Zinc Phosphate Grey Primer 5L

Bought this with 5l of the black one coat paint (which goes on well, but actually needs two coats) but found it to be almost unusable due to its viscosity, and tendency to thicken further still despite regular agitation, when decanted into a kettle. Built two handrails and gave up with this primer on my second, switching to good old red oxide instead. It's a bit distressing to apply finish like this to all your hard work, especially as all the other materials bought with it were great quality. No instructions on the tin to maybe help with use, doesn't help, either.