316 vs 304 Stainless Steel Mesh: Why It Matters Near the Coast

What makes steel “stainless”

Stainless steel is steel with at least 10.5% chromium in it. The chromium forms a very thin, invisible skin on the surface of the metal. That skin is what stops rust. If it is scratched, it heals itself.

Salt is the one thing that skin struggles with. Salt in sea air settles on the metal and slowly breaks the skin down in tiny spots. Once that happens, the steel underneath starts to mark.

What is different about 316

316 stainless steel has an extra ingredient: a small amount of a metal called molybdenum. It makes the protective skin much better at standing up to salt. That is why 316 is called “marine grade”. It is the grade used for boat fittings and for handrails on seafront buildings.

304 stainless steel does not have that ingredient. It is a good metal and it is used everywhere, from kitchen sinks to appliances. It is simply not made for salt.

Tea staining: what goes wrong with the lower grade

When a less resistant grade such as 304 lives in salt air, it can pick up a brown discoloration. The trade calls it “tea staining”, because it looks like a tea spill that never quite wipes off.

On a security screen, tea staining shows up as brown marks on the mesh. You will see it every time you look out of the window. 316 marine-grade stainless steel has much higher resistance to this kind of corrosion.

How close to the coast is “close”?

The guidance we work to is simple:

• Within 3 miles of the ocean: 316 is most certainly the grade to use. That covers Manhattan Beach, Hermosa Beach, Redondo Beach, Santa Monica and the west side of Torrance.
• Within 30 miles of the coast: 316 is still the suggested grade. Sea air travels a long way inland. That covers Gardena, most of Los Angeles and a good part of the valleys.
• Other harsh spots: the same advice applies where there is heavy pollution, strong wind or high heat.

In practice, that means nearly every home we work on is in a 316 area. So 316 is what we specify.

“But isn’t thicker wire stronger?”

You may hear that a 0.9 mm wire in 304 steel is stronger than the 0.8 mm wire in 316 mesh, because it is thicker. It sounds logical. It is not the whole story.

What counts is how much pull the wire can take before it breaks. That is called tensile strength. A thicker wire made of weaker material can fail sooner than a thinner wire made of stronger material.

Meshtec, which makes the mesh, publishes the numbers. Its 316 wire is rated at about 900 MPa of tensile strength and its 304 wire at about 800 MPa. So the 316 wire is made of the stronger material, which makes up much of the difference in thickness. Either way, wire thickness on its own tells you little. Ask what the finished mesh has been tested to.

The mesh also passes the knife-shear test used to rate security doors and windows. That test is exactly what it sounds like: trying to cut through the mesh with a blade. See how the tests work.

For salt in particular, Meshtec reports that its mesh passes a 3,000-hour salt-spray test (ASTM B117). The mesh and frames are also powder coated for extra corrosion resistance.

Questions to ask any installer

1. What grade is the mesh? You want to hear “316”. If the answer is “stainless” with no number, ask again.
2. Who makes the mesh? A named manufacturer can back up its claims.
3. What about the frame and the fixings? The mesh is only one part. Ask what the frame is made of and how the mesh is held in it.
4. What does the warranty say about corrosion? Ask to see it in writing.

For our own screens: the mesh is genuine Meshtec stainless steel, used in the Majestec range of doors and windows. Majestec offers the mesh in 304 or 316 grade, and we specify 316.

On warranty, Majestec’s brochure describes two parts: a 10-year powder-coating color warranty on the mesh and frame panels, and a one-year warranty on hardware such as hinges, closers, locks and rollers, with terms and conditions. Ask Roman for the warranty terms that apply to your screens.

Does 316 still need cleaning?

Yes, a little. Marine grade does not mean maintenance-free. Salt and dust still settle on the screen, and it will look better if they are washed off now and then:

1. Brush off loose dust with a soft brush.
2. Wash with mild soapy water and a soft cloth or sponge.
3. Rinse well with clean water and let it dry.

Avoid harsh or abrasive cleaners. How often depends on how close you are to the ocean. Ask Roman what he recommends for your home.

The bottom line

If you live in a beach city, or anywhere the sea breeze reaches, the grade of steel is not a detail. Ask for 316 by name. A screen should still look good in ten years, not just on the day it goes in.

See how the screens look on real homes in our gallery, or read about security screens in Manhattan Beach.