Measure the length of the drapes to determine the number of hook-and-loop fastening strips to purchase. You can find hook-and-loop fasteners with sticky backs at a hardware or home-improvement store.
Lay the drapery with the backside facing upward on a flat surface. Remove the backing from either side of the hook-and-loop fastening strip and run it horizontally along the top edge of the first panel. Repeat running a second piece of the fastening strip along the top edge of the second panel.
Slip on a pair of rubber gloves and a respirator before mixing together 1/2 tablespoon TSP (trisodium phosphate) and 1/4 gallon lukewarm water.
Dampen a large kitchen sponge with the TSP concoction and wipe down the cement walls above and on both sides of the window. Wet a separate sponge with water and rinse off the TSP solution. Allow the cement surface to dry completely before continuing.
Center the remaining side of the hook-and-loop fastening strip approximately 1 to 2 inches above the window, or higher if the drapery panels are longer. Attach the strips to the wall with a cement adhesive.
Allow the cement adhesive to dry for at least one to two hours before attaching the fasteners on the drapery to the fasteners on the wall. Run your hand across the drapery to firmly attach both sides of the hook-and-loop fasteners together.