Block laying

Sample panels
In order to establish the general standard of blockwork, mortar, jointing and workmanship, it is recommended that sample panels erected prior to building. Regardless of which finish is selected, such panels are much more effective than written words or photographs in defining and specifying the quality of work required.

Storage on site
The blocks should be carefully unloaded and stacked on their bedding faces on a strong level surface near to the position where they are to be used. They should be protected against rain and in a manner which allows air to circulate between the blocks. Particular attention should be taken to ensure protection of the block arrises.

Block laying
It is recommended that block layers should use blocks from alternative cubes whilst proceeding with construction. This will maintain the natural appearance of the finished wall. Block laying should be discontinued during heavy rain unless the work is protected. When work stops for more than an hour or two, especially overnight, the top of the work should be protected against rain, snow and frost. The face of the work should also be protected against splashes from the ground, from scaffolding and from other construction activities.

No block laying should be carried out when the temperature is at or below 3°C.

Bond
Blocks should be laid to achieve a good bond not less than one quarter the length of the block. The precise bond of the wall is largely at the discretion of the designer provided it satisfies the recommendations of BS 5628: Part 3. Other patterns are of course possible but may require the use of bed joint reinforcement.

Cutting
Whenever possible, the use of standard half-length or purpose made blocks is recommended. Hanson also offers a cutting service enabling the majority of specials to be cut at the works. When site cutting is unavoidable, this should be carried out using a power driven masonry saw.

When wet cutting is used for facing blocks, excess fines from the cutting process should be removed from the finished face, using the minimal amount of water possible and allowed to dry. It should be noted that a cut face may have a different appearance to a moulded face and whenever possible, any cut face should be built into the walls. For non-facing blocks, the use of a hydraulic block splitter or traditional bolster may be employed.

Chasing
Where the use of hollow blocks is not possible and chasing is necessary, a rotary chasing machine or mechanical disc cutter is recommended. Vertical chases should not exceed one third of the wall/leaf thickness and horizontal chases should not exceed one sixth of the wall/leaf thickness. In loadbearing walls, the effect of a reduced cross sectional area caused by chasing should be checked. In no event should chases impair the strength or stability of the wall.

Fixings
Hanson’s range of aggregate blocks provides a good background for all but the most demanding of fixings. Joinery fittings and external claddings may be securely fixed to the blocks. Special fixings will be required for heavy loads and manufacturers of proprietary fixings should be consulted. Door and window frames may be fixed directly to lightweight blocks. Otherwise, the frame should be fixed by having metal straps screwed to the frame and bedded in the mortar joints. Hollow blocks abutting door frames should be filled with mortar or concrete, and if the doors are heavy, the infilling concrete should be reinforced with vertical steel bars.

Cleaning
Ideally, the best method of achieving satisfactory finished work, free from unsightly staining, mortar accretions and smearing, is prevention and good workmanship. On facing work it is also advisable to keep finished areas of walling covered as the contract proceeds, to avoid splashing and staining from other work.

When using proprietary cleaners, especially on facing units, ensure that these are applied sparingly and immediately washed off with clean water, otherwise acid attack on the block surface can occur. Pressure washing of masonry is not recommended.

If covering throughout the contract has been adequate, lime blooming is unlikely to be a major problem and any small deposits of free lime will weather off naturally. If the units have become thoroughly wet, then lime blooming is likely, but fortunately will tend to occur rapidly and should be accounted for in the general cleaning down.

Jointing and pointing
Tooled joints highlight the clean arrises of the block and accuracy of the coursing. They enhance the scale and appearance of the walls. A light bucket handle tooling is recommended for both internal and external work. Raked joints should be used with caution and limited to the highest quality of blocks and workmanship.

Flush joints are not recommended either for facing or work to be decorated.

For general background work, joints should not be left proud but struck off as work proceeds.