I want to start by recommending that you start in a small bedroom, so that you do not over commit yourself in case you decide that you would rather hire a contractor to do it for you. The technique that I am going to describe is one that I personally use every day, in fully furnished homes. It is very basic, and I think that is why it works so well.
If you cannot empty the room that you are going to be working in, then push all of the furniture up against the walls to provide as much working area as possible in the center of the room.
You will now cover the entire floor with the 4 mil thick plastic. You will notice that it comes folded neatly in a roll. When unfolded, the plastic will open to 12’ wide, by however long you unroll it. For example, in a 10’x12’ bedroom, you would unroll the plastic across the 10’ width of the room and cut it. It would then unfold to 12’ across the length of the room. It does not need to be right up against the edge of the baseboard, just within a foot or so of the wall is fine. Use you Duct tape to tape the corners down, so that you have a nice secure barrier over your carpet. (If you have a wood floor or delicate surface, I recommend using a “safe-release” tape of some sort, so you do not damage the finish on the floor when you remove it).
Now that your floor is covered, it’s time to protect your walls. Grab your small ladder or step stool (depending on your ceiling height), a roll of masking tape, and the .035 mil thin plastic. You are going to be taping at the top of the wall, right where it meets the popcorn ceiling. Run a strip of tape along the very top of the wall, sticking just the top half, and tuck the plastic under the bottom half of the tape as you go, so that it hangs down to the floor. This will cover your walls and furniture, leaving only the popcorn ceiling exposed.
Start above the door, which is also where you will finish, overlapping by about a foot. You will have one continuous sheet of plastic all the way around the room, with only one opening (the start and stopping point) above the door. If the ceiling has any vents or light fixtures, take them down or wrap them in plastic as well, so that they don’t get dirty.
Now that everything is covered, you need to tape the bottom end of the wall plastic to the floor plastic, using masking tape, to create a seal. This will leave only your ceiling exposed, and keep your room nice and clean. Don’t get discouraged if this is taking a long time. Believe it or not, you are half-way done with the whole project!
Ok, your room is sealed up and it’s time to get dirty! The first thing that you will need to do is assemble your water tip. The pieces will al screw together, creating an adapter that will allow you to screw the adjustable water tip onto your garden hose. I recommend using a squeeze trigger of the hose, and then screwing your water tip on it. This way, you can turn the water on and off without having to run outside each time.
Adjust the water tip to a medium mist, so that most of the water is hitting the ceiling, but not dripping. Wetting the ceiling is just like spray painting. Several light coats with a few minutes in between are MUCH better than one heavy coat. If your ceilings have never been painted, it may only take one coat to loosen the popcorn material. If it has been painted, give it a few with several minutes in between each coat. Test it by scraping it with your 6” putty knife. When it’s ready, it will come off nice and clean.
You’re almost done! Now you need to assemble your scraper – your 12” putty knife and pole. (This is a cheap and simple alternative to what the professionals use, but it serves its purpose well). Lay your 12” knife handle on the last 4 or 5 inches of your pole, and Duct tape it firmly to create an extension handle. This will make scraping easy, without having to do it form a ladder.
Now start anywhere you’d like, and scrape the popcorn. It should come right off, leaving bare drywall or the original plaster ceiling behind. If you start to tear the surface, you need to adjust the angle at which you are scraping. When you have removed the entire popcorn ceiling, sweep it with the broom to get any loose pieces off, especially around the edges.
Now that all of your popcorn ceiling material is on the floor, it’s time to roll it up. Start at the door again, and slowly un-tape the plastic from the walls, folding it inward as you go around the room. Once the wall plastic is down, fold the edges of the floor plastic inward like a burrito. Then start at the far end of the room, and roll it tightly, working your way towards the door. It should be nice and tight, and stuff it into a trash bag.
That’s it! You now have a clean surface that is ready for refinishing. I highly recommend having a drywall contractor take it from here, as it is a task that requires a high degree of skill and experience to do.