Concrete finishing....all you want to know.

[DDA52]

The first finish hit.

The water is dried up and all the concrete is crusted over at this point. Now is time to cut it open and let it breathe further. This is called the first hit. You will start using a trowel at this point. If it works up to a soupy mess, get the float back out and use it. All areas will need to be hit again. Edges, perimeter and interior. Run the edges exactly as before, just use the trowel this time. They will start to take shape and begin to look like they should. They will take two more hits and that is all. They will finish first as will all the edge of the slab. This is due to the fact it is done by hand. All hand work will finish faster than machine work. Against the forms will finish faster too. They tend to suck up the water and will speed up the setting process slightly.

Now comes the interior of the slab. As to when this gets done depends greatly on how you will be doing it. By hand, you will need lots of help. It will need to be started as soon as you can get on it with knee boards and not sink. This is due to the fact that it takes much longer to finish by hand and you will need the extra time. The knee boards we use are simple. They are 3/8 plywood, 32" x 24". You need two. One to work on and the other to move to when you are ready. Even if you machine finish the slab, you will need knee boards. They are needed for fixing oopses, and for working around pipes on the inside of the slab. To work the concrete at this point, it is best to use both a float and a trowel. Use the float to cut open the crust and then lay it back down smooth with the trowel. Take out all the marks in front of you and then move onto the next board. Pick up the first board and put it on the slab in the direction of travel behind you. Then repeat the trowel cycle.Do this over the entire area. You may run into wet spots. Just go around them or wait them out and then proceed. Don't get onto it too early or you will spend all your time fixing craters that you make by sinking into the concrete.

Use the float or trowel you are not using at the time to lean on while you are working the surface. Don't use your hands. The concrete is chemically active and can eventually burn you if you don't clean it off of you. It will also suck all the moisture out of your skin and dry it out badly. Cracking will follow. It isn't fun.

Now, if you are using a trowel machine, everything is different. You put it on when you leave a footprint about 1/4" deep. Then you slowly work the surface at a slow speed with the blades almost all the way down. If you hit a dry spot, speed it up, raise the blades slightly and or add a little water. Make passes along the form first and then start working in. Make sure the passes overlap by almost half. This will keep you from floating in a ripple into the surface. You want to fill all holes and craters with the machine or trowel at this point. Never leave anything behind for later...later will be too late. Pay close attention to footy prints too. This is when the most are left in slabs. Once it is all cut open, let it breath and keep an eye on it.

[DDA52]

The second finish hit.

When you cut the slab open on the first hit, the surface was left looking wet and rough. This next hit will start to smooth it out much, much more. The difference will be very noticable. It should be done as soon as the surface will start to smooth over with the trowel. Work the edges again as before. This time when you go behind the edger with the trowel, reach in as far as possible. This will give the machine an edge to work to and keeps it from having to come in close to the forms. Work the entire areas that are ready and wait out the ones that aren't. The perimeter will need only one more hand hit now.

If you are doing the interior by hand, get on it as fast as possible and get after it. It will take more time this go round. The concrete will be stiffer and you will probably need to use two hands on the trowel in many places. Work everything as before. It usually isn't necessary to cut it open again, unless it is too hard. Just smooth it all out with the trowel and be extra careful not to dig any holes and be sure to fill any you find or make. Move as fast as possible because time is getting short as to workability.

If you are machining the concrete, start the second hit about the time you barely leave a footy print. 1/8" deep would be the earliest it will work. This time, you want to travel 90° to the direction you went last time. Each seperate hit should be 90° to the last one. That can get tricky when you have several areas at different hits due to wet or dry spots. The overlap on the passes now should be about six inches or so. Again, make sure to get all the footy prints and fill every hole. You may need a touch of water in dry spots. Use it sparingly or you will have to go back and do it all over again. Work the whole slab this way. By the time you are done, you will need to check the start point. It will be close to being ready for the third hit. When you finish a hit with the machine, it is best to work your way back to or very close to the start point.

Edit: You will want to raise the blades a little at this point with the machine. Each time you raise the blades, you are applying more pressure to the surface. That is what will actually finish the surface...WHEN IT IS READY.

[DDA52]

Third hit.

The edges will need one more final hit. You will be hitting them with the trowel mainly. The edging should be done. Hit any areas that look like they need it. The concrete surface will start to get very slick and the color will get darker slightly. Once you hit all the perimeter again, the edges are done at that point.

The interior hand hit will be the toughest yet. The concrete will be hardening up rapidly now. You will most likely not be able to sufficiently fill any holes and oopses, so be careful. You will need to put a lot of pressure on the trowel and it will also be raised up much higher than before. Both hands are needed at this point. If you use only one hand, you aren't doing anything to it and are wasting valuable time. Do the whole thing once more and that will just about do it for the hand hits. If any spots look fuzzy, yes it will actually look fuzzy, these will need to be hit again. Wait them out and finish up. Once all the slab looks and feels slick, that is it for the hand hits. You are no longer able to do any more to it by hand.

The third hit with the machine is much the same. Begin it when you are just about NOT leaving a footprint. This hit will slick the surface over even more and it will take on a fuzzy look. Some parts will start to shine a little and feel very smooth. That is what you are looking for at this point. Again, as before, travel 90° to the previous hit and overlap 6 inches. This time, go in close to the forms again. This will tie it all in slickness-wise and make it look more even. Do it all and then look at the shiny spots. They may be ready for the last final hit.

[DDA52]

Last hit and burn with machine.

When the fuzzy spots start to lay over and shine when hit with the machine, you are then ready to hit it all. If it stays fuzzy looking, stay off and wait some more. You can't force it to dry up by hitting it early. It actually does the opposite and makes you have to go back and start over. This is really true of all the machine hits. On this hit, the blades will need to be raised some more again. Lower then if they tear up the surface or if it keeps fuzzing back up.

When the fuzzy spots start to finish, it will get really slick. The color will also get very dark as compared to what it was before. It will start to get a "burned" look. This is when it is ready to pour on the coals with the machine and burn or burnish the floor. This is not a necessary step. Once it defuzzifies, it is really done. The burnish makes it super smooth and much easier to clean up.. Now, not all machines can burn a floor. It takes a high horsepower and heavy machine to do it right, but a small one can do it, just not as well or as long. My machine weighs 350# and has 11hp. It can actually make two burnish passes if I time it right.

To make a burn pass, raise the blades up as high as possible without making scratch marks in the floor and give it all you have in the HP dept. Hold on, too. This will make the machine very grabby on the floor. Mine will sling me like a rag doll if I let it. I will usually hit it once or twice and make it shine like a mirror. Then at that point, I am done..more like done for. When I was younger, it didn't kill me like it does now....must be getting old.

The floor is now done. If you are applying a curing compound/sealer, now is the time. If you are saw cutting contraction joints, now is the time if you have an early entry saw, otherwise, the next day for a regular concrete saw.

Now I know I didn't cover absolutely everything and I am sure I have forgotten some things....but this will give you a very rounded picture of what to expect. Every mix and every job is different, but the principles are basically the same, no matter where you do it. There are also many different ways to approach finishes...BUT there is only ONE end result. As long as the end result is the same, it isn't necesarily a wrong procedure to use. All that matters is that the concrete gets down flat and smooth.

[DDA52]

Ok, now that I have typed all that, I will now say this. What I have described is a LOT of work. You will only get one chance at it, also. There are no do overs or anything like that. Concrete is extremely unforgiving and could care less if you are ready or not. It dries fast in the warm weather and faster when it is hot. In the cold, it will take forever. There are a lot of little ins and outs that can really only be gained by experience. I have personally finished well over 6 million square feet and I am still learning about this stuff. If you have any doubts about it...GET HELP!!! A ruined floor is there for a lifetime since most can't afford to redo it. I know I can't. Doing a small patch or a few sidewalks is a far cry from finishing a floor and it should not be treated as such.

When I reccomend getting help, I am not necesarily meaning let the pros only do it. You can hire day finishers to help. I do it all the time and I am in the business. It is an industry standard. These "hired guns" work by the day and will work for just about anyone. Most are very good and will be able to handle anything. They usually have all the tools they need, including machines. To pour and finish a 1000sf floor, a good finisher and two laborers can make easy work of it. When it gets bigger than 1500sf, you may need two finishers. That is still cheaper than turning it over to a full crew and will get the same results at a lower cost. Just something to think about. It is done all the time. You do all the prep and grunt work, and then bring in the hired gun when it comes time to pour...and YOU help him. You get to learn more that way, too. Most learn they never want to do it ever again, but at least they did learn something. I will answer any questions I can to help.

[MAC702]

Originally Posted by DDA52

I will answer any questions I can to help.

I hope to pour in about 3 months. Make an opening in your schedule.

[jer29_11_13]

Originally Posted by DDA52

Screed time.

...The fact that you can't reach from side to side means you have to add a grade mark in the middle for later.
...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 down...at 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.

This is the part I'm having difficulty with... that's why I was going to set interior 2x4 forms to screed to and then remove as I move along as you have explained in the next paragraph. Do you have a pictures of this aspect?

Originally Posted by DDA52

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.

This may sound dumb but I didn't realize I can walk in the concrete , I guess I need to get a pair of boots, you should add these to the essential tools list

Originally Posted by DDA52

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. It also looks like you are doing some wierd dance.

Now it is time for the bull float.

Thank you very much Don for explaining everything!

[jer29_11_13]

Originally Posted by DDA52

The first finish hit.

Now, if you are using a trowel machine, everything is different. You put it on when you leave a footprint about 1/4" deep.

When using the knee boards is the 1/4" footprint depth the same test to know if you can walk on the slab?

Originally Posted by DDA52

Then you slowly work the surface at a slow speed with the blades almost all the way down.

Not being familiar with a trowel machine, how do you adjust the blade angle?
Also how do you fine just finishers, the companies I've spoken to want to do the whole job?
Thank you Don!

[rmack898]

Thanks Don for taking the time to post this. I did my own 1600sf floor two years ago and it is HARD work. The one thing that I overlooked was the pre-pour, check it over, look at everything. I didn't measure the door height to make sure that the truck could get into the building and I wound up having to pull concrete 20' from the end of the chute on the first pour (my back still reminds me every now and then). You need to double and triple check everything before the first truck shows up. I looked at the door opening and thought the turck would clear the opening with no problem........WRONG. Check everything.

[Pile Buck]

Originally Posted by rmack898

I didn't measure the door height to make sure that the truck could get into the building and I wound up having to pull concrete 20' from the end of the chute on the first pour (my back still reminds me every now and then). You need to double and triple check everything before the first truck shows up. I looked at the door opening and thought the turck would clear the opening with no problem........WRONG. Check everything.

Now that’s one pizz pour truck driver, can’t get an 80,000-pound + concrete truck in a building.


If’n I was there I would have shown him how to do it :evil: