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Surface Preparation |
The need for proper surface preparation prior
to painting cannot be stressed enough. It has been said many
times that INCOMPLETE OR IMPROPER SURFACE PREPARATION IS
THE PRIMARY CAUSE OF COATING FAILURES. Thus, the surface
should be prepared whatever way is necessary so that it will
receive the paint properly. Indeed, the condition of the surface
plays an important role in achieving the degree of adhesion
required for effective performance. If the surface is covered
with loose, chalky paint there may be excellent adhesion between
the new paint and the chalky material; but this will be of
no value since the chalky material will not adhere to the main
surface. Dirt, grease, mechanical defects of all types and
old paint in poor condition are a few of the factors which
contribute to poor surfaces and which must be compensated for
by proper surface preparation.
Thorough cleaning of the surface is the fundamental objective
of all surface preparation methods. In order to select the most
practical method (since they range anywhere from light brushing
or a simple solvent wash to heavy sandblasting), careful consideration
should be given not only to the nature and condition of the surface,
but also to its size and shape, available equipment, type of
coating to be applied and the service environment.
Surface preparation differs for each type of surface
which you may paint. The surfaces which we address here
are as follows:
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Metal Surfaces |
All metal surfaces must be clean and free of rust,
mill scale, grease, oil, dirt and other foreign matter. If this
is not observed, drying, adhesion and serviceability of any coating
will be affected adversely.
Metal surfaces contain many minute pores which provide
anchorage for the paint film. When these pores are filled
with dirt, rust, grease or scale, the paint is unable to
adhere properly to the surface and cleaning is required.
When rust is painted over without removing it, the rusting
continues under the new paint film until breaking through
the surface and causing film failure.
Terne metal surfaces must be abraded with steel wool or
abrasive paper prior to painting. Galvanized metal must be
cleaned well in order to remove all surface film. Use P&L
Duosol or a strong solvent to achieve this.
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Plaster Surfaces |
New walls and ceilings often require attention
before priming. Preparatory work may include patching and spot
priming.
Patching: Cracks and holes in plaster walls require
skilful patching to insure a smooth, professional finish.
Map Cracks: Deep cracks must be cut out and patched
before primer and paint are applied. The correct preparation
of a deep crack or hole includes cutting away loose or bulging
plaster from the edges and then undercutting it so that a
cross section looks like an inverted 'V'.
If the bottom of the crack or hole is wider than the top,
patching material will be keyed to the surface and will not
fall out. After undercutting, dust out the opening, then
prime with Suprime 10 or Suprime 11.
Unless the edges are sealed before patching, the dry plaster
will absorb excessive water from the patch and it will ultimately
crumble. Patching materials are abundant but vary in composition.
Any well known brand of patching plaster or ready mixed acrylic
spackling compound is recommended. An even better method
than 'V' notching is cutting away loose or bulging plaster,
then employ a 2 1/2" wood scraper and scrape along the direction
of the crack, the scraper being centred over the crack at
all times. The scraped area should have a uniform depth of
1/8" to 1/4". This area is dusted out and primed with Suprime
10 or Suprime 11. Fibreglass mesh is then applied, followed
by coats of drywall cement. Finally, the patch is sanded
smooth and is ready for spot priming.
Spot Priming: After the patch dries (a minimum of
15 hours should be allowed for drying), and is sanded smooth,
dust completely. Patches invariably absorb more paint than
the surrounding areas, especially if the wall has been previously
painted. Patched areas, therefore, must be spot primed before
they are painted. When a patched wall is to receive a two-coat
repaint job, spot prime the patch, then apply primer over
the entire wall and finish with the appropriate top coats.
New Plaster: New plaster should always be dry before
it is primed and painted. Dry plaster contains less than
15% water; but, there is no simple, reliable test for determining
the moisture content. If plaster must be primed and painted
before it is thoroughly dry, Suprime 4 Latex Wall Primer
offers a greater margin of safety than other primers. Efflorescence
and suction spots may require special attention when priming
new plaster. Care should be taken in proper cleaning and
complete sealing of these potential trouble spots.
Efflorescence can occur on new plaster applied to a masonry
surface. It results when moisture in new masonry carries
water soluble salts from the masonry to the surface of the
plaster. Priming and painting obviously cannot correct the
problem because efflorescence will continue as long as the
masonry is damp. This condition does not harm the plaster;
but it may cause the paint to blister, peel or stain. Efflorescence
is best prevented by furring the wall prior to plastering,
thus separating the plaster from the masonry.
Suction spots are areas in plaster walls that soak up the
primer to a greater extent than the surrounding surface.
Such spots, which can be detected by a difference in the
lustre of the dried primer, may cause a variance in the lustre
of the finish coats. Suction spots should be given a second
coat of primer before the finish coats are applied. Generally,
an alkyd primer such as Suprime 11 is used.
Plaster walls to be painted, from which wallpaper and glue
sizing have been removed, should be treated like new plaster.
The painter should be well aware of the many
problems which may result from painting improperly sealed
wet plaster, particularly peeling of the paint film, softening
and darkening of the paint and the development of possible
paint colour changes. Also, the paint film may not dry properly.
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Drywall Surfaces |
Drywall and plasterboard of many types, made from
gypsum, paper, pulp and various other compositions are used extensively
in new construction. Be sure all nail heads are set below the surface
and spackled over. Joints should be taped and covered with a suitable
drywall joint compound, sanded, smoothed and dusted or vacuumed before
priming.
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Concrete & Masonary Surfaces |
It is commonly believed that masonry surfaces such
as concrete, stucco, common brick and concrete blocks are painted
only for decorative purposes. These surfaces, because they are
somewhat porous, are painted or finished many times for protective
purposes to keep out moisture and to prevent dusting and spalling.
Concrete and Concrete Masonry: Unpainted concrete
surfaces must be properly prepared in order to prevent poor
adhesion of primers. Form oils and releasing agents need
to be removed from the surface. Usually, a good washing with
a detergent will remove the oils, releasing agents, dust
and dirt.
Concrete sets in a short time, but the hardening or curing
process continues for up to 96 days. When concrete is completely
cured there is no longer active alkali on the surface which
will cause paint to discolour, crack, peel and generally
deteriorate.
Efflorescence is a white deposit which frequently appears
in masonry surfaces. These deposits are soluble salts present
in almost all masonry which have been leached out of the
concrete by moisture. Primers will not adhere properly over
efflorescence.
Efflorescence can be removed by washing concrete with a
commercial solution of muriatic (hydrochloric) acid. The
normal cleaning strength is achieved by taking 3 or 4 quarts
of water and adding a quart of muriatic acid to the water (CAUTION:
Always add the acid to the water - NEVER the reverse!!!).
Follow the acid wash with a clear water rinse.
CAUTION: Muriatic Acid (Hydrochloric Acid)
will cause severe eye and skin burns. Use in well ventilated
areas. Wear appropriate protective equipment leg. safety
goggles, neoprene rubber gloves and boots). Consult supplier's
material safety data sheet.
Concrete Floors: Concrete that is hard and smooth
should be etched so that paint can "grip" the surface. The
etching may be done by using a solution of one part muriatic
acid to eight parts water. Use a wooden or plastic bucket
and apply with a stiff fibre brush. Allow solution to remain
on the surface until bubbling stops. Then rinse with ammonia
water followed by clear water. New floors should age at least
three months before painting. Use Pratt & Lambert's Withstand
Latex Floor Paint for basements or other concrete floors
subject to contact with wet earth.
Sandblasting: On masonry surfaces where the cracking
and scaling is extensive and adhesion of the paint to the
surface is poor, sandblasting is often the only proper way
to prepare the surface for the new paint.
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Interior Wood (Transparent) |
In addition to its utilitarian functions, wood
provides an ideal medium for aesthetically pleasing decoration.
Finely finished wood can be a major decorative feature or provide
a subtle background for other effects. The grain and figure patterns
of fine woods add highlights and shadows. Proper finishing helps
to develop and enhance natural wood beauty; or, when necessary,
subdue an overly flashy grain.
New Surfaces Sanding: Before any finishing
material is applied, the wood surface should be as smooth
as possible. Mill dressed lumber frequently is unsuitable
for the application of fillers, stains and varnish and requires
finish sanding to eliminate minor defects. Always sand in
the direction of the grain.
Filling: The filling of open-grain woods, such as
oak, mahogany and walnut helps build a beautiful, smooth,
transparent finish. P&L Paste Filler or P&L Filler/Sealer
is used to fill the pores of open-grain woods so that varnish
will dry with a smooth finish, "free from pin holes". Popular "open
pore" effects are obtained by omitting Paste Filler prior
to staining. Close-grain woods do not require filler.
Staining: Stain is employed to develop the natural
beauty of both hard and soft woods without obscuring grain
and figure patterns. There are many varieties and types of
stain but generally break down into wiping stains, spray & wipe
stains, and dyes. With proper equipment the amateur finisher
may use any of the above but the easiest and most consistent
stain to use is an alkyd wiping stain. These stains can be
brushed or rag-wiped on, left to penetrate into the wood,
and them wiped with a lint free cloth to remove excess stain
and also help uniform the colour. In certain cases it may
be added to the filler so that staining and filling may be
accomplished in one step. Alkyd stains have limitations.
High chroma and especially deep or rich colours may be available
only in spray & wipe or dye systems, or a combination there
of. Please consult us when you have such a project - we would
be happy to recommend to you what alternatives you may have.
Varnishing: The final operation in building a beautiful,
transparent finish is the application of two or more coats
of varnish to protect the surface and further enhance the
beauty of wood grain and figure. The number of coats used
will be determined by the effect desired and the durability
required.
Pratt & Lambert's Varmor Clear Finish and 38 Clear Finish
are recommended for interior trim, panelling and other woodwork.
At least two coats should be used for high quality work.
When dry, each coat should be lightly sanded with a fine
grade sandpaper. For open pore effects, Satin or Dull are
preferable to Gloss for the final coat. These lustres closely
resemble the finish obtained when a gloss varnish is hand
rubbed. For hardwood floors, Varmor will insure maximum beauty
and durability. On open-grain woods, either can be applied
over a coat of FillerlSealer.
Previously Finished
For any interior wood surface where previous clear finish
(not paint or enamel) is dull or worn, but not cracked or
peeling to bare wood, simply wash the surface with solvent
to remove accumulated wax, dirt and grease. Wipe with clean
cloths while the surface is still wet. Sand lightly with
fine paper until smooth and remove all dust with a tack rag.
Proceed to Varnishing operation.
For any interior wood surface (except floors) where the
previous clear finish is badly worn, chipped, crazed or peeling,
remove old finish down to the bare wood by sanding or using
paint and vamish remover. Bleach out any undesirable stains.
Wash the entire surface with solvent and allow to dry. Finally,
sand with fine paper until smooth and remove all dust with
a tack rag. Proceed to Staining and Varnishing.
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Interior Wood (Opaque) |
New Surfaces
In building a fine opaque finish, surface preparation is as important
as it is in building a fine transparent finish. Sanding and knot
sealing with shellac may be required. The first requisite of a
fine opaque finish is a smooth wood surface. The proper grade of
sandpaper will vary to some degree according to the wood. After
sanding, all wood dust must be removed from the surface before
priming. After surface preparation, a coat of Pratt & Lambert's
Suprime II Primer is applied. This product is formulated to provide
a perfect foundation for subsequent coats. When dry, the primer
should be lightly sanded. This will remove "nibs" and dust that
might have settled on the primer while drying.
Previously Finished
When the surface of previously painted interior woodwork
is in good condition, cleaning and sanding may be all the
preparation required. Grease, dust and dirt should be removed.
Traces of wax, if any, should be removed with a solvent,
followed by a thorough washing using a non-sudsing detergent
in hot water. (Solvents dissolve wax but do not remove it.
Detergents in water envelop the particles and carry them
away.) Rinse with clear water thoroughly and allow to dry
before finishing. Be sure all wax has been removed before
refinishing.
Surfaces previously coated with gloss or semi-gloss paint
or varnish should be roughened, using abrasive paper, usually
after cleaning with a strong washing solution. The surface
must be absolutely dry before sandpapering or repainting.
Disintegrated, chalked or powdery areas should be sanded
carefully and thoroughly. Paint does not adhere on such areas
Paint which lacks elasticity or which has hardened and
become embrittled on ageing may scale or chip. Ideally, paint
should expand and contract with the wood whose dimensions
are changed by variation in moisture content and temperature.
When the paint is scaled or badly chipped it is usually necessary
to remove it down to the bare wood. The undamaged bare wood
which results after removing old paint should be treated
very much like new wood.
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