Pressure Treated Wood Q&A
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What is the difference between green pressure treated wood and brown pressure treated wood? I recently purchased a preservative that says "for green pressure treated wood." I have a 5 year old PT deck, so is this the product I want to put on it?
Fresh PT wood arrives at the lumberyard green (in color) right from the factory, but over time weathers to a gray color. Some stain and sealing products will not work on new PT wood because of the high moisture content caused by the manufacturing process. See our article on PT wood in the article index for more info... http://www.naturalhandyman.com/iip/infxtra/infpre.html
If your deck is over a year old, it has sufficiently dried out, so you can use any exterior stain or preservative with confidence, whether it is intended for PT wood or not!
The old floor on my outside wooden deck is in very bad shape. I am unsure whether to refinish it (which would require stripping and also replacing quite a few rotten boards) or replace the entire deck surface. It is currently made from 2" thick by 6" wide Douglas fir planks. I like the look of cedar, but the lumberyard suggested I consider pressure-treated wood and a product called TREX, which is a synthetic wood, as alternatives. Apparently there are a lot of choices out there. Do you have any comments concerning the different options?
Cedar is a fine natural decking product and many people prefer it for aesthetic reasons. Cedar, like the other naturals decking material redwood, does not shrink appreciably or warp. It has a long life and a natural resistance to insects and fungus. However, this resistance is not permanent and the actions of the sun and weather will eventually take a toll on the exposed surfaces. Therefore cedar decking should have an annual application of a clear sealer for maximum life. Of course, it can also be stained or painted.
If you would prefer a tougher decking with a longer life than cedar, two options are pressure treated yellow pine or one of the synthetic decking products such as TREX or plastic lumber. Pressure treated wood decking can be purchased in two thicknesses… nominal 2" thickness (actual 1 1/2") or 5/4" thickness. Pressure treated (PT) wood will not rot BUT should be sealed annually to protect it from the weather and the sun. Over time, unprotected PT wood tends to crack and splinter without this added protection. Since PT wood can shrink and twist as the preservative evaporates… fresh PT wood is installed while still somewhat "wet" with preservative… it is not uncommon that a few deck boards may need to be replaced within a few years of installation. This twisting can actually pull nails and split boards! To minimize these problems PT wood should be sealed immediately after installation with a special PT wood sealer. This slows down the evaporation and thus minimizes shrinkage. If you plan of using a stain or paint, it is wise to give the surface at least six months after the initial sealing for proper adhesion.
TREX boards, available in 5/4" and 2" thickness', are composite products made from 50% recycled plastics and 50% real wood fibers. This combination makes TREX somewhat more stable than plastic lumber (at a given thickness) and more durable than any 100% wood product since it is virtually impervious to moisture. TREX is not rigid enough to be used as a structural support… it is strictly for decking purposes. TREX does not require any preservative or treatment and weathers to a gray tone. Though not necessary, it can be painted or stained if desired… but this will add to your maintenance chores! TREX is available at most lumberyards and some home stores.
Plastic lumber is made from 100% recycled plastic and is available 1" and 2" thickness' for decking, and is also available in a 1" tongue-and-groove style. Plastic lumber is not only available as decking… an entire deck can be built from plastic lumber components! Plastic lumber is totally impervious to moisture so no sealing is necessary. It is available in a wide range of colors, which is good because it does not hold paint or stain well. Finally, since there is no toxic component as with PT wood, it can also be used indoors in showers, damp basements, etc. One downside is that this product is less widely available than TREX or the other wood products.
One critical issue in choosing a retrofitted decking material is the "center-to-center" (c-t-c) distance between the supporting floor members, or joists, of your existing deck. Every decking material has a maximum c-t-c distance for adequate strength without excessive flexing. Cedar, PT wood and TREX in 5/4" thickness have a c-t-c maximum of 16. 2" thick TREX and PT wood can be installed with a maximum c-t-c of 20". Plastic lumber of one inch thickness requires a maximum of 12" c-t-c because it is not as rigid as PT wood or TREX. However plastic decking is available in 2" thickness that can be used on 16" centers. Keep in mind that if your decking is diagonal, you may need more reinforcement under the decking since the actual center to center may be 20" or more.
Another critical difference between these products is in the installation. Though all products can be installed using screws or nails, there are differences in each product's reaction to temperature changes. Cedar does not shrink or expand significantly so board spacing during installation remains constant. Pressure treated wood tends to shrink as the moisture from its chemical treatment evaporates, so most installers leave no gaps between the boards… shrinkage will take care of that! Both TREX and plastic lumber will expand and contract with temperature changes, so allowances have to be made in positioning the boards to allow for these changes… or else the decking may buckle! The temperature during installation is also important… installation at low temperatures requires more initial spacing than installation at high temperatures.
All the decking products mentioned can be installed with decking nails or screws, though the high-tech pullout-resistant nails used for PT lumber are unnecessary for the other products
I'm building a platform out of pressure treated wood. The
dimensions are 17' X10'. This platform is to have a pre-made
storage shed placed on it. I estimate that this platform will be
required to hold about 2,000 lbs of weight. I was wondering if I
frame the platform with 2" X 4" PT. and insert blocking
every 16" on center, will this be sufficient for this amount
of weight? Or, should I use 2" X 6" PT? Thanks for time.