Pressure Treated Wood and Stainless Steel - Page 1
Forum section: electronics / general

author: bostonman
author_rank: Super Contributor
timestamp: December 29, 2023, 04:08:55 am
content: From what I've learned, stainless steel hardware wasn't safe at one time to use with pressure treated wood because it corrodes the hardware. The new type of pressuring treating methods are safe for hardware.A few years ago I built a workbench using PT 4x4s and stainless steal bolts. After removing the bolts for reasons not worth getting into, I noticed they were discolored.I'm wondering why this occurred and whether PT wood is truly safe for stainless steal.

author: Dan123456
author_rank: Regular Contributor
timestamp: December 29, 2023, 06:01:07 am
content: Can you share some pictures of the bolts?While I can’t imagine the wood would be doing much real damage to the bolts, it could possibly be due to the specific fungicide they use in the treatment.That said, I can’t think of much that would attack stainless more than regular steel!Maybe it converts the chromium in the stainless to hexavalent chromium compounds or something?Edit: oh and how old is the wood? I was just doing some reading and it appears they changed the chemicals they used in late 2003It used to be Chromated Copper Arsenate so at a guess that might react with stainless (although I don’t 100% know and would need to dig further)https://www.protoolreviews.com/what-is-pressure-treated-wood-lumber/

author: IanB
author_rank: Super Contributor
timestamp: December 29, 2023, 10:10:57 am
content: Quote from: bostonman on December 29, 2023, 04:08:55 amYou have to define what "safe" means for your purposes.At one extreme, "safe" could mean that the bolts carry a load and that damage could result to life or property if they fail.At the other extreme, "safe" could mean that the bolts result in cosmetic discoloring of the material they are attached to.In the middle, "safe" could mean that the bolts corrode to the extent they cannot be undone, requiring them to be drilled out and replaced.What is your version of "safe"?

author: Dan123456
author_rank: Regular Contributor
timestamp: December 29, 2023, 11:07:53 am
content: Quote from: IanB on December 29, 2023, 10:10:57 amOh that’s a very good point!I was thinking about the human health safety implications more than the hardware failing when talking about the chemicals reacting with the stainlessIf the discolouration was a crusty mix of hexavalent chromium and arsenic, it probably won’t hurt the bolt much, but if you were to lick it on the other hand…

author: Ian.M
author_rank: Super Contributor
timestamp: December 29, 2023, 12:49:23 pm
content: https://en.wikipedia.org/wiki/Crevice_corrosionStainless alloys are often highly susceptible to corrosion in a damp or wet environment if oxygen can't freely reach the entire surface. The metal salts in pressure treated wood + ambient moisture, or even just the moisture in the wood, provide an electrolyte and an electrochemical corrosion cell forms between the exposed passive surface, and the oxygen deprived active surface. I have seen pits the size of a split pea form in the surface of a stainless shaft under the lip of a seal in equipment that was put away damp and dirty and left undisturbed for a few months. It didn't pit significantly in normal use as the shaft movement kept any water under the seal oxygenated.

author: bostonman
author_rank: Super Contributor
timestamp: December 29, 2023, 03:36:14 pm
content: QuoteI guess it would be this version of safe.I'll check if I still have the bolts, but, what I remember: the wood was relatively new, maybe purchased in 2015. They were PT 4x4s (purchased from a lumber store, not Home Depot or Lowe's) being used to build the legs of a workbench.Thankfully I saved the product spec sheet (and receipt) for the hardware I purchased to build the workbench and apologize. Apparently I used zinc-plated steel bolts and swore they were stainless steel (all the other hardware such as nuts and washers were SS though).The bolts I used were from McMaster-Carr (part number: 91247A564).Description: Medium-Strength Grade 5 Steel Hex Head Screw, Zinc-Plated, 1/4"-20 Thread Size, 5-1/2" Long, packs of 25.What I remember was the bolt had white residue. It was only in the wood for about six-months (maybe less), and, when I removed them, they had residue that had me question whether they were getting corroded; possibly failing over time.My current need is using stainless steel through (most likely) PT wood, I wanted to confirm the research I did confirmed the new chemicals used for PT wood is safe for stainless steel. Remembering the white residue on the bolts from a few years back, and thinking they were stainless steel, I began wondering whether I shouldn't use PT wood.The reason I state I'm not certain yet on whether I'll use PT wood: the application is 3/8" SS threaded rod suspended vertically. I plan to drill a hole directly through a 4x4 horizontally laid across joists, and the threaded rod directly through with a nut (probably a coupling nut for extra strength) on top to hold it.The reason I may not go PT wood is due to concern over the 4x4 developing a crack and splitting over time. My thought is to maybe go with wider than 4", however, the part I wanted to rule out was stainless steel bolts and PT wood combination being an issue. Since I just realized the previous application was zinc plated, it seems maybe the white residue doesn't apply to this situation.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 29, 2023, 04:40:30 pm
content: Perhaps the real question is why you are using pressure treated wood in an application that does not involve ground contact. It is more expensive and has health concerns (minor) when cutting and shaping. I doubt if the rafters you will be resting this on are pressure treated.

author: bostonman
author_rank: Super Contributor
timestamp: December 29, 2023, 05:03:06 pm
content: Good question.I’m finding any 4x4s at stores in my area come as PT only.Maybe I’m not looking hard enough, but at least Home Depot online states all their 4x4s are PT.

author: Dan123456
author_rank: Regular Contributor
timestamp: December 29, 2023, 05:22:18 pm
content: Quote from: bostonman on December 29, 2023, 03:36:14 pmAh that’s ok and makes more senseWhen I was reading through stuff before I found the below which talks about the “white rust” which sounds possibly similar to what you are talking abouthttps://www.creia.org/assets/images/conferences/2015/pt_lumber_corrosion_no_printing_only_post_%20skipwalker_matteson.pdfMost places I was reading said it is recommended to use either stainless steel or bolts with heavy galvanisation with it so sounds like it is best practice and don’t believe the stainless will hurt the wood

author: bostonman
author_rank: Super Contributor
timestamp: December 29, 2023, 05:36:23 pm
content: Hurting the wood wasn’t my concern; unless you were being sarcastic. My concern over the wood splitting is exclusively over stress and time causing cracks that grow and split the wood where the rod is going through.From reading, stainless does seems safe. I made the mistake of thinking the white rust was on stainless bolts.I plan to look for a larger piece of wood anyway, but, as mentioned, wanted to first rule out chemical conflicts.

author: SeanB
author_rank: Super Contributor
timestamp: December 29, 2023, 06:35:20 pm
content: If you are worried about the wood splitting best is to get some nail boards and nail them into the ends, which will stop the wood splitting. PT lumber will split, as it is guaranteed that, unless it has been done properly, which is slow, that it will lose moisture, and split otherwise. Just use a nail board on the end grain, and if you are concerned a cradle to spread the load from the bolts across the lumber.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 29, 2023, 11:23:04 pm
content: Quote from: bostonman on December 29, 2023, 05:03:06 pmMust be unique to your area. Home Depot here has 8 foot non-pressure treated 4 x 4 in eight foot lengths. But only pressure treated in longer lengths. Another option would be to use doubled 2 x 4 which Home Depot says they have in lengths to 12 feet in non pressure treated forms and a couple of wood species. If you glue to two pieces together or use sufficient nails or screws the strength is equivalent to the 4 x 4.Don't know if you have figured out how to get your beam into the attic. In many cases long beams are impossible to maneuver into existing construction, so building up in situ from smaller pieces makes sense. Done appropriately the strength can be very close to or even exceed a single piece beam.If getting them in in one piece is an option you might want to look into laminated wood beams. Very strong, and warping, splitting and other concerns are minimized. Will require some thought to get an appropriate interface to your rods, and they are not an off the shelf item.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 29, 2023, 11:54:18 pm
content: Quote from: bostonman on December 29, 2023, 05:03:06 pmTry Menards:https://www.menards.com/main/building-materials/lumber-boards/timbers-logs/c-13131.htm?ipp=36&Spec_WoodSpecies_facet=Douglas+Fir&Spec_WoodSpecies_facet=Southern+Yellow+Pine&Spec_WoodSpecies_facet=Species+may+vary+among+Spruce%2C+Pine+and+Fir&Spec_ProductType_facet=Timber&Spec_NominalThicknessxWidth_facet=4+x+4I didn't check what might be available in your area. Douglas fir (which is not really a fir) is my preferred, SYP is a second choice. It's strong, but a bit resinous and harder to work. "White wood" is good for most non-structural, indoor applications. There are other woods, such as hemlock, but it is not widely available. Cedars are good for rot resistance, but are considerably weaker.

author: bostonman
author_rank: Super Contributor
timestamp: January 01, 2024, 04:53:43 pm
content: I haven't had a chance to read through everything until today.Someone mentioned the beam length and possibly being unable to fit it up the attic. This is a good call, but I shouldn't have an issue as the beam will be long enough to catch about five joints (six-feet or so) - but certainly something to consider. My attic has pull down stairs, and, with the right angle, I'm sure I can fit that up there.In any case, my thought was to go with a piece of strut across the wood to spread out the force, but the strut is expensive. My other thought is to get 1/4" aluminum, maybe 4" x 6" piece, and use it as a "washer".The main question seems to be answered and that is PT wood will not harm SS threaded rod (or any SS hardware).Now I'm just trying to think more about wood that will distribute the weight and not split. Initially I planned to use the 4" x 4" only, but I look at the cracks on the legs for my workbench and visualize the 4x4 splitting in half and the threaded rod falls out. Thinking more now about a 2" x 10", washer/nut, and then a 4" x 4" on top of that with coupling nuts, but, the nuts on the 2x10 wouldn't be very tight. it would be use to "catch" the threaded rod should the 4x4 splits in half.As for Home Depot not having regular (i.e. non-PT) 4x4s, it was only one location I looked at, however, I'm sure they exist either at HD, a local lumber store, or one further away. It's not so much about buying a 4x4 at this point, more about which size to go with as I visualize a 4x4 having

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 02, 2024, 05:50:42 am
content: Go to the website for Home Depot or Lowes or other big supplier of your choice. Look in the Simpson ties section, where they have joist hangers, post supports, hurricane ties and the lot. I am sure that you will find something that appeals to you for spreading the load (perhaps even add a fender washer or two). Look through them all as there is quite a bit of overlap in functionality and pricing varies from modest to OMG. I have on several occasions found the perfect fit for my application in the OMG category, but found something else that served if less than perfectly for far less.The relatively short length of beam you want gives you lots of options on lumber choice. If you want maximum strength and zero chance of splitting get a half inch hardwood plywood sheet and rip it into four inch wide strips, and then laminate the strips to the thickness you want.

author: bostonman
author_rank: Super Contributor
timestamp: January 02, 2024, 04:26:44 pm
content: QuoteUsually when I visit HD or Lowe's, or various places of similar nature, I browse the isles exactly for what you suggested. Not because I'm looking for something, but I mentally absorb the inventory allowing me to be more creative for future projects.I'm sure many options exist and I am going to give more thought. Due to the holidays and stuff that came up, I was unable to devote any attention into this. Usually when I give thought to these type of applications, I don't think about making it work today, I think about longevity, potential issues that can occur over time, and accessibility for future repair needs.