Remove any furniture from the rug and spread it flat on the floor. If it is a sunny day, place plastic sheeting on your porch and set the rug on it. This will prevent the floor under the rug from getting damp.
Fill a misting spray bottle with water. The bottle needs to mist, not squirt, or the rug will get to wet.
Mist the edge of the entire rug. You need the rug to be slightly moist but not soaking wet.
Place the heavy items on the edges of the rug. Work your way around the entire rug and check that the edges are pressed flat and not curling under when you add the bricks or cast iron.
Let the rug dry before removing the heavy items. This could take a few hours depending on the thickness of the rug.
Repeat the misting and drying process if necessary. Thick rugs may take 2 to 3 rounds to stay flat.