Weak mortar mix

[68breakbreak]

Hi,
I recently had a builder build a single story concrete block (single skim with piers) outbuilding for me. I did a solid job preparing the foundations and floor myself, and hired a builder to lay the concrete blocks (I will finish the roof. Myself) I am concerned because after 3 weeks, the mortar appears very crumbly. If I pick out an exposed piece of mortar, I can literally crumble it in my finger to dust, or I can take a key and easily cut into the mortar. Furthermore, I have been able to push the lintel off the block work, and another small cut block has also dislodged. The mortar seems to resemble sand more than mortar I have seen elsewhere. I can brush loose bits off the blocks.

I was initially concerned because only 3.2 bags of cement seem to have been used with about 800kg of sand. When I raised this with him at the time, he insisted he used 5:1 mix,but I can't see how.

Should I be concerned?

The rest of the work is good, level plumb.. Perhaps his labourer made the mortar mix wrong?

 

[r896neo]

Something is clearly wrong with the mix. It cant be frost this time of years and 1 week is plenty for it to set to a hard strong mortar so most likely they skimped badly on cement.

If it was done to a price then I think he has deliberately tried to save a few quid by using less or if you supplied the cement then probably the labourer has made a mistake and then been too embarrased to say.

Either way it needs to be re-done if its that bad. It might be possible to rake out and repoint it but it may be quicker to rebuild before carrying on. At least the blocks will be easy to clean off...

800kg of sand should be using 6-7 bags of cement.

 

[68breakbreak]

Thanks.. I brought the materials, and he had 10 bags of cement to get through so it doesn't really make any sense as to why he would skimp on it. But for some reason he has....

 

[stuart45]

Often used to happen when labourers gauged with shovels, as you tend to get more sand on the shovel than cement.

 

[^woody^]

Is the wall pointed? Or is it being rendered?

Is the mortar soft internally and externally?

Pointing gives the joint a hard face, and it's common for internal joints to be flushed up, which could well appear to be soft.