Mortar mix went bad on a Friday job in Tulsa

Last Friday I was laying block on a small retaining wall in Tulsa and the mortar kept slumping no matter what I did. I figured it was the heat or my mix ratio, so I kept adding more Portland and re-mixing in the wheelbarrow. After about an hour I noticed the sand looked off, kind of clumpy and dark, and sure enough the bag had gotten wet sometime in storage. I had to tear out four courses and redo them with fresh mix, which cost me the whole afternoon and an extra bag of mortar. My brother-in-law runs a supply yard and told me to check for hard lumps in any sand older than a month, especially if it sat outside. Now I keep my sand in a sealed tub on the truck and I test a small batch before I commit to a full wall. Has anyone else had a bad sand delivery ruin a straight run of brickwork? What do you do to dry out sand that's been sitting in damp weather?

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harper_wright9d ago

Did you ever think the problem might not be the sand itself but where the sand was made? I ran into this a couple years back and it turned out the guy I was buying from screened his sand off a river bottom and never washed it, so it was holding salt and junk that made the mortar act weird even when the bag was bone dry. The clumping you saw could be from damp, sure, but dark sand is a whole other clue, that usually means it sat in dirty water or got mixed with topsoil somewhere down the line. Drying it out in the sun on a tarp works for surface wetness but it won't fix sand that's got clay or silt in it, you'll just be spreading the same headache across the wall. Next time you get a load, grab a clear jar, fill it half sand half water, shake it, and let it sit overnight, if you see a layer of mud sitting on top of the sand you know the batch is bad before it ever hits your board. That jar test has saved me more afternoons than any tarp or sealed tub ever did.