Choosing Materials for Arches and Pergolas
If you are building an arch or pergola from scratch as opposed to buying one in kit form, then it will help to familiarize yourself with the basic construction materials. Most building supply stores have displays that are well set out, clear sales literature, and expert advice readily on hand, which means that you should soon gain sufficient knowledge of the various products and quantities required for you to get started.
Concrete and Mortar
Most large custom-built arches or pergolas need a footing to hold posts firm, or as the foundation for bricks. These are formed from a layer of crushed stone topped with concrete — a mix of aggregate (mixed grades of gravel), cement, and water. The mortar used between bricks is a mix of sand, cement, and water. You can prepare both concrete and mortar yourself or buy prepared mixes from a supplier.
Quantities and Mixing
Until you gain some experience, it is easy to under- or overestimate amounts, so ask suppliers for advice. Concrete for footings is often a mix of one part cement to six parts aggregate mixed with water. Mortar for brickwork is one part cement to five or six parts builder's sand, mixed with water and plasticizer (an additive to make mortar easier to work). Keep in mind that large building suppliers display detailed information to help you choose materials. Ask for kits and heavy, bulky construction material to be delivered to your door. For small projects, buy small prepackaged mixes of concrete and mortar.
Hardwoods may be used for construction, but they are expensive and more difficult to work with than softwood, which is most commonly used. Softwood for garden structures is supplied already pressure-treated with preservative. It may be bought as sawn lumber, which does not have a planed finish, or planed all around. Planed lumber is more expensive but more suitable if you wish to paint or stain your pergola.
Rafters that are notched and nailed onto overhead beams not only give a stronger fitting but also look more pleasing than ones that have simply been nailed into place. A T-joint joins two pieces of wood at right angles to one another. A half-lap joint is similar, but at least one notch is at the end of the wood. A sturdy and streamlined effect can be gained by cutting a notch in both the beam and rafter so that they fit flush in a halving joint. To make a joint, cut each side of the notch with a saw to the desired depth and make a series of saw cuts in the area of the joint with same depth. Measure and mark where your joint should be, then carefully chisel out the notch with a mallet and sharp wood chisel.