When sealing the very best time to seal is when the concrete has fully cured and all the moisture has left naturally, this is typically 28 days. As you can imagine this guideline is rarely kept to, therefore if it must be sealed sooner at least 7 days should have passed since printing. This is because the type of sealer used will react with moisture. This also means that there should be no damp patches or evidence of moisture whatsoever, as it can cause the surface to take on a milky appearance.
Also ensure all buckets and brushes used are completely dry and clean.
Pour the sealer either neat or diluted with cellulose thinners or xylene (dependent on weather conditions) into a bucket and brush into the surface with a medium to soft broom with natural fibres. Make sure you brush it well in, to allow it to penetrate the surface of the concrete. Do not allow the sealer to lie on the surface. It can usually be walked on within an hour, but no vehicle should be driven on for a minimum of 48 hours – longer if possible as it actually takes around a month for the sealer to cure properly. Always add a non-slip additive to the sealer for the final coat.
Do not seal in the direct sun around midday – try to do it early in the morning or later in the evening.