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Fasteners in coastal region

Fasteners in coastal region

The project in question is located on the Gulf coast, roughly 50 feet or so from the water.  In addition to the main structure, we will be adding a boardwalk, gazebo, dune crossover and the like.  Would galvanized fasteners or SS fasteners be better in this situation?  What type of SS would we use?  I know of 304 and 316 as being common structural fasteners.  Cost is not a concern.  Let's assume that we will be using bolts, nails and/or screws.  The design has not been determined yet.  I'm just trying to get a handle on fasteners before getting into the actual design.

RE: Fasteners in coastal region

Depends what material you are fastening, you should try and keep the connecting metals as similar as possible.

Zinc and aluminum have similar reactivities. Galvanised members adjacent to stainless steel can have local corrosion isues unless electrically isolated by neoprene washers(or similar).

RE: Fasteners in coastal region

It really depends on the base materials to be fastened (galvanized or painted steel? stainless steel?) and what type of maintenance/replacement is considered appropriate.  Type 304 really does not have sufficient resistance for this type of application, so if stainless fasteners are desired/required, then definitely go with Type 316.  Threaded fasteners are covered by ISO 3506 (Grade A4 or A5) or ASTM F 738 (Property Class A4).  There is some good information available from SSINA and The Nickel Institute as well:

RE: Fasteners in coastal region

Bronze or Monel fasteners are the choice of boat builders, best if used with wood.

RE: Fasteners in coastal region

Fastened material is wood.  We don't know the species yet.  It could be PT or could be naturally resistant.

RE: Fasteners in coastal region

Be careful with treated wood, some treatments are highly corrosive.


RE: Fasteners in coastal region

There are deck screws made that are called 'double galvanized', it is actually a heavier weight galv coating.  These are what you would need.
If you can, run all of the screws from the bottom, not the top or sides.  This way salt water will not collect and have a chance to concentrate on the fasteners.  I know that this is a pain, but I have built decks where we made sections 'upside down' then installed them in order to do this.  It looks better too.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Fasteners in coastal region

Would you expect any problems mixing SS fasteners with galvanized connection hardware?  I'm using both G185 light-gauge connectors (Simpson) and hot-dipped glavanized steel plates and angles.  

RE: Fasteners in coastal region

Yes, potentially.

The stainless steel will accelerate the corosion of the much more active zinc. We combine these two materials a fair bit but we are careful to specify neoprene washers (or similar) to minimise electrical contact.


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