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sugar soap

n. An extremely powerful detergent used for washing surfaces prior to painting.

Wikipedia
Sugar soap

Sugar soap as typically found in Commonwealth countries is a cleaning material of variable composition sold for use on surfaces affected by greasy or tarry deposits which are not easily removed with routine domestic cleaning materials. When in dry powder form it looks like table sugar thus causing the name.

The solution is alkaline and its uses include cleaning paintwork in preparation for repainting.

Usage examples of "sugar soap".

In the kitchen are bottles of 80-proof vodka to make the translucent rose geranium and brown sugar soap and the patchouli soap, and I steal a bottle of vodka and spend my personal burial money on cigarettes.