HAVE ALREADY ANSWERED THIS IN MY EARLIER POSTS, REPEATING IT AGAIN;
Contractors have tendency to use burnt oil which is available cheaper in the market which works as a form release agent.
However, as Engineers, we overlook the disastrous effects it can have over the set concrete as well as the reinforcement which is coated with this oil and is generally not washed with detergent etc to remove the oil.
As a rule, I have been enforcing the use of " form release agents " like Fosroc -Reebol Wb / or Sika -Separol " and so on.... These form release agents dry out in about 15 min of application and hence create a film on the shutters and are easy to de-shutter. However, due to the cost contractors do not use it.
If we consider the effective use then these release agents work out cheaper as the shutters are protected at the same time giving you more repetition in turn becoming cost-effective to both the contractors as well as the client in case shuttering is in his scope.
It can be used on following type of shuttering:
Steel formwork - coverage @ 40-50 sqm/lit
Plastic formwork - coverage similar to steel
Timber formwork - coverage @ 20sqm/lit
Aluminium formwork - coverage similar to steel
Off late cost at site per litre is about Rs 140/lit and comes in 200 lit capacity, 50 lit so actual cost for timber shuttering works out to Rs 7.5/sqm and steel/alln/plastic shuttering works out to Rs 3.75/sqm.
Use of rollers makes it easy to apply at the same time giving good coverage as compared to the burnt oil which is generally applied thick with katha, goni , cotton waste and what not......
Have been using Razon's Shutter Coat SC 17000 oil for mivan aluminium formwork shuttering. Good release and best part is after 4-5th curing cycle oil washes out leaving no oil adhearing to concrete making bonding of any paint, putty or plaster hassle free. I checked it has neutral pH value so it is safe for form work. Costs around 25-30 paisa a sqft.
Good product, reasonable cost and good result for shuttering