Weight map brush tool not painting?

Wouldhe

Hi, 

I'm sure I must ne doing something stupid here but...

I followed one of the turorials on using weight maps to adjust dforce behaviour.  The red mask is visible on the object just like in the tutorial but the brush itself does nothing - is there a setting to activate / add to / remove from the mask that I'm not seeing?

 

 

Mada

Press Alt while using the paintbrush and it will subtract instead of add :)

Wouldhe

Thank you Mada!!!!!