Gentlemen,
I need to sink a substantial RSJ into the earth at the end of the garden to form a stable base for an antenna mast. I'll be digging out the earth, sinking the RSJ in to a depth of about 3' and pouring conrete in up to ground level to make sure it doesn't move. The question is, what is the best coating to apply to the bare steel before placing it in position?
Thanks,
CD
Well, something with zinc in it I'd say, The big issue is at ground level, I've found. It seems that around the surface of the concrete is where they generally rust. I had some angle iron in for a similar reason and it always was going rusty no matter what I put on the darned stuff. Somebody once told me I should have used Red Oxide paint, but I don't think that exists any more due to its toxicity. Engenamal maybe, but the best I found was that stuff that inhibits rust then a liberal coating of zinc paint all over it. Brian
The steel will be fairly protected from atmospheric oxygen by the concrete so should not rust unduly. You could try a chromate primer I suppose. Or coat it with epoxy.
A tip, if I may.
Make a sleeve from thin metal which slides over the RSJ, so you can slide it out if needed.
My mast, a Tennamast, came with a 100mm square ground post. It was supplied with a sleeve as described.
While I’ve never needed to move the ground post in 20 years or so, the option is there. My mast is galvanised- including the ground post- but I used some waxoyl in the sleeve, partly as a lubricant, partly as protection, and partly as it was to hand- grease would have done.
New steel lattice road sign uprights have something that looks like a bitumen based paint to about a foot above ground level (I spent a long time in a queue at road works with nothing much else to look at).
Marine epoxy paints are designed to keep steel ships from rusting in sea water, so should be effective, although almost certainly expensive.
You could, of course, just use an even more substantial RSJ and not worry too much about a bit of rust, as it has lots of spare strength.
How long do you want this thing to last? The design life of a new-build house is taken to be 60-70 years while the design life of a National Grid pylon is stated at 80 for the structure and 40 for the cabling, insulators etc. The design life of a steel beam is in the order of 100-150 years so even if it is stuck in the ground it will probably outlast its surroundings.
As for coatings, metals4u.co.uk state that their RSJs already come with a red oxide primer. I imagine the same is true of other suppliers so the job's already been done.
Nick
Get a concrete fencing repair spur (or two) and concrete them into the ground. Then bolt the aerial or whatever on to spur.
My father buried a steel post in a lump of concrete in 1955. By 1975 the post had rotted above ground. It was fine inside the concrete
I didn't say it wouldn't rust. Like the SS Great Britain. That rusted, but Brunel had made the hull so thick that rust that would have eaten away a more modern ship, didn't destroy it.
Err, not true. The salt has got into the steel and once it was brought back to Bristols warm humid air it deteriorated quickly so now it has a false 'sea' of glass and below the glass it is permanently kept warm and dry with lots of expensive air conditioning. God knows what the energy bills required to do that now cost.
I was supporting your position with a practical example. 20 years is pretty good going and the bit below ground was still in the concrete when it was excavated en masse. The pole rotted mainly because it got filled with water.
Sorry, I thought you were giving an example of how quickly a post can rot :-)
I have a 4" x 4" x 0.25" square tube post in my garden to support a light. That has been in place 30 years without any signs of rust. However, I did paint it with original Hammerite before installation and filled the centre with well tamped down concrete after, so it couldn't fill up with water.
My point is that it did survive to be preserved and that was down to Victorian over-engineering.
Or use stainless steel. Thats what our irrigation control stuctures use now.
The best coating is concrete. But slope the top surface away from the post, and have it above the surrounding ground level. Make a simple wooden shutter as a collar to allow the concrete to be above the ground.
The best material I know of, is 3" diameter iron drain pipe. Doesn't need a finish :-)
We did a project with that back home, and it's still there after forty years. Has not tipped over, nor snapped off. I always get a chuckle when I see it, and it's still there.
Paul
Years ago an enineering group in the North of England were asked to survey and report on the condition of the support structures of the winding engines. They discovered that after years of miners taking a last minut widdle before going underground the bases of the frames were thick with rust' Like a fur coat.
If its a lattice mast like the old Strumech ones then they normally came with a ground post, but such things are now very expensive new, and old ones leave the post behind, so I do hope that its man enough for the job if its a tilt over jobby. Brian
Sounds optimal! Pity we don't have any reclaimation yards in my neck of the woods. My only option is to pay some scally to nick one off the town hall. ;-)
Didn't work too well with the Forth Road Bridge.
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