The decision to choose a survey marker or rebar cap usually boils down to two essential questions: Does it protect against corrosion, and will it stay put?
While we usually think of exposure to the elements as the cause of most corrosion, the culprit for survey markers is actually the direct contact between two dissimilar metals in the marker and rebar.
The chemistry of survey marker corrosion
For survey marking in particular, corrosion occurs when steel rebar and aluminum or bronze markers, which have different electrode potentials, are fitted together. This process is called galvanic corrosion, and is the same electrochemical system most batteries exploit to generate voltage and direct the flow of electricity.
In the simplest terms, when two metals with different electrode potentials come into contact with one another and an electrolyte (moisture in the case of a survey marker), one metal acts as an anode while the other acts a cathode, creating a path for electricity to flow.
However, just as the anode on a car battery degrades over time, the small current generated by the survey marker and rebar will degrade the positively charged aluminum or bronze––eating away at the marker or cap until it becomes dislodged from its base entirely.
Two ways to battle survey marker corrosion
In addition to chemical corrosion, poor product design can also lead to improper fitting, which can cause markers and caps to loosen over time.
Good caps should never wobble when tapped into place. While most manufacturers attempt to prevent this with a tapered cone socket designed to fit more tightly onto rebar, this simple fix doesn’t address the problem of chemical corrosion, which requires more than just a change in shape.
At Berntsen, we’ve developed two solutions that not only separate the metals from direct contact, but offer a stronger metal composition that stands up to the elements and other wear and tear:
1. The SureGrip insulator
The SureGrip insulator fits in between the marker and rebar to isolate the aluminum or bronze from the steel in order to prevent galvanic corrosion. When installed, the durable plastic insulator deforms around the shape of the rebar, filling the hex shaped socket for a super-tight compression fit.
These simple insulators greatly reduce the effects of galvanic corrosion while making installation no more complicated or difficult. No special tools are needed to install these enhanced markers and caps.
2. Stronger, more durable alloys
In addition to greater strength at the point of connection, our aluminum survey markers and caps are orbital forged from 6000 series aluminum––the same alloy used to construct our rotating rod monuments, which is significantly stronger than the typical 99% pure aluminum found in other markers and caps.
For bronze survey markers and caps, years of extensive internal research and testing led us to introduce a 97% copper, 3% silicon bronze alloy, offering the best corrosion resistance, strength and durability available. Since pioneering the movement away from leaded brass markers and monuments years ago, we now exclusively use this silicon bronze alloy for all cold forged survey markers and caps.
Tips for installing survey markers and caps
These enhancements come without any additional installation steps––simply place a mark about 1.5” from the end of the rebar, drive it into the desired depth and tap on the cap with a lixie hammer.
Watch our instructional video below for helpful installation tips or click here download our Installation Instruction Guide for a detailed reference out in the field.
Want to learn more? Browse our aluminum and bronze survey marker product pages for available sizes and product specifications.
Have questions or want to discuss your next project? Click here to contact us or request a catalog.