If all ground were level, a lot of construction would be easier. Unfortunately, the earth is not flat, so yard pavers must sometimes be installed on uneven areas. There are design techniques to cope with these situations. All pavers -- brick, concrete or stone -- must be laid on a firm base of gravel and sand or, in extreme conditions, concrete. The first thing you must to before installing pavers is assess the ground. Use a long board and a level to determine slopes and valleys. Draw a diagram showing major changes in the area where you will work.
Build walkways on unlevel ground by accommodating to the terrain. Incorporate slight slopes -- some drop will help drainage. Design around major obstacles, like big rocks or deep drops. A curving walkway may have more visual appeal. Use steps or terraces on steeper slopes. Build steps on steep slopes about 1 foot wide and 1 foot high. Make terrace steps on lesser pitches, with long gentle slopes leading to short steps. Secure step edges by turning pavers sideways or on end. They must be solid enough to retain the ground. Lay flagstones as individual stepping stones down a slope.
Assess the terrain for a patio. Find out if humps hide boulders or other solid elements. Check dips and valleys to see if they result from a leaky drainage pipe or are natural drainage depressions. Remove boulders, move the patio away from them or incorporate them into the patio, depending on size and other conditions. Replace any leaky drain pipes. Divert natural drainage to other areas -- the water must be eliminated, so it does not flow over or under the patio surface. Use a shovel to make swales, gentle depressions in a yard, to change the drainage pattern.
Level a patio on extreme terrain with retaining walls on one or two sides. If the slope is extreme, put a retaining wall on the down side, made from paver bricks or blocks, and another on the opposite side. If the pitch is moderate, a single wall may suffice, with one side level with the ground. Build these walls with mortar to make them solid and to hold the weight of dirt, base and pavers behind them. If the walls must be more than 1 foot high, build in steps at entry points.
Excavate the paver area with a shovel or excavator. Dig 6 inches deep for walks, patios and other paving that will not bear heavy weights. Dig at least 8 inches for driveways, and deeper for any that will handle big boats or other heavy vehicles. Lay gravel first, 2 inches for walks and patios, and compact it firmly. Use medium gravel, 1/2 to 3/4 inch. Start with larger gravel for driveways, then add a smaller course. Finish the base with at least 2 inches of medium sand. Do not use coarse construction sand or fine mason sand.
Smooth the sand base by moving a 2-by-4-inch board across it. Jiggle it side to side to set the sand firmly. Lay bricks or blocks in any desired pattern, but always alternate seams and gaps. Set flagstones to fit the outline of the patio; these will be of random width and length. Use a level to make sure the surface is level. Tap pavers firmly into place with a rubber mallet.
Finish any patio, walk or paved surface by sweeping sand into the gaps. Use polymeric sand, which has a binder that seals joints after wetting, for a stronger installation with less likelihood of weeds penetrating.
Put a layer of landscape fabric or plastic before laying the gravel base if grass and weeds are likely to grow up through the pavers. Always outline walkways with metal, plastic or concrete curbs to prevent pavers from shifting.