The production of a high quality, durable, industrial floor is
completely dependent on the type and condition of the surface to
which it is applied.
Therefore, before the start of all contracts, thorough
preparation is essential, having first assessed surface
strength, flatness, surface profile and any possible
contamination. These factors will all influence the ultimate
quality and serviceability of the finished floor.
Any short cuts taken at this stage of the contract WILL NOT SAVE
MONEY especially when compared with the cost of repairing or
replacing a failed floor.
Click on images below for a larger view
Concrete subfloors meant to receive high performance coatings
and overlay systems should have sufficient compressive and
tensile strength to withstand dynamic loadings. They should also
have adequate surface strength.
Generally, concrete floor slabs in these situations have been
designed to have a minimum compressive strength of 25 MPa. There
are a number of non-destructive test methods available for
evaluating the strength of existing concrete floors. A Schmidt
hammer is probably the best known and most readily available
device for this application, but they do not give definitive
values and should only be used to compare readings taken from
the same slab. A minimum of two readings per 10m²
should be taken, recorded on a grid and analysed. Where surface
strengths appear doubtful, direct tensile strength can be
measured using the "pull off" method. eg Elcometer. These values
can be used to predict compressive as well as giving a good
indication as to the expected bond/adhesive strength of the
coating or overlay. Subfloors should have a
tensile strength value in excess of 0.75 N.
Captive Blast Cleaning
A metallic abrasive (steel shot) is used in shotblasting
machines to scour the concrete surface. Shot is propelled by a
rotating wheel, impacts on the concrete surface and rebounds
into a recovery unit. A pneumatically driven vacuum system
collects dust and shot, separates the two materials, recycles
the re-usable shot and removes the dust through a filter system.
Manual, self-propelled and ride-on models are available to suit
Good control of dust is one of the major advantages of
shotblasting. The machines have been used in without problems.
Since no water is used the surface is immediately ready for the
application of systems that need a dry surface. Shotblasting is
typically used for cleaning and scarifying to depths up to 3mm.
In preparation for epoxy or polyurethane coatings, fine shot is
used to produce a very light etching (brushblast) of the
surface. A brushblast breaks the laitance on the concrete
surface and opens pores, to improve the adhesion of the coating.
When a topping or overlay system is to be placed, an aggressive
blast exposes sand particles. A deeper exposed aggregate blast
leaves protruding coarse particles to provide an excellent
Three factors control the surface profile obtained:
a) Size of abrasive
b) Amount of abrasive
c) Rate of travel
In general 50m²
per hour can be prepared using a mid range machine.
Scabblers use compressed air to hammer piston mounted bits into
the concrete surface, and provide a rougher surface than is
achieved by shotblasting.
For horizontal surfaces push and self-propelled machines are
available. The self-propelled machines offer some of the same
features as shotblasting - mobility, speed, optional vacuum and
Scabblers can remove up to 8mm of concrete surface in one pass,
but production rates obviously depend on the condition and
strength of the existing floor. Self-propelled scabblers cannot
concrete immediately adjacent to walls unless a special
attachment is fitted. Needle guns of hand grinders with vacuum
attachments are available for this application. Scabbling
operations are dusty, unless a vacuum attachment is used.
Alternatively, wetting the surface to be scabbled will help to
control dust. Scabblers are also noisy and produce vibration.
Skilled operation of scabblers is necessary. If improperly used,
the result can be a cleaned but damaged concrete surface with
loosened aggregate articles.
Click on images below for a larger view
Machines for scarifying concrete can be known as planers,
scarifiers, milling machines or rotary cutters. Unlike scabblers
in which bits move vertically to hammer the concrete surface,
planers apply a rotating circular cutting wheel to precisely
control the depth of removal. These machines have different
styles of inter-changeable cutter assemblies that are used for
cleaning, grinding and light or heavy planing. Planers are
normally available in push type or self-propelled models,
powered by compressed air, petrol or electricity. A fine
adjustment is used control the cutting wheel height and in some
models cutters can easily changed when a different surface
texture is required.
Planing machines generate a lot of dust. Wetting the surface
will help to control this but a more effective means is an
optional vacuum dust collector. Like scabblers planers are noisy
and create vibrations.
High Pressure Water Blasting
High pressure water blasters are sometimes used to prepare
concrete surfaces in specific environments . These units have
been used in applications ranging from laitance removal to
hydrodemolition of concrete. The depth of removal is controlled
by adjusting water
pressure, speed of nozzle as it passes over the surface, and the
speed of the machine itself. A recently developed system
incorporates a vacuum that sucks up waste water and debris to
dispose of a selected site. This system lessens the obvious
problem of excessive water and disposal of watery waster.
Advantages of high pressure water blasting include:
||No dust created.
||Noise is minimal.
||No mechanical vibrations.
||Machines selectively remove deteriorated concrete leaving
good concrete intact.
It is not possible to set rigid rules on the selection of
surface preparation techniques, since each contract has its own
Having made a selection therefore , it is in the interest of the
applicator and client to conduct a preparation trial, so that
standards for future preparation can be agreed, and the adhesion
of the floor finish can be assured.