Pressure-treated wood is a type of lumber that has been chemically treated to resist rot, decay, and termites. It is typically used in outdoor projects, such as decks and sheds, and can weather well below and above ground. The International Building Code requires this treatment, as it helps prevent moisture from reaching the wood.
There are two main types of pressure-treated wood: above-ground and ground-contact. Above-ground wood is made from softwood lumber, typically southern yellow pine, which is chemically treated to resist rot, decay, and termites. The boards are not naturally resistant to insects and rot, but they can be treated with linseed or tung oil, which work by penetrating the wood and seeping into the grain to provide protection. Linseed and tung oil are naturally occurring seeds from the tung tree.
Pressure-treated wood is ideal for outdoor use, as it is not naturally repellant to insects and rot. However, not all pressure treatments are created equal, and the two main types of PT lumber are above-ground and ground-contact. On average, it is recommended to treat outdoor wood every 12-18 months, making it an annual job.
In most cases, treated wood is ideal for outdoor use, while untreated wood is best for indoor use due to manufacturing processes. If the wood is above grade and will dry out during rainstorms, cedar should suffice. However, pressure-treated lumber should not be used for anything that comes into routine contact with skin, so pine and other natural woods are recommended.
In summary, pressure-treated wood is a strong and reliable option for outdoor projects, especially for structural elements like decks and sheds. It is important to consider the weather and the type of wood used when selecting a pressure-treated wood for your project.
📹 Some TREATED LUMBER Rots Faster Than Others! WHAT’S THE DIFFERENCE?! (Ground Contact Vs. Non-GC!)
Did you know that there are multiple varieties of TREATED LUMBER? And that some treated lumber will rot much faster in certain …
Is untreated wood OK outside if painted?
Untreated wood can survive outdoors but requires regular maintenance to maintain its integrity and prevent pest damage. Treated wood can last up to twice as long as untreated wood due to its enhanced resistance against rotting and insect infestation. Researching treated vs. untreated wood is crucial for making a house feel like home and avoiding issues or regrets down the road. Regular maintenance, pest prevention, and regular maintenance are essential for a long-lasting and comfortable home.
Should exterior wood be pressure treated?
Pressure-treated wood is suitable for all outdoor projects, provided it is not naturally resistant to insects and rot. There are two main types of pressure-treated lumber: above-ground and ground-contact. Above-ground lumber is suitable for outdoor applications at least 6 inches above ground, such as deck railings, fence pickets, porch flooring, and joists and beams. Ground-contact lumber, with a higher chemical concentration, is better protected from soil, vegetation, rain, moisture, and other agents that can cause decay and rot.
It is used when wood comes in contact with the ground or is installed less than six inches above the ground, when it will get wet frequently, when air circulation is poor, or in tropical climates. Common uses include structural posts, garden boxes, wood foundations, and landscape walls.
Can you leave wood unfinished outside?
In order to safeguard outdoor unfinished wooden furniture from the detrimental effects of sunlight and precipitation, it is recommended to utilize protective covers or to relocate the furniture indoors during the summer months. In order to protect the furniture from the effects of winter weather, it is recommended that an additional layer of protective finish or wax be applied.
Will untreated wood rot outside?
If your outdoor wood is untreated, it’s crucial to treat it immediately to prevent rot, fungi, and weathering. Use a wood preservative, either a wax-enriched preservative or a wax-free preserver, for an all-round coating. If the wood is dip-treated or paint-stained, it may fade after 6-12 months and provide less protection against the weather. Treat this with a wood stain, paint, or preserver. You can treat un-treated or dip-treated wood at any time.
Why is pressure-treated wood bad?
Metal salts found in PT lumber can cause skin ulceration and festering due to their presence on the surface. Sawdust from cutting or sanding wood can also contain arsenic, which can cause short-term health effects like headaches, dizziness, muscle spasms, and a garlic odor. These symptoms vary depending on the amount and duration of exposure, and should be reported to the Occupational Health Clinic or a doctor. The hazards associated with PT lumber are significant and can be harmful to workers.
What are the disadvantages of pressure-treated wood?
PTP (Plastic Toppered Timber) is a popular choice for decks and porches due to its resistance to the sun and its ability to change color, crack, warp, and cup. It may also be susceptible to mold, rot, and insect damage. However, with proper care and maintenance, PTP decks can have long, beautiful, and useful lives. Regular wetting down is crucial, especially if the deck spends many hours in direct sunlight. If an irrigation system is in place, it can be included in the timer’s cycle.
Stripping, cleaning, and staining with UV-protective exterior wood products is also essential for protecting the investment. For decks with average sun exposure, once a year is an adequate frequency. You can choose from transparent sealers, semi-transparent or opaque stains, or exterior paint. Semi-transparent stain offers good protection with a slight color enhancement, while opaque stains offer the same protection but with more noticeable wear and tear from foot traffic.
Does all exterior wood need to be treated?
Building codes dictate where treated wood can be used, typically in areas with moisture risk. Outdoor wood should be pressure-treated, while interior design wood like cabinetry or furniture doesn’t require the same level of treatment. The AWPA states that the type of wood treatment depends on its usage, and extra steps are needed to finish pressure-treated wood in indoor or outdoor projects that may come into contact with humans or pets.
The chemicals in pressure-treated lumber are pesticides, so handling them with the same precautions as any potentially hazardous material is crucial. Wearing gloves and face protection is recommended, as sawdust from cutting the wood can be irritant.
How long will untreated wood last outside?
Untreated wood is less durable than pressure-treated lumber due to its lack of protective chemical preservatives. It deteriorates quickly when exposed to elements like rain or snow, often within a few years. However, for indoor use where exposure to extreme weather and pests is minimal, properly cared for natural woods can last indefinitely. The choice between treated and untreated wood depends on project needs, location, budget constraints, and aesthetic preferences.
What is the difference between outdoor wood and pressure-treated wood?
Pressure treated lumber is not as strong as regular wood, but it resists elements better due to chemical preservatives added. This helps maintain its integrity in conditions that would cause normal wood to rot. Front Range Lumber offers value and selection of quality treated lumber at competitive prices in Lakewood and Fort Lupton, Colorado. Lumber prices fluctuate due to market conditions, but they stock a wide selection of different types and sizes.
Should outside wood be treated?
In outdoor environments, untreated wood is susceptible to a number of detrimental effects, including ultraviolet (UV) radiation, silvering, greying, and moisture damage. These factors can collectively lead to the proliferation of mould and the deterioration of the wood through rot. To clean, sand, stain, and finish outdoor wood, it is recommended that an outdoor wood preserver be used to protect it from biological growth. It is further recommended that the wood be treated with the preserver annually or once a year, depending on the finish used.
Is it okay to use non-pressure-treated wood outside?
Non-pressure treated wood is generally not recommended for exterior structures, but cedar, redwood, and IPE are common species used for exterior decks due to their natural resistance to weathering. Cedar can weather naturally with minimal structural degradation, but requires annual sealing maintenance to maintain its original color and appearance. Low-maintenance decking options include composite, composite vinyl-capped, and PVC, as well as aluminum decking, which is a metal variation on plastic polymers. However, there is no “maintenance-free” decking, and there is no “maintenance-free” decking.
📹 Do Wood Treatments Really Work? UNEXPECTED RESULTS
3 years ago I set up an experiment to find out if wood treatments actually work to protect timber from rot, decay and wood boring …
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Swedish wood technician here. I work with VPT(Vacuum Pressure Treatment) chemicals and processes. When treating at home you will only get a surface coating. The industrial processes use vacuum and pressure to penetrate into the sapwood. Unfortunately for guys in UK, you dont have any third party inspections making sure that the timber actually is use class 3 (above ground) or use class 4 (in ground). In the nordics we have the NTR quality scheme. This makes sure that the timber both contains the correct amount of preservative per m3 (retention) and that all of the sapwood is penetrated (for pine). UK is a market where some of the treaters takes shortcuts and the timber would not pass an external audit. The battens you selected was most likely use class 3 and makes them unsuitable for ground contact even if the treater was doing everything by the book
South African Wood Technician here! Much respect for setting up this test 3 years in advance! You might find that after a longer period the results will be even more in favour of the pressure treated lumber. We in South Africa also use the H1-H6 system as I’ve seen the Aussies state in the comments, most commonly used with CCA and Creosote, although some other options like ACQ are also available. The different treatment levels indicate different amounts of the preservatives used and also very strict standards and rules for the penetration of the preservative as set out by the SABS (South African Bureau of Standards). I did tests for a pole manufacturing plant as a student drilling core samples out of poles and measuring the depth of penetration of the preservative (in this case it was poles used in agricultural industry and treat to H4 standard because it would be planted in the ground and thus be in permanent contact with the ground) to determine if the process being used was still effective. After the results of my tests we altered the treatment schedule and made sure the moisture content of the poles were correct before loading the vacuum chambers. This had a significant impact on the penetration and thus the longevity of the poles. Remember whenever pressure treated timber is cut, one needs to re-apply treatment to the exposed area so as to not leave a gateway for fungus, rot, and insects to get to your untreated core! For anyone interested, more information about the South African Standards can be found on the South African Wood Preservers Association (SAWPA) website.
It’s well known that if it’s under water it lasts longer. I’m from The Netherlands and in Amsterdam you have a lot of old houses next to the canals, often they are build on top of oak pillars and they often are in perfect shape even after 100+ years due to fact they are in the ground surrounded by water. The main culprit that kills them is if water levels drop and oxigen reaches the wood, oxigen is the killer.
I work at a pressure treating plant and in the comment of you saying the moisture content is high is an understatement after we pull the lumber out of the pressure pot. It’s normally about twice to three times. It’s standard size. It’s unbelievable how much water it could soak up for about an hour, the lumber is like of waterfall with the amount that pours out of it even up to three days. It is still coming out at a pretty good rate. We normally keep the lumber on a drying pad for a week before it gets shipped out.
Just an observation by a 69 year old. I recently tore down an old shed on my property that was made out of pressure treated lumber that was bought, best guess in the 1980’s. That lumber which had been exposed to moisture and elements for all these years was in amazingly great condition. So much so that I took the time to remove old nails and salvage it for reuse. The wood was so hard, removing some of the nails was impossible. I don’t know how these boards were treated back then, but it is clear the treatment has lasted a lot more than modern lumber.
Not an expert by any means but my theory is that; the self wood preserver doesn’t penetrate deep into the wood fibres. Thus creating a water resistant film on the surface. This film seems to actually be acting to keep the moisture in the wood ergo accelerating the decay process. A similar thing can often happen in bricks plastered or painted in synthetic materials like gypsum plaster or plastic paints. Sure they partially create a barrier, but once the water is in it’s locked there with little opportunity to evaporate and ultimately making the bricks break up into powder. On that note Kieth – you’d probably really like a guy called Peter Ward on YouTube who diagnoses damp issues in old houses and helps resolve them! Great article bud! Keep it up!
I saw something on wooden ships.. When it came to the rate of degradation, parts of the hull that got submerged then emerged in a repeating pattern fared the worst. Parts of the hull that remained underwater at all times saw the least amount of degradation. You need water AND oxygen to rot wood quickly.
As a builder I have noticed the same problem with self-treated and even some painted wood items. The treatment keeps the wood from drying out once it gets wet — so it stays moist and provides a perfect environment for the funguses and microbes that feed on the wood — and it rots right out in a few years
I think you’ve proved that the sealer you are using is garbage. Any wood that touches the ground should have a preservative that has copper in it, you can get the same stuff they use for treated wood The treatment you used is probably not rated for ground contact. Big difference between a deck sealer and one used for burying in the ground.
My grandfather informed me that sealing ( he referred to wax /oil coatings) all faces of the wood allows water to permeate in over time but allows very little to escape back out. Creating a warm and wet haven for microbes, fungi and bugs. He told me to leave the non weather exposed side of the wood bare or burnished with no preserver applied, “To let the wood breath and dry out”
UK Farmer here… only posts I use have been pressure treated with creosote or left soaking in it for > a year. You can buy creosote from ag’ merchants in 40 gallon drums. Wood quality is important, far north tight-ringed pine is fine. Heart of oak, chestnut & acacia are good but pricey – NOTHING beats posts saturated with creosote. 👍
Can I just call out the level of production on this article, I’ve been perusal your content for years and the presentation to camera, cut pieces to tell the story along with the experimental narrative is top tier – Thoroughly engaging article, simple to follow and really professionally done. I’ve always been a little sceptical on self treating wood preserver. Built a log store (Picture in Profile) and used self treatment on some of the cut ends of the structure which have already shown signs of softness. I built the door out of floorboards but painted and soaked them in Smiths Penetrating Epoxy Sealer after a recommendation from a neighbour who owns a wooden boat and swears by it, the door is pretty much in the same condition 3 years later despite being open to the elements.
I replaced a deck I build in 1985 in June and there wasn’t a single rotted board in that deck. I actually left the joists in place and used trex for the decking. I dumped some of the scraps from the build behind my shed and those are still not rotted even after being in contact with the ground for all those years. The arsenic pressure treated wood is truly incredible.
I also have had similar results with wood treatment, but with the most popular US brand, which actually made the wood hold more moisture and rot faster than untreated wood. I am talking about Georgia yellow pine which is very dense and strong, so I was very disappointed in the treated wood. I had put on X3 coats, so that was not an issue here. Wow after only X3 years the treated wood was worse that junk. But thank you for doing this test.
Thanks for doing this – I must say I’m shocked how poorly the pieces you treated turned out. I have several sections of decking – factory pressure treated – that are +40 years old and are in great shape. They are largely protected from sunlight (north side of house). I also have a privacy fence I built +30 years ago (pressure treated) – my wife and I had several arguments over treating/staining the fence – I was adamant the fence would not be stained. THere is a bit of warping here and there, but no sign of rot.
For the submerged, you’d need to submerge them separately in the future. The treatment from the pressure treated wood will get into the water and offer protection from organisms for all the wood. The reason pressure is used to get the chemicals in is because it would otherwise take a great deal of time for deep penetration. But since you soaked them for 3 years, you basically (I assume) distributed the treatment chemicals into the other wood pieces and to a deeper depth than you could with pressure. Very interesting results, and great result learning about the self-applied treatment. Very interesting that it’s essentially degrading the wood.
I have some interest in wooden boats and, in fact, built one twenty five years ago. It had two coats of oil paint and spent most of its short life upside down outdoors. Though recoated in year two, it had the beginning of rot by year four. I have seen a number of boat building articles where an orange coating has been applied. Do you know what it is? I would just like to add that these coatings are highly POISONUS ! I had a bad reaction several years ago, after removing the rotten bottom plates of walls built in the 1940’s. Thanks for the article.
Very interesting info on the technicalities of pressure treatment. We made raised beds using treated wood, where we grow veggies, so good to know we’re not eating some sort of arsenic. We also never bothered with additional treatment on the sawn ends – they seem to be holding up very well (into maybe their fifth year now), but who knows what’s hidden under the soil… My uncle was crazy for creosote. He had a bunch of huge pigeon lofts and everything got a coating of it. I think even his bicycle got a couple of coats. Surprising results on the tests!
We moved into our current house 31 years ago, over that time I’ve replaced the fence panels on the left side of the garden once, 3 years ago. The original panels had lasted at least 28 years, Whereas the fence on the right has been replaced 3 times now. The difference between them was that the previous owner had diligently creosoted the left side panels regularly. I also did a few times as he left a large tin of the stuff. But when it ran out I couldn’t buy any more. Also our side gate is still the original one from when the house was built 63 years ago, it was also heavily creosoted up until my tin ran out. My observation from this is that creosote was very effective, even if a little unsafe!
I swore by creosote when I was younger, mostly because I liked the smell of it made a lot of garden furniture for my family and had found 4 big pre ban jugs of it in an allotment shed we cleared out the stuff I put creosote on is still going strong to this day (still smelling strong too) everything else has rotted away
Wooden posts will generally always rot / break at ground level. Yonks ago, we use to mix 50/50 old engine oil & Creosote to try and delay things a bit. There is another idea, a heat shrink plastic wrap type of thing. Put over the post at just above and below ground level and use a heat gun to shrink to the contour of wood. With wood being organic it’s going to rot at some stage ! Try using using solid plastic posts, as heavy as concrete, were being made from recycled HDPE or PET by a Dutch company.
As a non-professional person, i love working with wood and make my own stuff. i don’t let wood touch the ground but i do have large amounts of wood exposed to UV and weather. I have treated wood with many things in the last 20 years and i have discovered many interesting things. where can i send you some pictures with some explaining? thank you for you time doing this, pretty much confirms my theories of: only stain it to look nice or find something that really works.
Chromated Copper Arsenate – not available for residential use in the US since 2003. I have PT CCA wood used for various applications around the home, as fence posts, for the bones of a raised two level octagonal deck, and for replacement jambs on a two car garage before new tracks and garage doors were installed. All of these were installed prior to 1995. The fence posts were removed in 2008 as the use of the area changed. I was able to pull all posts intact out of the ground. After cleaning off the dirt, these could have been placed back on the rack and sold and no one would have known the difference. The garage door jambs still show no rot at the concrete apron contact points. The deck was stripped of its original cedar decking in 2009 and all PT CCA 2×10 joists exposed and inspected. There was not a single area of concern and the deck was then redecked with IPE. Since being able to work under the low clearance deck to rewire some lighting in 2023, I detected no rot in areas that I could access. I’ve since worked on some client’s projects that had PT (all installed after CCA) ground contact lumber that was either beginning to rot or was significantly rotted. All was replaced. Conclusion? You are buying an extremely inferior PT residentially classified product these days.
Goid article and discussion. Here in north America, if you use wood for a pier for a portion of a home over water pressure treated is not required as it typically will not rot. It lasts longer than reinforced concrete. Anecdotally they say that during highway construction in the backbay of Boston which was contructed of hundreds of thousands of trees set on end in the water and then covered with soil over 250 years ago they pulled out trees in tact with virtually no rot.
After this article, and reading the comments, It now makes total sense why that American TV show with the southern guy hauling logs out from the swamp was making such good money. The water was preserving untreated logs and milled timber that were a hundred years old. I always figured there was no way this stuff wasn’t rotted out with all that time soaked in the mucky water. It was so confusing.
The wood preserver you used requires a waterproofing overcoat otherwise it just washes out into the environment. I recently spent along time trying to get my head around the different options for wood treatment and this article has been useful in confirming what I had learnt. The simplest way of understanding is to think of treatments being split into two approaches: biocidal or water resisting. Many products are just one or the other. There aren’t many that do a good job of both. Barretine Wood Preserver seems to be the only one I could find but even that specifies that it is not for in-ground usage. I think I’ve concluded the best option is probably to just go down the water proofing route and use a silicone based treatment such as Roxil Wood protection liquid/cream. This is also less polluting to the environment. No biocide is needed if the wood is kept dry.
I was taught that the main purpose of treated wood is to prevent insects from eating it….NOT preventing the wood from moisture or sun. We would buy borate in powder form, dissolve it in water, and use a pump sprayer to soak untreated lumber. If you plan on putting lumber into dirt you’re going to need a moisture barrier like bitumen (black tar). You may have noticed wooden telephone poles have that black tar around the base.
One thing I can’t help but notice is that half the samples are at the end and exposed on three sides, while the other half are sandwiched in the middle of others. I think this accounts for why the ‘PT with cut end’ out performs the ‘PT with uncut end’ and probably also why the untreated out performs the self treatmented.
Cor Blimey Keith, a can of worms indeed! I’m faced with rebuilding our garden bench, the slats were at the ‘dangerous’ end of their life so this has raised my eyebrow. I’m considering a finish like a yacht varnish to really seal the wood. I’m getting on a bit and ‘constant’ maintenance is not my thing anymore. Thanks for this timely eye-opener, Keith and crikey, you were already in that workshop 3 years ago!
I would suggest revisiting the self treated lumber. Im unsure if anyone has pointed this out but the treatment you applied said to the leave the end grains in the treatment for 3 minutes. You said yourself you only dunked it. To follow that britians humidity level is fairly high with all the rain yall get, one hour may not have been enough dry time betwen coats.
I’m sorry, but you should have done a little bit more thinking about your experimental design. The boards on the end have more surface area exposed to soil than those in the middle. Why wouldn’t you separate them each by a few inches of soil? Your experiment would be far more useful and valid if you had. As is, your results are highly biased towards the inner boards.
With posts, the rot seems to occur where it meets the soil. You can get plastic sleeves which go around the post which are supposed to work well. The other thing I have always wanted to try, is what if I just painted/soaked the bottom 6 inches of each fence post where it meets the soil with old motor oil every year and tipped some around each post too. i.e. soaked the bottom bit near the soil surface in oil. Your experiments makes me wonder if fence paint preservative products are actually worth it if just bought to preserve fence panels?
i cooked an untreated pine timber in used motor oil, basically i deep fried it for about an hour. i’ve been using it as a block for my car trailor jack for about 5 years now and it shows no signs of rot. i get these timbers from my work as scrap dunnage and i have had many of the same size and what i find is that after a few years they usually become soft and break apart, as they are a soft pine. i have serious thoughts of building a trough in which i can hot oil bath full length timbers for use as fence posts.
Many people recommend mixing deisel or motor oil with borax and glycol for homemade wood treatment. Supposedly it works quite well. Unfortunately glycol and diesel are both banned by the EPA for that use, so if they find out you painted your shed with it, they’ll likely fine you and make you tear down your shed.
I’ve replaced a lot of failed fences, and come to the conclusion that NO wood should ever be in contact with soil. My standard replacement procedure now is to use a large farm jack to pull the rotted ends out of their concrete footings. That sometimes requires a bit of drilling to split the stubs in half. What you end up with is a perfect 3.5 to 4 inch form for setting a steel fence post in a bit of new concrete. You can use standard chain link posts with some post-to-wood hardware, or one of the new steel posts designed specifically for attaching horizontal 2x4s. The cost is not much different. The new type of post actually lets you fasten vertical fence boards on both sides, with no additional hardware in case you need a good looking fence on both sides. My problem with treated lumber is dimensional stability. It can shrink, warp, or cup as it dries out. If you use it immediately after carefully selecting it at the lumber yard, you can build in such a manner to force it to not change much. (Hint: Use clamps and ratchet straps to force it straight before you fasten it.) If you store it until it dries out, you have to stack it to minimize warp and cup. It still shrinks, but that’s why treated sticks are usually and inch or two longer than their claimed length.
In the USA, there is a BIG difference between pressure treated wood that is sold for above ground use versus PT for soil contact and below grade use. Which was the PT treatment grade that you used???? By and large, we can expect that a pressure treated 4×4 rated for below ground use, like a mailbox post, will last for decades. I live in Florida (high heat, high humidity, lots of rain) and my mailbox and fence posts are perfectly serviceable 30 years after they were installed. In fact, when I re-fenced my yard, we left the posts in and re-attached the new fencing to them.
Neat test, TU. Have not read all the comments but the one thing (minor flaw) I saw in your execution was not separating the pieces of wood. In other words the two outer boards received more environment than those sandwiched in the middle where they were more “protected” by the outer boards. Just a thought….TU agn.
I am very curious to see a similar test with the wood being treated with Sodium silicate ( aka waterglass), thermally modified wood (pyrolisys), Yakisugi wood (burned surface), chemically altered wood (acetylation). These techniques are being marketed and sold as giving wood a very high durability, which for some is true i believe. I have a little exoerience with some of these but never tried to test it to the limit. It might take some more then 3 years though.
i noticed that the pieces were placed close together, possibly providing the inner pieces less chance to dry out. the outer pieces/sides would generally be better off I’d assume. in our country, CCA treated wood is still widely available and is pretty standard when purchasing ‘outdoor rated’ timber. creosote is also available and is generally used for outside wooden sheds and is very low maintenance as it penetrates and does not peel as other coatings may do.
the samples which were towards the end has higher chance of drying out due to them having one less “neighbor” which is consisnt with your results that the ones on the ends were doing better. regarding the ones in water, its possible things leached out in the water and was absorbed by the others. a better tests would probably be to have 4 different water containers
Did you coat the end grain of the cut on the pressure treated wood? Most of these products specify that you should cover all end grain with a primer as the core is not protected by the pressure treatment except on the factory ends. Most people don’t do this off course as it’s hidden in the datasheet from the manufacturer and rarely mentioned by the building stores that sell it.