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Re: Removing structural plaster from shotcrete

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Original pool plaster is structurally bonded to the gunite shell. It's
impossible to remove this layer without pulling out some gunite. It seams to
me you have a large concrete repair project on your hands.

I would venture to say that the removal of the dense cement plaster cover
will result in corrosion of the rebar, now that it is exposed to the
elements. Ultimately, you may be applying a corrosion inhibitor over the
rebar.

As for the crack, or cracks, the method of repair would probably depend on
whether it forms at the 'hinge' (transition from shallow to deep end). More
importantly, the appropriate repair method may be dictated by the cause; for
example, if it's settlement related and the pool exists at the top of a
non-conforming slope.

If the cracks are injectable, this would be 'blind-side' injection into a
more porous (probably moist to wet) concrete, or rather gunite. Not an easy
thing to spec out in terms of structural resins.

I would lean towards a moisture insensitive epoxy gel, using pressures that
would accommodate the particular crack widths. I would use a cementatious
(perhaps hydraulic and preferably white) cap seal, because I would grind it
down later and would feel uncomfortable with the bonding of new plaster onto
the surface area of repair if it has been smeared/coated with resins.
Getting a cementatios cap seal to handle significant pressures would be your
challange! Further, I would take quality control very seriously as
un-catalyzed resin in a swimming pool shell would be disastrous.

Good luck.

Steven A.
Los Angeles


Structuralist wrote:

> I have been asked to review a problem with a local swimming pool. The
> pool was constructed of reinforced Shotcrete (pneumatically injected
> concrete) that ranges from 4" thick to 5-1/2" thick. The rebar appears
> to be within one inch of "air" and three inches to earth. A 1" plaster
> was applied over the shotcrete and tile was added around the perimeter
> at the area above the water line.
>
> There was a crack in the pool and the ower decided to remove the plaster
> and create a new shotcrete shell within the existing. His contractor
> removed the plaster using a jackhammer and took off enough of the
> concrete below the plaster to expose the steel in parts.
>
> Here are some questons I have:
>
> 1. What other methods can be used to remove plaster without doing so
> much damage to the concrete below.
>
> 2. If there was a crack in the concrete, is there a standard for the
> crack repair in a pool and what is it? Is it less destructive and less
> costly than the method that the contractor took to strip the entire
> interior of the pool which the owner is claiming cost him $35,000.00
> including the new shell.
>
> 3. It seems to me that minor cracks (which this appears to be) are
> repairable by injection epoxies or injection grouting and then resealing
> the surface with either plaster or another epoxy or elastomeric type
> finish. Any suggestions?
>
> I am trying to get an idea to justify what was done or to find out what
> options for pool repair is available that will correct a minor crack. I
> was intending on contacting my representative from Chem-Rex to see which
> of their products would do the trick. Assuming the owner wants the same
> finish as he had, what are the alternatives to such drastic demolition
> and repair as he had chosen?
>
> Thanks
>
> Dennis
>
> Regards,
> Dennis S. Wish, PE
> Structural Engineering Consultant
> mailto:structures(--nospam--at)engineer.com
> (208) 361-5447 E-Fax
>
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