Updated: Jun 2, 2019
This technique is so simple, and one of many ways I can teach you to create the latest in interior concrete finishes.
To get started you'll need some tools and products:
A very flat, exterior grade acrylic paint tinted to a light grey colour: preferably a product that contains a slightly textured stone.
A water-based wash, tinted to a complimentary but tonally darker grey colour.
A roller (medium nap), extension pole, elastic bands, muslin cloth, roller tray, brushes.
Cut out a piece of muslin cloth to the rough size of a tea-towel and open out the fabric. Then wind the material unevenly around the roller and attach with a couple of elastic bands. You've just built a rag-roller.
For best results you'll need two people, so find someone you can work closely with and still be friends.
Okay, to get started roll two coats of your light grey, exterior flat acrylic paint on to the wall (obviously, let the first coat dry before you apply the second). Then, leave the wall to dry completely. You don't want any moisture trapped in the coating or this will affect the final finish.
The following day two applicators will complete the final finish. Using a relaxed and random criss-cross brushstroke, one of you will apply an even layer of the darker coloured wash on to the paint surface. Work in an area as wide as your shoulders, move from the the top of the wall to the bottom of the wall, and don't stop: keep moving across the surface and keep the edge wet. Most importantly, don't move too far ahead of the second applicator: you're working together as a team.
As the first applicator applies the wash, the second person rolls the rag-roller across the wall and removes most of the wash. The remaining wash will leave a coloured texture on the paint surface. Keep the wash-edge wet as the two of you work your way across the wall, brushing and ragging.
For edges and corners you can't quite reach with the rag-roller, simply dab the wash lightly with a small ball of muslin. Any accidental marks created on adjacent walls should be wiped away immediately with a damp cloth, so keep a rag in your back pocket.
Now that your application is complete you'll have a natural looking concrete finish on your wall that was incredibly simple to achieve. And, if you ever want to change the appearance, simply paint directly over the top.
I hope that helps and please email if you have any questions.
And a short, Carl's helpful hints video.