Overcoating ZINGA

ZINGA can be overcoated with a topcoat to give a coloured finish to the structures. Like all porous Zinc rich coatings, care should be taken to ensure compatibility of the topcoat with ZINGA.

Under practical conditions, we advise the use of a sealer to avoid any problems with the compatibility of the topcoat.

It is not possible to give an extensive list of products which are or are not compatible with ZINGA. Every topcoat has its specific characteristics which make compatibility on ZINGA more or less likely.

We can only give general guidelines to detect whether or not it is likely that a topcoat is suitable for use on ZINGA or not.

General guidelines

Listed characteristics below can give a good indication on the compatibility for ZINGA.

Paint type

Never apply alkyd paints on ZINGA. The alkyd will react with the Zinc and make it saponify.

Water based products can cause formation of Zinc salts underneath the topcoat, resulting in bad adhesion. Water based coatings should not be used on top of ZINGA.

Drying time

In general, fast drying paints perform a lot better on ZINGA. Fast drying paints allow less time for the solvent of the topcoat to penetrate the ZINGA layer and consequently damage its cathodic capacities. Ideally, the paint should not have a touch dry time (20°C) of more than 1 hour, with 2-3 hours maximum.

Acid formation

If the topcoat forms acid products upon curing, this can affect the ZINGA coating. Information on the product formation upon curing can be found in MSDS sheets.

Time for complete cure / polymerisation

If a paint is fully cured, it can no longer affect the ZINGA layer. If this cure time is short, the impact on ZINGA is also reduced, insuring better compatibility.

Sulphates in binder and/or solvent

ZINGA is sensitive to sulphates. Therefore topcoats containing sulphates should be avoided.

Testing compatibility

If a topcoat is used directly onto ZINGA, it is advised to always perform a small test application on a test plate. This prevents problems on a big structure and also gives the applicator the chance to get to know the product.

Mist/Full Coat Technique

To avoid bubbling of a topcoat or sealer over ZINGA, we advise to apply the paints using a mist/full coat technique.

A thin coat of sealer or topcoat is applied over the surface of ZINGA before a full pass of the coating at the normal film thickness. This thin film penetrates only the surface layers of the ZINGA and seals its surface. Also relatively porous, the mist coat presents little obstacle to the passage of air from these upper layers.

First, a thin continuous layer is applied which gives air bubbles easy passage through the film. The first mist coat also provides a barrier for aggressive solvents in the topcoat.