Leaking joint at window jamb

[neilp1]

The joint between my upvc french door jamb and blockwall is leaking rainwater and making the plastered internal reveal damp. The joint between the jamb and wall is about an inch wide and 3 inches deep and was filled with expanding foam by the window installer. I have cut away the external render to expose the foam and temporarily covered the joint with plastic sheet while it rains again.
Should I cut out the existing foam, clean out the joint, spray or brush apply a waterproof sealer before filling with expanding foam and rendering over?
Thanks for any useful advice.

 

[Burnerman]

A one inch gap is a bit on the big side but you have the idea.....in the absence of any upvc capping strips I'd point the gap up with sand and cement.
John

 

[footprints]

I think I would look at some UPVC cloaking strip siliconed into place, this sort of thing.

http://www.wickes.co.uk/invt/162619