The Shed – September-October 2019

‘Hot-tyre pick-up’

(HTP) ... is a very

common problem with

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Left: A painted floor

with HTP

Below: The dried

test strip which has

been sprayed with

a little water. The

water soaks into the

uncoated concrete,

but beads on the

sealed surface

900ml of water several times. It is
important that the acid be added to the
water, rather than the water be added
to the acid. This is because heat is
produced when concentrated acid and
water are mixed. If, say, a small amount
of water and a larger amount of acid
are combined, the great amount of heat
and the relatively small volume of water
leads to a high temperature, usually
high enough for the water to instantly
boil, blasting hot, concentrated acid
out of the container. This is a drastic
situation, because the concentrated acid,
particularly when hot, reacts with skin
and eyes causing irreversible damage.
Your clothing will never be the same
either. I wore rubber gloves, gumboots,
and safety goggles while mixing and
using the diluted acid and took care to
not let it splash on the steel legs of my
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move), as they would also have reacted
with the acid.

Applying the acid
I drizzled the acid solution over the
concrete using a plastic watering can
bought for the purpose. My old galvanized
watering can, which I inherited from
my mother (you can still see the price
written on it in crayon: 29/6), would
have reacted with the acid, dissolving
the metal and making hydrogen gas.
A slight foam of carbon dioxide gas

bubbles was formed as the acid and the

concrete reacted together. I spread the

acid using a scrubbing brush on a pole,

trying to get a complete coverage of

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to be sealed. The alkaline substances

in the concrete neutralize the acid, so I

had no reservations about squeegeeing

the liquid out of the shed door onto the

grass outside.

The water blaster was again employed

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out the door.

To get the sealer to bond with the

concrete it is essential that anything on

the concrete’s surface — like dirt, oil, f