I am currently working on a new build house in London which has brick arches over the windows. I have seen arch supports on other houses, all of which have discoloured -- some considerably. The architect has suggested Catnic thermo-plastic arches, the Catnic brochure says that they are completely weather-proof. Are they any good? do they need treating? Some of the arches will be in places not easily accessable so regular treatment is not practical. Any help or suggestions appreciated!