54 CONSTRUCTION FIXINGS
Fixings for
Brickwork
In the third of this series Mark Salmon shares
some of the solutions offered by members of
the Construction Fixings Association for coping
with this most awkward of materials. Most will
be familiar to you but there may be a new idea
or two.
rickwork! Of all the problems your concrete and brickwork. In brickwork the whereas shield anchors are less reliable in
B customers bring to you I suspect
among the most awkward are those
involving fixings to masonry - brickwork,
separately retained segments expand
readily making setting easy (See figure 1)
perforated bricks. Other expansion
anchors such as throughbolts or hammer
set socket anchors are not suitable for
blockwork and stonework. Due to bricks and should not be considered.
space limitations I am restricting this One of the most common applications
article to brickwork but many of the into brickwork is the fixing of door
principles apply equally to blockwork and window frames. Frame fixings
and stonework. Bricks may vary in made of nylon are now very well
strength from as little as 5N/mm2 up to developed for these uses with clever
70N/mm2, they may be solid or have designs that will get a good grip
holes all the way through and all are irrespective of whether the brick is
joined together - or held apart - by hard or soft, solid or perforated.
mortar which may vary just as much in But if your customer needs a really
strength and may not even be there in strong fixing that will work in this wide
some cases. The depth of a single skin range of possibilities then it is the resin
brick wall will be a mere 102mm thick anchor that may provide the best
and a modern drilling machine can solution albeit requiring a degree of
easily punch its way through the back care. This is also the area that has seen
of the brick long before the tip the most developments over the last
reaches it. twenty years. The injection system is
Where older buildings are now well accepted as it has the
constructed from 9" solid brickwork flexibility to cope with poorly filled
you not only have to cope with some mortar joints while plastic or steel mesh
of the softest bricks around and the sleeves will give a strong fixing in
weakest mortar joints but the gap and the large expansion ratio gives a perforated bricks. Most people are familiar
between the two leaves may well be strong grip even in enlarged holes with this concept as illustrated in figure 2.
devoid of mortar. common when powerful drilling A mesh sleeve of plastic or wire is inserted
The fixer's problems are compounded machines are used in softer bricks.
by the fact that quite frequently he has no The high expansion ratio can
idea what the substrate actually is before crack the bricks in larger
he drills into it, and sometimes not diameters so M12 bolt diameter,
afterwards. If it's plastered or rendered he requiring a 20mm diameter hole,
won't be able to avoid the joints but he's is usually the limit. The variety of
standing at your trade counter expecting configurations from hex bolt and
your staff to sell him a fixing that will bolt projecting to hook and eye
work in whatever material he encounters. versions means this is one of the
There is a truly bewildering array of most versatile fixings available.
fixings available nowadays to fix into Thin-walled sleeve anchors will
brickwork. also work in bricks. These have a
The shield anchor is the most obvious much smaller expansion ratio than
place to start. The “original expansion shield anchors so tend to be less
anchor” - shield anchors are still widely strong and less inclined to crack
available and well proven for both the bricks. They will work in
perforated as well as solid bricks
56 CONSTRUCTION FIXINGS
into the drilled hole and filled should really be used to share the load in case one fixing is These are very important for
with resin before the stud is weaker than expected. safety critical applications but
twisted into place thus When load capacity is critical and the strength of the brickwork should be born in mind for
displacing the resin to bond is unknown, tests on site are needed to determine the loads less critical jobs too. We need
with the brick adjacent to the which may be applied. A Guidance Note detailing how to do this to think about the position in
mesh or form a hard mass in may be downloaded from the CFA website at the brick and in the wall.
the void to give a strong wwww.fixingscfa.co.uk. It includes a technique for working out Ideally individual fixings
interlock. The same technique the allowable loads but if this looks complicated there is a should be positioned within
may also be used, with longer simpler one on the website in the FAQs. the meat of the brick, say
mesh sleeves, for fixing into Having thought about the choice of system it is worth reminding 35mm from the end of a solid
solid 9" brickwork where the your customer - if you get the chance - of the positioning rules. brick and on the horizontal
gap between the leaves may centreline, this minimises the
be devoid of mortar. But there risk of bricks cracking and, in
is a technique that avoids the the case of frogged bricks will
need for mesh sleeves and can miss that void. Within the wall
be tailored to provide the itself we need to make sure
strength needed. Figure 3 there is enough structure
shows two diagrams. For light surrounding the fixing to
loads the embedment depth is support the required loads.
limited to 80mm thus avoiding This means never fixing closer
the loss of resin into the gap. than 280mm from the edge of
For higher loads the idea is to a wall, never go closer than
bond the stud deep in the 1000mm to the top of an
remote leaf by drilling to unrestrained wall, avoid putting
180mm. Resin is then injected two fixings into the same brick
to fill the hole in the remote - if joints can be seen this
leaf. The overall strength of the means a minimum spacing in
anchorage comes from the stud the order of 100mm but if
being bonded into the remote plastered or rendered a
leaf which gains strength from minimum of 275mm must be
the front one. Any loss of resin allowed. If the load is high and
into the void does not matter. the application is safety critical,
The point to remember is that avoid putting fixings into
embedment depths between adjacent bricks. This means the
the two risk most of the resin minimum spacing between
being lost into the void. fixings will be 350mm if joints
The strength of modern are visible and 500mm if not!
resins and the versatility of the Again there is more to this than
injection system means it can one might have thought and
cope with blind fixings through more advice is available on the
render where the hole may be website in the FAQs with
drilled into a mortar joint but Guidance Notes covering a
in this case multiple fixings range of associated subjects.
