Mixing Quikcrete

[yatg]

What's been your experience with mixing up Quikcrete or other bagged mixes lately?
Doesn't seem to be as good as it used to be.

Did a small pad a couple of weeks ago and followed the directions instead of winging it.
It called for 4 pints (1/2 gallon) of water for a 60# bag.
Added a big yogurt container of portland, 1-1/2 pounds, per bag and another pint of water.
Mixed in a barrel mixer for several minutes.
The mix was dry as your granny's ***** and unworkable.
Ended up added another couple of pints, more or less, to make it normal.
This was consistent with all the bags mixed.
4 pints might be enough for a fence post, but not for a finished surface.
Used a hand tamper to compact it in the form, and still ended up with small voids along the edges.
Its as if there wasn't enough fines in the mix.
Next time I'm going to add some extra sand.

 

[mcbane]

My experience is that the mix started out with very little portland cement and was then stored for a long time in very humid conditions, so some percentage of the originally supplied portland has already reacted. To remedy that issue I usually add around 4 lbs portland. I use an electric mixer and add only enough water to make it workable.

Regarding the water, ideally your water/cement ratio is around 0.4. And if the mix, including added portland, is similar to a 5 sack mix, it has 8.5 lbs of unreacted portland in it. So a 0.4 w/c ratio would require around just under 1/2 gallon of water. In theory you added enough water, but that 0.4 w/c ratio presumes that all aggregate is "saturated surface dry" condition. Ready mix is delivered dry, so the dry-as-a-bone aggregate will absorb some of the water. The easiest fix is to keep track of how much water it takes for the first batch of concrete to reach a workable consistency and then measure out that same amount of water for subsequent batches.

 

[Leaflessshadetree]

Sounds like you are adding about the same amount of portland that I do. I rarely measure water as the amount varies on so many other conditions but 1/2 gal/60lb bag sounds like a good starting point.
Did you wet/oil the forms and wet the ground under the slab? I work down the inside of the forms with a shovel, trowel or rod as I pour and I vibrate the outside of the forms (a pneumatic hammer works great but a small sledge works OK).

 

[Davefr]

Same here. The Quickcrete from home centers is ****. (Long on aggregate and short on Portland cement.) I also spike the mix with an extra helping of cement to give it some much needed strength.

 

[Dan in Pasadena]

OP: You're messing with the water/cement ratio by randomly adding Portland cement. I agree their water callout is low. I think the callout was 4500psi and I can tell you that it'll likely develop significantly more than that - probably in the 5200 to 5800pis range unless you ruin it by watering too much.

 

[Dig Doug]

I just mixed 35 -60lb bags by hand and then use the rapid set Red 15- 60lb bags for the top layer so it would go off quickly to get a good finish.

we did 3bags at a time, add water and mix as needed! I like to add a 1/2 shovel of Portland cement to each batch to make a better mixture, I believe you get a better finish.

we didn’t measure the water added but made the bottom batches a little more wet than the top Batches.

turn out awesome. And customer like the end result!

 

[Renegade1LI]

Better off buying the high strength, it;s worth the extra buck, either get the 5000 plus it's fine for small stuff.

 

[pcmeiners]

"What's been your experience with mixing up Quikcrete or other bagged mixes lately?
Doesn't seem to be as good as it used to be."

Years ago I stopped using Quikcrete without adding portland, garbage without the addition as the company was super cheap on the portland, as if portland was expensive.
Have a project needing a concrete pad, so I figure I would try Sakcrete concrete mix from Home Depot. I was shocked, it mixed up like true concrete, plenty of portland.

Correction, I thought it was Sakcrete, but it is Quikcrete high strength, a massive improvement since the last time I used it (10 years ago).

 

[yatg]

I'll try the high strength QC next time.

Local HD doesn't have Sakcrete. Lowes has it, but its 30 miles away.

Project was an irrigation pump pad. 3' x 6'. There's a decent slope down to the canal. Part of it was poured last year, was flat but not level because I was too lazy. Decided to build a cover on top of it this year so capped it with another pour, 8 or 9 80# bags to get it reasonably level and 7 60# bags the next day for the top 3".