How To Clean Black Off Brick

I just thought I'd report back with my experiences. The pressure washer is the way to go, at least as far as I am concerned.

I looked at using the acrylic to paint the bricks but there's an awful lot of them and that stuff is expensive. Nonetheless I bought a gallon and gave it a try, but the surface of the bricks is so rough that it is a real pain trying to get good coverage with the acrylic. I reckoned that even using plenty of thinner it was still going to cost several thousand Baht in paint and take me weeks to complete the job.

A Thai friend has a pressure washer and he was happy to lend it to me for a week. It's not one of the famous brands like Karcher, but an Imperial Airman pressure washer, rated at 107/214 bar. Here's a picture:

As mentioned above, it's fun to use, takes the black marks off the bricks effortlessly, and the result is quite rewarding. I didn't want to overdo things, so I limited it to around an hour a day, and finished the whole place inside a week. That included cleaning the black stains off some large lumps of ornamental white coral that are scattered around the garden. Now it's all nice and clean I should apply the acrylic, but as mentioned it's too much work and expense. I'd far sooner spend the money buying myself a pressure washer and then once a year get it out and clean the brickwork as necessary. On a hot day it's a nice way to spend an hour, splashing water all over the place. Plus it has many other uses like cleaning the car and motorbikes, cleaning the patio and path tiles, and so on.

A great recommendation thanks, Pib, and thanks to all the other posters for your interest and help.