After scrupulously following the water/mix ratios as directed on the bag of Quikrete 1101 (3 quarts max for a 60 lb. bag) and following prescribed, standard procedure for pouring slabs, i.e. placing and consolidating pour first, striking off and floating with a magnesium hand float second, then re-floating to compact aggregate after bleed water evaporates, the finish still turned out rough and honeycombed in spots, with visible aggregate stone and sand atop the cement filler. What accounts for this bad outcome? The only thing I failed to do was to water the gravel base before the pour. Could this be responsible for cement/water mix being sucked into dry base and ground by capillary action? A more reasonable guess is that the Quikrete mix just didn't have enough Portland cement. My questions are what are the possible causes of this failure and what is the best way to correct it. Slab is 16 ft x 7 in. Thanks!

I am certainly not a concrete guy but I would say that your mix is to stiff (dry). Following directions is great but sometimes you have to use a little judgment also. Of course temperature and humidity are big factors here.

Your mix should be loose (wet) enough for the aggregate (gravel) to sink below the surface as you strike it off and trowel. When striking off, your strike board (2x4) should be move back and forth in a sawing manner as you strike it off. That causes the gravel to sink below the top surface. I'm sure you know this but when mixing you add the mix to the water. You put the water in the mixer and add the concrete. You don't add the water to the concrete mix. The bagged stuff has the minimum required cement. When I am doing anything other than filling post holes, I get a bag of cement and add a shovel full of cement to each bag of redi-mix.

Mix was too dry or poured in very hot conditions and set too fast. Small gravel should not be seen.

Probably too little water to start with, too late on finishing due heat/fast set and placing too slow (it simply got away from you). No sign of a wet cure, resulting in drying out too fast. Strength is considerably lessened. Dry base material didn't help for sure.
What was your curing procedure if any? Key word is too dry from start to finish.
QUIKRETE® - Concrete Mix (Data sheet for Mix 1101)
Instructions make provision for additional water for workability, and recommend a slump of up to 3 inches.
A sufficient amount of water is also required to react with the cement. Precautions are essential for hot weather concreting.

"If a slump cone is available, adjust
water to achieve a 2" - 3" (51 - 76
mm) slump "

Quote:

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Originally Posted by smearcase

Probably too little water to start with, too late on finishing due heat/fast set and placing too slow (it simply got away from you). No sign of a wet cure, resulting in drying out too fast. Strength is considerably lessened. Dry base material didn't help for sure.
What was your curing procedure if any? Key word is too dry from start to finish.
QUIKRETE® - Concrete Mix (Data sheet for Mix 1101)
Instructions make provision for additional water for workability, and recommend a slump of up to 3 inches.
A sufficient amount of water is also required to react with the cement. Precautions are essential for hot weather concreting.

"If a slump cone is available, adjust
water to achieve a 2" - 3" (51 - 76
mm) slump "

---

Pour was last Sunday, so curing is going on right now, with a sprinkler. Some cement has appeared since water curing began, so maybe I'll put up a photo after a week of curing has finished. You have motivated me to get a slump cone!

Quote:

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Originally Posted by ma0641

Mix was too dry or poured in very hot conditions and set too fast. Small gravel should not be seen.

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Temp was 70F, and water amount was close to the prescribed limit, which, according to the instructions on the bag, was 3 qt. per 60 lb. bag.

Quote:

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Originally Posted by hkstroud

I am certainly not a concrete guy but I would say that your mix is to stiff (dry). Following directions is great but sometimes you have to use a little judgment also. Of course temperature and humidity are big factors here.

Your mix should be loose (wet) enough for the aggregate (gravel) to sink below the surface as you strike it off and trowel. When striking off, your strike board (2x4) should be move back and forth in a sawing manner as you strike it off. That causes the gravel to sink below the top surface. I'm sure you know this but when mixing you add the mix to the water. You put the water in the mixer and add the concrete. You don't add the water to the concrete mix. The bagged stuff has the minimum required cement. When I am doing anything other than filling post holes, I get a bag of cement and add a shovel full of cement to each bag of redi-mix.

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I did have a problem striking off-the 7 in.x 16 ft. slab was not flush with concrete on one side, so complete and correct sawing across the form on one side and old, high slab on the other was not possible. I did my best to compact it level during strike off. Re. mixing, I, an amateur with bag mixes, just followed Quikrete's/Sakrete's recommendations and video instructions to pour water onto the mix. Re. your recommendation to add cement, you are not alone. Here's one customer review among 222 reviews of Quikrete 1101-80 Cement, at Lowes.com: "ADD TO IT!

SUGAR BEAR
Location:YORK ,PA.Level of Expertise:Expert
June 26, 2011


Poured over 80 feet of sidewalk 2 ft X 12 ft sections at my home, after pouring and floating ,edging and cutting joints, waiting to set to put light broom finish , I found it would always leave a rough sand finish even using a a fine 12 inch hand brush,, so after first poured section I bought 94 # bag of portland cement type II and ADDED 2 SHOVELS OF THIS TO EVERY 80 LB. BAG OF CONCRETE MIX , DRY MIX IT FIRST THO,, AND IT MAKES FOR BETTER finishing of edging , cutting joints, IT GIVES IT A LITTLE MORE CREAM TO WORK WITH and a beautiful BROOM JOB."

Quote:

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Originally Posted by smearcase

Probably too little water to start with, too late on finishing due heat/fast set and placing too slow (it simply got away from you). No sign of a wet cure, resulting in drying out too fast. Strength is considerably lessened. Dry base material didn't help for sure.
What was your curing procedure if any? Key word is too dry from start to finish.
QUIKRETE® - Concrete Mix (Data sheet for Mix 1101)
Instructions make provision for additional water for workability, and recommend a slump of up to 3 inches.
A sufficient amount of water is also required to react with the cement. Precautions are essential for hot weather concreting.

"If a slump cone is available, adjust
water to achieve a 2" - 3" (51 - 76
mm) slump "

---

You may be right about the concrete running away from me. Temps were not hot, and the pour was in the shade, but the mix seemed dry and was difficult to work with. Bagged concrete manufactures instill the fear of using too much water into novices, who comprise most of their customers. No doubt that advice has its limits. I'm wondering if mixing bag concrete for even a 1/10 cu. yd slab such as this one allows for too much drying to occur. For the garage apron slab to be replaced next to this little strip, I may call in a ready mix truck. Too bad-my HD has Qukrete on sale for $2 per 60 lb. bag. X D

The advice about adding too much water is absolutely good advice. Water cement ratio (weight of water divided by weight of cement) is the most important common factor affecting ultimate strength (curing is right up there too). But there has to be enough water (minimum water/cement ratio) to react with the cement to create a paste to coat the aggregates.
2.7 cubic feet? One tenth cubic yard. 16 feet by 7 inches by ? Computes to be 3 -1/2 inches deep ???
Whether I understand the dimensions correctly or not, if vehicles are going to be traveling over this concrete, there is only one answer for your question ( "My questions are what are the possible causes of this failure and what is the best way to correct it."): Remove it, determine what the minimum thickness is allowable (we used 6 inch for driveways but that was a state highway standard, building spec might be 5"), and replace it. A portable mixer which you can rent for a reasonable amount may be your best option. Some areas are minimum 2 cubic yards for redi-mix.
Also, you may have caused some of the damage with the sprinkler (I didn't catch that comment before) if you started before the concrete had hardened sufficiently. Wet burlap applied at the correct time is a better curing method. Good luck.

[QUOTE=smearcase;3674456]The advice about adding too much water is absolutely good advice. Water cement ratio (weight of water divided by weight of cement) is the most important common factor affecting ultimate strength (curing is right up there too). But there has to be enough water (minimum water/cement ratio) to react with the cement to create a paste to coat the aggregates.
2.7 cubic feet? One tenth cubic yard. 16 feet by 7 inches by ? Computes to be 3 -1/2 inches deep ???
Whether I understand the dimensions correctly or not, if vehicles are going to be traveling over this concrete, there is only one answer for your question ( "My questions are what are the possible causes of this failure and what is the best way to correct it."): Remove it, determine what the minimum thickness is allowable (we used 6 inch for driveways but that was a state highway standard, building spec might be 5"), and replace it. A portable mixer which you can rent for a reasonable amount may be your best option. Some areas are minimum 2 cubic yards for redi-mix.
Also, you may have caused some of the damage with the sprinkler (I didn't catch that comment before) if you started before the concrete had hardened sufficiently. Wet burlap applied at the correct time is a better curing method. Good luck.
[QUOTE=NM156;3674803]Slab is 5" deep, 16 ft. long, and 7" wide, which is appox. 15/100 of a cubic yd. or 9 bags of 60 lb. concrete per concrete calculator apps and online widgets. Slab is a strip directly beneath a garage door, replacing a greatly cracked section of floor. Sprinkling commenced the following day, when the concrete was rock hard. I covered it with plastic sheet for the first 24 hrs. Appearance has improved quite a bit in the 5 days since the pour. Cement must be filling in spaces between the aggregate as curing continues. Nonetheless, the conclusion is that I made some amateur errors. Advice much appreciated.