Im throwing a list together with very brief notes about various ways to demarcate control points (not property corners or legal boundaries). Im sure I missed a bunch & was hoping for some words of wisdom from the group.
So far I have...
Mag nail – Need to predrill a hole to be used in concrete but can be used directly in asphalt. Extremely stable, has a dimple for precise centering and can be used with tags for easy identification.
Scribe – Easy to set in concrete with a carbide tipped laminate cutter. Extremely stable. Grooves help with centering. Use a paint pen to mark it up.
Rebar – Scrap rebar common on most construction sites & can be cut to size easily to match ground type. Use a center punch and paint pen to create a dimple for centering. Countersink in the ground to avoid it being disturbed. A plastic cap can be used for identification and centering.
Spike – Typically more readily available in bulk compared to rebar but not as stable. Harder to use a center punch to create a simple for precise centering. If being used for layout avoid adjusting by hitting the actual spike and instead compact the earth on the opposite side you want the spike to move.
Hub and Tack – Less stable and more susceptible to disturbance than a rebar or spike depending on soil type. Good for layout as the hub needs to only be set approximately and then the tack can be used for precise demarcation.
Concrete pillar and brass cap – Very stable and well definable center point for control on bare earth. Takes the most effort & time to establish. Brass caps can also be set in existing concrete by drilling a hole and using grout. Typically used as primary control for long-term construction projects.
Rothbucher OPFA disc – Can be used on a variety of horizontal or vertical surfaces and allows for quick and easy use of all OPFA prisms. Can also be used like a mag nail when set with a masonry screw on the ground. Allows for very precise centering.
Center punch – Typically used on steel vertical faces in conjunction with magnetic nests ball prisms or a Rothbucher magnetic pot prism. Very stable. Allows for quick deployment of a prism above line of site obstructions.
Retroreflective target – Typically used on smooth vertical faces. Clean surface, ideally with alcohol, before applying sticker. Adhesive prone to failing over time in inclement conditions. Very susceptible to error induced from taking a reflectorless measurement at an oblique angle of incidence.
Circle adhesive labels – Used only for temporary situations on finished flooring where destructive demarcation isn’t acceptable. Commonly used for setting control inside of buildings post construction. Use packing tape to cover labels to increase durability slightly.
I used to set masonry cut nails in asphalt for turning points when running levels and points on a line for construction surveying.
In the US, rebar is probably not the best choice for control points because it is so widely used for property corners. In our city the Streets department uses 1/4" square bars for control to differentiate them. That is probably backward for BC.
Someone may post a picture of a used cotton picker spike, which comes with a center divot.
In our church parking lot I put stainless steel screws in some of the curbs as control for the main stall lines in case we sealcoat in the future.
And we've seen lots of stories of axles, rifle barrels, etc. for corners, that would also serve for control now that they probably aren't used for new work corners.
In the US, rebar is probably not the best choice for control points because it is so widely used for property corners. In our city the Streets department uses 1/4" square bars for control to differentiate them. That is probably backward for BC.
Someone may post a picture of a used cotton picker spike, which comes with a center divot.
In our church parking lot I put stainless steel screws in some of the curbs as control for the main stall lines in case we sealcoat in the future.
And we've seen lots of stories of axles, rifle barrels, etc. for corners, that would also serve for control now that they probably aren't used for new work corners.
Great point about the rebar & that is interested about using square bar for control as you alluded we do the exact opposite in BC. Square bar (Iron Pins) for property corners.
Down here in Florida it's common practice at the company I work with to also use rebar with a plastic cap denoting "Trav Pt" as control. Is this not common across the all of US? Or for other Floridian companies for that matter?
Brass caps can also be set in existing concrete by drilling a hole and using grout.
The BP markers from Berntsen are much quicker to install and are very durable. I mostly use them for marking boundary corners, but occasionally set one for control (mostly bench marks).
I have been using 8" dock spikes for 25 years now. I predrill a dimple in each one and after pounding them in a inch or so below grade touch the top with a magnet. For the most part they hold position well and are easy to find with a metal detector many years later.
Dittos on the Bernsten Brass Plugs. There are suppliers other than Bernsten as well. You will want to invest in a rotary hammer and the special countersink drill bit to install them. Which is something, but not too much. That rotary hammer has other uses. One drawback is that the plugs are non-ferrous, so they don't make the Schonstedt ring. But since you usually put them in concrete curbs and sidewalks they are generally pretty easy to find. They can be set in asphalt, too. I work primarily in urban/suburban areas and maybe 75% of my control marks are these plugs.
I'll use 1/2" x 24" rebar with a red plastic cap for control in soil/dirt. Our state law mandates 5/8" rebar for boundary marks so the chance of being confused for boundary is somewhat reduced. Those rebars make up maybe another 20% the control marks I set.
Of the remaining 5% most will be MAG Spikes. These have a very large head with a divot. Analogous to cotton gin spikes. Occasionally I will go with a MAG nail in a drill hole in concrete.
I regard wood hubs and MAG nails in asphalt or sidewalk joints as temporary control. I expect them to have a half-life of about 1 year. Oh, sure. A few will survive much longer. Around here wood hubs are frequently completely rotted away in 2 years.
One final note: When working in populated areas it often pays to look around before setting a new control mark. Very often a very serviceable mark set by the last guy is already present.
Down here in Florida it's common practice at the company I work with to also use rebar with a plastic cap denoting "Trav Pt" as control. Is this not common across the all of US?
It is very common everywhere I've been. Except in B.C. Some guys worry about it a lot, but it only rarely causes a problem. A homeowner is just as likely to mistake a blue gumball for a property corner as anything else.
I was trained not to set a control point where someone might be searching for a property corner. Did we quit that practice? Also was trained to figure out fairly quickly if a monument was a property corner or something else. If you can't you are possibly not ready for prime time. Back to my cave.
These are the go-to for control points in concrete here, 6mm bit in rotary hammer drill for the shaft and a 10mm bit to countersink. If you get the ones with stainless nail then you can put a punch mark in top of nail for greater centering certainty.
Or for other Floridian companies for that matter?
Here at Orange County Public Works in Orlando, FL we use red caps marked O.C. TRAV POINT on 5/8" rebar. We do come across traverse point caps on rebar from private companies.
I was trained not to set a control point where someone might be searching for a property corner.
Great training, especially true on my current project where I did find a traverse point IRC very close to where a boundary corner was supposed to have been. Especially annoying are control points set close to street intersections because the surveyors wanted an unobstructed view of the streets.
Berntsen make a magnet the fits below the plug when you use the countersunk bit, the really make them sing. In addition to setting them in concrete, they work well in asphalt as well if you're looking for something a little more permanent. I've found that mag nails with washer tend to get ripped out quite often.
On the dry side of an island volcano, I've used 1/4"-3/8" Ramset nails for control on exposed rock (which is frequent). They last years. In 10 yrs doing it I haven't seen one lost or destroyed, even on active heavy construction sites in traffic areas. Cheap and come with their own colored rubber apron, but I'll sometimes add a marker. Downside may be that there's not a lot of iron there. For less frequent areas where it looks like there may be enough dirt, 16" #4 rebar with a plastic cap. I have had to drill into subsurface rock and install with construction epoxy a couple times though.
On the dry side of an island volcano, I've used 1/4"-3/8" Ramset nails for control on exposed rock (which is frequent). They last years. In 10 yrs doing it I haven't seen one lost or destroyed, even on active heavy construction sites in traffic areas. Cheap and come with their own colored rubber apron, but I'll sometimes add a marker. Downside may be that there's not a lot of iron there. For less frequent areas where it looks like there may be enough dirt, 16" #4 rebar with a plastic cap. I have had to drill into subsurface rock and install with construction epoxy a couple times though.
Does the volcanic rock activate the metal detector?
Does the volcanic rock activate the metal detector?
The basalts (dark colored volcanic rocks) commonly found in the Portland area do. Quite strongly in many cases.
I'm partial to these for setting points in asphalt. Can usually drive them down flush so a snowplow isn't as likely to rip it out. Little beefier than a mag nail. The 3" are my preference over the longer ones, mostly as I can have a few in my vest rattling around for when I need one. Mag nails seem to have a way of escaping my vest in the parking lot and taking up residency in someone's tire, which turns out isn't a great way of making new friends.
Just because I'm paranoid, doesn't mean they aren't out to get me.
Does the volcanic rock activate the metal detector?
Yes, probably 10% of the time in some areas, which is way too often. I think volcanic rock (mostly basalt) has a higher metallic property the higher it's sulphur content so it varies within the same rock type. Solid iron nearby will "override" the effects of the weaker rock, but many times I'm searching, I kick, dig or scrape dirt out of the way, stick maggie back over the spot and it's silent. Then find it's a 1" rock in the last pile I kicked that's setting it off. Not true for the entire island though. Many places maybe have enough soil to reduce this effect, but it seems I get it pretty regularly.
I have been using 8" dock spikes for 25 years now. I predrill a dimple in each one and after pounding them in a inch or so below grade touch the top with a magnet. For the most part they hold position well and are easy to find with a metal detector many years later.
Awesome tip for making a center point!
We have areas of volcanic rock here, it's usually magnetic and makes finding pins more challenging. Sometimes they really set the detector off.