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19.

ADHESION

Galvanised Steel provides a difficult surface on which to achieve good adhesion. Good surface preparation will prevent most types of potential adhesion failure. The table below may be used as a guide to the causes of adhesion failure and the solution to avoid this occurrence before use of Hammerite Direct to Galv Paint:

Cause of adhesion failure

Remedy

Surface contamination – oil and grease

Degrease with dilute detergent

Formation of soluble salts (particularly applicable to weathered galv)

Degrease with dilute detergent

Chromate factory pre-treatment

Abrade to remove

New galv with large and bright spangle – predominantly zinc

Weather until dull before application of DTG or use phosphoric acid etch primer followed by Special Metals Primer

Corrosion of the zinc

Refer to Section 6 – ‘For Rusted Metal Surfaces’

Etch primers or ‘mordant’ solutions

Only use phosphoric acid etch primer – other acid based primers do not cause adhesion failure but will affect the thickness of the galvanised coating

Reaction between DTG and zinc (formation of fatty acid soaps)

This is inevitable but sound surface preparation (degrease and abrade) and the selection of alkyd for this product maximises the adhesive strength of the product. Prolonged performance will result from the use of Special Metals Primer.

Water – any flaws in the painted substrate (scratches etc) can allow water to get under the dry paint film to encourage lifting of the paint particularly where water is allowed to stand or pool on the surface

Sound surface preparation will prevent the product coming off in sheets where this does occur. High risk surfaces should not be recommended for application with this product (flat roofs must be avoided).

20.

VISCOSITY

5.0 poise - 8.0 poise at 25ºC (ICI cone and plate viscometer) depending on colour/finish.

21.

SPECIFIC GRAVITY

0.90 - 1.16 at 20ºC depending on colour/finish.

_________________________________________________________________________________________

Technical Data Sheet Page 8

Issue date November 2007

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