Finishing off a slab?

[hovrens]

I am building a 22' X 17' slab for a room addition that will extend off the current slab foundation. I have never built a slab before but feel I can! I feel I could build square, level forms but worry about the final finish after the pour. I undertand air bubbles need to be excreted and tamper the rest. What else needs to be done to make sure the top is flat and does not sag? Any other advice is appriaciated as well?

[mreynolds]

I was in your shoes a couple of months ago, the biggest thing I did was a side walk. I gotta tell you the most important thing you can do is plan ahead for the pour and have more people than you need. It is somewhat merciless in that you only have x amount of time to work with it, wait to long and its over. For our pour we did a 24x24 pad, split in three bays. As we got to the end of screeding one bay, we had a guy float where we started. There were also two other guys behind pulling and pushing concrete into our screeds. It was a major team effort. Had we not had the extra help, the concrete would have set up before we finisihed the slab. Here is a great web site to check out that has some good info http://www.quikrete.com/diy/project_01.html 8)

[Rich]

Concrete is one of those things like hauling hay... nobody seems to want to help when you actually need them. Pouring concrete takes 2 things - brute force and awkwardness. It can be back breaking work if you're not prepared like mreynolds stated. There are several methods of pouring concrete to the correct elevation.
1. Guess - not recommended
2. Place elevation pins to the elevations you want at a certain distance apart and place wet screes between them and then screed between the wet screeds. Logic plays a big part in this... don't "paint" yourself in a corner.
3. Put screed pipes in and screed between them. A screed pipe is a 2" pipe that is placed on stakes or some type of concrete stake where the top of the pipe is at the final elevation desired. They are placed a certain distance apart (depending on length of screed board) and screeded between. As you screed to the end of the pipe you pull it and place it back down in the next line. You then have to go back and fill in the place where the pipe was.

This is only the beginning. Then you have to bull float it and edge the edges. Then touch up the edges with a "mag" and finally hope that you're not too late to steel trowel it to a smooth finish or broom it.

Read the article mreynolds posted too.

[mreynolds]

So these pipes actually lay horizontally in the concrete? We used boards for this same manner. Then we dog eared our screed rail to run down either side. I had the grade pins all ready and was going to try the wet screed method but I chickened out. :shock:

[Rich]

Yep. I've never used boards but I'm sure they would work the same. I like using wet screeds. No pulling boards/pipes and reworking what you've already worked. The grade pins are only needed where you may have a valley for water drainage - otherwise I use a laser level and shoot all benchmarks with that.

[hovrens]

I am thourough and do a job the right way. Without ever doing this before would would you recommend go for it or don't even attempt this! If I built the forms and got help from someone who knows how to finish be sufficient?

[Rich]

I think with a little upfront planning on your part and someone who knows a bit about finishing you'll be just fine. The biggest part is knowing what you're up against at the start. After that it's just work. Then a little talent with the finish. Let me know if you have any specific questions before you start.