Mixing Concrete
 

I need to fill a hole in my basement slab, which was cut using a concrete saw, to repair a bit of drain pipe. I'd guess the amount of concrete I need is not more than 1/3 yards. Likely much less. Maybe 3 SF. I may be able to source one of those small mixers. If not, can't I just mix this mud up in a big plastic pan?

I have a concrete trowel. I think I know which end is the handle. :)

You can purchase premixed bags of concrete at Home Depot, Lowes, or places like that. I think they weigh about 80 lbs each and cost about $4.00 per bag for the 4,000 lb stuff. Just add water and mix it up with a shovel in a wheel barrow next to where you will be working until you have a good consistent mixture and pour in the hole. One yard of concrete is good for 98 square feet when the depth is 3.5" so you won't need much if you only have 3 square feet...Maybe two to three bags give or take.

3 SF at 4" to 6" thick is only 3 60# bags.

If you have a heavy duty corded drill, I use a 5 gallon pail and one of these: Paddle Mixer

For small amounts I use a 5 gallon plastic pail and a 1/2 hp drill (big drill) with a mud paddle (used for mixing drywall mud) on it. It's surprising how little water is actually needed to mix up a bag.

Shop around for your concrete. Menards has 60 lbs bags of pre-mix for $2.00 or around that on sale.

HD sells mixing boxes (plastic troughs) get a couple bags of concrete mix, one of the boxes, and a flat shovel (the shovel is rectangular, not rounded). Those items and your trowel are all you need. Use the shovel to mix the crete and shovel it into place. Put 1 3/4 bags of dry mix in the trough, use the shovel to make a bowl in the center. Pour half the recommended water in the “bowl” mix mix mix, add more water until you either get the right consistency (a heavy paste) or you over do it. If it gets too soupy add some mix from the 3/4 bag you set aside. Shovel into place. Smooth with trowel.

Put the mix in a five gallon bucket add water put the top on and roll it around on its side a few minutes, flip it on it's lid a few times to get stuff off the bottom. When ready take the top off pour the mixture into the hole. Repeat as necessary to fill the hole. Use a trowel and a float to level and finish.

I use the wheelbarrow but have used 5 gallon buckets too. Mix with shovel. Use less water than you think.

I know a good idea when I see it. :cool:

I can't take the credit, I learned it from Bob Villa about twenty years ago on this old house. I use it all the time. You can even down size for small patch jobs using a wonton container.

Good luck with he project. SmileWavy

I've got a concrete mixer but have never used it. A wheel barrow is so much better.

Arghhh...I can still hear the calls for "More Mud!" from when I was a mason's laborer during college.

I discovered in my teenage years working for a local dirty contractor that you don't really mix concrete. Instead, you drag the dry concrete into the pool of water in the middle of the wheel barrel. Continue doing that until you get a certain consistency then dump it on your form. In my entire life, I mixed no more then 20 wheel barrels of concrete so I am no expert but I have seen the men do it more time then I would care to admit.

Funny.

My concrete guy shouts: "Looks like we are short, We need a few more bags, who's going to get the goddamn thing."

Me: "Oh, client just pulled up. Have to go see em."

Bags of ready mix and a mortar tub from H.D. The bags of ready mix are 2/3 c.f. so you'd need about 14 bags for a third of a yard.

They vary in size (and can in price too I discovered..stores 1 mi apart!) ...40-80lb bags here. I bought about 25 bags a couple of years ago ....the less H2O...the stronger it will be.....just enough to work it.

Use a hoe and a wheelbarrow. Put the concrete mix in first. Make a hole in the mix, put water in the hole sparingly. You’ll need less than a gallon for an 80# bag so start with about 1/2 a gallon and add as needed. Work it back and forth until the water is mixed in.

Put the concrete in the floor and agitate it to push the stone down a little. Using a 2x4 long enough to span the hole, screed off the concrete to the correct elevation.

When the concrete has cured to the point that it can withstand some pressure from the flat of the trowel start smoothing it with the trowel, gradually increasing speed until you’ve got the desired finish.


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Raw unmixed cement dust is very caustic, and bad for your lungs. Don't be mixing it in a basement or stick your head into a cloud of said dust while mixing.

Dumping it from the bag....hold breath, dump & run....preferably up wind :). The beginning of a great workout....

LOL, so you'll pay $40.00 for that vs. use a five gallon bucket you likely have free in your garage? or worst case $2.50 new including lid at HD or Lowes? :confused:

When my son was 3, we did a similar project at my dad’s place.

I mixed it up in a 5 gallon pail and my son wheeled it to the cut out in dad’s garage slab in his kids plastic beach wheelbarrow. It took a bit longer than my dad thought it should have but at 3 years old, he wheeled his first concrete job.

With the leftover concrete we made hand prints in margarine cups.

Mixing a bag of concrete in a 5 gallon bucket sounds like trying to do an engine rebuild through the tailpipe. Granted, I've never done either, I guess its possible. And I hate messing up my wheelbarrow.
A mixing tub is cheap and lets you see the entire mix and work it evenly. It's is the only way I'll do small batches.

https://www.homedepot.com/b/Building-Materials-Concrete-Cement-Masonry-Concrete-Tools-Mixers-Concrete-Mixing-Tubs-Pans/N-5yc1vZaq89

Thanks, everyone. I should actually measure and calculate. My guess is that these 14 bags would be WAY too much. I think I actually need closer to 3-4 CF. Using the 5-gallon bucket idea, I think it would be prudent to leave plenty of space in the bucket for faster mixing, but I think it will only take a couple of buckets worth. I do not have a vibrator, which concerns me a bit. I've seen them used, which tells me there is invariably too much air in the mix. I have another question:

A concrete saw was used, leaving very smooth sides. Will I need to 'profile' those smooth cuts in order to get the new concrete to bond with the old? Should I get the old concrete, and the ground below the opening, wet to promote adherence?

IMHO air in such a small patch is not a matter for concern. I don't think adhesion is an issue either. Water from the new mix will wet the existing walls. Roughing those walls wouldn't hurt.

You can use a concrete bonding agent on the sides of the saw cut or make your own with some white glue, water and a old brush. Mix the water and white glue and paint it on the sides of the cut.

As to wetting the area it can't hurt. Adding water before the pour makes sure the concrete doesn't have the water pulled out of it while curing.

If you think it is a concern you can buy a bottle of adhesion promoter . It is milky white in color and you brush it onto the existing concrete to help the new concrete stick . I doubt it is needed for what you are doing .

When I say 2/3 cu. ft./bag of H.D. ready mix, I'm going by the ones I've bought at local H.D.s and comparing the cubic feet of my projects with the number of bags they required. It was consistent overall. The bags weren't big, but I don't remember exactly what size but 40 lb. comes to mind. The price at the time was around $3/bag.

I have to say, this board is simply amazing. This spring I'll be pouring a mini foundation next to the building main foundation and was wondering how the new concrete will stick to the existing foundation vs. just crack away from it. That and I will do sections at a time pouring two long strips, letting those set and then slowly pouring a 12' by 50' floor, section by section. Now I know to use adhesion promoter.

Going to get a serious mixer off of CL.

Yes leave some space in the bucket to allow the material to move around easier and mix. You wont have an issues with air in the mix. First you are mixing in small batches. Pour the mix in the hole and tap with a stick to help settle a little. Mix the next batch, pour repeat. A vibrator is for when there are large deep pours such as a poured wall that is six, eight feet high or a footer that is all poured at one time. You need to vibrate the air out of the bottom in order to eliminate voids that could weaken the wall or footer structurally. You are pouring a basement floor. What is it four six inch thick at most? Also it isn't structural. There won't be the amount of air in your mix as with a cement truck or a portable mixer. They have blades on the inside that when spinning folds the air in to the mix. If a mix is mixed looser (more water) less air gets trapped. The tighter (less water) makes the mix thicker and traps more air. If you are concerned make your mix a little looser.

You don't need to bond the new concrete to the old. In fact the cut simply made another expansion joint. That is a good thing. It's not a bad idea to get the old concrete damp not wet. Don't worry abut the bottom.

HF mixer, CL mixer, or just rolling a 5gal bucket small mix is best.

Concrete takes a lot of work to get it all done right.
Dry mix is stronger
Covered with plastic, long cure, and fresh thin layer of sprayed water.
=Slower = Better.

Plan ahead:
-Rebar tied/welded before.
-Including slope of forms. Total water drainage plan. Runoff of rainstorm water away from foundation.

The new foundation may not stick to the old foundation. We need more info but, the footers may need to be tied together. That would depend on your local codes. If so that would be done using rebar. It may also require chipping out some of the old footer to expose the rebar where the new footer meets old. The foundation, the blocks most likely willy simply but up to the old block with a mortar joint.

Not sure code will allow you to pour your footer in sections. That is supposed to be a continuous pour generally with a rebar cage inside. This would also require a vibrator to ensure a solid pour with out voids.

If you really want the new patch of concrete to be tied in to the slab you could drill in some anchor bolts into the side of your slab, if your slab is thick enough. The new patch will shrink so it is wishful thinking that you will be able to really bond them together. There are expanding grouts available but usually for smaller width gaps.

For bonding hard rock--to mortar--to hard rock.....I've used Acryl60 product as a bonding promotion agent for the mortar.

It seems like weak acrylic paint primer chemical to be honest. Water based.
Apply as prescribed.

Easy on the lungs. Not sure of overall results.

Its a patch in a slab, so lets not over think it.

Superman, how big is this patch? How deep? Look up concrete calculator on the net and plug in the numbers. Just pick up a typical concrete mix and you should be good to go. I suggest a wheel barrel and a hoe (get the one with a couple of holes in the blade to make mixing easier) like someone mentioned. By him saying that, I know he's done this before. Forget those plastic mixing tub unless its a bag or two max. You want to save your back and working standing up. Doing that on the floor will kick your ass, especially if it more then 6-7 bags unless you like to suffer and mix 100 lbs of concrete on all fours. Were there any rebars under there when they cut the floor? You can epoxy rebars back on there if you like, its not really necessary depending how big is this channel? This could just be a simple fill it back up with concrete or it can be a little bit more then that. Without photos, its hard to tell. Stay away form those 5 gallon buckets unless you like to weight lifting.

Hey Shuan, I am not sure if I know exactly what you are doing. got a pic or two? When I hear foundation and pour in sections doesn't sound like music to my ears.

If what you say and what I am thinking are the same thing, it is way easier to build the forms and hire a concrete truck and a pump service and be done with it in one day instead of mixing by hand and going to get all the bags of concrete all the different times. Again, that's if you like weight lifting and exercise that Toyota truck of yours.

Respectfully, I don't think so. I'm not a trades guy, but I've been working with construction industry people for nearly 30 years. Drywall mud dries, and shrinks. Concrete cures, and does not shrink. At least, that has been my impression.

This project is for a rental, about an hour away so I cannot take pictures easily. The hole is in the slab, not the stem wall or footing. I'd guess it is 8" deep and about...five SF. Plus, it has a big waste pipe in it and a big cast iron elbow (these will be replaced). Seriously small concrete pour. Probably more than one bag, less than four. I really should measure. "Look" is right. I should not over-think this. I tend to over-think stuff. Sound familiar? It's better than under-thinking stuff.

Supe- your hole may be 8" deep but I doubt very much your slab is 8". It's not more than 6" and I would bet it is 4". After the repairs are made to the pipe make sure you cover them with dirt before you pour the concrete. You don't need much 1/2"-1" is plenty. You do not want to encapsulate the pipe in concrete.

I think its more like 4" also, but drcoastline is correct, cover with soil and be done with it. Pack in a good amount of soil and make sure its compacted with your foot and leave about 5" or so for the concrete. Its holding human traffic so 5" is more then enough.

My God! Two pages on how to mix concrete and fill a hole? Are all you guys snowed in and got nothing better to do? :rolleyes:

Go to YouTube. Must be 50 videos on how to mix concrete, SmileWavy

Thanks guys. Here's a bit more of my vision (which is only a vision, have a long time before it reaches 50+F on a regular basis). The pavement in the parking lot at work is soft and cracked and uneven and generally crap. I want to pour an X deep by maybe 8"x8" base against the concrete building, about 50' long. I am thinking I could sink tubes into it for poles or some kind of anchor that I can bolt U-channel to and make a temporary roof. In front of the base I want to pour a pad for cars to park, and work on in the summer time. Maybe build a well for my scissor lift.

Jeff, I wouldn't mix it by hand, I'd probably get something like this:

https://boston.craigslist.org/gbs/hvo/d/cement-mixer-honda-engine/6767805307.html

So it's only a dream right now. I think March I'll really start to plan.