General Preparation
Let us assume that the wall has been built and cured. After the wall has dried and matured for a few months, we first apply a coat of cement primer (white). Irregularities of the surfaces can be rectified by applying putty before painting is started. For example, in ordinary house construction, we can use plaster of Paris as putty. For superior work as in showrooms, special copolymer emulsion putty which is suitable for exterior and interior and also contains the primer coat is also available in the market. They are, however, costly. It is more convenient to first apply white primer on cement-plastered walls before applying putty.
The
white background obtained after applying white primer shows up the
irregularities and then, the putty can be applied more effectively. This
procedure also reduces the amount of putty required. The putty coat is rubbed
with sandpaper to smoothen the surface. After that, one more coat of primer can
be applied, and it is allowed to dry for 10 to 12 hours before applying the
chosen paint as the undercoat. The following points are important in this case:
1. Oil and acrylic paints, and distempers do not fare well
if there is alkalinity in the surface to be plastered or if the wall has been
previously whitewashed with lime. Hence, it is essential to apply
alkali-resistant primer on these whitewashed surfaces before applying the
prescribed paints.
2. While painting the exterior walls, all molds, algae,
moss, etc. should be removed
3. When efflorescence is seen in the brick wall, water
should not be used to wash out the efflorescence. If water is used, the salt
may be absorbed back into the pores and precipitated again on the outside when
it dries out. Hence, the deposit should be brushed and cleaned in the dry state
itself. We may use acid etching
Procedure for Painting New Buildings
As we
have seen in the last section, fresh concrete, cement, and lime plaster have
moisture in them. They are highly alkaline. Hence, it is preferable to paint
these surfaces only after 3 to 6 months when the plaster work is completed.
Even then for new works, it is considered better to use primer paint to start
with. These primers are special paints for new works.
In
addition, there may be pores to be filled. Hence, we use a filling-in compound
or a filler coat. Thus, in all new painting works, we have the following five
operations:
1. Cleaning
the surface by proper sandpapering (The sandpaper we use for different
surfaces is different.)
2. Application
of primer coat
3. Filling
the small dents with a filler coat
4. Application
of the first undercoat of the paint
5. Application
of finishing coats
Thus, in addition to the main paint, we must use the primer
coat and the filler coat in the new works.
Primer Coats
The names of some of the primer coat paints used for
building works are given in Table
Note: The covering capacity of these primers is about 18 to 20 m2/liter per coat
Filler Coats
As
discussed above, the third operation in painting is to fill the small dents
(that are on the object) with filler coats. For example, we usually use wall
putty on the walls. When using enamel paint, we generally use a paste filler
coat.
The
wall putty can be prepared by mixing powdered chalk (whitening) with 5% to 10%
enamel paint (commercial grade) and 25% to 30% water. These are mixed well to
form a homogeneous mixture.
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