Hi guys, i'm pretty new to mapping and to Hammer. However, I've been having some issues with gels and droppers.

I have read the tutorial in this page:

http://developer.valvesoftware.com/wiki/Gel_(Portal_2
I did exactly as it says there, I've also seen tutorials on youtube and i still have no idea why i can't get the gels to work properly. I have set allow paint in map to "yes", i have put lights on my map and made sure to run RAD on fast or normal. When i compile the map and test it i can see the gel falling, but it doesn't paint the floor or wall, but it is there, because if i go where the gel fell i can jump higher.
I'm following all the steps, why the gel doesn't paint anything?