Steel in soil connundrum

[ReverenceEng]

I have a client that wants to hilti a cantilever steel post (for a sign) to a slab, but IN a planter...with soil. I have advised protecting the steel with some sort of concrete pedestal / sonotube/etc, but they want to be able to easily dig out the dirt (about 3-4' deep) and remove the sign or swap it out if need be in the future...without hacking away at concrete. Other solutions include a small spread/concrete block they can just lift into place and then anchor to that.

However, the only thing I want to focus this thread on is the steel in soil. We know it's not a good idea, especially in a planter where there are sprinklers, and especially when we have fasteners, welds, and anchor holes. In my book, not good to have this stuff exposed in the dirt.

My client has offered using a waterproofing paint that is spec'd for the masonry (going on inside of planter) but I just don't know...gut says no, but I don't have a real good reason for saying so...

Anyone have any insight or experience with this in general or specifically with the CMU water proofing "paint"?

 

[BAretired]

How about galvanizing the steel post?

BA

 

[ReverenceEng]

I have suggested in the past for them to have the assembly shipped off after fabrication to get hot dipped, but "it costs too much" for the project price...says they...however, I have also read that even HDG steel in soil still isn't a stellar idea...

 

[hokie66]

A bitumastic coating should be suitable. Won't last indefinitely, but for a small thing like this which can be replaced, it should last for a few years. But hot dipping it would be much better.

 

[oldestguy]

Can you set the post inside a 3" (or other)PVC pipe which first if filled with cement grout freshly placed? If "belt and suspenders" concern coat first with tar.

 

[SlideRuleEra]

If you use paint, go with one intended to protect steel underground. Bitumastic 50 is used on driven steel H piles and other long term in-ground steel. It is very "nasty", but works fairly well.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[txeng91]

I have specified Xypex waterproofing on the interior or exterior face of basement walls before. While it keep water out, it will also keep water in, so it might do as much harm as it will good if water can still get into the planter from the top.

 

[Ron]

Agree with hokie66 and SRE....use a bituminous coating....even roofing cement will protect it better than any paint you'll put on it. Bitumastic 50 is excellent for this. I would dip the post and base plate a couple of times with drying between if you can. Otherwise just put several coats on it.

 

[HouseBoy]

Working on a elevated deck rehab now with steel cols embedded in concrete slab and below grade BPs.
Here what that looks like after 25 years:

 

[XR250]

Go stainless. Cheaper than you spending any more time on this for one sign assembly

 

[JAE]

I would go with bituminous coating or another possibility is to install the column/base plate, then use a PVC tube or some other kind of non-ferrous tube or pipe to rest over and around the column/plate assembly and then fill the thing with grease. At some later date - they could remove the soil and pull off the pipe/grease and remove the column. Or some other wrapping material around a thick coat of grease could work too.

Check out Eng-Tips Forum's Policies here:
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[MotorCity]

User thicker steel for all elements exposed to soil. Consider it as a sacrificial thickness of steel.

 

[Nor Cal SE]

I'm not a coatings expert, but it looks like others have already provided good insight on that front. I also like MotorCity's idea to go thicker-than-needed with your tube steel walls, and you can explain to the client that the slight increase in material cost will be negated by the longer service life, potentially years longer. I would combine these two items: thicker steel walls plus coatings as recommended by others.

I would also think about putting to the client in writing, perhaps with a simple e-mail, a recommendation that they thoroughly inspect the steel every 5 years and take recordings of steel wall thickness. There is no guarantee they will implement these recommendations, but at minimum you will always be able to prove that you advised it.

 

[XR250]

I would also think about putting to the client in writing, perhaps with a simple e-mail, a recommendation that they thoroughly inspect the steel every 5 years and take recordings of steel wall thickness. There is no guarantee they will implement these recommendations, but at minimum you will always be able to prove that you advised it.

I still don't get why you don't use stainless. Do you really think the client wants to pay you to write this CYA letter or even inspect the steel every 5 years?
Have you had it priced out both ways?

 

[Nor Cal SE]

I think stainless column is a completely valid option worth considering. My experience is that almost no client will want to pull the trigger on it due to cost, or sometimes also due to long lead-time for the member size required. However, there is certainly no harm in presenting the benefits of stainless to the client. My thoughts above would apply to the scenario where stainless has been taken out of the discussion.

 

[canwesteng]

I'd look to use stainless anchors at least. I don't believe there is an issue with cathodic corrosion if the fastener is stainless (not so if the fastener is galvanized), but I would confirm before proceeding. The post can be coated with tar and replaced at failure. This is assuming the consequence of failure is small, but if the post if 40' in the air this is probably not approriate.

 

[XR250]

I think stainless column is a completely valid option worth considering. My experience is that almost no client will want to pull the trigger on it due to cost, or sometimes also due to long lead-time for the member size required. However, there is certainly no harm in presenting the benefits of stainless to the client. My thoughts above would apply to the scenario where stainless has been taken out of the discussion.

I was under the impression that this was a small sign as you indicated it would attach to a slab. It should not be a problem to get a stainless member for that.
If it is big, then yes, that could be an issue of significant cost and lead time.

 

[Gousey]

Can you allow for drainage through that location? In the past I have adopted a combination of Hot Dipped Galvanized sections and connections and have specified a drain pipe wrapped in geofabric below the location of the connections. Granular fill can then be provided to your desired surface level.

Bituminous paint is a simpler option, however if shortcuts are taken with the application your structure will deteriorate without anyone knowing about it.

I would never use steel sections that are not treated to be in direct contact with soil - it just isn't good practice.

 

[ReverenceEng]

wow! thanks for all the participation - good for this project and learned a lot.

it is indeed a small sign on a slab in a planter, about 10' tall. My client is a large sign company that rolls these out like clockwork so although stainless steel "could" be procured, they prefer to use what they have on their shelves where possible to keep manufacturing flowing.

Normally I spec bituminous paint or a two-part epoxy for smaller things, bituminous only for a bit larger, and sometimes even just go with concrete cover for much larger ones with larger expected service lives. They don't like the bituminous because it is "messy" (says them).

Thanks for all feedback!