Furniture Making Blog

An Introduction to Outdoor Furniture

I f you've ever made a picnic table or a planter, you know that the art of making "outdoor" furniture is unique, different from any other type of woodworking. The methods and tec hniques are a careful blend of cabinetry and carpentry — a finished outdoor furniture project looks like a piece of furniture, but it's built like a house.

The reason for this, of course, is the weather Out of doors, your project has to survive extreme changes in temperature and humidity. When building outdoor furniture, you have to plan ahead for the distortion and decay that happens when wood gets hot, cold, or wet. And — this is just as important — you have to provide a way for the wood to shed the rain and dry quickly to prevent as much of that distortion and decay as possible.

Outdoor Furniture Joinery

Water tends to collect wherever two pieces of wood join together. Consequently, outdoor furniture hits as few joints as possible, and those joints are usually very simple — butt joints, lap joints, maybe an open mortise and tenon. This decreases the surface area of any board that is in direct contact with other boards. In other types of woodworking, the purpose of joinery is to increase the board-to-board surface area, so that you get a stronger glue bond.

Outdoor furniture joints are also cut with a good deal more "slop" than what you may consider acceptable. A good outdoor lap joint should have of slop to allow the wood to swell in wet weather, and to let it dry out when the rain stops. Again, this is in direct contrast to other forms of woodworking, where a sloppy joint will be a weak joint because the glue won't bond properly to all the surfaces.

One reason that you can safely use sparse, sloppy joinery in outdcx)r furniture is that the parts are rarely glued together. Out in the weather, wood expands and contracts enough to break even "waterproof" glue bonds. Only small parts that barely swell and shrink, such as screw plugs and dowels, can be successfully glued in place. larger parts must be held together with hardware — nails, screws, and bolts. As in carpentry, it is the hardware, rather than the joiner)', that holds the finished project together.

Another reason is that the joiner)'does not contribute much to the overall strength of the project. Strength is pt^vided by design — wo adjoining parts are often braced with a third part. Again, this is similar to carpentry, where a builder always tries to "complete the triangle" to make the structure stronger and more rigid. If the parts properly brace each other, a sloppy joint won't wobble or work itself loose.

When it comes right down to it, the joinery in outdoor furniture has little to do with holding the project together. The joints simply make the pieces fit in such a way that they won't collect water. Hardware and design do the actual "joining."

Outdoor Furniture Materials

While it's important to keep the wood in an outdoor furniture project as dry as possible, water is not the enemy. Wet wood is just its strong as dry. Hut wood that gets wet and stays wet becomes a fertile breeding ground for bacteria. The bacteria digest the wood fibers, reducing them to dust This is what causes the wood to decay and rot.

If you can prevent the bacteria from growing, you can keep the wood strong — even though it stay's soaked. Certain types of wood resist bacterial growth, and will last longer out in the weather than other varieties. In order to make your outdoor furniture projects last, it's important to pick the right wood. No matter how carefully you make the joints, the areas where the parts touch will tend to collect water.

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Absolutely the best woods to use art the tropical varieties. in particular teak and mahogany. These woods are saturated with natural oils that either repel the water or make the wood fibers inhospitable to bacteria. These oils are part of the tree's natural defense against the moist, humid environment of the tropical rain forests.

Unfortunately, because teak and mahogany have to be imported, they are expensive. There are several domestic varieties that are almost as rot-resistant as the tropical wckxIs and are somewhat less expensive. These are redwood, cyf/ress, and all types of cedar

Of these, the best is Atlantic white cedar (sometimes called "juniper''). White cedar becomes even more rot» resistant after it's cut and cured. In the early 1800's, shingle-makers along the east coast "mined" fallen cedar trunks from swamps and bogs. They found that the dead trees made Ik iter quality, longer-lasting shingles even though they had been buried in mud for scores of years. White cedar is also one of the few woods that is resistant to the ravages of salt water. It's a bit hard to find — particularly in the West — but if you live on a coast, it may be worth the search.

The least expensive alternative for most of us [»pressure-treated lumber. This is domestic pine that has been poisoned with various preservative chemicals, so that bacteria won't grow in it. To make sure that the wood is poisoned all the way through, it's placed in a "retort" or pressure chamber. All of the air is pumped out. taking with it most of the moisture in the wood. Then the retort is fltxxled with preservative and pressurized to at least

175 pounds per square inch. This drives the chemicals deep into the wtxid.

When purchasing pressure-treated lumber, there are two things to look for. First of all, some pressure-treated lumber is more rot-resistant than others. Treating mills work with diff erent solutions of preservatives, and consequently some wood retains more preservatives than others. Hie American Wood Preservers Bureau ( AWPB) has a rating system for the degree of "retention," and most mills stamp this rating onto their lumber. A rating of l.P-2 indicates low retention; this wood should not be used in direct contact with the ground or water. For wood that sits on or in the ground, you need a rating of l.P-22 or better. (See Figure 1.) For most outdoor furniture projects. LP-2 lumber is adequate. However, if the project will rest on the ground or in an extremely wet location, use I.P-22.

Secondly, pay attention to what sfxiies of wood you're buying. This, too. should be stamped on the lumber. Not all woods arc well-suited for pressure-treating. Southern yellow pine, red pine, and ponderosa pine all retain preservatives well. Douglas fir. spruce, white pine, and most domestic hardwoods do not. Don't Ik- fooled by lumber that's labeled "southern pine." litis is not southern yellow pine; it's just another name for white pine.

Once you've chosen a rot-resistant wood to build your outdoor furniture project, you'll then need to select rust-resistant hardware. Not only docs water create a fertile environment for bacteria; it also promotes the corrosion of many metals. Common nails and untreated hardware

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2Common naiis and hardware corrode in the out ot doors, staining your protect Use galvanized or plated hardware instead

1/Look for the A WBP stamp on pressure-treated lumber. A rating otLP-22 or higher means the wood can be used in direct contact with the ground

2Common naiis and hardware corrode in the out ot doors, staining your protect Use galvanized or plated hardware instead vnin iumiu i hon iooitixm >h i'ltlnituri!

will rust quickly, staining the w<xhI with long, dark streaks. Eventually, the nails and hardware will disintegrate. (See Figure 2.) lx>ok for nails and hardware that have been "galvanized." This means that the metal has either been dipped or plated with a zinc alloy to resist corrosion. Most common screws are made from zinc chromatc, a material that won't rust when exposed to fresh water. However, if the project will be used near salt water, purchase brass or stainless steel screws.

A Few Tips for Making and Finishing Outdoor Furniture

As you build outdoor furniture, here are a few general tips to help make the work a little easier and the finished project last a little longer:

• When you place boards side by side, as on a table top, leave V»"-lA" space between each lx>ard to allow the wood r(x>m to swell and shrink. Wood will expand up to '/«" across tfx'grain for ever)' 12" of width. Expansion with the grain is negligible.
• If you attach the board with nails, drive each nail at a slight angle. Vary this angle back and forth with every nail. ITiis "hooks" the parts together.

Whenever possible, try to orient a board so that the "bark side" faces a/) in the completed project. (See Figure .V) This helps the lumber shed water.

• If at all possible, never attach a board with the end grain facing up, exposed to the rain. Cap it, turn it on a lathe, or cut it at an angle to help the end of the board shed water.
• Seal the bottom ends of legs with melted paraffin wax or spar varnish to keep them from soaking up water.
• On those few occasions where you need to glue a small piece in place, use waterproof epoxy or resorcinol glue. Epoxy usually dries clear, and resorcinol cures to a dark brown.
• If you intend to apply a preservative stain or paint to the project, apply the first coat before you assemble the parts. This ensures that all the surfaces will be coated.
• You can paint or stain pressure-treated lumber, but it's wise to wait a month or so and give the wood a chance to dry out. There's no need to keep it in your shop while it dries; the lumber will dry well enough for painting out in the sun.
• Avoid finishing outdoor furniture with polyure-thane. Most brands of poly-U dry too hard to expand and contract with the w<x>d when it's placed out of doors. After a year or so, the finish will peel off. Use spar varnish or a 1:1 mixture of spar varnish and tung oil instead.
• If you plan to finish your outdoor lurniture project, cedar and cypress accept finishes better than other species. Kedw<x)d, white pine, and sugar pine are also g(x>d choices for finishing. Western yellow pine and hemlock are okay if the surface is prepared and primed properly. Southern yellow pine, fir, and larch are not good choices. They may cause the paint to peel and crack after relatively short exposure to the weather.
• The denser a w<xxl is, the harder it is for that wood to accept a finish. For that reason, avoid wixxl with wide bands of dense "summerwo<xT (summer growth). These are the dark lines in the annual rings. If the summer-wood is present in narrow stripes, with wide bands of lighter "springwood" ( spring growth ) in between, then you can be relatively sure the wood will take a finish well.
• Quartersawn and rift-sawn boards take a finish much better than plain-sawn. However, few lumberyards carry quartersawn or rift-sawn stock anymore. When you do find it, it's very expensive. To make the finish last longer on plain-sawn boards, turn the bark side up or out, where it will be exposed to the weather. The finish adheres better to the bark side of plain-sawn hoards than it does to the pith side.

3 Assemblo projects so the boards are bark side" up. wherever possible This helps shed water and prevents cupping To decide which side of a board is the bark side, look ¿it the end grain

roind hgnh tabu and benchbs

Round Picnic Table and Benches ound picnic tables arc so much more conducive to good conversation than ordinary picnic tables. Each person sitting at the round table has an unobstructed view of everyone else. Consequently, no one feels left out or ignored. Unfortunately, most round picnic tables have a drawback that sometimes disturbs the conversation. Usually, each bench seats two people. If someone wants to sit down or get up, at least one other person has to move.

This particular table and bench set solves that problem. Each person has a bench all to himself. There's no need to beg anyone else's pardon if you need to get up for a moment. And there arc eight seats, so there should be no lack of seating, even for large gatherings.

roind hgnh tabu and benchbs

round picnic ta1hj; and benches