I would'nt seal them - they are never dry enough
How do you mean? Is it because they always go cloudy or apear white like salt a few days after sealing?
Oidinary seal won't stick to clay paviors, it will become detatched as the molecules wont "fit" ito the clay structure like on concrete blocks. If you pick at the white areas with a stanley knife blade you will be able to lift the seal off in small flakes. Resiblock superior will be ok but that has its pitfalls as it's not xylene based and you can't soften it if owt goes wrong.
There is a resin seal xylene based you can use it's altered in some way to work on clay even some flags and stone like granite and you can re emulsify it to re work it
