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Question DetailsAsked on 12/11/2014

what type of wood preservative is best on pressure treated wooden fence posts?

I am planning on installing a wooden stockade fence in the spring. I would like to know what type of wood preservative I can use on the wooden posts to be under ground. I have heard different answers ranging from none to driveway sealant. Should I purchase my posts at a home center or at a lumber yard?

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I wonder why a stockade fence - unless you are planning on staving of herds of buffalo or hordes of zombies, in which case you need about 5-6 foot embedment and 8-12 inch posts rather than normal 3-4 foot embedment. The problem with stockade fences is two-fold - every upright piece is embedded in the ground say 3 feet, so you are buying almost 50% more wood than you need for a normal fence. Also, all that extra material is in the ground, so needs to be protected from rot - or rots away faster. Perhaps the issue is your terminology - stockade fence is posts (usually raw wood tree trunks) drilled or driven into the ground, like a frontier fort. Post and plank is the typical cedar wood fence you see everywhere - google this search phrase for photos or lots of different - images of types of wood fence
My recommendation - go with normal post and plank fence with posts in the ground every 6-8 feet, cross-bars near top and bottom to nail the boards to and normal upright 2x6 or similar planks with whatever spacing or shadow-box effect you want down to within a couple of inches of the ground but not touching. If you have to have tight ground contact to keep a small animal of gdigging dog in, then add a line of sacrificial ground-contact treated timbers or concrete curb trenched in at ground level and run the planks down overlapping that, so their bottom ends do not prematurely rot. The longest-lived post will be creosoted (which stays sticky and smelly) or pentachlorophenol or CCA - copper chromium arsenate, but these are illegal in some states and for sue in most areas subject to stream flooding or running surface water; or ironwood and similar very resistant tropical woods. Next best, excepting the exotic tropical woods and heart redwood, would be ground-contact copper treated wood (the green stuff (copper napthalate or copper napthenate or similar), not the brown Wolmanized you get a box stores) - preferably for the posts as well as for the horizontal members where you have wood-to-wood member contact that can stay damp for a long time. It is possible to restain this a dark color and in a few areas get it in brown from the mill (usually special order), or buy brown-stained copper napthalate (or similar mineral spirit or naptha based products made to touch up cut ends). Either way, recoat the in-ground portion and all cut ends - I recoat with two coats about 4 hours apart for the in-ground part plus about 6 inches above ground level, if not entire post, and one new coat on the horizontal pieces. Ditto on field boards if not cedar. The reason for the recoating is the current treatment "standard" has been watered down dramatically in recent years, to about 1/3 what the old chemical retention used to be, plus the chromium and arsenic compounds that were in the old ground contact wood has been taken out because of eco-hysteria, so the product is less thoroughly impregnated in the wood AND less effective chemically against both insects and rot/fungal attack. You can see it if you cut a piece of treated wood - the green treatment used to penetrate to the core except at the densest knots, now you are lucky if it penetrates half way into a 4x4 or even sometimes not even halfway in a 2" piece of material. Yes it costs more in laborto retreat (but not bad if laid out on blocking and sprayed) and takes some drying time for the above-ground treated boards before erection, but will last another 10-30 years beyond the normal 15-20 year life of ground-contact treated wood. From what I have seen at box stores, I would definitely buy it at a lumber yard - not only higher quality (better treatment, straighter grain, less open knots and fewer warped pieces) but generally cheaper too. Be sure to buy kiln dried wood that is not yard wet in storage, otherwise it will not take the treatment well and will warp badly as it dries. One other thing - for longer life and less splitting of the support members, using cad-plated or stainless screws or hot-dip galvanized Teco nails with galvanized Simpson metal brackets instead of direct nailing or bolting the horizontal members to the posts will give a longer life too - both longer fastener life, and if properly installed with a very slight gap between beam and post (or beam and bracket with some brackets) provides an air gap so the ends of the beams do not rot out prematurely, because they can dry. When using brackets be sure they use ones that hold the beams tightly, and also allow you to remove and replace beamsif necesaary down the road without having to remove all the face boards to get at the screws/nails. Faceboards stay on MUCH longer if applied with cad-plated or stainless screws too - both because of longer life than galvanized nails or normal galvanized or cement coated deck screws (which also make almost immediate stain streaks on the boards below them) but also they have larger heads than nail-gun nails, so don't get knocked/pulled or frost-jacked off so easy. This is particularly important if you have energetic kids or large dogs (or a goat or sheep). One other suggestion - whether or not you stain/seal the field boards (generally not necessary with cedar or redwood unless you are trying to retain the natural color), you should make sure to keep the bottoms of them off the ground so water can drip free and evaporate at the bottom, and seal the top with a stain/sealer or clear sealer to prevent water/snow falling on the tops from soaking into the boards - can make quite a difference in field board life. One other tip - if concreting posts in, make sure they pull the posts up a couple of inches after the concrete is in, t be sure the bottom is concrete protected too, not in contact with the ground, otherwise it can rapidly rot out from the bottom up. If in an area with ground-nesting yellow jackets, hornets, termites or carpenter ants or such you definitely need ground-contact treated posts. And bear in mind, hornets and yellow jackets LOVE fir and cedar fibers to build their nests with, so untreated fences of those materials can actually attract a lot of them in the summer nest-building season. Of course they build their nests near easy sources of building materials, so to protect kids and pets you may need to use all treated wood, or stain/seal the fence after it is built to reduce this. Going with the above suggestions will generally increase your cost 20-30% over base level cost depending on whether you replace concreting in the posts with the treatment (concreted is longer life in general but not required in most areas unless fence is over 6 feet high or a very high wind area, and concreted and treated longer still). However, assuming you consider your house as a live in forever situation, can up to double its life. of course, if looking at moving in a few years then you might opt for the low-budget version, even so far as to go with wolmanized wood (which can still be retreated for the below-ground part). but muy recommendation - do NOT use plain pine - will look shabby inno time. Plain cedar, redwood (the most common but more expensive woods) as well as hemlock/fir (mixed forest grade) and douglas fir make decent fences but will warp more than the first two. You can find more suggestions and thoughts on different types of fencing, and typical costs, in the Home > Fencing link in Browse Projects at lower left.

Answered 4 years ago by LCD




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