OK, for the parging lesson go the the following post - http://forums.citytv.com/forums/thread/357464.aspx
As for the Deck painting, it could have failed for several reasons. You will now have to scrape and sand the existing finish until you have removed most of the paint. If you can get it to the bare wood again, that would be best. There are people that will come and prepare the deck surface for you if you don't want to tackle this part of it. Once you have a good clean surface to work with, try using a solid covering stain product that will penetrate into the wood surface. You need to ensure that you have a dry surface to work with. Then, you need to make sure you don't do this in the middle of a hot sunny day. Morning or early afternoon is best so that you don't have direct hot sunlight on the surface. Make sure there isn't rain in the forecast. Now if you're lucky enough to meet all of these requirements, you can start staining. You can use a roller to apply the stain if you wish, however, you will want to go over it with a brush to ensure that it is driven into the grain of the wood and not jsut sitting on top. You may have to put a second application. If you can meet all of these criteria, there is no reason why the finish shouldn't late you for at least two seasons.
I hope that helps - probably not what you wanted to hear though!
Good Luck!
Ramsin