Architects feel this technique offers aesthetic and structural advantages. Thin-bed architecture is pure, colour-intensive, strong and durable. It gives the building a hi-tech and modern image.

The main principle of thin-bed masonry or glued brickwork is the thin joint.

Depending on the kind of brick that is being used, the joints will be between 2 and 6mm wide. To obtain those thin joints a specific kind of mortar is used, a 'glue mortar'. This glue mortar is applied in such a way that it does not come to the face of the brick. It is a recessed joint.

In a traditional brick facade, the joints account for about 20 per cent of the surface.

The colour of the joint has a strong effect on the final appearance of the facade. In the case of thin-bed masonry, the thickness of the joint is reduced to 2-6 mm, accounting for less than 10 per cent of the facade. On top of that, the glue mortar is applied in a recessed way, which means that the mortar is hardly visible. The joint is nothing more than a thin line of shade. This means that the colour of the wall is completely determined by the colour of the brick. To improve the colour intensity even more, the architect has the opportunity to match the colour of the glue mortar to the colour of the brick. Some glue-mortar suppliers offer six standard colours, but they can also make specific colours on request. A matching glue-mortar colour can also avoid possible stains.

The joints have always been the weakest link in the facade. After a certain number of years they require some maintenance work.

Since the glued brickwork no longer has any actual joints, and since the glue mortar is very strong, a thin-bed masonry facade no longer requires any maintenance and is extremely durable.

The glue mortar complies with all the demands on traditional mortar, but is of a definitely higher quality in certain aspects.

Firstly, the glue mortar is stronger than traditional mortar: it can accept tensile stresses that a traditional mortar cannot. This lets the architect use bricks in a way that he has never done before:

he can be creative with brick bonds: a stretcher bond is no longer necessary for the structural strength of the wall. That means that the architect can play with brick bonds, such as stack bond for example, or a block bond (stretcher bond two-by-two);

he could even use the brick the other way around, that is, using the face of the brick as the laying surface and thus creating a wall with a thickness of no more than 65mm.

That way the architect could even use, for example, the frog of the brick as a feature in the concept of the building, by using the frogged surface as the face of the brick.

The tensile strength of the glue mortar is also an advantage in creating windows or other openings up to a certain width, without any other lintel support. In the Netherlands, a project has been completed with window openings of up to 4.5m. In that case, some bed-joint reinforcement was used to avoid damage in case of cracking.

After only one day, the glue mortar reaches the binding strength that a traditional mortar obtains after 28 days. This quick binding process reduces the risk of efflorescence and storm or rain damage.

The glue mortar has also a good 'standing' power, which means that the bricks do not start to 'swim' after a certain number of courses and that the height of a wall that can be laid in one day is no longer limited. Glue mortar is available in three types, A to C, with type A for use with high-suction bricks and type C for use with low-suction ones.

The glue mortar also has the advantage of being water-repellent. Every brick is surrounded by a water-repelling layer, so the bricks can no longer exchange water with each other. This means that large concentrations of water in a gable and really saturated facades belong to the past.As a consequence, the ageing process is delayed. This does not mean, however, that the facade becomes totally water-resistant. Water barriers and DPCs have to be applied as usual.

Glue mortar is not applied with a trowel but with a glue machine. This consists of a mixing tank, in which the dry glue mortar is applied and mixed with the right doses of water. A pump underneath the tank pumps the glue mortar through a hose, ending in the glue gun.

The mouth of the gun is profiled in such a way that it creates two strings of glue mortar. Those strings are applied on the laying bed of the fresh brickwork. To create the vertical joints, some bricks are put in a rack, headers up, so that the double string of glue mortar can be applied across the headers of those bricks. These bricks are laid on the double glue mortar strings on the fresh brickwork, each time with a 'buttered' header placed against a 'naked' one.

The position and thickness of the glue strings can be adapted, so the right amount of glue mortar can be applied and the face of the bricks remains clean. Since the glue mortar sets quickly, it is vital to clean the machine after use to avoid blockages.

Almost any kind of brick could be used for thin-bed masonry but the type and, more specifically, its dimensional tolerances, determine the final result.An extruded brick tends to give thinner joints, compared to a soft mud brick, for example. On the other hand, small imperfections in the brickwork will show more when you use an extruded brick, just as with traditional brickwork.

A frogged or perforated brick can also be used, but the consumption of glue mortar will be higher. In terms of economy and structural performance, a solid brick or a perforated brick gives the best result. Two types of adapted bed-joint reinforcement are available: a thinner version of the Murfor of Bekaert, known as Brixor2, or a polyaramide reinforcement. Wall ties also need to be adapted to thin-bed masonry, with a thin, flat end to fit into the thin joint.

Applying glue mortar is not difficult, but it requires training to get used to the glue machine, to learn about the right dosage of glue, maintenance and cleaning and to learn about the practical issues on site related to thin-bed masonry.

Although the bricklaying in glued-brickwork applications is an efficient technique, it is slightly more expensive than traditional brickwork. This is mainly due to the equipment needed and to the cost of the glue mortar, but also due to it being a more exclusive technique. Contractors often need a push to start using it, but once they understand the advantages, they are convinced.

Generally speaking, this technique can offer architects a whole new range of tools that will let them be creative with bricks.

Brick has always been inherent in British architecture.

It is a traditional building material that has proven its qualities and durability over many centuries. The added value of glued brickwork offers new aesthetic opportunities, even better durability and new and improved structural qualities. Thin-bed masonry is a quality jump.

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