I'm posting in the hope that someone unconnected to this issue can help shed some light!
we had a rear extension (flat roof) completed early last year.
Over the winter external cracks started appearing in the render all around the extension. The coping stones on the parapet walls also had cracks directly beneath them in the mortar. (this was also accompanied by a leaking roof which confused the problem as we thought they were linked).
Anyway after getting a few roofers round to see what the problem was they all immediately said that the coping stones were too small and not providing enough of an overhang, causing water to run back into the wall and run down them which had caused the deterioration and cracks.
we went back to out builder who agreed but for some reason has tried to find any solution other than replacing the coping stone (he says the next size up is too big but this seems strange?). He said that the reason this happened was because the rendering was done before the coping stones were added which meant it was too think in places. Anyway we have now had all the render repaired and there is now a seal up to the coping stones all the way round.
They have also cut a groove in the coping stones all the way round to provide a drip edge, but I think this is too close to the render still. It's less than 20mm to the wall and in some places it're pretty much right next to it where there is so little overhang in the stones.
Are there any solutions at this stage that does not involve replacing the coping stones completely? Would lead flashing on the coping stones help? I really do not want to have to wait until next winter to see whether our walls crack to know whether the problem is solved!
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