Is it ok to use these with chestnut oak. I've used some other types of connectors before and oak just ate them up, but would galvanized be ok for our shed? For screws, I want to use the spax exterior screws. Thanks.
I'm guessing you are using the chestnut oak for siding ???
The info on Spax exterior screws says "Though rust resistant, these screws are still susceptible to oxidation and should be countersunk to reduce the risk of the wood staining. " so you may get staining, but I'd think they wouldn't waste away. Not sure what you meant by "oak just ate them up" other than staining the wood around the fasteners. I'd avoid the 'galvanized' as it can flake off when driving them in and then corrode from the exposed steel.
Nope the chestnut oak is the joists. Once I used some cut nails in oak and they rusted away a good bit. So, instead of galvanized I should use zinc plated? Thanks.
Where was the moisture coming from that caused the nails to rust away? That would be the culprit, IMO. Dry oak won't rust nails, I don't believe.
The oak was AD. The oak were using now for the building is probably 30% moisture, so I'm leaning to stainless.
The metal condenses moisture as far as I can tell. I've removed plated lags after a week in green logs and they had started to rust. Oak will destroy fasteners and the rusting fasteners destroy the surrounding wood, not scientific I know, just my observations. FPL has done some studies on this if you want to search there. Stainless is good for oxidation, good luck driving it though,its soft, predrilling helps. Zinc is the metal in galvanizing, when you buy plated screws it is usually just electroplated on, very thin. Hot dipped is better, double dipped is thicker still. Do not mix stainless and galvanized, as in stainless fasteners and galvy hangers. Simpsons more heavily galvanized connectors are labelled ZMax.
As an aside, the reason the new treated is so corrosive is that in eliminating the arsenic, they lowered the chromium and increased the copper content. The increased copper is far enough from steel on the galvanic chart that a strong electrolisis field is set up. Basically the wood is arcing to the fasteners. Zinc is a sacrificial anode that is slowly consumed while protecting the base metal. I view the acidic oak as an electrolyte, don't know if that's correct or not. I've been using the teflon coated fasteners and they seem to work good on everything I've tried them on, oak, cedar, treated, pine. Less pricey than stainless and hardened to boot, the coating is tougher than galvy and a barrier instead of a sacrificial.
I googled up this article on galvanic corrosion if you want to research an aside ??? ::) :)
http://www.mcnallyinstitute.com/CDweb/g-html/g002.htm
Another aside, the old forged nails, predating cut nails (these are the old ones that are tapered on all sides not just 2) don't corrode nearly as much as the newer (post civil war) ones. I've heard some people say it was the wood charcoal vs. coke. I tend to believe that the silica in hand wrought iron was not completely removed and formed a protective glass skin over the metal.
I spent 30 years as an electrochemical engineer and I couldn't explain it as well as Don's post. Excellent info, and all correct. Oak is aggessive because the acidity makes the metals more soluble, it breaks down the passive layers that surface oxides form. Good advice on the teflon coating - they work because they are well insulated from the active materials. Any situation that has two different metals in contact is a candidate for corrosion.
Thanks a bunch guys. I guess we'll use the spax triple zinc coated with teflon stuff on the outside then.