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Power Trowel 101

davidmeiland | Posted in General Discussion on March 21, 2005 01:56am

The local rental shop has a couple of these, about 3′ diameter. I’ve seen them in use a couple of times. I’ve got my own 24×36 shop slab coming up and am debating (months in advance) the merits of finishing myself vs. bringing in a crew (megabucks) to do it. My skills include steel trowel finish by hand on smaller stuff, and I can get enough hands and backs onsite to place the mud if that’s what I want to do.

What are the basics of using a machine to polish a slab? When do you start using, how long, etc.? In the back of my mind I remember learning that overworking the surface of concrete can be a problem.

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  1. gdavis62 | Mar 21, 2005 02:13am | #1

    Timing is more important than technique, and very little of the latter is needed to work a spinner.  Go watch one being used for a while, ask the operator what's going on.  He'll tell you it steers just like a floor polisher.

    But when to get up on the crete, and when to stop polishing, that takes a little know-how.  But keep testing at the edge with your hand-held steel trowel . . . it'll tell you when the time is about right to hoist and go.

    I prefer a "sand" finish in something like a garage, where the floor can get wet, but a polished one for an indoor slab.

    I've used a walk-behind only enough to tell you how it in fact does steer.  When I was involved in commercial work, the finishers we used had two-wheel riders.

    1. davidmeiland | Mar 21, 2005 02:24am | #3

      I used one a little bit this week, mostly someone else ran it. I think the guy in charge pulled the trigger too early, because it picked up little bits of sand and cream and spread them around. Eventually it started polishing but it seemed like we should have started later. I'm wondering if there will be spalling later because the surface was overworked.

      The slab I'm going to do needs to be very flat and glassy. It's going to get acid stained and will be my shop/studio floor for a while, probably a long while. Problem is, to get a good finishing crew I need to bring them from off-island and that's megabucks and a sick schedule hassle... thus I'll probably attempt it myself. Done nice broom finish quite a few times, steel a few times, nothing large. Pizzas and beer will get me a half-dozen guys over here to rake, screed, and bullfloat, maybe a little bit of kneeling too.

  2. Notchman | Mar 21, 2005 02:20am | #2

    I would suggest you find a cement finisher who will tutor you on your slab the first time.  That's what I did and I paid him $150 to get me started and then he hand-troweled the edges and corners while I ran the whirlybird. 

    Once you get the hang of it, and know when to fire it up and get the angles set on the blades (and you'll be changing them as the slab begins to go off), it's kind of like buffing a floor.  Not really difficult and the results are worth it, not to mention less wear and tear on your shoulders and knees.

    But, at least in my case, the rental yard machines are pretty new, with crisp edges on the blades which are less forgiving than one that's had some break-in time.

    1. davidmeiland | Mar 21, 2005 02:32am | #4

      The guys here... not your top-of-the-line finishers, at least the ones I know. There's an off-island crew that comes over to do large slabs and Bomanite, and they make it look easy and perfect. Not sure I can afford them... guessing that 3 men for the day plus travel time = $2000 +/- and they're worth it for the big stuff.

      1. Notchman | Mar 21, 2005 02:44am | #5

        Well, Gene Davis's comments were good.... and depending on the weather the day of your pour, you can probably start a little later than when you'd be laying out knee boards to hand-trowel it. 

        You want to start with the blades pretty flat and with the speed down a bit, you can dial up the angle until it starts to dig, then back off.

        I'm sure you'll do just fine.

        1. brownbagg | Mar 21, 2005 03:05am | #6

          wait till you can walk on it without leaving an indent. spinkle with water and take your time. do not let it dig.

  3. User avater
    hammer1 | Mar 21, 2005 06:11am | #7

    Often there are two separate procedures. The first one is floating. There are some shoes that fit over the trowel blades. When floating, you set the blades somewhat flat with the knob at the top of the handles. We will bull float the floor right after the pour. This is the long handled float that you do by hand. As the concrete dries, you will not be able to leave a fingerprint without pressing down with some pressure. There is a silvery sparkle to the surface that will leave and turn matte. you need to stay on the site and keep checking. If you take off and go to lunch, it will almost surely get ahead of you.

    When running the machine, you lift up on the handles or push down on them to make it move side to side. Like a floor buffer. It takes a bit of a delicate touch. When you first start it up it will want to take off on you and you can't stop it with brute force. Make sure you aren't wearing sneakers or you may be missing some toes. After floating is a good time to do the perimeter by hand. When you take off the float shoes, you will need to tip the blades up a bit to keep them from digging in. Too much and they will start picking up little stones, not enough and they will carve a big circle. Just like hand troweling, you need to slowly find the right angle. Usually two times with the finish blades is enough.

    When you first do the floating, a bit of the surface may stick to your shoes maybe every fourth step. If each step leaves a print, it's too early. When it is time to finish, nothing will be sticking to the shoes but a grinding step may leave marks. You don't want any lug soles on. The smoother the sole the better. You are better to be a bit early than too late with any of the troweling. You can always stop when you're early. Throwing water on it when you are late doesn't help much. It's fun and easy once you have made a few passes.

    Beat it to fit / Paint it to match

    1. ponytl | Mar 21, 2005 07:23am | #8

      alot of rental machines have "combo" blades a wider blade that you can both float & finish with... like the rest of the advice it's not hard and does require timing and "touch" I happen to like super slick which also equals HARD surface and that will take several passed timed out... yes sometime you can add a little water and i even keep some dry portland on hand... if you are plan'n on acid stain'n then sometimes you can get a better result if when the bleed water comes up dust the surface with white portland then machine trowl it in you will get a very dense slick surface that will use less acid stain for the same look as if you had just finished the grey cement... arounf here the HD rents a really nice looking machine... I've never rented one but i always keep it in mind if I'n finish'n and I blow up one of mine...  oh yeah if you've never used one... I think I'd go with a 36" machine to learn with...  but with whatever size you go with find some hard slick concrete and cover it with water and practice get'n the feel of the machine... keep the area flooded and after 15 min you'll know how the machine reacts to forces... less is better...

      pony

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