Painting a Silo

Question:

One of my predecessors put the water tower too close to one of our silos when we moved to our current location. The tower is blowing damp air and small water droplets onto the silo causing it to rust.

My problem is that I've tried three paints in three years to prevent this, but all have failed and peeled away in less than a year. The silo is always sanded down and painted over a long weekend. I believe the last two paints I've used were polyurethane, the first a single-component, the second a two-component paint. I've considered epoxy paints, but I've heard that they don't weather well outdoors.

I'm currently working to put a physical barrier between the silo and tower, but I still need to repaint. Can you recommend a treatment that may work better for me? P.F.

Answer:

The physical barrier may not help. Airflow around it may still allow damp air and water droplets to wet the silo. To be effective, the barrier may have to be prohibitively large or may have to completely cover the silo. You are right about the epoxy, they do chalk and fade on outdoor exposure.

It sounds like you have a real problem. My first guess is that the substrate was not properly pretreated. Don't despair! Your problem can be solved. All you need is a properly pretreated substrate and the "right "paint. Since you previously painted over a long weekend, you must already realize that the substrate has to be dry before repainting. In case you don't realize it, you must shut off the water tower and dry the substrate before pretreating and painting.

Remove the rust and peeling paint from the silo by mechanical abrasion using sanding, blasting or wire brushing methods. After the rust and old paint are removed, the substrate must be painted as soon as possible to prevent flash rusting and subsequent paint failure.

The paints chosen must be able to withstand moist atmosphere exposure conditions. I recommend a two-coat finish system. A good choice would be marine paints for splash zone exposure. They are available from people who sell commercial ship and pleasure boat supplies. They can provide you with primers and topcoats in all colors including battleship gray. On the other hand, if you want to mix and match or otherwise choose your own finish system, I recommend a two-component epoxy polyamide zinc chromate primer topcoated with a two-component polyurethane enamel. They are available from people who supply architectural paints. There are also waterborne primers and enamels available for marine exposure.