I'm living in the european lowlands - a small sedimentary flat strip of land starting in the north of France and slipping north over north Belgium aka Flanders, the Netherlands and Denmark.
Soils are fertile, here, and providing water (to make beer), food (to grow wheat & potatoes), and the prime material to build houses, at the time.
In ol' times when people settled down, they started digging. They searched the soil with the right texture and composition - the higher the clay content, the better. The soil was digged out, mixed with water, kneaded, smashed into molds, knocked out and set apart in a kind of tower - a pile of unfinished bricks.
Once they had modelled enough, they set fire to the tower and let it burn. Mud became brick, red brick. Not one brick was the same. In the middle of the burning tower, where the temperature was highest, bricks could become 'glassy' - the silicium content became glass - and those bricks were very hard. Not red, like 'normal' bricks, but black.
With those bricks, and a mixture of clay & unslaked lime (portland cement didn't exist yet), hundreds of thousands of houses were build.
I'm telling you this because I've great interest & respect for old knowledge & methods and because we're restorating and old farm.
Built of bricks, billions of bricks - not of a mix of concrete & a lot of industrial prefab stuff like most actual buildings...
Walls need to be repared & rebuild, and instead of buying new bricks I'm using a fallen down wall to recycle them. Using original stuff, respecting the soul of the buildings, not disturbing the energy of the place.
'Cleaning' bricks is time-consuming. Everyone knows the method of hammer & chisel, well, after a few bricks I decided to DIY.
If you don't have the tools, make them.
With a angle grinder I modified a hammer my father gave me long time ago, resulting in 'the ultimate cleaning tool to restore old bricks', called 'Gustavs Hammer' - my father's name.
Honouring the ol' ones, you know.
Take hammer & angle grinder.
Cut the hit side of the hammer in a 'V'.
Cool the hammerhead in used motor oil (to kind of restore temper, a bit).
Get out cleaning bricks.
Safety goggles & gloves!!!
Hold a brick in your left hand and smash on it 'the hatchet way' with Gustavs hammer.
Try to hit on the junction between joint & brick instead of your hand. With a lucky hit the old jointing will fall off.
You know how they started to build the Chinese Walls?
By setting the first stone.
Good luck, and keep on cleaning.