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Subfloor Preparation

The Subfloor Preparation Guide describes the different types of procedures available to produce the most acceptable substrate possible, ready for the installation of one or more of our products.


Surface preparation is a vital part of any contract.
Improper or inadequate preparation can cause
premature failure of the system. It is the
intention of this Subfloor Preparation Guide to
describe the different types of procedures
available to produce the most acceptable
substrate possible, ready for the installation of
one or more of our products.

All aspects of subfloor preparation and floorcovering installation
should be carried out in accordance with the appropriate standard.

During the laying of the floorcovering a temperature of at least 18°C
must be maintained, along with a floor temperature of at least 10°C.
The type and condition of the subfloor has a direct influence on the
installation and performance of a floorcovering and the importance
of subfloor preparation cannot be emphasised too strongly. Before
the final treatment to bring a subfloor up to the standard required
for the application of floorcoverings to begin, the condition of the
base must be investigated and any necessary treatments or repairs
carried out.

Certain systems may be ‘tolerant’to lower standards of preparation,
but lower standards should not be accepted without careful
consideration of their implications i.e. the increased potential for
premature failure, which is counter productive and expensive to
rectify. Where application involves questionable substrates the
installer must exercise extreme caution and advise the client of the
attendant risks involved.

Old or new substrates contaminated with oil, grease, fat or
chemicals, faulty concrete, inferior grades of concrete, floors with
large cracks or crevices, poor asphalt and tiles are not satisfactory
bases for our products. Some severe conditions cannot be
corrected by normal preparation techniques and the only remedy
may well be to uplift and relay the complete subfloor.

Any substrate forming the base on which an F. Ball product is
applied should be designed to withstand all structural, thermal
and mechanical stresses and loads which will occur during service.
A substrate should remain stable and be provided with any
expansion, contraction and crack inducement joints as
necessary. Cracking, unevenness and faults in the
substrate may be reflected through the surface treatments
and floorcoverings. It must be acknowledged that any
shortcomings or failures in a subfloor could lead to a
premature failure


The following British Standards should be referred to when
specifying and installing F. Ball products or systems:

BS EN 312 Identifier, Particleboards

BS 5325 Installation of textile floorcoverings

BS 6295 Specification for mastic asphalt for building and
civil engineering (limestone aggregate)

BS 8201 Installation of timber and timber based products

BS 8203 Installation of resilient floorcoverings

BS 8204 Code of practice for concrete bases to receive
in-situ floorings


Good design and subsequent installation practices to receive F. Ball
products or systems are essential for the success of the finished
floor. In order to minimise problems and save possible additional
costs, it is essential that specifiers, clients, main contractors or
installers of subfloors such as concrete and sand/cement screeds,
should have tested and be satisfied that the surfaces are to
specification and are adequate for the intended use.

The company recommends the procedures mentioned in this
guide for the preparation of concrete, screeds and other surfaces
prior to the installation of our products. The objective being to
ensure the subfloor is sound, smooth, clean and dry before laying

This information is primarily concerned with floors although general
information can be extracted in the case of vertical surfaces but extra
consideration should be shown due to possibly greater absorbency
of many of the surfaces i.e. brick, blockwork, plaster, etc. Obviously,
vertical surfaces do not usually have to withstand the same degree
of wear and tear that horizontal surfaces are subjected to.

Coverage rates of materials may be affected by the selected method
of surface preparation.

Considerations - Old Concrete and Screed Surfaces

Old surfaces are often contaminated, worn or degraded.
They often present a greater risk than new substrates.
BS 8204 should be used as a guide to good flooring
methods. In order to minimise problems and save
additional costs, it is essential that specifiers, clients, main
contractors or installers of F. Ball systems on old concrete
bases and screeds have the floor tested, and are satisfied
that surfaces are adequate for the intended use. A surface
tensile pull-off strength of at least 1.5 N/mm2 onto a
prepared subfloor is required before the application of
further underlayments and serves as a good guide as to the
integrity of the floor.

The depth and type of contamination should be checked
to ensure that removal and subsequent adhesion can be
ensured. It is often advisable to take cores from the most
contaminated areas to be sure of penetration depth and
the soundness of substrate. For instance, oil can penetrate
many centimetres into concrete, and although the surface
may be cleaned, it can migrate back to the surface.
Adhesion of a DPM, underlayment or adhesive may be
compromised or in the worst cases be non-existent. If in
doubt, do not progress any further without management
instructions. Further discussion with our Technical
Services Department may be advisable before proceeding.


Laitance is always present on new concrete bases and screeds
and should be removed. Laitance is formed from a mixture of
water, cement and the fine particles of the screed or concrete
mix that is brought to the surface when trowelled. As the
concrete or screed cures this mixture dries to form a crust or thin
layer, known as laitance on the surface. The wetter the mix, and
the more it is worked or trowelled, the thicker and usually the
weaker the laitance will be. The thickness of laitance may vary
from, in the best cases, barely measurable – to the worst
examples, 6mm or more. Scoring the surface with a steel edge
(i.e. a screwdriver) until the main aggregate in the mix is reached
will determine the thickness of the laitance.

Laitance has relatively poor adhesion to the mass of the
aggregate in the mix. It is friable and weak, and can therefore
either delaminate when trafficked or be subject to impact
damage or may go to dust when abraded by traffic. Therefore,
the new floor surface needs to be bonded to the exposed
aggregate in the base on which it is laid. The heavier the floor
traffic, and the greater the temperature fluctuations that the
floor is subjected to, the more important this is. Laitance is a
major cause of failure within concrete floors. Failure to remove it
may lead to failure of the surface treatment or smoothing
underlayment. Unless it has been removed by previous surface
preparation techniques, laitance may still be present on old
concrete and screeded floors. Removal is vitally important.

Surface Preparation Techniques

The most frequently used methods of surface preparation of concrete or screeded floors are:

(i)Vacuum recovered dust-free shot/grit blasting
(ii)Mechanical planing

Floors and their uses vary enormously. Therefore, each method must be judged on its merits and full account be taken of the working environment in which the preparation has to take place. For example, scabbling may be a perfectly suitable method of preparing a floor in an unoccupied site. However, the resulting dust and noise may preclude it in many other situations.

Dust-Free Shot/Grit Blasting

This is the fastest and most efficient form of old and new
floor preparation and laitance removal, available to date.
The machines used vary in size and are generally operated
by specialist concrete preparation contractors or flooring

Horizontal and slightly inclined surfaces are impacted and
abraded by steel abrasive propelled at high velocity by the
machine. At the same time the abrasive shot/grit and
resultant debris is contained and reclaimed by powerful
suction processes. The shot/grit is cleaned and recycled
for immediate re-use. The abrasive shot/grit and debris is
deposited in environmentally safe containers by the
machine while it is working. Up to 1000m2 of flooring may
be completed in a day. This is a dry process and floor
laying may often continue while preparation is
progressing in adjacent areas. In many cases old coatings
and other contamination may be removed by this method.
Dust-free shot/grit blasting is far quicker, quieter and
cleaner than mechanical planing, scabbling, etc.
The disadvantage is the general inability of the machine to
remove exceptionally thick, hard or flexible materials i.e.
certain epoxy or polyurethane floor surfaces. The specialist
contractor using these machines will advise in more detail.

Mechanical Planing

Often referred to as ‘concrete planing’ the machines used carry
rows of rotating cutters tipped with tungsten. The removal of
laitance and other forms of surface contamination are excellent.
The profile left by the machine is dependent on the spacing and
type of cutters installed by the operator.

The surfaces may be grooved or flat and are rougher than using
dust-free grit blasting. Greater thicknesses of the substrate can
be removed quicker and more effectively than by grit blasting.
Mechanical planing is slower and noisier than other methods
but when attached to a suitable vacuum cleaner reduces dust to
an acceptable minimum.


Technique for the removal of laitance and surface deposits.
Scabblers come in a range of sizes from hand held electric models
to the larger machines run by compressed air that have a rotating
hammer action. With the larger machines, by using different flails
on the drums, a range of textures and profiles may be achieved.
The smaller hand held machines can be used for the removal of
paint as well as preparing sand/cement screeds or concrete. N.B.
When preparing the subfloor ensure that the correct surface
regularity can be obtained with the machine chosen.


Grinding machines are designed for precision, control and safe
operation. The process is provided by diamond, tungsten or resin
bonded grinding plates fitted to a single or multi-headed machines.


There are a number of methods of abrading which include
the use of STR machines, carborundum blocks, or using
abrasive papers etc. These have their limited uses and are
not generally used on larger areas.

Final Checks

Hardeners and surface membranes frequently interfere
with adhesion and should have been removed by one of
the methods described above. Prior to coating or topping,
concrete or screeds must first be: free of all contamination
and laitance; strong enough to support the coating or
topping under the conditions for which the floor is

Concrete and sand/cement screeds must be left for
construction moisture to dry out before floorcoverings are
laid. Readings greater than 75% RH should be treated with
STOPGAP F75, F76 or F76HP Waterproof Surface
Membranes (WSM), following preparation of the concrete
or sand/cement screed detailed.

STOPGAP ISOLATOR MEMBRANE can be used in certain
situations as a fast track alternative for damp floors.

Immediately prior to applying any coating, topping or adhesive,
ensure that dust from any preparation method employed is
removed by vacuuming wherever possible. Preparing concrete
may be a dusty operation. Appropriate PPE should be worn and
good ventilation should be provided. Protection of walls,
furniture and equipment should be planned.

Residues or spillages of other trades such as plaster, paint,
cement, oil and sometimes roofing tar are frequently present in
new constructions and should be removed. Plaster and cement
can be chipped up and wire brushed. Paint should be
mechanically removed.

Oil, fats and grease are best removed by steam cleaning, using a
good detergent, or by hot compressed air blasting and further
treatment with a special primer. Animal fats cannot be removed
by washing. If such contaminants have penetrated into the
surface (which is usually the case) the only way of removing
them is mechanically. This means dust-free grit blasting,
scarifying, scabbling or hot compressed air blasting. Remedial
work in meat processing and engineering plants, for example,
remains a very difficult problem. Usually removing the
contaminated concrete and re-screeding may be the only
solution. Cores should always be taken to determine the depth
of penetration and can assist in deciding on whether or not it is
possible to prepare a surface for overlaying. It may be necessary
to carry out adhesion tests to ensure adequate adhesion is
obtained on a contaminated surface.

In certain circumstances the presence of oil may stain the
new decorative floorcovering. If water flows under
partitions, walls, cover mouldings, equipment bases or
furniture, these areas will take longer to dry out and may
delay the installation. Putting paper or polythene sheet on
the floor to keep it clean can retard the drying time.

If old concrete has never been overlaid or painted it should
be treated the same as new concrete. More emphasis must
be placed on cleaning, and repairing any cracks, holes or
eroded areas. Often the best procedure is to remove all
contaminated and unsound concrete.

If necessary, repairs to damaged floors should be carried
out using products such as STOPGAP 400 REPAIR
compound prior to applying smoothing compounds
(please contact our Technical Services Department for
further details). The specific concrete repair material must
be checked for compatibility with the surfacing system and
be of suitable strength for the environment of the finished

Non-Absorbent Surfaces

Surfaces that will not allow water to pass through them can be regarded as non-absorbent. Surfaces such as ceramic and quarry tiles, granolithic, terrazzo, paints and to some extent power ?oated concrete can all come under this heading.

Coated Surfaces

Traditional floor paints such as those based on oil or acrylic
emulsions should be totally removed. Epoxy or
polyurethane paints can be overcoated providing they are
in good condition and well adhered to the substrate.
Coatings vary considerably in this respect and we would
suggest you check adhesion by prior testing to ensure a
satisfactory bond is achieved.

The coating should be cleaned using STYCCOCLEAN C140
then either primed with neat STOPGAP P131 followed by
the recommended smoothing underlayment or the
adhesive applied direct to the paint (please contact our
Technical Services Department for further information onproduct selection). However, in the majority of cases identifying
the type of paint or coating will be difficult and it is most likely it
will be brittle, worn, peeling or flaking off the substrate and is
therefore not good enough to receive either a smoothing
underlayment or adhesive. The easiest method of removing old
paint is usually dust-free shot/grit blasting.
Note: certain paints and coatings may allow moisture to pass
through them and checks should be made for moisture before
progressing further work.


Certain paints and coatings may allow moisture to pass through them and checks should be made for moisture before progressing further work.

Chemical Hardening and Waterproofing Admixtures and Curing Agents

All these products are designed to generally repel water from entering into the concrete or screed or to form a barrier to prevent moisture escaping. In both cases adhesion will be impaired if a water based smoothing underlayment or adhesive is applied.

The substrate should be prepared by mechanical means such as shot/grit blasting. If a waterproofing admixture is known to have been used, further testing should be carried with the proposed system to ensure complete compatibility and adhesion to the host substrate.

Some acrylic based curing agents may be overcoated with certain STYCCOBOND adhesives and advice should be sought from F. Ball Technical Services before proceeding. If in doubt always mechanically prepare the surface.

Waterproof Surface Membranes (WSM)

Membranes such as STOPGAP F75, F76 or F76HP can be
overcoated with smoothing underlayments or certain adhesives.
When applying a smoothing underlayment onto a waterproof
surface membrane, the surface should be primed with neat
STOPGAP P131 and allowed to dry before proceeding with the
underlayment. STOPGAP 100 RAPID may be applied directly
within 24 hours of cure. Adhesives such as STYCCOBOND F40,
F41, F46, F47, B93 and B95 can be applied direct to STOPGAP
F75, F76 or F76HP.


Please refer to the data sheets or Technical Services for further information on these products.


The asphalt should be flooring grade, comply with the
requirements of BS 8204 and be the correct grade for its
service condition. Providing the flooring grade asphalt is
in good condition, sound, strong, has not suffered rutting
or any sign of softening and is free from any form of
contamination, the surface should be cleaned with
STYCCOCLEAN C140, rinsed with clean water and allowed
to dry. The surface should then be primed with neat
STOPGAP P131, allowed to dry followed by the application
of 3mm of the appropriate STOPGAP smoothing

Ceramic, Terrazzo and Quarry Tiles

Providing these are sound and well bonded to a solid base
with no cracks or lipped tiles present, these should be
cleaned to remove all traces of contamination such as
polish etc, then primed with neat STOPGAP P131, allowed
to dry then skimmed with a minimum 3mm of the
appropriate STOPGAP smoothing underlayment. Heavily
glazed surfaces should be mechanically prepared by shot
blasting, or grinding with a coarse abrasive to aid adhesion
before priming.

Terrazzo and Quarry tiles are unaffected by dampness but
may be sufficiently permeable to allow the passage of
moisture vapour and are often laid in areas which do not incorporate a damp proof membrane. Where this is the case,
these bases should be covered with a layer of flooring grade
asphalt complying with BS 8204. Alternatively, the use of a
surface WSM such as STOPGAP F75, F76 or F76HP can be
applied, providing the substrate has been sufficiently prepared
by mechanical means, the grout lines raked out and the floor
thoroughly cleaned and allowed to dry. In both cases this should
be followed by priming with neat STOPGAP P131 and allowed to
dry before applying 3mm of the appropriate STOPGAP
smoothing underlayment.

If either method is not possible, lift the tiles and relay the floor.
STOPGAP ISOLATOR Membrane may also be used under certain


Old installations may involve a substrate consisting of ash, which can become unstable if covered up. Checks should be carried out to establish the integrity and make up of the substrate.

Power Floated Concrete Slabs

These should be treated in the same way as traditional concrete and sand/cement screeds. In some cases it is possible to use a pressure sensitive adhesive or tackifier such as STYCCOBOND F40, F46, F47 or F41 direct to the power floated slab, providing the moisture content of the slab is below 75% RH. Checks should be made with Technical Services before proceeding.


1. Most power floated slabs will be treated with a curing agent. In most cases this will be acrylic based, however, wax based curing agents or certain silicate based products may be present and will inhibit the bond to these surfaces and should be removed by mechanical means such as shot/grit blasting.

2. Power floated concrete slabs, especially those treated with curing agents, will take a considerable amount of time to dry, waterproof surface membranes such as STOPGAP F75,F76 or F76HP should be used if a fast track floor installation is required.

Adhesive Residues

Any old adhesive residues should be removed by mechanical methods such as scraping, shot/grit blasting and grinding etc. Certain underlayments are able to cope with only minimal traces of firmly adhered and hard adhesive residues are not water soluble. At least 75% of the floor area should be exposed. This will be followed in most instances by the application of neat STOPGAP P131, allow it to dry and then proceed with the appropriate STOPGAP smoothing underlayment. Please refer to Technical Services for product selection.

Any remaining adhesive on wooden floors should be overpinned with flooring grade plywood or hardboard and thoroughly secured at 100-150mm centres (see wooden floors).


1. If in doubt remove all traces of adhesive residues back to a sound and well-prepared substrate.

2. Highly trafficked areas and those subject to high temperatures such as conservatories, should be mechanically prepared to remove all adhesive residues, primed with dilute STOPGAP P131, allowed to dry and a high strength smoothing underlayment applied such as STOPGAP 100, 200 or 300 followed by the recommended adhesive.

Existing Floorcoverings

Most floorcoverings such as flexible vinyl, linoleum, rubber and textile floorcoverings must be removed and the substrate thoroughly prepared before fully bonded floorcoverings can be laid. Whilst there is a risk involved, some vinyl or similar type floor tiles can be overlaid providing they are firmly bonded to the subfloor and all traces of polish or any other contaminant which would prevent good adhesion are removed e.g. With STYCCOCLEAN C140 Floor Cleaner. If this cannot be achieved then the tiles must be removed, and the substrate suitably prepared.


Certain vinyl tiles were made using asbestos, and professional advice should be taken before proceeding to remove these types of tile and their adhesives. Generally with older buildings, these types of tiles were often laid on floors that did not contain a DPM.

Composition Floors

Floors constructed of magnesium oxychloride cement or
polyvinyl acetate/cement will be adversely affected by
dampness rising from the ground if they are covered with
an impervious layer. Unless it can be established that the
composition floor is adequately protected against rising
damp, it must be removed and the base made good before
floorcoverings are installed. If the floor is protected against
damp then cracks and small hollows should be patch filled
and the whole area skimmed with a minimum 3mm of the
appropriate STOPGAP smoothing underlayment.

Calcium Sulphate Screeds

In all cases, calcium sulphate screeds, which includes
anhydrite and Alpha hemihydrate type screeds, should be
sound, smooth and dry.

All laitance should be removed during the initial grinding
stage, however, this is not always the case and checks
should be made prior to proceeding with the application
of any material. If laitance still exists, this should be
mechanically removed by further grinding/sanding and
the dust must be fully vacuumed off. It is imperative that
checks are also made to determine the moisture content
of the floor and this is carried out using a hygrometer in
accordance with BS 5325, BS 8201 and BS 8203.

A reading of less than 75% RH must be obtained before
priming using STOPGAP P121 which should be allowed to
dry before the application of the appropriate STOPGAP
smoothing underlayment or STYCCOBOND adhesive.


F. Ball recommend that a RH value of < 65% should be
obtained before priming with STOPGAP P121, before the
application of the appropriate STOPGAP smoothing underlayment
or STYCCOBOND adhesive for all wooden floors.

Wooden Floors

All wooden floors must be structurally sound, level, smooth, dry
and clean. Adequate ventilation should be provided to
suspended timber floors at ground level to ensure that the
moisture content of the wood is maintained at equilibrium.
Worn or uneven floorboards should either be replaced or
levelled by sanding, planing or by patch filling with STOPGAP
GREEN BAG/114 Liquid or STOPGAP BLUE BAG/114 Liquid
underlayment before finally covering with flooring grade
plywood. Sheets should be positioned, with joints staggered
and secured at 100 – 150mm centres. (See BS 8203 for details).

Wood blocks laid on ground floors must have an effective damp
proof membrane incorporated in the subfloor. They may be
overlaid with a suitable grade of plywood screw fixed at the
centres outlined in BS 5325 and BS 8203. However, it must be
ensured that the wood blocks are well bonded and remain fully
secured to the subfloor and that the plywood overlay and wood
blocks remain dry during the life of the installation. If these
conditions can not be met, then the wood blocks must be
removed and the subfloor made good with either a flooring
grade asphalt (complying with BS 8204) or a modified
sand/cement screed incorporating an effective damp proof

Wood blocks are not suitable for direct application of
sheet or tile flooring because of the continuous differential
movement of the blocks and the risk of the wood block
design transferring through the floorcovering surface.
Provided the wood blocks are smooth, sound, level and
securely bonded, they should be overlaid with flooring
grade plywood. Any uneven areas should first be patch
filled with STOPGAP GREEN BAG/114 Liquid smoothing
underlayment. Wooden floorboards including butt jointed
and tongue and groove boards can be overlaid with a
minimum of 6mm plywood overlay, screw fixed at the
centres outlined in BS 5325 and BS 8203 to provide a rigid
substrate. They may then be primed using dilute STOPGAP
P131 and a minimum thickness of 3mm of STOPGAP 700
FLEX applied.

Wood mosaic panels require overpinning with flooring
grade plywood in all cases. This is not practical on solid
floors and panels should therefore be removed.

If panels laid over a flexing timber floor need patch filling,
STOPGAP GREEN BAG/114 Liquid smoothing underlayment
should be used. In all other respects wood mosaic panels
should be treated as for wood block.

Chipboard should comply with BS EN 312 flooring grades, type
P4 to P7. It is essential that floating chipboard and other
composition boards are dry, as a gully may develop between the
skirting board and the edge of the floorcovering as the boards
shrink on drying.

In all cases chipboard, plywood and hardboard must be primed
with dilute STOPGAP P131 as recommended.

Raised Access Modular Floors

These are designed to give ready access to underfloor services. All modular units must be structurally sound, level, smooth and free from contaminants. New floors should be degreased using STYCCOCLEAN C141 and allowed to dry before applying the adhesive. Backed carpet tiles secured with a tackifier such as STYCCOBOND F41 are suitable for this type of base.
Broadloom carpets are not suitable in this type of situation.


It must be appreciated that these recommendations are general.
Modifications may be required according to the floor system used
and the service conditions under which the surface has to
adequately perform. If there is any doubt seek further advice from
our Technical Services Department before proceeding with
the application of our products.

The company will be pleased to check advice given by a
contractor or applicator of F. Ball products. However,
because we may be unaware of every situation where our
products are supplied, it is impossible to check all sites
where F. Ball materials are used. This information is therefore
to be used only as an informed guide to floor preparation
methods. The responsibility for the preparation of any
substrate must remain with the installer. Because of the wide
variety and uses of our materials, the Company is always
more than willing to offer help and assistance with individual
flooring problems.

The detail in this information guide is given in good faith and
is based on results gained from experience and tests.
However, all recommendations or suggestions are made
without guarantee, since the conditions of use of the floor
and the placement of materials are beyond our direct control.

(Please contact our Technical Services Department for
further advice).