Coating Reference Handbook - Hempel

HEMPEL
CHECKPOINT PREPARATION GRADE P 9
CONCRETE
WHY?
Insufficient cleanness (Preparation Grade) will result in laitance, efflorescence,
form oil or contaminants being left on the surface.
Laitance is a weak cement sludge layer formed on the surface during casting.
Due to its low strength it will peel off together with any coating applied on
top of it.
Efflorescence are salts coming from the inside of the concrete. They will cause
osmosis and blistering of the coating.
Form oil or other slip agents are used to ease the removal of casting forms after
the casting. They act like oil and grease impairing adhesion of the coating.
CORRECTIVE ACTIONS:
Areas insufficiently cleaned for laitance must be recleaned using a method which
can remove laitance, e.g.. abrasive blasting, mechanical cleaning, water jetting
or acid treatment.
Efflorescence must be removed by mechanical cleaning (small areas only) or
by high pressure hosing.
Form oil must be removed by degreasing.
PREVENTIVE ACTIONS:
Instruct operators of proper preparation grade, i.e. set standard.
Evaluate if working conditions (light, access) are suitable for the work.
HOW TO DETECT:
Visual
Acid treatment involves the use of strong acids which are
severe etching solutions giving off fumes as well.
On disposal take care where the acids are going.
It is recommended to avoid acid treatment whenever possible.
INSPP9, ed1 28/07/95 EMi