Cannot use a concrete block with less than 14N/mm2.When we spec a 10.4 usually

Thank you for your question, I am assuming you are relating to the published data for the HY270 resin injection mortar. The 270 is our most widely tested product into masonry / block materials however it is impossible to test every variation of masonry units. If your unit is physically larger and has a higher or equal compressive strength to one, we have tested then it is possible to use that blocks design resistance as it would be conservative value. Of course, if you are not able to make a comparison then you would need to conduct testing to establish the allowable resistances.