Block Paving

Brush it regularly and wash it down with warm soapy water or a patio cleaner. If you do use a pressure washer, keep it on a wide fan setting and a moderate pressure, and hold the lance well back. A narrow high pressure jet blasts the kiln dried sand out of the joints, which is what loosens blocks and lets them shift, so always re-sand the joints after a heavy wash.

They are almost never growing up through the blocks. Windblown seed settles in the joints and germinates in the dust and grit that collects there, so the problem is nearly always empty or dirty joints. Brush or scrape the growth out, treat any remaining roots, then refill the joints with kiln dried sand or a polymeric jointing compound and compact it in properly.

Sinking is a sub-base problem, not a block problem. It usually means the area was not dug out deep enough, the wrong stone was used, or it was not compacted in layers. Missing or weak edge restraints let the whole surface creep outwards, which shows up as dips and widening joints. It is fixable, but the blocks have to come up so the base can be put right underneath.

It is optional rather than essential. Sealing makes the surface far easier to keep clean, gives you a much better chance of lifting oil and fuel stains before they set, and stabilises the jointing sand so it washes out more slowly, which in turn keeps weeds down. It also deepens the colour. Always let a new driveway weather for a few months and get it properly clean and dry first.