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Re: Galvanized bolts req'd in PT wood?

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First, let's decipher the alphabet soup:
CCA is chromated copper arsenate--this is the chemical that was "outlawed" in 2004 (it's actually still available for agricultural uses--I guess the arsenic disappears if a cattle eat it after it leaches out of their feeding trough...)
   Some of the new treatments are:
   ACZA--ammoniacal copper zinc arsenate (hmm, still has arsenic...)
   CC--copper citrate
   ACQ--ammoniacal copper quaternary
   CA--copper azole
   DOT--disodium octaborate tetrahydrate
The only one that I specify for mudsills is DOT--it is less corrosive than CCA was, and it is non-toxic to humans.

When ACZA first came out, a contractor friend of mine used some wood treated with it to build some stairs. He told me that within six months the hot-dipped-galvanized post caps were turning into piles of gray powder.

Another contractor on an on-line forum reported that ACQ-treated sills had reacted with plain-steel anchor bolts within a matter of months to the point that the bolts had lost about 40 percent of their cross-sectional area.

Reports like this from the real world have led me to specify only DOT for treated wood (where the wood is not exposed to water--the DOT leaches out if exposed to rain or ground water). Otherwise I specify stainless steel for anchor bolts, anchor rods at tie-downs, nails that are driven into or through PT lumber, and any framing anchors.

Some articles I have seen suggest using Vycor or some other membrane to separate PT lumber from framing anchors. While this could work if workers *carefully* isolate metal from wood, you still have the issue of nails driven into the PT lumber. I don't see a way around using stainless steel nails for copper-based treatments.

There's more info at my website: www.shearwalls.com/treated_wood.html

This issue concerns me a lot; shear wall panel nailing and mudsill anchors can quietly corrode and we will not find out until a bunch of "new" houses slide off of their foundations in a future earthquake.

Thor Matteson, SE
www.shearwalls.com



From: "Jeff Smith" <jeffsmith7(--nospam--at)comcast.net>
To: <seaint(--nospam--at)seaint.org>
Subject: RE: Galvanized bolts req'd in PT wood?

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Correct me if I am wrong, but if you specify Ilevel Strandguard treated sill plates you do not need to use galvanized fasteners or barriers, since their
zinc borate does not increase corrosivity.

I have been specifying HDG anchors, washers and plywood sill plate nails at CCA pressure treated sill plates and any thing else that comes into contact. I specify a barrier between holdowns and the treated plate, such as polyken
tape or Grace Vycor. See
http://www.strongtie.com/ftp/bulletins/T-PTBARRIER08.pdf

Jeff

 _____

From: bart(--nospam--at)nbse.com [mailto:bart(--nospam--at)nbse.com]
Sent: Saturday, September 06, 2008 6:01 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Galvanized bolts req'd in PT wood?


Diane,
I share your interpretation as well and do not think it applies to anchor
bolts as pressure treatment does not usually occur through the entire
thickness of the plate.
(not to mention the holes are larger than the bolt...technically not in
direct contact) However.....when the building dept./and/or inpsectors are
adamant, I have told the contractor to wipe the bolts with solvent and
paint....it usuallly has done the trick...

bart

----- Original Message -----
From: "Gould, Diane"
To: seaint(--nospam--at)seaint.org
Subject: Galvanized bolts req'd in PT wood?
Date: Thu, 4 Sep 2008 15:29:19 -0700

2007 CBC/2006 IBC Section 2304.9.5 states that "fasteners" for PT &
fire-retardant wood shall be galvanized, stainless, silicon bronze, or
copper. 2001 CBC/2000 UBC Section 2304.3 also stipulated this requirement. On a wood-frame job currently in construction, we have pressure-treated sill plates and the inspector is saying that galvanized anchor bolts (sill bolts
and hold-down bolts) are a "code requirement".

I understand the new preservatives can be much more corrosive than the old
stuff, but was of the impression that bolts are of a large-enough diameter
to not pose a concern.  I had thought I read that somewhere but I cannot
find any published code language, commentary, or interpretations to support this position. Also, I started thinking, what about the washer? Is that a
"fastener"?  It's in contact with the PT wood - does that mean it needs to
be galvanized too?  I could not find a definition of "fastener" in the
CBC/IBC.

I've been away from wood design for awhile and am feeling a little rusty, so
I'm hoping someone can give me some guidance on this.

Thanks in advance,

Diane C. Gould, S.E.
Senior Structural Engineer
DGS-RESD-PSB
Design Services Section
707 Third Street, Suite 4-105
West Sacramento, CA 95605
(916) 375-4219 phone
(916) 375-4916 fax
<mailto:diane.gould(--nospam--at)dgs.ca.gov> diane.gould(--nospam--at)dgs.ca.gov


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