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mskin003 12-06-2011 01:44 PM

Concrete Stilt Repair
2 Attachment(s)

Please allow me to thank you beforehand for taking the time to read my post.

I am currently looking at buying a concrete house on concrete stilts in the Florida Keys.
While walking around the property I noticed that a couple of the stilts seem to be cracking and falling apart (3 out of 12 stilts). To my uneducated eye, it looks like the rebar inside the concrete is swelling up and causing the damage.

I have attached some pictures (sorry for the quality) of the 2 main problem stilts. Do you experts have any opinions on how big a repair job this is and how much it could possible cost?



nealtw 12-06-2011 05:10 PM

When air and water both get to the rebar it will rust and break concrete. The damaged posts will need to be replaced and the rest will want to be inspected really close. As far as big deals go, this is about as big as any.

BridgeMan 12-13-2011 02:57 PM

In a salt water environment, rebar corrosion is accelerated. And significant corrosion causes the steel to gain in volume, resulting in tensile forces in the concrete in front of it. Enough tension, and the concrete delaminates and breaks (spalls) off. If you have the opportunity, go back and lightly tap on all of the columns on the property, wherever you can reach, with a hammer. Locations where you hear a hollow, dull thud sound (as opposed to a higher-pitched, "ringing") indicate delamination, corroded rebar underneath, and eventual spalling.

As a DOT bridge engineer in a former life, I've supervised and inspected the repair of hundreds of similar (bridge) columns. Properly done, such repairs can last dozens of years; improper repairs will not last a year in salt water environments. In severe cases, temporary shoring has to be installed to support the overhead loads while the deteriorated concrete in the columns is chipped away, removed and replaced.

Before making an offer on the property, I'd strongly suggest you get a few lump sum quotes from qualified contractors for completely repairing all of the columns. You may find the quotes to be larger than the asking price.

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