Buying & Mixing Cement

[Spencer]

I will be picking up my new 3-point cement mixer this weekend. I have never mixed my own cement so I will take all the advice I can get. I'm probably using the term 'cement' improperly here. I am refering to some sort of redimix product in a bag where you just add water. My first project will be putting up a 16 foot tube gate. I also have a new post hole digger so the gate will be the first time I use that as well. I plan on using 6x6 treated posts for the gate. The 12" auger I bought is still on order so the 9" is all I have for now. I guess I will use the nine and enlarge the top one foot or so with a shovel for extra cement.

So what type and brand of cement should I buy for setting the posts? Hopefully I will be starting my pole barn project by the end of April so the gate will be good practice for me. Will the type of cement mix for the gate posts be different than the posts for the pole barn? I plan on making some sidewalks later in the summer and I am assuming that I would use a different type cement mix for that, right?

Any tips on getting the right cement/water mixture? What is the best way to clean the mixer? Should I have the cement for the posts go up above the grade level and try to have it pitch away from the post to shed the water?

I know that most people don't mix their own cement anymore. Most of you will probably think I am foolish for buying a mixer. I will still hire out my big jobs like the pole barn floor. I just wanted to be able to do my own small jobs. I travel around the country for my work and my schedule is always changing. I don't ever get to plan anything ahead of time. I want to be able to do a little bit here and there when I get a few hours.

Spence

 

[Harv]

<font color=blue>most people don't mix their own cement anymore</font color=blue>

Not sure why that would be true, Spence. It's still the most cost effective way to go.

I think we had a discussion about this a while back, but I use the ready-mix bags for small jobs and call a cement truck for the really big jobs. Much of what I have done has been in between, and that's when I get a pickup truck full of the sand and gravel (aggregate) mix plus bags of cement. If I needed more than would fit in my truck, I'd have it delivered and dumped as close to the job site as I could get.

What size aggregate? What ratio for the mix? Heck, I just told the folks at the cement yard what I was doing and they gave me what I needed, along with good advice. They always mixed the sand and gravel for me, too.

<font color=blue>What is the best way to clean the mixer?</font color=blue>

After your last pour, just rinse your mixer out as best you can with water and then toss a few shovelfuls of the sand/gravel mix in there and let 'er run for a while. Sands itself nice and clean with no effort on your part. That's important.

 

[Egon]

Spencer:

There are people who have spent their entire lives doing research on the questions you have asked. Here are some items my ancient memory can dredge up. By now they may no longer be proper.

Aggragate will be different sizes depending on the intended use. It is important that it be well graded [ large to fine particles so there are few voids and less cement is needed ] It should also be clean and contain no vegtable matter.

Cement should probably be a portland type 5 which is phosphate resistant if any ground contact is envisioned. Air entrainment agents are also advisable.

Strenght of the final concrete will depend how much cement, proper amount of water and the strength of the aggragate. [Ultimate stength depends on that of the aggragate]

Stength of sidewalks are usually around 2500 psi. For foundation walls or structural components this will increase.

I always prefer to add a little cement to the prepackaged mixtures just for added strength.

When making your own from scratch the normal practice is: three shovels of aggragate, one shovel of cement and just enough water to make it fluid but not runny. This is hard to describe. Industry bases it on a slump test which will vary according to design requirements. A little extra cement will not hurt if in doubt. Be sure to mix longer that you think is required.

Do not vibrate or move the final pour to much as this segregates it all and weakens the end produce. Use shovels not hoes or rakes for spreading and then screed level.

To cure the surface should be kept damp. Covering in plastic will do this or a spray of water after the surface isn't affected by the droplets. There are also comercially available sprays that will do this. Forms should be sprayed with a release agent for easy removal.

If you want to make odd shaped free standing items and have to batter a form one can add a little lime to make the mixture sticky.

Hope this helps. The information is minimal and presentation deplorable but it's early and the coffee hasn't kicked in yet.

Egon

 

[mikim]

For filling post holes I just mix the redi-mix bags with water til it looks right in a wheelbarrow. A mixer would be good if you're going the 1-2-3 route as the other guys have already explained. I weighted the decision on a mixer by the question "do I really have enough small projects to warrant the expense?" I'm sure you can get a better mix using one though. The aggregate in the bags isn't as good as if you bought it separate - and you can mix your portland in as needed for strength. anyway you go it's work!
mike

 

[Alan L.]

The only advice I can offer is:

1. Wear gloves - that portland will eat the skin off your hands.

2. Don't get the mix too wet. It seems to be much stronger if not allowed to get runny.

Alan

 

[jasonf]

When I used my 3 pt Mixer, I would get a pile of sand, and a pile of gravel delivered, and then put in a bag of cement mix, along with the gravel and the sand then add water, Use those gloves, it really will eat the skin off your hands./w3tcompact/icons/frown.gif After dumping the final load, I would use the hose sprayer to get out the loose stuff, then I would put in a shovel full of gravel and a couple medium sized rocks and let it tumble to clean itself for a few minutes, then dump. It really worked out pretty well, the rocks would breakup and cement that was set up on the paddles and the gravel would scour the inside of the drum. I had an old old mixer that was a steel drum, I don't know if the new ones are some sort of plastic, if so I would use smaller rocks, so I wouldn't crack the drum. The dumbest thing I ever did was sell that mixer that I had bought at an auction for $25. I sold it when I was moving, with an old tractor I had. I then bought this current place and now I will probably pay $700 for a new one that won't be made anywhere near as well /w3tcompact/icons/mad.gif. Oh well.../w3tcompact/icons/sad.gif Hope this helps.....

 

[Robert_in_NY]

We mix a lot of concrete by hand still. Most jobs only require about 5 bags so it isn't worth it to have a mixer on site. We also mix cement by hand when working with blocks as it allows us to mix what we need and if we need the mixture a little dryer we just pull some more from in the pan. The mixers are nice if you are doing a lot and don't want a truck or can not get a truck where you need it but for a couple bags you can mix it by hand in a couple minutes. Enjoy your new toy and when you are mixing you want it to be fairly wet but not runny. Best is when you can scoop a shovel full and it stays heaped on the shovel but slides off nice and easy. Too dry and it is hard to work, too wet and it is hard to work. Try it and if you have to add some more mixture so be it. Take care and have fun.

 

[Spencer]

The site is ready, I have the permit, the lumber is delivered, now all I have to do is build my pole barn. I don't think I will be doing any big pours of cement myself but I do plan on mixing my own for the posts, sidewalks, etc. I got some sand and gravel delivered in bulk instead of buying it by the bags. I had the guy that delivered all of my fill sand go and pick up the 60/40 mixture and deliver it to me. The concrete company wanted $85 for delivery (any quantity) and my sand guy did it for $60. I just had him get a full load (18 tons) since I have the room to store it any many projects in the future.

So since this gravel/sand mixture is already mixed to 60 percent gravel and 40 percent sand am I correct in thinking that I should use 5 shovels of 60/40 to 1 shovel of portland cement? I am thinking that I will dump one of the 94# bags of portland out and see how many shovel fulls are in one bag so that in the future I can just dump the full bag into the mixer and know how many shovel fulls of 60/40 to add. I know there are a lot of variables on how much water to add but what would be an average amount of water to add when using a full 94# bag?

Thanks

 

[Youare]

After consulting The Complete Concrete Masonary and Brick Handbook by T.J. Adams I have it sounds like too much work.

They recomend putting the sand in the mixer first then adding the portland cement, let that tumble around a minute or two then add the stone or aggregate. Once this mix has tumbled a bit add water slowly until you have the proper consistancy. The cement does not want to be too wet as this affects the strength after it cures.

One thing they do caution is do not accept cememt that has been mixed for more than 20 minutes. The reason is the chemical reaction which hardens the concrete has already started and will be weakened if the cement is mixed for more than 20 minutes.

As already stated a slump test is the only true way to determine the proper moisture content of mixed cement. A little more portland cement in the mix is better than a little less. The more cement the stronger the mix.

If the ground is dry where you are going to pour concrete is is wise to wet it down. Dry ground will suck the moisture out of the concrete too fast and cause it to be brittle really weak.

Cement is hard on the skin so wear gloves.

Randy

 

[accordionman]

SIR,
my comment is in regard to your putting cement,( concrete ) around the post
on your pole barn. do not do this. the post, even though treated will go bad much
faster than they would if you just used fill dirt around them. the company that put
up my pole barn, (WICK) does not put concrete around the post, and they do not
recommend this. when they put the post in the ground, they put a large concrete
circle in the bottom of the hole, and level it. the post has a cross brace fastened
near the bottom to prevent pull out during high wind conditions, and the holes for
these are 4 ft. deep.
accordionman
william l. brown