Before the advent of mass production, most furniture was largely handcrafted by artisans. Of course, time has moved on and construction techniques, mechanical tools, and methods have advanced significantly. But in choosing outdoor furniture, it's very important to take note on how the particular item is assembled, how the joints are made, what fixings are used, the strength of the individual components and the quality of the finish.
For commercial outdoor furniture, which needs to withstand not only the weather but also mistreatment and neglect, the centuries old joining method of mortice and tenon is still generally preferred. A well-made item of furniture, with mortice and tenon joints will be solid, with tight joints and will last for years. But of course the extra time and care taken in this method of construction means the price will inevitably be higher of the furniture item.
To speed up construction and keep costs down, allot of furniture is now constructed using a dowelled joints. Whilst not as strong as traditional mortice and tenon joints, a dowelled joint can give many years of good service. In fact a lot of furniture may use mortice and tenon joints for the main structural elements but dowels for the more decorative elements in the design - a perfectly acceptable compromise. Of course any adhesives used should be water resistant, something that is not really possible to check, but generally this does not seem to be a problem in practice, except maybe in really low cost outdoor furniture.
For added strength, some makers will combine brass fittings with dowelled joints to ensure the dowelled joints are pulled together and kept as tight as possible.
The cheapest method of construction uses metal fixings only. Often these are used with kit-set or knock-down self assembly furniture, as it allows the homeowner to save more money by assembling the product themselves. The downside is that such furniture is generally not as strong and involves regular tightening of the fittings, as they tend to bed into the wood with continual use of the furniture. Also inferior quality fittings may be used which are neither made of corrosion resistant metals such as brass, nor have a high quality plated finish, so can be subject to rusting or other corrosion at quite an early stage.
Another less obvious problem with tables in particular, is swelling of the wood. As wood generally expands at a different rate in its longitudinal and tangential planes, this means that as the timber gets wet or dries out, unsightly gaps can occur at joints, or in the worst cases, the timber twists out of shape, if the maker has not taken sufficient care at the design stage. You need to take care for example with some wooden table tops, if the middle of the table is a more complex design with elements running both straight and perpendicular. Most manufacturers will leave small expansion gaps at the end of the longitudinal wood sections to allow for some expansion and contraction. With some more stable wood species such as teak, this is typically not a problem, but with some other species, expansion in both directions can be significantly different and problems can arise.
Take note also of the finish of the piece. With certain wood species, the grain of the timber can be rather coarse, so unless the edges of the piece are sanded well, it's possible to get splinters. Take particular note of the end grain. Many manufacturers apply a special oil coating or wax to the end grain to prevent the ingress of water and help to prolong the life of the furniture. Most manufacturers will apply some type of initial protective coating, although this is generally a rather basic coating which tends to enhance the colour of the wood rather than contributing to any particular preservative properties. To ensure a longer life, it is thus recommended that you give your furniture a further coating with a good quality decking or furniture oil very shortly after you purchase the item, and certainly within the first six months of its use.
And so, in conclusion, when looking at purchasing outdoor furniture, the important points to consider (apart from the durability of the wood species) are the type of joints, the thickness of timber used, the quality of any metal fixings and the actual design aspects of the particular piece.
