Determining The Hardness Of Concrete - Husqvarna PG400 Operator's Manual

General Principles
General rules for using diamond tools when grinding
follow below. As with all rules, there are exceptions or
occasions when they do not apply.
Diamond grit size
Changing the size of the diamond grit to a smaller particle/
grit size will effect the performance of the diamond tool in
the following ways:
• Create a finer scratch pattern.
• Increased service life of diamond tools.
The opposite will occur when changing to a larger
particle/grit size.
Binding agent
Increasing hardness of bond will:
• Create a finer scratch pattern.
• Increased service life of diamond tools.
• Decrease production rate.
The opposite will occur when making the metal or resin
bond softer.
Number of diamond tools under the machine
An increased number of tools under the machine leads to:
• Reduce pressure on each individual diamond
segment - reduce wear rate on diamond segments.
• Reduce load on the machine and cause the grinder to
draw less current.
• Create a smoother scratch pattern (particularly on soft
floors).
The reverse happens if you reduce the number of tools
under the machine.
Summary of diamond principles
The diamond tools must be worn in order to give a high
grinding efficiency. The wear on diamond tools can be
affected by the following factors:
• Pressure.
• Hardness of bond.
• Diamond grit size.
• Number of segments under the machine.
• Adding an additional abrasive (e.g. sand, silicone
carbide) on the floor will increase wear.
Generally, the faster a diamond segment wears, the faster
the productivity will be. By varying the above factors,
changes can also be made to effect the following:
• Scratch pattern.
• Current draw of machine.
• Flatness of floor (see next section).
• Ease of operation.
12 – English
OPERATING
Determining the hardness of
concrete
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
selection
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
segment.
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.