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DDA52 09-16-2006 11:06 PM

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. :rolleyes: So, I figure if I put it here, anyone, including me, can find it. :D

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. :rolleyes:

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. :D

DDA52 09-16-2006 11:36 PM

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.

DDA52 09-17-2006 12:00 AM

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. :D

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. :rolleyes: 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.

DDA52 09-17-2006 12:44 AM

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 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. :D

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. :eek:

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.

DDA52 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. 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! :eek: 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. :cool:

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. :D

moe1942 09-17-2006 08:37 AM

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.. :D

DDA52 09-17-2006 01:53 PM

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Thanks, Moe. :)

Ok, now it is time to place the concrete. You will want to check the mix before you start pouring it out. Just have the driver dump a little bit in the chute. It should be wet but not soupy. If it is too dry, add water in 5 gallon increments...that is about the easiest increment to guesstimate on their water gauge. Be very careful not to get it too wet. When too wet, it is easier to place, but this will make life more difficult when finishing. Finishing is a time when you want easy, not difficult.

Once you get the water right, start dumping it in the forms. Be careful not to pile it up too much. That will make you work twice as hard moving it around. The man on the chute is the one who should control how fast the driver is discharging the concrete. Tell him to slow down or stop if it gets to be too much. It can be a tough balancing act sometimes.

Once you get the concrete poured out, deep forms should be vibrated or at least rodded to get the bubbles and voids out. On shallow forms, use a hammer on the outside. Just hit it enough that you see some water and paste oozing up along the form, and move on. With the vibrator, make fast movements and don't stay in one place too long. The vibrator moves a lot of concrete and will blow forms out very easily. If there is a brick lug or some type of form that concrete needs to go under, use a hand float to ram it under, packing it in under the form. A hammer blow on the lug will tell you if there are any voids. If there are, it will sound hollow....pack it again. Just be sure not to hit it too hard, you don't want the form to move on you.

While or after the vibrator/rodding is being done, it is time to rough grade the concrete. Using the rakes, try to get all the high spots knocked down and fill any holes. This will make it easier to screed in a minute. Once that is done and even while, one or two guys can start floating the forms. The concrete needs to be flush, not above or below, BEFORE you screed it off. This will make it easier for the man on the screed to keep it flat and level. Otherwise, the screed will hve a tendency to ride up on humps. This is not a good thing. Using the hand float, run back and forth over the edge about a foot or two and flatten it out and fill any holes. It needs to be fairly good, but not perfect. That will come later.

Edit: If you are pouring multiple trucks, pour out the first one and then begin the screeding. Don't pour out the whole slab to start with. Do it in either full trucks or small sections to keep from pouring too much, or having to move too much from one spot to another. It will also give you a tiny breather in between sections.

DDA52 09-17-2006 03:50 PM

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Screed time.

Now that it is all prepped, the fun starts. Read that as back breaking work. :rolleyes: The screed board is what you will use to grade the concrete. Basically it will be a long straight board that you will drag across the top to level it off. I use magnesium 2x4's specifically made for this purpose, but a good straight 2x4 will work also. If this is a small pour, the screed can go from form to form. That is an easy one. Just drag it across the forms until it is all level. If you create any holes, fill them up and do it again until perfect even and filled.

Larger pours create a problem in the screed dept. with wood screeds, you don't want to go over 16'. It will bend too much if you do. When it bends, you risk it getting off grade more. So, stay 16' or less. The fact that you can't reach from side to side means you have to add a grade mark in the middle for later. This should be done way before the pour, btw. We wet screed all of our stuff. We basically set a stake in the middle with a grade nail on it. The nail is later floated around creating a grade point to start at. Then we connect the dots so to speak from form to grade point and back to form, thereby going completely across the forms with a level line in the concrete. The way the line is made is by lightly dragging the screed across the concrete until it is filled up and leveled off at that point. The line should be about a foot or two wide...whatever you come up with is fine. Then you start leveling the slab off using that point and the form. At the form, you just bear the wet line, you can't. You have to use a light touch and float the board across the line to maintain the level. You have to be careful not to wipe out the line or you will get off grade. This is a tough way to do it, but is the easiest way in the long run. As you are dragging the screed across the top, someone will be behind it in the direction of travel, filling in holes and or moving away excess concrete away from the screed with the concrete rakes. On long boards, it is best to have two or three men doing this. Small ones can be done by one easily. Just keep doing this until you run out of conctrete, or finish. Once an area is screeded, stay out of it. Do not walk across it again. If you do, you will have to rescreed it again.

The other way to set grades is by actually seting a 2x2 form in the slab for the screed to run down. This creates a solid place to run the screed board on and is a more stable grade point. It also creates more work in the forming as well. It will aslo have to be removed before you are done and the holes filled. This can be tough as the hole left by the removed form can only be wet screeded out. You do this by taking a short 2x4, say three or four feet long, and lightly drag it across the top, taking away the excess and filling any holes. Be sure to fill in any and all foot prints while doing any screeding. Don't wait until later..get them as they are made. Saves time and "oops's" later. In the pic, you can see Jose using a short board to fix a spot as described. Unfortunately, I don't have any of us on the screed, because it was all hands in the deck until it was done. :rolleyes:

Ok, now that it is all graded or screeded, the time for the jitterbug has arrived. Now it is legal to walk in the freshly screeded concrete. Just climb in and turn around. You operate the bug by walking backwards and tamping the concrete as you go. You want to b sure to tamp out any footprints as you go. The bugg should not be slammed into the concrete. Just tamp it hard enough to wipe out footprints and leave a grate pattern in the surface. If you hit it too hard, it will leave holes and they can be tough to fill with the bull float. It takes some practice to walk and tamp backwards at the same time. You usually get it down about the time you are finished. :rolleyes: It also looks like you are doing some wierd dance. :D

Now it is time for the bull float.

DDA52 09-17-2006 04:56 PM

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Bull floating.

The bull float is a long magnesium float on a pole that will smooth out wet concrete in preperation for finishing. It will fill holes and push any rocks the jitterbug left behind. It will also wipe out all marks left behind by the bugg. The floats are usually 42-48" long and 8-10" wide with a smooth bottom. They are used with poles to reach way out and across the slab to get it smoother. The poles are usually 6-8' long and will either screw together or snap together. The old lift style head is the most common. You start out with the poles down low to raise up the leading edge of the float, push the float out across the slab, raise the poles to lift the edge closest to you, and bring it back. The best type head is the rocker or chain drive head. You can move it to and fro without raising the handles. It uses a chain drive mechanism that raises or lowers the float by twisting the handle. These are by far the best and easiest to use.

To float out a slab, begin one foot in the forms...don't start at the edge. If you do, it will pull concrete away from the edge. Push the float out across the slab going at a good clip, but not too fast. Keep the edge up about a half to three quarters of an inch. Go out as far as you can and bring it back, low and slow. Watch and see if it fills all the holes and makes it make the surface smooth. If not, do it again and again until it gets it done. If you have to do it more than three times, move over a foot and then try it. It will have a tendency to make a rut if you don't move it. If it makes a rut, it can be easily fixed by running over the rut from different angles or just by moving the float over again. Once that run is done, move over and set the float down again..this time with a six inch overlap and repeat the cycle.

Pay strict attention as to whether or not it is leaving any marks and filling the holes. You can move paste around by elevating the float higher and pushing more paste to the hole. Once you reach the hole, drop the float at the hole and resume normal height. Sometimes this may need to be done several times to fill a good hole. If the surface does not seem to have enough water on it, a light...VERY LIGHT spray of water will help. A water bucket and brush will work best on small spots. Just be sure to float out all the marks you make.

Bull floating is easy enough to do. With care, it will work out well even for a novice. It will also make a huge mess if you are not be careful. ;) This is the first step in the finish process. If you miss something here, it will bite you later. :eek:

DDA52 09-17-2006 10:58 PM

Now that the bull floating is done, it is time to do a few catch up things. First and foremost, clean up the placing tools. Bugg and bull floats esp are needing it by now. The rakes and screed as well...get 'em all clean now.

The next step is to run the edges and get all the areas that the bull float messed up along the edge fixed. Run the edger along the forms and get all the edges run for the first pass. They will not look perfect yet. They will actually still be a little rough. The main thing to do here at this point is to get all the rocks moved away frm the form. They are a royal pain later and are extremely easy at this point. The edge is probably too wet at this point to really hold the shape of the radius as well. Just get it close. After theedger is run once, go and float out all the marks it left. This can be done at the same time as the edger so you don't have to go back.

Now the slab is all floated and setting up. You should be seeing some mix water rising to the surface. This is what should be happening. You can take a short break at this point. The mix water needs to dry up before the set will really take hold. You need to be watching it closely, though. Keep an eye out for dry spots and areas that turn a whiteish color. These will be your hot spots and will need extra attention later. The surface will eventually start to crust over. This is normal and exactly what you want it to do.

Edit: Directly after the bull floating and initial edge work is done, that is the time to place any embeds, that is bolts, plates or any thing to be embedded in the concrete. Do it any later and you will have troubles getting it in.

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