[TowerTalk] how much rust is too much?

[Matthew Kaufman]

On 10/13/2014 9:16 PM, Donald Chester wrote:
> It doesn't look too bad from the photos. Surface rust is to be expected. I would carefully inspect the base to see if most of the steel is still there.

Gotta figure out a way to measure that... maybe find someone with an 
ultrasonic thickness meter?

>   The guy anchor looks OK as well, but I would inspect it right where it goes into the concrete. Look for any signs of corrosion or cracks in the steel.

Will be clearing each excavation a little more and then putting a camera 
right at the joint and getting good pictures of each.

>   
>
> What looks worrisome with yours is that it appears the base pier is below grade, and the rest was back filled with dirt. I can't understand why whoever constructed the tower didn't raise the base pier a few inches above the ground just to make sure none of the steel would come in contact with the ground.  Perhaps someone added topsoil to the area after the tower was built.

It is on a slope below the building. What I think happened is that the 
slope eroded down and slowly covered up the base and bottom of the 
tower, and nobody thought that was a problem.

The slope continues below, and so my plan was to dig out a couple feet 
around the base and down a couple inches, fill to the level of the base 
with drain rock, and then install concrete retaining pavers on three 
sides, backfilled with drain rock. The fourth side I'll just re-open to 
the low side of the hill, and so no water will be able to collect in 
there once I'm done.

Don't want to do that big a project if I need a new tower, though :)


> If the integrity of the structure still looks good after careful inspection, I'd  clean everything off really well, and paint over the rusty metal with oil base aluminium paint or cold-galv.  I've found the aluminium paint to hold up longer than cold-galv in the spray can, but the brush-on stuff might be better.
>
> Then I'd dig a drainage ditch and remove the top soil down below the level of the concrete for a radius of several feet round the base of the tower, assuming the ground slopes downwards in at least one direction. Otherwise, you will need a sump pump to keep the base dry, if you can't find some way to keep the water flowing away naturally.

See above... really easy to get the water to just flow naturally away, 
and to ensure that the base never gets covered back up with dirt.

>
> One thing. DON'T even think about back filling the hole with concrete to get it back up to grade. The base pin and  plate is a far better way to do it than the typical Hammy Hambone method of burying the bottom section of tower in the concrete.  You want the tower to be able to sway and give a little under high wind conditions. Fixing the base solidly in the pier buried under concrete causes movement of the tower under wind conditions to put all the stress on the tower sections, possibly causing failure at the welds under extreme conditions. Besides, back filling with concrete would be  no guarantee of a perfect seal between the old and new concrete, and any additional rust would then be hidden from view - not good.

Yeah, that was my biggest concern... burying ongoing rust in concrete 
just feels like a disaster waiting to happen with no way to monitor 
what's going on.

Thanks for the input,

Matthew