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In the building industry, products such as
bricks, concrete and plaster
can contain either cement or lime.
The acidity and the alkalinity of these ingredients usually evaporate
as they're exposed to oxygen over a period
of twenty-eight days when they usually will stabilise.
We need to make sure that the surface before we paint
is at a normal level where the acidity and the alkalinity
have stabilised. And we can check that
with Litmus paper.
TIM: Litmus papers, or pH papers,
come in a package containing a quantity of strips.
We use one strip
for each test that we conduct.
Each strip when applied to the surface and wet with water will
change colours and indicate
an acidic or alkaline reading.
If both acid and alkaline levels are even, a neutral reading will appear.
A neutral reading is perfect to begin painting the surface.
This is basically how you do the test.
Just take one little strip
and I'm going to apply it to the concrete surface
in this situation.
TIM: Then apply a little bit of distilled water.
And I leave it there for about
thirty seconds.
TIM: So now after thirty seconds has passed, I then take the package
and compare it to
the strip.
And as you can see,
the colour matches...
probably between seven and eight.
Probably closer to seven,
which is a neutral reading.
Meaning that it is
neither acidic
or alkaline.
There could be a number of reasons why masonry surfaces need to be tested;
it could be that the surfaces haven't adequately dried within the
twenty-eight days that we allowed,
and the acidity and the alkalinity levels haven't stabilised.
Or it could be that the builder has,
putting the windows and the doors, and the plaster hasn't had the opportunity to dry
adequately.
Or it could be that a pipe has broken and moisture is coming through the wall.
Whatever the reason is,
we've gotta make sure before we start painting
that the surfaces we're painting
are not acidic,
or have high levels of alkaline.