Need advice painting dirty concrete flooring outside

[OM2]

We have concrete flooring outside the back of the house.
I'd been meaning to paint for 3 years.
Summers nearly gone... I was planning to paint.

PROBLEM: how do I clean?
I tried using a pressure washer last night.
It worked - kind of - but was taking strips of the concrete off!
Some of the dirt is green stuff - some sort of mold or something I guess.
I can try using a broom and washing down.
But any other suggestions??

Paint: I'm guessing I have a few days only.
I need a very course paint.
Where can I buy from?
Going to b&q now. Any other suggestions would be great.

Also... What items do I need? Brush? Roller? Anything else? Spirit?

Also... How best do I protect the wall from the paint? I'm guessing masking tape won't be good enough?

Thanks.

 

[opps]

Is it just a patio type slab of concrete? If yes then it probably doesn't have a damp proof membrane, meaning that ground moisture may cause anything you buy from B&Q to fail.

I think you might need to apply a 2 part epoxy resin but they won't be cheap and you have to ensure that you mix the product correctly.

https://www.permagard.co.uk/advice/damp-proof-concrete-floors

Read the above and then email them to make sure that they have a suitable product. Remind them that it needs to be able to absorb ultra violet light given that it is out doors.

I would not expect a domestic pressure washer to break down concrete, are you sure it wasn't washing/blowing away cement used to fill cracks.

Bleach and a brush will remove the green mould. What ever product you use, you need to remove that, otherwise the paint will sit on top of that rather than the concrete.

Another company to ask for advice

https://regalpaint.co.uk/floor-paint/concrete-floor-paint/

To be honest they were two of my quick google searches, I have never used either or their products.

Good luck