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retarder in slabs

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I am interested to know what everybody thinks about the use of retarder in
concrete slabs. 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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