I know this isn’t really about tools, but you guys have been so helpful about my other questions, I thought I’d try.
So the guardrail next to the stairs and wheelchair ramp in front of my building are apparently made of ungalvanized, unprimed steel. The paint is cracking, and where it is cracking, water is entering and creating rust. But that I can deal with, by removing all the paint, prime the rail with something rust-resistant, and repaint it.
I am concerned about the mounting plates where the rail is bolted to the concrete pad. I was able to lift one of them a few inches, and chunks of rust fell off. Apparently water is seeping under the plate by capillary action. I tried to prime the underside of the plate, but I think that isn’t enough.
If it were up to you, how would you prevent the underside of the mounting plates from rusting? I have tried to think of some kind of barrier that would prevent water from being trapped against the plate, but I am coming up short.
Another HOA board person suggested putting clear silcone around the outside of the plate, to prevent water from seeping underneath, but I understand water can wick up through the concrete itself.
Any ideas? Thanks! And if you know of other forums where I should be asking these things, let me know.
That’s what I’d suggest
The steel mounting plates are probably suffering from several different sorts of corrosive attack.
Where the steel touches the concrete and water seeps in and up (as you discern) through the concrete the steel is probably suffering form a phenomenon called differential aeration corrosion - where galvanic cells are being set up between different spots on the steel. The concrete itself may also be leaching out corrosive agents - similar to what happens to rebar when chlorides (e.g. from salt) are present in the concrete. Salt (e.g Halide ice-melter) if used around you railing will certainly accelerate this action. Since the railing and mounting plates were made of mild steel there is no cathodic protection afforded as might be the case if the steel had been galvanized (with zinc). Adding cathodic protection now would seem to be impractical. Thoroughly coating the steel with "rust preventative? paint may stem the tide a bit - but any holiday (because of incomplete paint application or that happens over time from damage) in the paint film will become a spot for corrosive attack. As you note - mild steel corrodes in a manner that causes flakes of rust to exfoliate and painted surfaces will often blister because of this. The silicone caulking idea may increase the longevity of the railing - but once exfoliating rust has started - it is likely to progress. If when applying the silicone - you can lift railing to force silicone under the mounting plate that might be better - but seems like a lot of extra work. As I said - adding cathodic protection - either with impressed current (probably not safe in this application) or by adding zinc plates under each mounting plate - would seem extremely impractical - and/or might cost as much as replacing the entire railing system with SS or Aluminum. Having once been in the business of pipe and metal fabrication/installation - including custom railings - I can attest that railing replacement would not be cheap - but maybe eventually necessary. Your HOA may wish to start building a reserve against this eventuality - do what you can now to slow the deterioration - and monitor the railing to make sure it remains safe. If your complex uses ice melting compounds in the winter - they may want to try using one of the other less corrosive (e.g. urea based) ice melting compounds around the railing.
Just take your used motor oil and pour it on and around the base plate. If you can use a cheap paint brush and wipe it on the bottom side. You can also put the oil in a oilier so you can squirt it under there or put it in a weed/pesticide sprayer and pressurize it and spray it under there. This works great for the underside of cars too (especially in the winter). Works every time.
I just thought that Stuart - the host of this site and the Toolguyd Blog would likely have some learned perspective on this - considering his PhD in material science.
Thanks! So you are suggesting surrounding the mounting plate with concrete patch? Wouldn’t water still seep in in the tiny gap between the patch and the steel? And wouldn’t water wick up through the concrete itself? I know it does generally.
Thanks! I will warn them not to use salt ice melter around the rails.
The problem with coating the underside of the plates (I also thought of something tar-based, like roofing compound) is that I can’t lift them more than an inch or so. I suppose I could unscrew very plate, but I imagine most of the bolts are rusted solid, and one plate is screwed down tight with broken-off Tapcon screws (see my previous post). And then, lifting the entire guard rail assembly would be a big job, as you can imagine.
I think what you say about saving up for a replacement is smart. (sigh)
Thanks for the idea. I am worried about the oil staining the concrete (we want to preserve property values and all that), and also eventually washing away. I thought of using something stiffer, like something tar- or rubber-based. But I can’t get under the plates very well. I might just try to swab some strong primer under there.