Efflorescence Problem

[drfeelgood]

Hi,

I'm using phosphoric acid to clean cement off clay pavers. The acid is 85% proof and I'm neutralizing it with sodium bicarbonate before I wash it off. But I'm finding the bicarb leaves a film of white efflorescence. I've checked that I'm using the correct amount, as the ph in the test mix is 7. I've tried scrubbing it off with a stiff bristled brush then hosing it off, but it comes back. It's like it's mixing with something in the clay and this is causing a chemical reaction.

Can I add something to the mix to overcome this problem, or is there something I can do after, that will eradicate the efflorescence?

Thanks in advance.