Laying stone masonry is quite different from laying brick and block. The material is irregular in shape and size and often must be trimmed in the field before placing it in the wall. Stones can be laid in a random rubble or ashlar pattern. Undressed or rough-dressed stone is used in rubble stone construction, and dressed stone is used in ashlar construction. Undressed stone has not been split, cut, or trimmed in any way. Rough-dressed stones have been split by the producer into rough rectangular units for easier laying. BEFORE YOU START All rubble stone and ashlar work should be laid on concrete foundations or footings. Also, make sure the stone is free of dust and dirt so that the mortar bonds well. Before laying dry, porous stone, wet it just as you would a high-suction brick. PUTTING THE PUZZLE TOGETHER Always trim and fit each stone before placing the mortar for it. Select and position the stones so that the joints are as small as possible. The more the stones interlock, overlap, and fit together, the stronger the wall will be. Trim undressed stone with picks and hammers using a series of firm taps. The most frequently used tools are a mason's pick with a chisel end and a hammer-headed chisel. After you have a good fit for a stone, remove it and place the mortar. Lay a full, deep bed of mortar about 2 inches thick. A 1:1:6 TYPE N MORTAR WORKS WELL A 1:1:6 portland cement-lime-sand Type N mortar is suitable for most stone construction. Greater compressive strength is generally not needed.