CLAY HOLLOW BLOCKS

• 1. Evolution Of Masonry Blocks

1. The evolution of blocks

Fired clay bricks underwent a spectacular evolution over the 20th century until they became the masonry blocks of today. Taking advantage of the technological advances in mass production, the main directions of innovation have been towards better thermal insulation and faster and more efficient construction. First, the holes appeared in the bricks, as the air cells provide the bricks with excellent thermal insulation properties. One of the following steps was to increase the height of the bricks, resulting in fewer courses to build, speeding up the construction process. The increase in the number of cells, and thus the cell ratio, further increased the insulating properties.

At the same time, sizes continued to increase as the large number of cells significantly reduced the specific mass. For most manufacturers, the height has remained constant at around 23.8 centimetres, assuming a mortar thickness of 1.2 centimetres and, thus, a vertical grid size of 25 centimetres. The blocks have also been widened in both directions, further facilitating construction: the 30 or 38 centimetres thick walls should be placed in a header course instead of a varied brick bond.

The mortar pocket appeared in many blocks, making vertical joints unnecessary. The same result is achieved with the tongue-and-groove joints. Eliminating vertical joints improves thermal properties and speeds up construction on site.

The developments’ next focus was to reduce bed joints to a minimum. The latest blocks are precision-planed, keeping the height grid at 25 centimetres, thus reducing the height of the joint to 1 millimetre instead of 1.2 centimetres. The mortar is now applied with a roller, or adhesive foam strips are sprayed between the courses. The lower material and water requirements also mean a more economical and environmentally conscious approach.

In line with the insulation requirements, the wall thickness has also been steadily increased to meet these needs without needing separate insulation. 44-centimetre wide blocks soon joined the 30 and 38-centimetre walls. The EU's current requirement for the U-value can be met by a wall built of two types of blocks without thermal insulation:

• A tongue-and-groove, 44-centimetre-wide, precision block with an innovative cavity system.

• A tongue-and-groove, 44-centimetre-wide, precision block  with a core that has internal rock wool cells instead of air cells. Thus, the thermal insulation is integrated inside the block.

• 2. Wall Junctions

2. Wall Junctions

The following example shows a 44-centimetre-wide clay block wall end, a wall corner and a Tee-connection with another 38-centimetre-thick wall. We have chosen precision-planed blocks with internal rock wool insulation. For the masonry, we follow the general rules of good wall bonding. First, we figure out how we will solve the critical wall junctions.

a) Wall ends

You don't need to think much about the wall end for either wall 38 or 44. In the courses of the wall, we want to keep a half offset between the headers, so we place whole blocks in the starting course and start the next course with a half closer.

b) Wall corner

One course goes out to the corner at the wall corners, and the other meets it from the side. In the next course, the same happens in reverse. The goal is to have a whole block below and above the connection joint to connect the turning courses, with the joint in the middle. This course still needs to tackle 32 centimetres of the 44-centimetre wall thickness. It is done with a 19-centimetre and a 12-centimetre closer, with their cut sides facing each other. The 1-centimetre gap between them is filled with adhesive. Then, for the finished corner, we place the whole blocks in the other direction. In the next course, in the opposite direction, place blocks 19 and 12 from the corner and the whole block to create the junction.

c) Tee connection

For Tee connections, we think similarly as for wall corners. We finish wall 38 in the first course at the inner side of wall 44, stopping the course with a whole block. While in the course above it, we will reach the opposite (outer) side of wall 44. Still in the first course, in wall 44, whole blocks should be placed with their centers lying on the side lines of wall 38 to ensure a proper tie-in. To the remaining part a bat of 12 centimetres should be placed, and the joints on both sides should be filled with adhesive. In the second course the connecting part of wall 38 is tied into wall 44 by a whole block, extending into wall 44 by 12 cm. The remaining part is again built up with a 19 block and a 12 closer, with the cut parts turned against each other and filled with adhesive of 1 centimetre width. In the second course of wall 44 the blocks are laid in two directions, with whole blocks on both sides of wall 38.

• 3. The Phases Of Construction

3. The phases of construction:

1. Above the foundation, on the surface of the reinforced concrete slab, we mark the external and internal contours of the walls, the wall corners, the wall connections, and the openings with a chalk line.

2. Horizontal damp proof course in 1 layer of modified bituminous membrane will be installed.

3. In the case of flat ground blocks, the perfect levelness of the first mortar layer is crucial because the minimum thickness of the joints in the subsequent courses will no longer allow for correction.
   Adjustment is carried out using a mortar-levelling tool and a levelling bar.
   The base layer of mortar is 2 to 3 centimetres thick, on which the setting points must be marked again.

4. Next comes the positioning of the leads, which are adjusted with a rubber mallet and a level.
   We start with whole blocks at the wall ends, a 19-centimetre closer at the wall corners, and a 12-centimetre closer at the Tee connection.

5. Then comes the laying of the intermediate blocks for the first course of one of the 44-centimetre wall sections.
   To do this, a line is stretched out between the set leads.
   At the corner, we add a half bat to the three-quarter closer as planned and fill the space between the cut elements with adhesive.
   The same is also done in all other cases where cut blocks meet other blocks.
   The whole blocks are joined together by pushing the grooves and tongues into each other without using any adhesive.

6. The intermediate blocks of the other wall section are laid similarly.

7. The first course of the 38-centimetre wall section is also built, and the joints are filled with adhesive.

8. The second course also starts with the laying of the leads.
   We again start with a 19-centimetre closer in the wall-corners, but this time, the block faces the other way.
   At the Tee connection, we place a 19-centimetre closer in the direction of the connecting 38-centimetre wall.
   At each wall end, a half closer is now placed over the whole block.

9. In all other respects, we will continue with the same masonry work as before.
   The level and the plumb are checked regularly with a level.

• Practice 1

• Practice 2

• Practice 3

• Practice 4