Separate wood and metal surface samples on a neutral background.
Material appearance only. The samples do not identify alloy, treatment, profile geometry or compatibility.
- Identify each metal and the exact support treatment.
- Wetting and chemistry act at the contact interfaces, including sheltered locations.
- The diagram maps questions, not a grade recommendation or corrosion service-life estimate.
Identify the support independently
Record the supporting wood product, treatment information, and labels available on site. Keep the hardwood surface material in a separate field. An attractive untreated face does not describe the substrate through which its fasteners pass. If treatment identity is unknown, mark it unknown and seek purchase or treatment records rather than inferring chemistry from color.
Build a contact map
Sketch the fastener path and show each material it contacts, including clips, washers, connectors, membranes, and flashing. Include the portion embedded in the support. This simple map helps reviewers notice that a proposed screw has more than one compatibility question and that concealed contact may differ from what is visible at the board surface.
Ask the right corrosion question
USDA's guide addresses metal corrosion in copper-treated wood and design strategies for reducing it. The practical question is whether the proposed hardware is accepted for this treatment and exposure, not whether a package uses the general word exterior. Obtain the applicable written compatibility information and identify any conditions that must be met for the intended use.
Keep barriers within their approved detail
If a separation layer is proposed, document its material, continuity, penetrations, and installation requirements. Ask how the fastener and connector are treated in that detail. Do not assume a strip placed between two broad surfaces isolates every metal contact or changes the embedded screw's exposure. Review the proposed assembly rather than crediting an unspecified barrier with complete protection.
Make substitutions visible
Compare the original and alternative fasteners by material, coating, dimensions, head, and intended application. Include the treated-support information in the substitution request. During receiving, photograph treatment tags and hardware labels together with their respective location records. Keeping those records linked is more useful than an invoice that simply lists deck screws and treated framing.
Identify the treatment, not just the colour of the lumber
The phrase treated lumber does not identify a preservative formulation, treatment level or intended use. Colour and a general product description are not enough to establish fastener compatibility. Retain the end tag, treatment mark, supplier information and relevant product documents before labels are discarded or packs are mixed.
Record the support material separately from the decking or cladding. A project can have an identified face material but an unresolved supporting member. The builder should keep that unresolved state visible even when the other selections are complete. A finished-looking board and clip model must not imply that the support has been accepted.
Compare both sides of the contact
The review needs the treated-wood requirements and the exact fastener or connector requirements. Include accessories that touch the support: clips, brackets, washers and related metal components. A suitable screw does not automatically make an undocumented bracket suitable. Likewise, a connector's material description does not authorize any screw that fits its hole.
| Needed record | Why it belongs in the review |
|---|---|
| Treated support identification | Establishes what the hardware contacts |
| Preservative and treatment documentation | Defines the treatment basis for compatibility questions |
| Fastener and connector product IDs | Prevents an alloy label replacing exact system identity |
| Exposure description | Distinguishes sheltered, persistently wet and chloride-related conditions |
| Manufacturer conditions | Preserves the limitations of an approval |
If the treatment manufacturer and connector instructions seem to disagree, keep the conflict explicit and request a coordinated answer. Do not quietly adopt whichever statement permits the desired product.
Moisture changes the service context
Wetness affects the corrosion environment of metals in wood. A support that repeatedly stays wet at a contact is a different context from a dry, accessible example. Describe drainage, shelter, water accumulation and relevant exposure without inventing a numerical corrosion rate or remaining life.
The USDA Wood Handbook treats wood preservation and fastening as distinct technical subjects. Their interaction must be resolved for the selected materials. General background cannot provide a blanket approval for all treated lumber and stainless or coated hardware.
Review existing supports as existing material
For a retrofit, the original treatment identity may be missing and the member may have a condition history that a new-product document does not describe. Photograph surviving marks and gather purchase or project records where available. Do not assign a likely preservative from age or appearance and then present that inference as verified.
Keep treatment identification separate from the condition and structural assessment of the support. Confirming one does not complete the other. If the required evidence cannot be recovered, the result should remain pending or follow an explicitly documented alternative review path. Continue with coastal connections when chloride exposure is also relevant, and connection submittal to assemble the outstanding questions.
Practical checklist
- Recover treatment identification from records or labels.
- Map all direct and embedded material contacts.
- Obtain product-specific treatment compatibility evidence.
- Document separation layers as part of the assembly.
Worked example
Hypothetical example: a hardwood replacement job retains existing treated joists. The team discovers that the proposed hardware review covered only the hardwood, adds the joist treatment record, and requests a complete compatibility response before purchase.
Limits of this guide
This guide supplies no universal coating thickness, acceptable treatment combination, or corrosion lifetime. Unknown treatment remains an unresolved input. Structural performance and any separation detail require acceptance for the actual connection.
Continue the decision
Map mixed-metal contacts before approving a connection
Building a fastener connection submittal
Record corrosion evidence without guessing remaining life
Connection worksheet