Hot Topics: Pouring Concrete Isn't Hard, But You Still Have to Do It Right
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Concrete is hard, but working with it shouldn't be. It's a mixture of art and science to get the ratios right and know how and when to screed and float. If you don’t have the magic touch, the Forum can help you set it right.
Original Post: First time pouring concrete, FAIL.
First time posting on this website, so please check me if I step out of line. As a weekend project, I decided to make a walkway out of concrete, did my little forms, made sure it was leveled and square, bought my Quickrete 60lb bags, began my mixing by adding water. I used a shovel to mix my concrete, poured in 6 bags, slab is about 3 ½ inches thick, and used a 2x4 to level the concrete and a floater afterwards to make it smooth.
Problem. Look at how it finished. It looks horrible, a lot of separation, not a smooth surface at all.
So tell me, what did I do wrong? Too much water? Cheap concrete from Home Depot? I plan on breaking this slab up and doing it again, but want to make sure I do it right.
Highlights from the Thread
Rough Rooster Member
You need to use a jitterbug to push the stones down and leave a sand cement mix for finishing. Google
First, if you don't mix your concrete in a mixer, at least do it in a wheelbarrow, not on the ground inside your form. Once it’s mixed, you place it in the form then screed it with a screed or board, sawing it off so it's completely full. Then once the water has bled off the surface you usually will hand trowel it and maybe broom the surface before covering it with burlap.
I used a wheel barrow and a shovel to mix the concrete, did 2 bags at a time.
Judging by the amount that it slumped and all the aggregate on top, I'd say you mixed it too wet, or else it would have stayed level with the top of the forms.
From looking at the pix, it looks like you did several things wrong.
First, you possibly failed to have enough freshly-placed concrete between the forms. It needs to be placed slightly above the top of the forms, and then struck off with a sawing motion of your 2x4 that keeps a steady roll of concrete ahead of the strike-off. If there are voids ahead of the strike-off, the finished surface will be too low. Yours looks like nothing was above the forms, but rather you just used a 2x4 to flatten the surface by pushing down vertically on the wet concrete (possibly between but not touching the forms), resulting in most of it being too low.
Secondly, you failed to bring up the fines after bleed water evaporated, done by repeatedly floating the surface using smooth, circular motions with a mag or resin float. Professionals usually do a final hand float with a steel trowel, making the surface "sing" with the fines. Beginners often fail to wait for bleed water evaporation, and start finishing too soon. This overworks and weakens the surface, forcing too much water adjacent to the coarse aggregate, resulting in lack of proper hydration of cement particles, and failure "to lock in" the rock with a rich mortar paste.
Thank you, I will definitely try out your recommendations next week when I try this again. I have a wooden float , do I need a trowel too?
Gunguy45 Super Moderator
No pro, but I found I get a better smoother surface using metal. As was said, you can hear when it's being done right. I use wood or a magnesium float to press everything down tight into the forms, then the thin steel for the final.
If you have a vibratory sander (not a random orbital) that can also help fill the forms. No sand paper needed, just run it around the top and sides of the form.
I must have 10 or more floats, trowels, groovers, and edgers. Not to mention all the brick and block tools. Almost all are from yard sales or giveaways.
Don't mix with a shovel, use a hoe. You will get much better leverage and mix using a hoe. You want the concrete when mixed to be "pourable", but not watery at all.
Over fill the form slightly, especially at one end, and work the concrete with a screed (a 2xsomething) from that side over. Working that side to side vigorously will help settle out air pockets as well as level it to the form.
You don't need a trowel... but you can always use a trowel somewhere. I prefer metal floats... like magnesium. But the cheaper ones will work ok as well. You want to work the top of the concrete so it is smooth... you are working the finer particles to the top, and the aggregate below that. It should have a very "slick" feeling as you work it. Search youtube for some videos of finishing concrete.