CI/SfB V

September 1998

Internal painting: Good Repair

tips and hints Guide 19
good repair

Internal decoration is But there can be snags: paints indoors.

generally quite you can, for instance, be This Good Repair Guide
straightforward and it is faced with painting on gives advice from BRE on
guide

less likely to cause damp or unsound plaster how to tackle some of the
problems than outside or dealing with persistent problems that crop up
painting. Modern paints mould growth on walls. during internal painting,
offer a wide choice of Sometimes there are where to use fungicidal
finishes and the techniques health hazards involved in paints, and when to take
needed to get a good finish removing old finishes or safety precautions.
are well known. applying solvent-borne

Painting new plaster

The critical factor in achieving a good painted
finish on new plaster is whether the plaster has
dried sufficiently. Excessive moisture can make
it difficult to apply most types of paint and may
also affect long-term performance.
If possible, give new plaster time to dry
thoroughly before decorating, otherwise
efflorescence (see overleaf ) can damage the
finish as the plaster dries. If the finish is
impermeable, water in the new plaster may
make the finish flake away from the plaster.
The drying time for new plaster varies,
depending on its area and moisture content, on It is important to dilute the first coat of emulsion paint
whether the building fabric was dry when it on new plaster to avoid the risk of disastrous peeling or
was done, the time of year and the level of flaking
heating. It can take as long as 12 months.
Always aim for slow drying out, to avoid several possible ways of doing this, including a
cracks in masonry materials and warping of hygrometer and electrical moisture meters. All
timber components. But, if necessary, drying of them need care in interpreting the readings.
can be speeded up: good ventilation is Obviously it may not be practicable to wait
essential, and there must also be heating. Don't for the plaster to dry out fully. To decorate
use portable oil or gas heaters as they produce a damp plaster the only safe finish is ‘contract’ or
lot of moisture. Dehumidifiers are helpful, ‘trade matt’ emulsion paint, and even these
providing there is adequate heating, but they may not cope with really wet conditions.
must not be run with external ventilation. Make sure the occupants know when
To find out whether new plaster is dry permanent non-permeable decorations such as
enough for permanent decoration, it is wise to vinyl emulsion paint or wallpaper can safely be
measure the moisture content. There are applied: usually after 12 months.
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Dealing with efflorescence

Painted walls can be badly affected by efflorescence, ie the crystalline deposits
caused by salts in the structure coming to the surface and drying out. They can
appear on top of decorations or even push them off.
Allow the wall to dry out and then wipe loose deposits away with a dry
cloth or brush and leave for a few days to see if any more appear. If
efflorescence is pushing off the decorations, strip down to bare plaster, allow
to dry, and brush down. Redecorate when no more deposits appear.
As a remedy for patches of efflorescence, BRE has found that it can be very
effective to treat the surface with undiluted alkali-resistant primer, which
forms an impervious film on the surface. However, this is not recommended
for whole walls or as a remedy for rising damp — this is discussed later.
Efflorescence can be a problem on newly
plastered surfaces and on damp walls in
Painting unsound plaster
existing buildings
Plaster surfaces to be painted should be sound and not powdery or crumbling:
very dusty and powdery surfaces provide little adhesion for paint films,
particularly emulsion paints, and there is a risk of peeling or flaking as well as a
poor finish. New walls should be rubbed down and the dust removed before
painting.
A useful test for the soundness of the surface is to press a strip of adhesive
tape on the wall; if there is little adhesion when it is pulled off and it brings
away loose dust and powder, the surface should be treated with a stabilising
solution.
Differences in suction due to variable or excessively porous plasters can
cause difficult or uneven application and variations in sheen, gloss or colour.
This can often be overcome by thinning out the first coat according to the
manufacturer’s recommendations or applying a purpose-developed sealer
coat. Alkali-resisting primers are also generally suitable, but apply them thinly
so that they penetrate the plaster and do not leave a glossy film.
Minor cracks and imperfections filled with powder fillers may introduce
areas of high suction. The difference in porosity can be evened out with a
suitable sealer, but it may be better to use a ready-mixed emulsion-based filler.

Redecorating painted walls

Before redecorating walls, make sure the existing paint is still adhering well.
If the original paint was water-borne and not very water-resistant, gentle
rubbing with a wet rag, or applying new paint to a trial area, will give some
indication of possible trouble.
Existing gloss paints should be lightly flatted or wet-abraded to ensure
good adhesion of new paint. Clean off areas of flaking paint. A sealer or
plaster primer can be useful on cleaned off areas.
Sound paint with a chalking surface should be washed down or preferably
cleaned with fine wet abrasive paper. Old cement-based paint is often
powdery and should be washed down and treated with a stabilising solution if
it is to be overpainted with a non-cement based coating.
If you do not know anything about the existing paint, paint a trial patch first
as failures can be costly.

Painting over wallpaper

Beware of painting over old wallpaper — it may have been printed with water-sensitive dyes
and the pattern can show through many coats of water-borne paints. The only solution is to
strip the paper. To find out whether that’s necessary, paint a test area.
 3

Treating damp walls

Painting a permanently damp wall is rarely successful, and the best long-term
solution is to find and cure the underlying cause. There was more about the
causes of dampness and suitable cures in Good Repair Guides 5–9.
If a permanent cure is not possible, there are various coatings on the
market, although none of them is sure to be successful. They are worth trying
if there is an alternative route for moisture to escape to the outside.
Proprietary metal foils, designed to take normal paint or wallpaper, can also
be effective sealers if the adhesive is not affected by dampness.
But applying impervious materials to damp patches usually causes the
moisture to reappear somewhere else. If the other side of the wall has an
impervious finish, such as tiles, the coating is unlikely to adhere for long.
In the worst cases, the only solution may be to batten off and line the wall
with plasterboard, or use a proprietary lathing system.

Fungicidal paints
One remedy for persistent mould growth is
fungicidal paint Getting rid of persistent mould on painted surfaces can be a major problem.
Surface mould growth is caused by regular or persistent dampness, usually
resulting from condensation, although rising damp, pipe leaks and rain
How to apply fungicidal paints
penetration can also be involved.
Step 1
As with any dampness problem, the only real cure for mould growth is to
● Remove mould growth by wiping the
surface with an approved proprietary
tackle the underlying cause. However, this can be very expensive. A cheaper
fungicidal wash, following the supplier’s or temporary solution is to use fungicidal paints. BRE has assessed some of
instructions. Only use products with a these paints and found that most of them are very effective (see photo, p 4).
Health and Safety Executive (HSE) The paints were first tested in the laboratory under very severe conditions
number. and then tried out in houses with a history of mould problems. A number of
● Keep windows open to encourage drying the paints kept the houses free of mould growth for at least two and a half
and reduce the levels of mould spores in years.
the air, and provide some heating.
Paints which help to reduce condensation are also on the market, and a few
Step 2
of these have been tested at BRE to find out their ability to resist mould
● Remove badly affected paint and
wallpaper, and apply a fresh solution of
growth.
the fungicidal wash generously to the
cleaned area. This makes sure that any Painting woodwork
mould growth remnants are sterilised
and won't regrow. The choice of finishes available for the inside faces of doors and windows is
Step 3 wide.
● Wait until the surface is dry before Although solvent-borne paints are still used for interior work, particularly if
starting to apply fungicidal paints. Always
a high gloss finish is required, there are certain limitations on their use indoors
follow the manufacturer's
(see page 4). Traditional white gloss paints may also suffer from yellowing as
recommendations on surface
preparation and application.
they age.
Water-borne gloss paints are suitable for indoor woodwork, and can be
applied over existing traditional paint or as a first coating. They can be as
Safety warnings! durable as solvent-borne paints, and have the great advantage that white does
● Do not remove mould growth by dry not yellow as it ages.
brushing as this can release a large One point to note — there is no guaranteed remedy for yellowing of white
number of spores into the atmosphere, paint over knots!
which can affect people with allergies. Single-glazed window frames and sills can take quite a beating from
● Wear suitable respiratory protection condensation. The paint is likely to need attention more often and there may
while removing moulds and preparing the
be rot in the lower horizontal sections of sashes, sills and window boards.
surface, to guard against inhalation of
spores and dust particles. Follow the
Repairs and treatment for decay may be necessary before redecoration. In
manufacturer’s recommendations for the these situations traditional solvent-borne alkyd gloss paints may be the best
use of protective clothing. choice because they can be easier to clean and may be more effective in
● Professional operators must take into protecting the wood from condensation run-off.
account the procedures required under Large areas of cellulosic linings (eg timber panelling or similar combustible
the Control of Substances Hazardous to linings) may have been treated with a special finish for fire resistance (eg in
Health (COSHH) Regulations. hotels, theatres, etc), so before you specify a paint to the decorator you need
to check whether the finishes applied need to enhance fire performance.
4

Safety precautions in painting

Vapour from solvent-borne paints
Solvent-borne paints give off solvent vapour during application which can be
a health hazard if there is not enough ventilation, even when painting small
surface areas.
New occupational exposure standards were introduced by the Health and
Safety Executive (HSE) in 1994 (Guidance Note EH40/94 ). Using solvent-
borne eggshell or gloss paints on large areas indoors can lead to exposure over
the limit, even when there is some ventilation, and the use of water-borne
products on walls is now encouraged instead wherever possible.
However, there are some applications where solvent-borne paints are
Laboratory tests at BRE clearly showed the necessary, such as commercial kitchens or where regular washing is required.
difference in effectiveness between In these situations measures must be taken to ensure adequate ventilation or
fungicidal paints extraction of the solvent vapour, or to provide the painter with approved
respiratory equipment such as an air-fed hood or mask.
Safety warning!
There are also some applications, such as painting interior timber doors and
trim, where water-borne paints cannot achieve the high gloss finish that is
Paint safely — protect your eyes
The main risk to painters, with both solvent-
often required. BRE has conducted tests to find out the risk of using solvent-
borne and water-borne paints, is splashing borne paints for small areas of trim.
paint into the eyes. They found that vapour levels from conventional white spirit-borne paint
The advice from UCATT, the Paintmakers can be kept to safe levels provided the ventilation rate is at least four air
Association and the National Federation of changes per hour. This can usually be achieved by opening all the windows
Painting and Decorating Contractors is: and the internal door.
Always wear eye protection, for all types of
paint, indoors or outside, when using a Treating old textured ceilings
brush or roller. In many old ceilings the textured finish was achieved with compounds that
contained asbestos. So there could be a health hazard in remedial work
involving removal or repair. If you are in any doubt about the composition of
the ceiling, call in the Environmental Health Officer (EHO) for advice.

Lead paint on woodwork

Until quite recently, woodwork was finished with paints containing lead. If
you are faced with the task of removing old gloss paint and you do not know
the origin, be alert to the possibility and seek specialist advice if you are in any
doubt.
If lead-based paint is still adhering well, the best solution is probably to
paint over it. However, if it is powdering or flaking, or there is a risk of the
paint being chewed by children, it will have to be removed. Again, you should
seek advice from the EHO. Leaflets distributed free by the DETR and British
Coatings Federation also give advice (see More advice! )
If your skin is sensitive or damaged, it is More advice!
also advisable to use a barrier cream or to Good Repair Guides are accessible, illustrated Good Repair Guides
wear gloves. guides to defect diagnosis, assessment and ● 5 – Diagnosing the causes of dampness
repair. The GRG series is available on CD-ROM. ● 6 – Treating rising damp in houses
More detailed advice is available in the following ● 7 – Treating condensation in houses
publications. ● 8 – Treating rain penetration in houses
● 9 – Repairing and replacing rainwater goods
Building Research Establishment
Information Papers Health and Safety Executive
● 8/95 – Interior painting of trim with solvent- Guidance Note EH40/94. Liverpool, HSE, 1994.
borne paints
● 12/95 – Controlling mould growth by using Department of the Environment, Transport
fungicidal paints and the Regions
Advice on old lead paint in your home. London,
Digests DETR, 1998.
● 197 – Painting walls: part 1—choice of paint
● 198 – Painting walls: part 2—failures and British Coatings Federation Ltd
remedies Old lead painted surfaces. Leatherhead, BCF,
1998.

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