Is is possible to put an overlay on a func_brush? In hammer everything looks good, but when I compile the maps and go ingame I see the overlays are not there on the func_brush.

No.

Best thing you could do is make a custom texture and apply it to the brush. Next best thing is to create a brush over your other func_brush (as thin as possible), apply your overlay on it and parent the brush with the overlay texture on it to the original func_brush.

Searching helps as well: post35135.html?hilit=func_brush%20overlay#p35135

post35028.html?hilit=func_brush%20overlay#p35028

post11961.html?hilit=func_brush%20overlay#p11961

But tnx for the links, fixed my problem