Hi, I bought my house in France 7 years ago. It was built in 1990 with those big red bricks that have honeycomb-like holes inside (Not a very technical description!). When I bought it, the house had not been rendered . After about 2 years I had the house rendered by a French builder who did a super job.
A couple of years later damp stains appeared all around the house up to about 80cms in height. When they dry out in Spring/Summer the stain turns white.
I don't remember the bare red bricks every getting damp - nor do I remember seeing an obvious DPC. I'm guessing that the damp is coming up through the render alone and not the bricks. Is this possible and if so what would I need to do to fix the problem.
Apologies for this lengthy question - hope someone can help.....

Did he render it down to the ground ?.

Yes he rendered it right to the ground. I had an idea that if I cut a "slice", say 10mm wide through the render to the actual brick, then fill it with silicone, it might act as a barrier to the moisture.

Any ideas??!!

If you cut through it and angle the cut upwards so the rain drips off the front edge and (A) leave the cut open (B) run your silicone,
(C) remove the lower render.

The builder should of fixed a bellcast bead just above the damp course when he first done the wall to stop what is happening now,
rendering down to ground height is never good and if done a gap is formed with stop bead under the bellcast bead.
To get a neat cut line stand a board against the wall and rest the cutting disk on it, you will see when you are through to the brick by the red dust.