The toilet ( a Thai style installation ) was leaking from under on the tank side.

I sealed the base with cement compond. See pic.

Since then it does NOT flush properly. The tank fills ok.

When you press and release the flush lever water rushes into the bowl

and sits there. There is NO siphoning action.

Did i blocked anything ( air intake for example ) by applying cement all around the base ?

Does it need air intake to flush ?

Your help would be appreciated.

Thanks Have a nice day

That is likely the problem - often there is no air exit pipe or they become blocked - so most likely it was only drawing from under the base and that has now been blocked. Look for a pipe on outside wall or in attic that might be an air vent that you can hopefully clear with blast or air. If not maybe have contractor cut floor behind toilet and install an air pipe to drain below it. They can remove and do such easily and only takes a couple hours (if outside wall or access available).

My father, God rest him, always called it the stench pipe.

you need one of these one way valves, to let the air in to the system to stop the vacuum, but not to let the smells out:

http://www.screwfix.com/p/floplast-push-fit-air-admittance-valve-grey-af110/78150

I have the same problem with one toilet as a air vent was not fitted to the tank & as it fills there is less room for air, when this happens I get the tank pumped out, this solves the problem until tank fills again which takes about a year.