Civil Engineering Reference
In-Depth Information
general, the weakest limes are used for the
softest substrates, e.g. NHL 2 on sandstone;
and the stronger ones, e.g. NHL 3.5 or NHL
5, on harder backgrounds, such as granite,
and where the weather conditions are
more severe or for buildings under water.
The NHL 2 limes are reasonably similar
in properties to the fat limes, and may
therefore sometimes be used on strawbale
buildings in certain circumstances. For
example, they may be applied very late in
the year, since a set as well as carbonation
would allow a little more protection against
frost; or the reason might simply be that it is
cheaper to buy bags of lime and mix them
yourself with sand and water than to use a
ready-mixed fat lime render.
screeds), using finer aggregates for different
surface finishes, or to contain under-floor
heating pipes. Advantages of a limecrete
floor are a lower environmental impact, no
need for expansion joints, and a breathable
floor. However, at the moment it is unlikely
to cost less than a cement floor because the
materials are not yet mass-produced.
The basic recipe is 1:3 NHL 5:well-graded
sharp sandy aggregate, 20mm down (mean-
ing the largest gravel in the aggregate is
20mm or
7⁄8
”), using the strongest hydraulic
lime.
All quantities are measured by volume.
It is very easy to use too much lime as it
easily fills space because it's light, whereas
sand is heavier to shift and harder to level
to be sure that enough is in the measure,
especially when workers are tired.
Limecrete
This is the name given to solid floor slabs
or bond beams made using NHL 5 lime
rather than cement as a binder. Lime has
been used in this way for thousands of
years, but the knowledge of its use has been
almost lost due to the dominance of cement
and concrete in the construction industry.
However, it has been brought back into use
by companies such as Ty Mawr in Wales (see
www.lime.org.uk) and adapted to changing
demands by adding particular aggregates
to the mix to provide solid floors that are
also insulated. The following is a method
for making a DIY limecrete floor. Because
different sands have different strengths
and properties it is not recommended that
you make a limecrete floor on a large scale
without expert advice from companies
such as Ty Mawr. Limecrete is usually laid
in depths of 100-150mm (4-6”); thinner
layers (50-65mm, 2-2½”) can be used (called
It is very important to measure out the
lime and sand quantities into containers
that are easy to use and don't create waste
(because they are hard to fill and the stuff
falls over the edge, etc.), and to make sure
that every batch you make is the same as
the one before. This is why mixing on a
large scale is much better done all at once
in a huge mixer - but so far we have not
been able to persuade concrete companies
to mix lime for us. However, there is now a
specialist company that mixes large batches
of limecrete, The Limecrete Company, based
in Norfolk (see www.limecrete.co.uk).
Preparation
Prepare the place where you want to lay
a limecrete floor as you would do for a
cement floor: dig it out, lay a stone capillary
