A call for assistance carrying cream building material (8)
I believe the answer is:
Here is my best explanation:
'building material' is the definition.
'a call for assistance carrying cream' is the subsidiary indication.
'call for assistance' becomes 'sos'.
'carrying' means one lot of letters goes inside another.
'cream' becomes 'best' (I've seen this before).
'sos' going around 'best' is 'sbestos'.
(Other definitions for asbestos that I've seen before include "'Fireproof substance, dangerous to health (8)'", "retardant", "Once used for safety, it proved dangerous", "fire protection", "I might end up lagging", "Fireproof material, now known to be dangerous", "Protective fabric", "Old fire-retardant", "Fibrous insulation material, dangerous to health" and "dangerous dust".)