Zakko wrote:
Is it alright to use washing soda (sodium bicarbonate) to clean and
degrease the emulsion paint on an interior wall before repainting?

I don't want to buy sugar soap just for this one job and I have lots of
washing soda.

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Is it true I should not use Flash because it leaves a shine of slippery
silicates and emulsion paint will not adhere well to this?

Washing soda is sodium carbonate BTW, which is likely to soak into the
plaster and leave a deposit of hygroscopic salts.
Even if this is a kitchen where the deposits are oily/fatty, hot water
and detergent would be a better bet