One of the best secrets to finishing concrete is to have well built, reliable and properly elevated concrete forms. If the concrete forms are perfectly built and they do not move during placement or finishing then the concrete itself will be perfect once it hardens.
Support your forms thoroughly as the weight of concrete can make even strong wood bow or bulge in the wrong areas. Avoid scrambling on concrete day and have forms that are overbuilt for your application. One sure way to make your concrete forms strong enough is to dig down into the ground to install the forms or even use the shape of the hole itself as the outside form.
How To Build Concrete Forms
When building the forms for your concrete you want to leave the top open to allow you to pass the screed along without catching on nails or hitting supports. This is why concrete form supports should be cut down below the top of the form to allow for easier finishing.
If you plan to remove part of the form for finishing before the concrete sets up as required by some specialty projects then be sure to use double headed nails to facilitate easy disassembly of the forms without extensively disrupting the placed concrete.
When finishing concrete the ultimate goal is to have a smooth and mostly level surface that does not pool water or conflict with the elevations of surrounding objects and structures. In most cases this will involve some pretty fine elevations to be set with concrete which can be difficult for a beginner. When building concrete forms you can set their elevation to exact heights using an elevation transit or laser level.
By setting reference points that you can use during placement and finishing of the concrete you will have a much greater likelihood of creating proper slope. As a general rule you should factor 1/8" to 1/4" per foot of you want water to drain away. You can also use finishing nails tacked into your concrete forms to run string lines to help you measure elevation on the fly and in difficult to reach areas.
If possible try to design concrete pours that allow you to screed all areas of the pour. For example if you could keep the widest point of your concrete at 9' you would then be able to screed the entire concrete pad with a 10' or longer 2x4 allowing you to get perfect elevation established in all areas.
This makes the concrete leveling process so much easier than accomplishing the same with tape measurers and string line grids. There is a reason that there are professional concrete finishers but if you want to save some money and do the job yourself then just change your design a little. If at all possible design your concrete projects so that you can complete them in multiple pours or in pours that allow you to span the area with a single screed tool.
After building your concrete forms you will likely need to add reinforcing steel to make sure the concrete can resist cracking and breaking. Steel working can be a real challenge for the average home owner even when working with some of the smaller rebar and reinforcing wire. Be sure to wear protective gear and work safely at this stage.
The most important thing to remember to to not let your steel reinforcing hit the sides of the form anywhere, or worse, be sure the steel is not sticking out above the top of the forms so that it will be exposed sticking out of your finished concrete. Use spacers designed for being embedded in concrete to help you place the steel in the correct locations.
Most concrete applications require 4" spaced reinforcing wire commonly available at any hardware store. 10mm rebar and 15mm rebar are commonly used for larger concrete applications and are tied into a grid using a steel tie wire. Rebar grids are commonly 6" 8" 12" and 24" on center depending on the strength needed. 8" on center would be like for a swimming pool and 24" on center would be additional strength for walkways and patios.