Hi @iamaem,
You know... you've actually hit on a very vexed issue believe it or not...
Paving like this, whether bricks or true pavers, is technically described as 'unitary paving', that is, it's paving comprised of separate 'units' - pavers (or bricks).
Here are the two schools of thought...
- Unitary paving should only be grouted with suitable sand.
The reasoning here is that paving is designed to move with both hot and cold expansion/contraction and with sub-surface movements such as clay soil swelling or shrinking. Sand brushed between will allow this movement while also locking them in place to stop rocking or sliding movements.
The sand will also provide a minor level of drainage.
Sand is then reapplied as needed. In most cases only every few years.
- Paving should be locked in-place with a cement-based grout.
The reasoning with this one is that it stabilises the paving, reduces maintenance and prevents weeds etc.
Personally... I always sand paving. The only time I would likely use a locking product would be is the paving was laid over concrete.
I see it's less hassle to re-sand as required than have to remove cracked grout and reapply it.
Now on saying that... technology has caught up with this situation and that's where the paver-lock type products come in as mentioned by @Brad . I haven't tried one of these yet but they do seem to tick all the boxes. They are sand-based with a gelling agent that binds it together remaining flexible without cracking risks.
Only tools required are a broom and a hose!
To get you existing paving clean, and it will be messy to do this... give it a pressure clean to remove chunky material then apply 30-Seconds or similar and give it a second pressure clean, you'll probably need a stiff broom too, before hosing it all clean.
If you plan to use a paver-lock type thing then do let everything dry completely otherwise it will start gelling as you try to broom it in.
Hope this helps.
