Is one coat of render ok for a garden wall?

I dont ever one coat anything personally and a scratch coat is applied for a reason otherwise why not one coat everything? the scratch coat should be no weaker than a 4:1 sand cement, waterproofer mortar with the top coat 5:1 mortar possibly with lime or hardener. Also applying a "thick coat" especially new block work will actually be harder to work with than the two coat method as mortar applied thickly tends to sag and peel away from the wall. It can be done though but its not really the way to do it and I see no reason to not scratch coat first as the same amount of materials will do both coats anyway as the scratch coat is only a thin application.

I agree with rgje.I wouldn't let him do it in this weather either:)