Screed additives explanation

[johnny2007]

Got quotes for a screed for an extension that has a step down (45/50mm approx).
One of them includes Flowcrete Isocrete SBR (Bonding Agent) and Flowcrete Isocrete SBR (Screed additive) and another only the Flowcrete Isocrete SBR (Bonding Agent), not Screed additive.
The guy at the screed company said that for domestic applications the screed additive is not required (saving of £300).
Can you explain the difference please and confirm what they said is correct.
In my days screed was sand, cement and fibres (if you were lucky) .

 

[SpecialK]

Not sure - Did you explain to both it will be an unbonded screed on insulation and a plastic sheet?

I went with gypsol screed - No additives were mentioned. It was £1k 25m2 at 55mm. Had it sanded after for about £100.

 

[johnny2007]

Sorry, forgot to mention.
This is going on existing screed.