kivy join two different texture

[Degenerate Tech]

i am doing a game .

i have created a scrolling  background from right to left by using one  image 

self.ct=Image(source='cloud.png').texture

self.ct.wrap='repeat'

self.ct.uvsize=(self.width/self.ct.width,-1) 

 and scrolling done by changing uvpos in a game_loop() which i am calling 60 fps 

 

But i want to scroll different two image in interval 20 second .I mean after 20 sec another image will scroll ...at same rectangle object....i think i have to join two texture side by side ..please tell mw how?