White powdery substance on inner attached garage wall

[jackogs]

We moved into our house in the early part of this year. The house was built in about 1980..

It has an attached garage, the inner walls are mainly a grey block which I think is called 'Thermalite'?

I took the chance while the garage was empty to paint the garage floor.

I have now noticed that about 2-3 inces up from ground level in the garage that there is a white powdery substance appearing on the grey blocks on a few places around the inner wall.

The grey blocks have started to crumble in a few places under the white powder too.

Have I created my own damp problem by painting the floor?
I assume that the paint on the floor will be a pig to remove if thats the cause...

What should I do next? I worry I have created a very expensive problem?

Any advice welcome...