Mortar strength

[akist]

I have looked at new blockwork mortar and it crumbles when I squash it in my fingers to a fine dust. It is 3 days old. The mortar below DPC is stronger, as I understand it to be more cement mixed in.

I was thinking of mixing myself one cup cement with 5 cups sand to see.

Is there a way to assess the quality of the mortar used for the blockwork other than my squeezing it and see how it becomes dust?

 

[noseall]

Is there a way to assess the quality of the mortar

Not without experimenting with several varying mixes or batches, all tested under the same conditions.

A relatively weak mix will set quite hard as long as it it kept damp and is prevented from drying out too quickly. A really strong mix will turn to dust if you spread a thin layer on a high suction surface.

Blockwork would much prefer a weaker mix.

 

[^woody^]

Any mix weaker than 1:5 will be crumbly and you will be able to scrape it with your finger. The face hardness of a joint comes from pointing, from compressing the face, not from the mix ratio.

 

[akist]

OK, yesterday I mixed 4 cups of sand and 1 cup of cement inside a little tub, because this is what they use for the blockwork, and now I have let it to dry to see what happens. It is grey-greenish in colour.

In contrast the builder's mix is yellow almost. The sand is kind of orange.

Edit: today I looked at my mix which I let dry yesterday, it is much darker then the builder's mix which is yellowish, it is also wet outside, I will leave it to dry another day.

As an aside, his mixture inside the mixer also started as grey-greenish but as it kept mixing for much longer than me, the colour lightened and it has ended up a medium yellow. Maybe mixing for a long time is obligatory?

I looked online for the right mix ratio, and I have seen from 3:1 to 7:1, does anyone know? They talk about "parts", so it goes by volume ? Therefore my 4 cups of sand and 1 cup of cement is called a 4:1 ? Because my mixture is way darker than the builders, so he is not using 4:1?