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Adding detergent to concrete mix? Answered

My father (sadly departed) used to add a dash of washing up liquid (detergent) to his concrete when mixing, and I never asked him why. I presume that is must have improved the 'workability' of the mix, or perhaps how easily it mixed. Does anyone else do this? What is the definitive reason? Would a small amount of detergent alter the final strength of the concrete under compression or flex? He was pretty smart, but I don't think he would have come up with the idea himself (although he was a chemistry teacher....).



Best Answer 1 year ago

Your father was a smart man! Historically detergent was added to concrete as an air-entrapment additive, which would keep small bubbles inside the concrete and allow small areas where the concrete could flex without cracking. Modern concrete takes this into account and adding detergent isn't required.

Great question!


1 year ago

Hi there, I have also used a cup of detergent per mix when rendering a wall. The detergent make the mix much easier to spread, smoother if I may say so. When rendering using regular cement mix, it is a real life saver. Rendering cement is more costly.


Reply 5 months ago

Hi you say a cup? Was that diluted and was that to a regular 4 sand to 1 cement mix?
I am rendering an outside garden wall and would like to give this a shot if you could give us your render mix recipe thanks.