Everybody on this forum understands the problem of plastic paint trapping moisture rather than protecting the surface from moisture. However, if you are like me, you will have had problems convincing friends, builders etc that this is what happens.
You might find the following pictures useful...
This is a 1970's solid concrete block wall which has been painted with an exterior masonry paint. As you can see, it has failed in many places which will allow in the moisture. On this wall this appears to be due to a failure of the paint itself rather than the render but I have examples of this too. The result is the same, moisture gets into the wall and then can't get out.
Just to the right of the above picture and below the window sill was a large paint blister. This point on the wall is well protected by sill of the window and there is no obvious failure of the paint anywhere near.
And the contents of the blister? Trapped water, what else...
In a modern building of cavity construction, having the outside layer damp isn't a major problem. However in older properties, trapping the moisture like this will just lead to damp internally.
You might find the following pictures useful...
This is a 1970's solid concrete block wall which has been painted with an exterior masonry paint. As you can see, it has failed in many places which will allow in the moisture. On this wall this appears to be due to a failure of the paint itself rather than the render but I have examples of this too. The result is the same, moisture gets into the wall and then can't get out.
Just to the right of the above picture and below the window sill was a large paint blister. This point on the wall is well protected by sill of the window and there is no obvious failure of the paint anywhere near.
And the contents of the blister? Trapped water, what else...
In a modern building of cavity construction, having the outside layer damp isn't a major problem. However in older properties, trapping the moisture like this will just lead to damp internally.