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New slab over old slab
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| tbasc@bellsouth.net 2006-04-21, 10:21 am |
| I'm involved with a project to build a new shed in place of an existing
one.
There is a slab in place that appears to be without cracks.
We have no idea of thickness. The slab is "L" shaped about 32'-0" x
18'-0" & 13'-0".
I want to pour a new slab over the old slab to raise the top of slab
above grade and to provide a thickened edge. I'd appreciate comments
on potential problems.
TB
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| Bob Morrison 2006-04-21, 11:21 am |
| In a previous post tbasc@bellsouth.net wrote...
> I'm involved with a project to build a new shed in place of an existing
> one.
> There is a slab in place that appears to be without cracks.
> We have no idea of thickness. The slab is "L" shaped about 32'-0" x
> 18'-0" & 13'-0".
> I want to pour a new slab over the old slab to raise the top of slab
> above grade and to provide a thickened edge. I'd appreciate comments
> on potential problems.
>
Tom:
I once specified a new topping slab for a floor subject to heavy wheel
loads. The topping could only be 2 inches thick so it had to be very
strong and we wanted to minimize shrinkage cracking. first, the existing
slab was thoroughly cleaned with muriatic acid and then coated with a
concrete bonding agent. Then concrete was applied.
Mix design:
7 sacks of cement per cu yd
3 gallons of water per sack
3/8" pea gravel
high range water reducer
This is a very dry mix. The 3 gallons of water per sack is just enough to
hydrate the cement, but not enough to allow the concrete to be placed.
That's where the high range water reducer comes in. This mix has a very
short "pot life" and will set up quickly with very little shrinkage. I
recommended to the contractor that he have double his normal finishing
crew.
From the dimensions you describe it looks like you could get away with
just 2 crack control joints.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com
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| tbasc@bellsouth.net 2006-04-21, 12:21 pm |
| Bob,
Thanks for the comments.
Tom
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| clintonG 2006-04-21, 1:21 pm |
| I would not pour over the existing control joints -- if any -- follow the
existing joints.
<%= Clinton Gallagher
NET csgallagher AT metromilwaukee.com
URL http://clintongallagher.metromilwaukee.com/
<tbasc@bellsouth.net> wrote in message
news:1145629119.343707.297540@i40g2000cwc.googlegroups.com...
> Bob,
> Thanks for the comments.
> Tom
>
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| R'zenboom 2006-04-21, 4:21 pm |
|
<tbasc@bellsouth.net> wrote in message
news:1145624060.540919.178980@g10g2000cwb.googlegroups.com...
> I'm involved with a project to build a new shed in place of an existing
> one.
> There is a slab in place that appears to be without cracks.
> We have no idea of thickness. The slab is "L" shaped about 32'-0" x
> 18'-0" & 13'-0".
> I want to pour a new slab over the old slab to raise the top of slab
> above grade and to provide a thickened edge. I'd appreciate comments
> on potential problems.
> TB
>
why not find out if it's already thick enough, and concider reducing the
grade level as an option!
--
R'zenboom
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| tbasc@bellsouth.net 2006-04-21, 7:21 pm |
| I wish the grade level could be reduced.
Slab sits at property line on two sides.
Third side is pavement.
This is a densely built area with houses built in the 1800s.
The shed itself was originally built in 1909 according to Sanborne
maps.
Board of Architectural Review wanted to save the existing shed.
(It's wrinkled tin with 2x4s @ 30" as framing for all but one wall.)
TB
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| tbasc@bellsouth.net 2006-04-21, 7:21 pm |
| No control joints.
Slab, although apparently sound, appears to have been done without
benefit of engineer or code.
TB
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