Concrete blockwork, either plastered or fairfaced, is the most common form
of wall construction on Irish farms. A wide range of block types and sizes are available
which provide varying levels of performance to meet the many needs of farmers.
The information given here is based on considerable experience of blockwork and
plastering. It gives practical details about materials and mixes and outlines important
aspects of detailing and workmanship. The recommendations are applicable to both large and
small jobs and are supported by an Advisory Service freely available to discuss special
problems
Before
starting even the smallest job, one should always:
Plan the job carefully.
Select mortar and plaster mixes suitable for their intended application.
Use only quality materials which have been proven under local conditions.
A little advance
planning can greatly simplify and improve the work. Always provide adequate storage space
and keep blocks, lime and cement dry prior to use. Make sure that the foundation provides
a level surface on which to lay the first course of blocks and with sloping sites, provide
steps equal to the height of a single block at appropriate points. Arrange overall
dimensions and openings to minimise or eliminate the necessity for cutting blocks.
Use only good quality
materials. Do not use freshly made blocks and protect blocks in storage from rain and
moisture. Fresh or damp blocks greatly increase the risk of cracking. Use only clean sand
already found to be satisfactory and protect it from contamination with clay. If using
plasticisers as a replacement for lime, use proprietary materials designed for use in
mortar and do not use substitute materials sold for other applications.
Improved workability is obtained by preparing the lime/sand mix the day
before and adding cement in proportion 1:6 immediately before use.
Care in lining, plumbing and levelling the first course of blockwork
greatly simplifies subsequent work. When this is complete, build up all corners for 4 or 5
courses. Sections of walling between corners are then completed from each end using a
string line and level to guide the work. Only small quantities of mortar should be spread
in advance so that the blocks can be finally bedded before the mix loses workability. With
double leaf walling, care is necessary to prevent mortar entering and bridging the cavity.
In winter, always protect sand, blocks and mortar from frost.
All building materials shrink and expand slightly due to moisture and
temperature variations. To accommodate these movements in blockwork, joints should be
provided in accordance with the following recommendations:
Free standing walls should incorporate joints at a spacing of not greater
than 6m.
Walls less than 1.5m high should incorporate joints at a spacing of not
greater than 4m.
To minimise the risk of shrinkage cracking occurring around doors and
windows the following precautions are recommended:
Use the correct mortar mix in accordance with Table I.
Protect all blockwork during construction.
Avoid the use of fresh blocks.
Incorporate expanded metal in all mortar joints immediately above and
below openings.
Prestressed concrete lintels should be built in with the textured surface
uppermost. They act structurally with the blocks and there must be an adequate depth of
bonded solid blockwork above for satisfactory performance. Blockwork should not be used in
the construction of containment structures without the advice of a structural engineer.
