Filling a gap of an internal wall with foam spray

[LuckyA]

I was thinking of filling a gap in the internal brick partition wall of the downstairs toilet with gun grade pu foam (Thermofoam perhaps). The gap is at floor level and allows a lot of cold draught to get in from the sub-floor and is hard to access as it is behind the discharge pipe of the bloomin toilet; I won't be able to fill the gap with bricks.

As far as I'm aware, Thermofoam has a very fine open cell structure. As I'll be applying it in a cold spot area does that mean it may be susceptible to condensation? I want to avoid this as the downstairs toilet room was treated for dry rot and would like to avoid any possible recurrence.

I'm also open to other suggestions.

Thanks guys for your help.

 

[endecotp]

Condensation appears on cold surfaces when the air is moist.
The surface of an insulation material will not be cold.

But reducing the ventillation by eliminating this draught may mean the air is damper, possibly resulting in more condensation elsewhere in the room.