Durability of Survey Points

What is a CM and ND?

I tend to countersink anything I want to stick around.

The continuing miserliness of some surveyors to not buy roto hammers is indicative of a unfortunate tendency of people to be penny wise but pound foolish. Nothing like seeing a control point for multi million dollar construction project as a nail in crack of concrete. 

This is a photo of a lot corner I marked a couple of years ago.  The point landed right on the edge of a new sidewalk, so I couldn't set a rebar or a 1" copper disk as I usually do.  I decided to drill into the edge of the sidewalk at 45° and set a nail and tag in lead.  Unfortunately, the newish concrete spalled as I was drilling, leaving a rough void a couple if inches wide.  So I borrowed an angle grinder from a guy who was working in the adjacent building to dress up the chipout a bit, and continued drilling.  What you see is a 10d (about 3" long) hot-dipped galvanized nail holding the tag solidly in lead wool.  I then mixed some quickset and applied it to smooth out the rough edges.  It's hardly the prettiest monument around, but I walked by it recently and it's holding up well.  The quickset has blended in with the parent concrete, so it doesn't look as ugly now as it does in the photo.

Posted by: @party-chef

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What is a CM and ND?

CM - Concrete Monument

ND - Nail & Disc

Posted by: @jim-frame

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This is a photo of a lot corner I marked a couple of years ago.

Great effort to set a point.

Posted by: @jim-frame

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What you see is a 10d (about 3" long) hot-dipped galvanized nail holding the tag solidly in lead wool.

I never heard of lead wool. Where did you buy it from? Does it work better than grout or epoxy? Have you ever reset a nail and disc in an existing hole in asphalt for whatever reason? If so, did you use cold asphalt patch or something else?

Lead wool -- it looks like steel wool, but is made of lead -- is used by plumbers to seal cast-iron pipe joints.  (It probably has other applications as well, but that's where I first encountered it.)  It's been at least 10 years since I  bought any, but it is/was available at any well-stocked hardware store.  The advantage over quickset or epoxy is that no mixing is required, and no setup time is  involved -- just pack the hole with lead, then drive in the nail.  As with all lead products, it's toxic and you should always wash your hands after handling it.  I don't use it often, but I keep some in the truck for tricky situations.

I consider points in AC pavement to be temporary, but on the rare occasions I have to set one, I prefer the 3" nails that Berntsen sells, along with a stainless steel washer.

Another option for setting nails in drill holes is solder, 1/8"

solid core kind without rosin or flux. It works just like lead. I cut a piece the depth of the hole and drop it in the hole and drive the nail. Sometimes it takes several pieces if the hole gets too big.

I consider MAG nails in asphalt to have a "half-life" of about 1 winter. That is, about half of all such nails set that way will be gone in a year, and half of those left will be gone in another year. And so on.  It is common for projects to get to construction 5 years after the initial survey. Using this formula, roughly 3% of the MAG nail control points initially set survive to construction. Not enough. YMMV, but the basic concept is true - MAG nails in asphalt are not particularly permanent.

MAGs leaded into concrete curbs are much more durable. Personally, I like to use Bernsten bronze plugs .

BTW, MAG nails and PK nails are distinctly different things, and the difference is significant. If you find an actual PK nail it probably wasn't set within the last 20 years.   

@norman-oklahoma 

Mark, I was thinking of you when I set, what might be my last, PK 3/4" PK nail last week.  I might have finally exhausted my strategic PK nail reserves. 

Posted by: @john-putnam

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I set, what might be my last, PK nail ....

If I find an actual PK I'll know who to call. FWIW, I keep a couple in my desk drawer so I can show people the difference. 

Posted by: @john-putnam

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strategic PK nail reserves. 

They could have been used as surveyor currency in a post-apocalyptic world

@norman-oklahoma 

I kept various surveyor caps in the truck. If you were not sure about setting a particular corner,  use their cap. ☺️ ☺️ ☺️ ☺️ ☺️ ☺️ 

I have a couple of @shelby-h-griggs-pls washers floating around the truck.

Posted by: @field-dog

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What's the durability of the survey points we set? I found one the other day while doing a plat check that I expect to be destroyed shortly after houses are being built. Please see the attached picture. I will set a CM under a sidewalk rather than cracking a sidewalk by placing a ND too close to the edge. I set a bunch of long PK-type nails & washers in a paved 2-lane road this week. I expect those to last for a while before the road gets repaved. I was entertaining thoughts of countersinking those nails & washers. Crazy, right?

-- attachment is not available --

 

That looks... kinda bad, but it's such an unfortunate spot.  I'd be tempted to do a witness corner 1' away instead maybe.

Posted by: @norman-oklahoma

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Personally, I like to use Bernsten bronze plugs .

I point out that, per Bernsten, brass washers run about $3.85 ea, and 2" mag nails $0.35 ea. Making the cost of the combination shown on the OPs photo $4.20.  Brass/Bronze plugs run $4.65 per, and are far more durable.  

Posted by: @john-putnam

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I have a couple of @shelby-h-griggs-pls washers floating around the truck.

This type of conversation is what makes this place great.