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Old 09-16-2006, 11:06 PM
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Default Concrete finishing....all you want to know.

I am going to do my best to lay out the basics of concrete finishing for you guys. I keep having to answer the same things all thetime, which I don't mind, and later I can't find them and have to type them out all over again. So, I figure if I put it here, anyone, including me, can find it.

This thread will cover finishing only. If need be, I can create another thread on rebar or forming, or whatever lese comes up. But for now, this one will be about placing and finishing. Seeing how this is SFT, anything could happen. Hijacking is expected. I'm not sure, but it may be required in the SFT bylaws....Cutter or Madam would have to make a ruling.

If you want something splained better or clarified, just ask. I will include pics when possible. I just looked in my archive and it seems I have lost a bunch of good ones when I cleaned the computer last. Too bad. Not to worry, I have the means to get more. That is the easy part. Explaining everything may be the hard part. We'll see. I will try to break it up as much as possible so as to gaurd against everyone getting bleary eyed. I hate it when my eyes glaze over on long posts.

So, here goes.
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Old 09-16-2006, 11:36 PM
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Concrete mixes.

The first order of business is deciding on a mix. 3000 psi is a regular, middle of the road mix. It is the minimum required by most engineers. You can get a 2500 psi mix or you can go higher than 3000 in 500 psi increments. You will want the 3000 psi mix for maximum workability. The 2500 may do fine, but it has less cement and usually more rock. That will make finishing much more difficult. The cement is what will add workability to the mix. Don't be fooled into thinking that if 3000psi is good, 4000 will be better. It isn't. Yes it has more cement. It also will set up much faster and get harder than the 3000. That will take skill and skilled men to handle. Stay with the 3000 unless there is a specific need. If there is a need, I recommend getting help, skilled help.

Rock size is another consideration. The standard rock is around 1 1/4 and will cover most applications. Driveways, slabs columns, piers etc. Thin toppings and the like will need a smaller rock, say 1/2" or maybe even 3/8. Curbs need a small rock and more sand as well. Curb mix is a standard mix with all ready mix companies.

If you need fast setting concrete, you can add calcium in the 1-2% range. It will make it set up faster, much faster bordering on too fast in warm weather. It should be used sparingly as the calcium is a salt and will eat the reinforcement over long times at high percentages. Straight cement mixes can do much the same thing. In cold weather, straight cement will work best, although it will cost more. Fly ash, a by product of burning coal, will act just like cement and is used to cut the cement in concrete making it cheaper. Some areas do not have acess to fly ash and will only offer a straight cement mix. The fly ash will slow the set down making it easier to work in warm weather.
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Old 09-17-2006, 12:00 AM
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How to order concrete.

It isn't hard. They will ask you questions and you give them what they want to know. I'll try to get it all down for you here so it won't be intimidating. I will cover the normal stuff, but not things like addresses and phone numbers. You can do that part.

First off, they will want the yardage. I will assume everyone already knows basic volume calc and move on. Get a little more than you need. Short loads will often have a fee riding on them. If you figure exactly 5 yards...add 10 or 15% for waste, accidents or irregularities in the base or forms. You can add more, but if dealing with a single truck pour, it is much better to get it all at once. And cheaper. With my area companies, anything under 5 yards includes a short load fee in addition to the regular per yard price. This is normal. Get quotes on this BEFORE you are ready as some are way higher to discourage small loads. Unless they are the only horse in town, you will want to shop around for the best price and closest plant.

They will want to know the mix strength you want. Tell them what you decided on, say 3000 psi. If you want straight cement mix, now is the time to tell them.

Next they will want water content or slump. Slump in a nutshell is the amount in inches the concrete will "slump" down when it is released from a test cylinder. The cylinders are cone shaped and are 12" high. Concrete is filled 50% at a time. It will then be rodded 50 times to get the air and spaces out. Then the last 50% is added and rodded again. The cylinder is then flipped over and removed. The amount the concrete falls in inches from the original 12" height is the slump number. A 4" slump is a good median number. There are lots of factors that influence how wet you want it. Cold weather needs less water, but still enough to work it, while hot weather will want more. Slopes= less water as well. If in doubt, get it drier than normal and add water on site. It is better to add because you can't take it out once it gets there...too bad, that would sure solve lots of troubles. You do not want to add too much. That will weaken it. Most batch recipes allow for a 30% increase in mix water because they already know we will add water. I'll do more on water later when I get to placing.

If there will be multiple trucks, they may want to know how far apart will they need to be spaced. For a slab being placed by hand, 30 minutes is a good starting point. If it is being pumped, then 10-15 minutes may be too slow or just right. You can always call and speed up if possible or slow it down as needed. Just make sure that the trucks do not stay on the job too long. They will charge truck time for waiting over an hour usually. It can get pricey, so avoid it if possible. Another tip is to order one truck or partial truck less than required. For example, you estimate 65 yards to finish...order 60 yards and then order a "kicker" when it is all placed to the 60yd point. It may take 5 yds more, or it may take much less. You don't want to have way too much or order two kickers..that is a bad thing, but if necessary you do it. When you place the order, in the case of the example, tell them 60 plus, and you will order out the last truck. IMO, the worst thing is to pour it out and still have one ormore full trucks waiting out front....if they can use it elsewhere, fine, but ifnot, you have to pay for the extra..not good.

They will also want a time to start. Don't expect them exactly at that time...sometimes they actually make it, most times they will be a tad behind. This is normal. Unexpected things always happen. Murphy's Law applies. If you are pouring a slab, start as early as possible. In the summer it will be easier due to the cooler temps during the harder work. The winter temps will make everything take longer, so get it down as early as possible and try to be done before noon if possible, or be ready to finish under lights...which may happen anyway in the cold.

That should be the common things you will be asked.
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Last edited by DDA52; 09-17-2006 at 12:55 AM.
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Old 09-17-2006, 12:44 AM
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Basic tools and what they are used for.

The tools you want will be dictated by the type of finish you are doing. Broom finish surfaces don't generally need as much work or tools as slick finishes. Since most of the questions revolve around shop floors, I will stay in that realm.

Concrete rakes...you will need several to move the stuff around before and during screeding. Shovels will work as well, but not near as well.

Shovels...self explanatory.

Buckets, at least two and at least one water brush. These are extremely necessary for finishing and clean up. Using a water hose to add water to a drying slab during finishing is a bad idea. It will always put too much on. A water brush will do it much better and will aid in clean up.

Screed board. This will be the board you will grade the concrete with. It should be as long as possible to make short work of the floor. Too long and it will bow too much. 16' 2x4's are ok and as long as wood should be. 12-14 are ideal. If that is too long for the forms, then get one about a foot wider than the forms. That should be plenty. Make sure it is super straight and doesn't have any kerfs and blemishes.

Hand float..wood, alu. or magnesium. Mag is better. They will be used to rough float all concrete after placing. This is the first pass. 15-16" is the best size for general work. I personally like using a 20-24" float, but it can be more difficult to use.

Edger in a 1/2" radius. A 3/8 radius can be used as well. I prefer 1/2 because it will end up looking better. These are for shaping the outer edge at the forms. It will also aid in form removal later when the edges are done with an edger. Not as much garbage all over the edge to hold it to the slab. The sheetmetal types are best. They should be stainless, although a mild steel one will work...just keep it clean. Most are 6" long and 6 wide. For a slab, 6" wide is a must. The little 4" and 2" wide ones are too narrow. You want one that will stay on top without fighting.

Jitterbug. this is basically a tamper for concrete. You use it right after the screeding is done to knock all the rocks down and bring more paste to the top for the bullfloat. It will also smooth out some irregularities left by the screed. It will also help consolidate the concrete a little, helping the air bubbles to work out and get rid of voids.

Bull float. This basically a long mag float on a long pole. It will be used after the screed and jitterbug to make it all as smooth as possible before it starts to set up. The better it gets before final finishing, the easier it will be later.

Steel trowel...they are the main finishing tool and Cutter's nemisis. :evil: They come in all widths and lengths. For a basic all around trowel, I'd start with a 16" stainless or spring steel trowel. Having a 12" around can be good as well for small areas around plumbing, etc. 4" wide is a good width. A bigger one will work, ( I use a 24") but will require more horsepower to use.

Trowel machine or power trowel. This may or may not be needed. Just depends on the size of pour. It can easily do the work of 10 men or more, but takes experience to run. It will do more harm than good in inexperienced hands. This one is best left to the pro's, but you should know about it. It basically floats and finishes the concrete. It applies pressure to the blades to make the concrete flat and smooth. It will also consolidate the concrete making it stronger and less likely to crack. The surface will also be more durable due to the extra consolidation.

Vibrator...this is necessary if you need to fill tall forms or beams and footers. It will vibrate the mix to get the air out and fill in voids along the forms. It is also the worst killer of forms. Forms will move easily if you keep the vibrator in one spot too long. As an alternative, a 2x2 or even 2x4 can be used to rod the concrete. It will do the same thing, but will take longer and use more horsepower.

OK, I think I got the basics....if not I'll add them later or on another post.

Most of this equipment is available for rent. With the exception of the trowel machine and vibrator, all can be gotten at Home Depot even.

Edit: I neglected to mention concrete boots. They will be absolutely necessary if you will be inside, in the concrete. Gloves may also be a good idea. I use the knit ones with the rubber fingers and palm. They won't stop the water, but will give you a good grip when wet, which happens a lot.
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Last edited by DDA52; 09-18-2006 at 11:39 PM.
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Old 09-17-2006, 01:22 AM
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Prep the area before pouring.

Get the path cleared ahead of time. This will eliminate a lot of headaches at the time of the pour. You would be shocked at how many pro's do not do this simple little thing. The trucks are 8' wide and around 11-13' tall. Trees and power lines will need to be looked at. Be sure of pipes, watewr meters, septic tanks and lines. Even though they may be 18" or more below ground, a concrete truck can still crush them. Make sure you don't have to go over any existing driveways or sidewalks...they may not survive without cracking or failure. You may want to reroute or consider another delivery method.

Other delivery methods are a concrete pump, wheelbarrrow, Georgia buggy, either manual or motorized, or even a Bobcat.

Pump..how can you tell if you need one? Basically, what I look for first is access. If I can hit three sides of a small slab, I am usually ok. Concrete trucks usually carry 14-16' of chutes with them. You have to measure from where they will be stopping outside of the forms. Go in about 14-16' and see what you have left. If there is less than 14-16 feet, you can pull that without killing yourself. If there is 15-20 feet more and that is all, you may want a second chute. I made one that sits on a sawhorse. It is simple corrugated sheet metal and a 2x8 frame. I'll post a pic. If the access is limited to two sides with longer pulls, that will kill a finish crew and will need a pump. Call the pump company for an inspection and to check the prices. They will tell you how long a boom and how much. I can get a 70-100 yd slab pumped for about 650 bucks. Larger booms will cost more. I had one that needed a 65m+ boom and it ran about 1000 bucks an hour! It all depends on access and how much pulling will be required. Too much=pump. Not much, do it by hand. They also have line pumps that are good for hard to get to places. The company inspector will know which will be best.

Wheelbarrows and Georgia buggies are basically the same thing. The buggy holds more and has two wheels...a definite plus. The motorized ones will let you ride on them and even dump the hopper for you.

I use a Bobcat all the time to pour. You can't fill the bucket all the way, but it is way faster than a wheelbarrow, esp on difficult terrain or when you are pouring a lot. You have to consider truck time when deciding on the wheelbarrow deal. Large pours will need a fleet of barrows and willstill take a long time.

More later... I'm getting crosseyed.
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Old 09-17-2006, 08:37 AM
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Great info Don. Could have used it 30 years ago. Have a concrete fix question but will deal with it in a seperate thread..I'm not going to be the first to hijack this one..
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Old 09-23-2006, 09:52 AM
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Don, I hope this goes with the topic. In case you haven't seen it at the hobart site. This guy needs help. Here's the thread title..

welding to a weld plate in concrete footing
Tumbleweed



Gotta run. I'm allergic to concrete..
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Don't pick a fight with an old man. If he is too old to fight, he'll just kill you... John Steinbeck

"If we ever forget that we're one nation under God, then we will
be a nation gone under". ~Ronald Reagan

We should have picked our own cotton...

I love my women hot and my beer ice cold..
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Old 09-23-2006, 10:23 AM
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Yup, I posted on it.
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