Coating Reference Handbook - Hempel

HEMPEL
CHECKPOINT COATED SURFACE P 24c
BEFORE OVERCOATING
WHY?
Variations in filmthickness influence drying and the protective properties
of the coating:
* Too low film thickness
* Too high film thickness
Too low film thickness may cause poor flow together of the film and result in
pinholing through the next coat and so on. Result will be an open film of
low dry film thickness resulting in premature blistering/pinpoint rusting.
Too high film thickness prolong drying time, and may cause sagging/ running.
If not respected also risk of sagging of the next coat and solvent retention
which will reduce the coatings corrosion protective properties and mechanical
and chemical resistance.
For antifoulings cold flow may occur.
For zincsilicates mud-cracking/flaking may occur.
CORRECTIVE ACTIONS:
For too low film thickness apply an extra coat of same paint, in case of primers,
sealer or topcoats. If intermediate you may be able to catch up in next coat.
It is very important that an uniform pinhole-free paint film is achieved.
For too high film thickness allow an increase in the drying time before
overcoating or taking into use. Provide good ventilation to all surface affected
during this period.
For zinc silicates mudcracked areas must be reblasted or scraped depending on
size of the areas and repainted.
PREVENTIVE ACTIONS:
Instruct in the right film thickness and how to measure continuously during
application (WFT-Gauge). Recommend areas to be subdivided and assist in
calculating the amount of paint going on each area.
Influence stripe-coating of areas difficult to spray.
HOW TO DETECT:
Dry film thickness gauge.
Observe that the gauge may penetrate into soft and uncured coatings leading
to too low readings. Therefore only use the measurements as guideline.
INSPP24c, ed1 28/07/95 EMi