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During renovation I have used all kinds of dry compounds, be it mortar, conrete mix, tile glue, grout, plastering mud, ... On every one of them the instructions say to add the dry mix to water and mix thoroughly.

Is there any reason behind this order?

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    It depends on the method of mixing, i.e. the available tools. If you use showels on a concrete floor instead of a container, you first mix the dry ingredients and then make a dip in the middle to add water. You simply cannot do it in the reverse order - there is nothing to contain the water. You compensate for the risk of dry globs by more mixing. – fraxinus Jul 2 '20 at 20:05
  • When we did fence posts, the quick-dry cement instructions said to add the dry mix first. – BlueRaja - Danny Pflughoeft Jul 2 '20 at 20:52
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    Completely random non-answer, but interesting nonetheless. We did a dark-colored grout on a tile job and some of the lines were just gray mortar colored afterward due to uneven distribution of pigment even though we mixed it for like 15 minutes using a drill. Appearantly it is essential to mix the grout dry before mixing with water. – trognanders Jul 3 '20 at 1:48
  • Here Ed says it is a good way to get the right proportions and remove clumps: youtu.be/PkDqc1LHPbA?t=240 – Mateo Jul 4 '20 at 16:34
  • You don't use a cement mill to mix your concrete? – Mast Jul 5 '20 at 17:41
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Yes, there is a very good reason. If you add water to dry mix in the bottom of the container, you get a nearly impossible to incorporate glob of the dry mix at the bottom.

On the other hand, if you add it from the top, it's much easier to get it all incorporated.

This works with everything from pancake mix to drywall compound.

Try it each way and you'll see for yourself.

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    +1 My morning hot chocolate mix works like that too. – Michael Karas Jul 2 '20 at 11:27
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    @MichaelKaras, one of my first childhood lessons: milk then chocolate, not the opposite! – Thomas Jul 2 '20 at 20:25
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    @MichaelKaras: With hot chocolate, it also works to add a bit of water first and stir to form a slurry, then fill up. (Easy to wet all the powder because clumps are not suspended in liquid; you can push on them with your spoon and break them up instead of having them slip away), – Peter Cordes Jul 3 '20 at 1:02
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    @MichaelKaras I have a hot chocolate mix that says to add the milk to the powder and it definitely mixes better that way. Weird. – Kat Jul 3 '20 at 16:08
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    Well, maybe with some pancake mixes, but I wouldn't extend this too far into the kitchen because flour has its own issues, gelatinizing and tending to form unbreakable clumps. This doesn't really happen with cement mix. Every solid/liquid system will have its own quirks - sometimes you need more than one strategy to match. – J... Jul 3 '20 at 16:26
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From Chemistry: "Do like you oughtta: add acid to water" . Besides the "glop" problem mentioned in the answer, there is almost always released heat when dissolving something in water. If you start with lots of reagent and little water, the water may boil, leading to rather undesirable dispersal of hot reagent.

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    Not always. Some substances absorb heat when dissolved. – Mark Jul 3 '20 at 2:05
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    When you pour one liquid into another, you get splatters. If you pour water into concentrated acid, the splatters will be mainly concentrated acid. If you pour concentrated acid into water, the splatters will be mainly water, or diluted acid. – Kaz Jul 3 '20 at 6:37
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    I think that ditty only really rhymes in new england. In any case, the reason to add acid to water is that the mixing is exothermic and there is a risk that adding water to concentrated acid can make the water droplets heat and boil before they disperse, making a messy, energetic, acidic, and dangerous mess. When adding acid to water the acid dissolves quickly in the water, keeping a low concentration, and takes the heat with it, spreading it out naturally. The other way, the acid rushes into the water droplet, making a high concentration and releasing much more heat. – J... Jul 3 '20 at 16:31
  • @J... how do other people pronounce "water"? – user253751 Jul 6 '20 at 10:04
  • @J... Ok, 'Do like you oughtter , add acid to watta" :-) – Carl Witthoft Jul 6 '20 at 10:25
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  1. If you pour liquid onto a powder, the powder gets disturbed and swirls up into the air. It can hit you in the face.

  2. The liquid beads up due to surface tension and runs down the hillock of powder without wetting it out. You get lumps forming, some of which which are dry in the center and require mechanical action to break up.

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    This answer is confusing. Some of the points do not support the advice to "add mix to water" like point #3. I don't even understand the point of #2. – Nelson Jul 3 '20 at 7:28

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