Wetting the wool and prefelt is not an exact science. Too much or too little water yields the same result, the piece won’t felt. I think it just takes experience to know how much water to use. I am felting up to eight layers of various materials so I will be using a lot of water.
I spray soapy water and diffuse it with my fingers to wet the pieces. There is an interesting conversation in the felting world about using hot versus room temperature water in the felting process. I haven’t seen a large difference using either so I generally use room-temperature tap water.
After wetting the wool I look for pieces that moved and put them back. I check that the piece is wet all the way through by carefully lifting a corner of the piece to see if the prefelt is wet. The prefelt is spotty with water so I turn the piece over and wet it from the prefelt side.
Another pair of hands, an extra sheet of plastic and another large board helps in turning the piece safely. The prefelt needs water in random areas. After wetting, the piece gets turned back over to the other side.
On areas that have too much water, I use a rectangle of bubble wrap to gently press the wool to move the extra water to the outside edges.
I cover the piece and let it rest overnight so the wool scales can start introducing themselves to the silk and other fibers.
I ended up using 4-5 bottles of water for each piece. There was water run off so I protected the wood floor with big towels.