Correct Stone Application

Today I stopped by a job site where the stones had to be removed due to poor installation. The pictures above shows the back of a stone that has been applied to the wall and has been removed. The back of the stone was struck with mortar around the edge of the stone. This creates a dry cup in the center of the stone. This causes two major problems using this technique. Number one, the stone does not become a solid piece with the scratch coat. When you tap on the stone you will hear a dull, dead sound. This is not a 100% adhesion with the scratch coat. The send major problem is the center void will act like a cup. When water (rain) is running down the wall, water will gather in the cup. Now, if the cup is full of water and the temperature just happens to drop below freezing, need I say anymore? Some people say by having the void on the back of the stone, this will create a suction to hold the stone on the wall. I agree, but, do a full mortar bed on the back of the stone and use your trowel to create a small divot and apply the stone to the scratch coat using a wiggle motion and pressure. The mortar will spread out around the edges. After a little practice one can master the amount of mortar to be applied to each stone. Ideally the edge mortar from each stone will join to form a good seal around the stones. This will ensure no water will get between the stones and the scratch coat. Whenever dealing with exterior siding, always think like water. Like Chevy Chase says, "see the water, be the water, feel the water, na na na na na naaaaa." The number one enemy to your home is moisture, so lets keep it OUT!!!