For the main deck, I would recommend a floor sander, similar to what's used for finishing hardwood floors. Put a 100-120-grit belt on it and take it back and forth along the deck in the same direction as the planks until you see bare wood. Once you have bare wood, I would apply whatever stain or sealant you want very quickly thereafter, as you have just removed a large portion of both the artificial and natural weather and bug resistance the wood had.
A handheld orbital or belt sander will get most of the stuff off the vertical components (handrails and pickets). You'll need a "corner cat" or other detail sander, or some elbow grease, to get the paint out of crevices and detail work.
You will not be able to avoid taking off some wood along with the paint. Paint (especially a product designed for this kind of outdoor application) will seep into the grain of the wood, and you will be removing wood before you see the color disappear and bare wood show through.
By the way, you will still need to maintain the deck after staining and sealing. The stain will last for quite a while, but you'll need to re-apply the water seal at least once a year, once every 6 months if you get a lot of rain.
When I used to do a lot of these for a building/renovation company, the approach our foreman recommended was to assume the drywall will need replacing anyway and just rip it out. That would let you remove that entire panel in 45 minutes, and then you can just pop a new piece of drywall in, which is another 15 minutes.
As you can see from your 45 minutes, the drywall is going to be ruined, so just bite the bullet - get in behind it and pull it all off. The use of a crow bar and hammer may help here.
If you are wanting to keep the tiles on the adjacent wall, make sure you have cut a gap in at the corner so you don't rip it out as well.
Also, make sure you have something over the drain, to avoid it becoming clogged (I know - sounds obvious, but people do forget)
Updated to incorporate comments
- Cement board and a vapour barrier are the only suitable backing for your tiles here. Drywall shouldn't have been in there to begin with.
- Watch out when hammering around plumbing, to avoid water leaks adding to your worries!
Best Answer
I have used similar scrapers with good results.For really fine details you might also get a dental type pick. Care must be taken with soft woods as you can scrape away some of the contours. The mutiple heads may make it easier to follow peaks and valleys.