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Husqvarna PG 680 Operator's Manual: Determining The Hardness Of Concrete

Floor grinder/polisher.
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Determining the hardness of
All concretes are measured by their compressive strength
and depending on which part of the world you are from,
different compressive strength indices (e.g. PSi & MPa)
are used. Generally, the higher the compressive strength
rating, the harder the concrete and therefore, the harder it
will be to grind.
But there are also factors other than compression
strength that determine how hard a floor is and which
therefore affect the choice of diamond tool. As it is most
often only the top layer (5 mm) that we are talking about
from a grinding point of view, the surface treatment of the
concrete and the condition of the concrete surface have
many times a greater impact on the choice of diamond
segment than the compression strength.
Surface factors to consider when making a diamond
Generally, if a concrete surface is very smooth (i.e. Most
likely it has been heavily trowelled/helicoptered), the
concrete will behave as if it has a high compressive
strength and therefore, require a soft bond segment.
Accordingly, if a concrete surface is coarse/aggressive
(e.g. rain-damaged, shot blasted, scarified, exposed
aggregate e.t.c.), the concrete will behave as if it has a low
compressive strength and therefore, require a hard bond
Surface coatings/contaminants (e.g. Epoxy coatings,
ceramic tile adhesives, levelling compounds/screeds) will
often have a larger bearing on what diamond to select,
than will the compressive strength of the concrete.
As a general rule, when grinding a concrete slab for the
first time and you are unsure about its hardness, always
begin with harder bond diamonds under the machine.
This will ensure the least amount of wear on the diamond
segments. If a hard diamond segment is not suited to the
application, all it has cost is a little amount of time without
wearing out the diamonds.
If performed the other way around (i.e. a soft segment is
used to begin with) and the concrete is soft or possesses
an abrasive surface or surface contaminant, it is quite
possible to wear-out a considerable amount of diamond in
very short period of time.



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