Prepare the footing for your limestone structure by either pouring a shallow slab of concrete where the structure will stand (most often used for planters, fountains and large walls) or by leveling and tamping the earth where the blocks will sit. Check your site for level before beginning to stack your stones.
Mix mortar for your limestone structure by combing 6 parts bricklayers sand, 1 part lime and 1 part off- white cement in the concrete mixer, adding just enough water to make it damp. The mortar should still be able to stick together, so go easy with the water -- you can always add more later.
Measure and mark out the length and width of your structure if you are building directly on the ground. If you are building a retaining wall, line the earth to be retained with sheet plastic, being sure to overlap the edge of the plastic by 4 inches if you need more than one sheet.
Lay the first row of blocks, leaving a 3/4-inch gap (or use the width of your thumb) between them. Fill all of the joints with mortar. Apply a lot of pressure when placing your mortar so that it gets all the way to the bottom of your first level.
Lay a 3/4-inch thick layer of mortar on top of the first layer of blocks where the next layer of blocks will sit. Lay the next layer of blocks in the first layer of mortar and apply mortar between the new layer of blocks. Continue in this way until you reach the top. Do not apply mortar to the top layer, only mortar the joints.