TIL a mortar mix problem cost me 3 days on a single garden wall

Honestly, I thought I had my ratios down perfect but the mortar kept crumbling after 24 hours. Took me two days of redoing sections and calling my old foreman to realize the sand I grabbed from the yard was way too fine. He said 'that's play sand, not sharp sand' and I felt like an idiot. Third day I mixed a fresh batch with the right stuff and it bonded like it should. Anyone else get tripped up by a simple material swap?

3 comments

3 Comments

anthony_wells1mo ago

Did you wash the sand first too? I've had fines dust mess up a mix bad, a quick rinse can save a lot of headache next time.

derekgibson1mo agoMost Upvoted

Wait, you mean you just dump it in dry and mix? I used to just grab sand from the bag and throw it in, figured a rinse was just extra work for no reason. Then I had a batch of countertop mix that came out all crumbly and dusty, like the cement couldn't even grab onto the aggregate. Spent a whole weekend grinding it down and patching voids. Next time I rinsed the sand first and it was night and day, the mix was way smoother and actually held together. I get why you do it now, that fines really do mess with the chemistry.

williamprice7d ago

Did you catch that video from that concrete science channel where they explained how the fines dust basically coat the aggregate and stop the cement paste from bonding? I saw it a few months back and it finally clicked why my early attempts at concrete planters were total garbage. They used a microscope to show how the dust particles are super fine and they basically create a barrier between the cement and the sand, so you get all these micro voids in the mix. It's wild because you can't even see the dust with your naked eye but it totally ruins the strength and finish. Once I started rinsing my sand with a hose in a bucket until the water ran clear, my concrete came out way denser and smoother. Your countertop story makes total sense now, that crumbly texture is exactly what happens when the cement can't grip anything.