[TowerTalk] USTower anchor bolts rusting

[Grant Saviers]

I have found that Rustoleum paints are tough and really hold up well if 
enough is applied.  Either spray cans or spray gun applied.  For bare or 
HR steel, I start with a coat of red primer, then a coat of grey primer 
so holidays are visible, then two coats of the finish color, usually 
yellow for equipment.  I have several things (trailer, fork lift boom, 
man basket, etc)  that have been outside 8 years in CA and 5 years in WA 
with no general rust, only small spots where they were chipped.  Big box 
and Krylon brands don't cover anywhere as well or last as long.  Powder 
coated stuff I've bought, once it starts to rust, makes a flaky mess.

RE phosphate conversions prior to painting - an very good way to prepare 
bare steel, but a bit messy by hand.   I was involved in salt spray 
tests of painted electronic cabinets and the phosphating made a huge 
improvement in durability.  Just as chromate/Iridine/Alodine conversion 
coating was our practice for bare aluminum.

I haven't tried aluminum paint in some time.  Certainly a lot cheaper 
than cold galvanizing.

Grant KZ1W


On 4/1/2017 0:58 AM, Donald Chester wrote:
>> Grant KZ1W wrote:
>> Another fix I use is spray zinc "cold" galvanizing as I had to machine
>> some custom steel spacers under the base plate for leveling.
> Something I have found that works better than "Cold-Galv" is ordinary aluminium paint, Rustoleum or similar brands. I have found that after a couple of years rust spots begin to appear through the Cold-Galv, but it takes many years for aluminium paint to rust through, and it adheres to the metal rarely  scaling.  I put my tower up in 1981, using a base insulator I inherited from a fallen broadcast tower.  The end castings were un-galvanised cast steel, covered with a mixture of rust and red  paint.  I stripped off the paint and sanded off the rust, then gave them a couple of coats of aluminium paint.  I've had to re-paint it once in the past 36 years the tower has been up.  The hot-dipped galvanising on the tower shows more rust spots than the aluminium-painted base insulator castings.
>
> I touched up the freshly cut ends of some galvanised steel straps I used in another antenna construction project using aluminium paint, and still no rust after  several years.  The paint blends in so well with the galvanising that you would think the whole thing was hot-dipped after it was cut.
>
> You don't have to remove all the surface rust, just the thick or loose scaly stuff.  A thin coat of rust that is still firmly adhered to  the metal soaks up the paint like a sponge soaks up water, and actually makes it adhere better.  A technique sometimes used for painting steel with any kind of paint, is to brush or spray on a weak acid solution first. After the solution is thoroughly dry, paint is applied.  The thin layer of corrosion helps hold the  paint on.
>
> Don k4kyv
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