Terrazzo divider strips: brass, zinc, and what to do with them

The thin metal lines that divide a terrazzo floor into panels are divider strips. In a mid-century Hillsborough County house they are brass or zinc, and they are worth getting right in a restoration: ground flush and bright, they make the floor look crisp; bent, missing or standing proud, they are the first thing your eye catches.

What strips are made of

The NTMA’s systems reference guide lists the options: “Zinc and brass are available for cement. Zinc, brass, plastic and aluminum divider strips are allowable for use in epoxy terrazzo systems.” Since mid-century Tampa houses have cement terrazzo, the strips are brass or zinc. The guide also gives the usual sizes: strips range from 18 gauge to half an inch wide, with 16 gauge or 1/8 inch the standard.

If you find plastic or aluminum strips, the floor is epoxy or a later installation, not original mid-century cement terrazzo. See cement vs epoxy terrazzo.

What strips do and do not do

Brass divider strips became widely available in the mid-1920s, the NTMA’s history notes, and opened the way to the patterned floors of the era. Over the decades strips have been sold as a way to let the surface move without cracking. The NTMA’s systems guide is more precise about modern practice: a strip over a joint in the concrete slab is where movement can happen, but “the dividers not located over concrete joints are strictly decorative. They do not function as leveling devices or crack preventers.”

For a homeowner that means two things:

• A crack beside a strip often sits over a slab joint. It is normal, and it is filled. See cracks along divider strips.
• A crack across the middle of a panel is the slab cracking, not a strip failing.

Where strips usually run

On a floor bonded to a slab, the strips that matter for movement are the ones over the slab’s joints. The NTMA’s systems guide says that to minimize cracking, concrete joint placement should follow the ACI 302.1 guidance, with concrete joints running off corridor intersections and corners, and that architects should design structural expansion plates between areas where major movement is expected. Other strips can be set to separate colors or as accents, and those are decorative. In a mid-century house that usually means strips at doorways and across rooms in a grid, with some of them over joints and some purely for looks.

Common strip problems

Prices match the pricing page.

Strips as a measuring stick

Strips are also the record of a floor’s history. A floor that has been ground hard before will have strips standing noticeably above the chips and cement around them. A house topping is a nominal half inch, per the NTMA’s definition of monolithic terrazzo, so a restoration takes only a thin skin. Strips that already stand well proud tell us to grind conservatively, and we check them before quoting.

Adding strips during a restoration

When a wall comes out and leaves a strip of bare slab, or two rooms have slightly different terrazzo, a new divider strip is often the cleanest answer. The NTMA approach to replacement is to run to an architectural break, such as a strip, so the edge looks deliberate rather than patched. A new brass or zinc line set along the old wall position turns a visible repair into a design line.

Getting it looked at

Send a close photo of a strip with a coin beside it, and one wider shot showing several. We can usually tell brass from zinc and see how proud the strips stand. The crack and hole repair page covers resetting and replacing strips with patches.