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retarder in slabs on grade

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I am interested to know what everybody thinks about the use of retarder in
concrete slabs on grade. We have recently had a situation where the
supplier added retarder to the mix. Unfortunately he added 7 units instead
of 0.7 units. The resulting slab was similar to pudding with a crust on
top. The surface was unfinishable because it crusted before you could get
on it. Then by the time the rest had set there was no a drop of bleed water
to be found. We are considering eliminating it from the master spec
altogether. In this instance there was no need for retarder as the plant
was within a half hour from the site and we have not had any really hot
weather yet this year. 

Any opinions as to the need for this. 

BTW the mix had a slump of 1 1/2" to 2" arriving on site at which time
super-p was added to bring slump to pumpable range at 4" to 5". This was
not my spec but was the owner's. They have used it a lot with great success.

David Handy, P.Eng.
dhandy(--nospam--at)trg.ca
The Thompson Rosemount Group, Cornwall, Ont. Canada
Opinions expressed are personal only.

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