Damp problem?

Hi,
Are you sure it's not condensation? Any damp will always find the coldest spot on the wall. Is this wall with the damp on a north face? Have you got plenty of ventilation in the house? I assume it's a cavity wall. Could be a wall tie be bridged (mortar on it allowing damp to track across)? Easy way to check this is call a chap in who does wall ties and he can check it easily with his boroscope looking into the cavity. The painted on silicone stuff on the brickwork may work if the brickwork's sound but even then it won't last very long. If it's porous, you're wasting your time. Even put on with a pressure spray, it's not effective. But you shouldn't have any sign on the inside wall even if the outer skin is saturated if the wall ties are clear. May sound daft, but have you got a leak from your heating system under the floor? We had that years ago when we had a new system installed. Seems you've done most things apart from the suggestions here. Not much else left! My guess would be condensation, particularly if it's a north facing wall. That or a bridged wall tie. If all else fails, then it's a call to a builder but even a good builder sometimes is stumped by damp.
Best of luck

Denis (ex wall tie installer and pointer)
December 2011