Rust Spots on Exterior of CIP Water Tank

[Trillers]

Greetings -

We are working on rehabilitating an existing concrete water tank 24'L x 12'W x 10'H constructed in 1998. The tank appears to be in fairly good shape and the owner indicated no leakage prior to it being emptied in 2017.

We want to make sure the tank is OK for recommissioning so will use HLM 5000 on the interior wall. We will waterplug any problematic appearing areas on the interior prior to application of the HLM 5000.

Two Issues:

1. TANK COATING: The owner would like the exterior treated with HLM 5000 which I am hesitant to do as I don't believe it will actually improve the tank integrity, and may pose greater issues with future maintenance.

2. EVIDENCE OF CORROSION: In a few exterior locations along the wall faces there are "rust" streaks and the owner would like us to determine the cause prior to painting the tank's exterior wall. The owner's rep has requested that we chip out the concrete until we reach the source of the rust stains before we determine what restoration methods should be. Since the stains are streaks no more than 2' long and there are only 5 of them I am of the opinion that we leave well enough alone.

Would like your thoughts on the TANK COATING issue.

For the CORROSION issue are there good references which address similar scenarios?

Thank you.

 

[hokie66]

That coating is intended as a waterproofing membrane. It may be appropriate for the inside surface, but not the outside. You don't want a membrane on both surfaces.

As to what to do about the rust streaks, I would have to see it. It may be a few places where the reinforcement is too close to the face. I think the owner's rep's request is appropriate.

Some testing for carbonation is appropriate, and even if you don't have carbonation to any extent, an anti-carbonation coating on the outside would be desirable.

 

[JAE]

I would agree with hokie66 on not painting both sides.

On the rusting - are you sure the rusting isn't from aggregates (vs. rebar)? Sometimes ferrous material "happens" in mixes and results in rust stains.

 

[Trillers]

Greetings HOKIE and JAE-

In full agreement with you on the coating.

Regarding the rusting - there was no spalling or cracking near the origin of the stains, so tend to think it is tie wire or form nails "inadvertently" left in place.

Thanks for the input gents - be safe and well.

Trillers.