It did this trick once before - and it worked. It demerged its US building materials businesses from its Australian operations and the sum of the parts turned out to have more sharemarket value than the whole.

But it's a trick that only works when share markets are rising and it only works on a sustainable basis if the two daughters of the demerger are able to flourish in their own right.

Clearly there is some scepticism about this among the investment banking community.

There are a couple of reasons for this. The first of which is that the demerger offspring might be a bit small - not to survive but to attract capital via the equity market.

The second is that one or the other might receive too much debt and - at this stage CSR chief executive Jerry Maycock isn't giving anything away about how it will be allocated.

Investors will need to be assured that the "sugar" baby, which has long had a highly volatile earnings profile, will have manageable debt which is rated by the agencies like Standard & Poors.

If investors believe either of the new businesses to be too small or too risky they will disappear off investors' radars.

When it last split, the offspring were both relatively large. CSR today is capitalised at about $2 billion and sugar accounts for around 35 per cent of its assets.

The rationale of leaving these three disparate businesses together is that they were counter-cyclical and provided a diversity of earnings.

But the CSR board is of the view that the smaller offshoots will be more focused investment opportunities for the share market purists.

The "building materials'' baby, which has been growing through acquisition, appears to have more opportunities to add to its portfolio of assets. It could even go the full circle and get back into heavy construction materials.

But it will be weighed down by the asbestos liabilities which it will retain.