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Drainage for garage floor?

| Posted in General Discussion on May 28, 2000 09:03am

*
Dear Derek,

JOB #1: You need “crack lines” – two lines forming a cross right down the centers would be ideal for this arrangement.

Because your walls are already up, you can’t float the concrete from the outside of the slab. So I see this as being a minimum 3 step procedure – the back two 10 x 10 sections, then one 10 x 10, then the last 10 x 10. You’ll need help to screed that, of course.

Finish the edge of each and then place the next concrete up to it the following work day. Should work out OK.

You should at least put 6/6 welded wire mesh into your slab – around here we like to use #3 rebar @ 18″ O.C. both ways.

JOB #2: When you say you’ll put a center drain – do you mean a drain, or just slope to the opening? That would make more sense, cost-wise, I would think.

In front of the garage door, you put a “box”, as you described it, w/ a grate that is rated for vehicle traffic (they come as a unit, 3′, 4″, and 6″ wide, in 4′ long sections; I get them from a Landscape and Irrigation supply house). At the end of this is attached your drainage pipe – the one you’ll bury.

Re: sand and gravel under the pipe – I’m down in Southern California, so I don’t know your local frost depths, etc. Ask around. But even here, where it doesn’t ever freeze, I shade it with about 2″ sand under.

Anyway, we use a plastic 3″ corrugated flex pipe – no holes (I’m assuming you just want to drain away the water collected in the “box”, right? Not providing drainage @ the foundation, also?). The flex makes it easy to follow your trench, and the ends are made to snap together – no gluing needed for this type of piping.

Hope that helps get you started – the guys at the supply house answered all my questions the first time I put one of those drains in.

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  1. George_L | May 28, 2000 09:03pm | #2

    *
    Dear Derek,

    JOB #1: You need "crack lines" - two lines forming a cross right down the centers would be ideal for this arrangement.

    Because your walls are already up, you can't float the concrete from the outside of the slab. So I see this as being a minimum 3 step procedure - the back two 10 x 10 sections, then one 10 x 10, then the last 10 x 10. You'll need help to screed that, of course.

    Finish the edge of each and then place the next concrete up to it the following work day. Should work out OK.

    You should at least put 6/6 welded wire mesh into your slab - around here we like to use #3 rebar @ 18" O.C. both ways.

    JOB #2: When you say you'll put a center drain - do you mean a drain, or just slope to the opening? That would make more sense, cost-wise, I would think.

    In front of the garage door, you put a "box", as you described it, w/ a grate that is rated for vehicle traffic (they come as a unit, 3', 4", and 6" wide, in 4' long sections; I get them from a Landscape and Irrigation supply house). At the end of this is attached your drainage pipe - the one you'll bury.

    Re: sand and gravel under the pipe - I'm down in Southern California, so I don't know your local frost depths, etc. Ask around. But even here, where it doesn't ever freeze, I shade it with about 2" sand under.

    Anyway, we use a plastic 3" corrugated flex pipe - no holes (I'm assuming you just want to drain away the water collected in the "box", right? Not providing drainage @ the foundation, also?). The flex makes it easy to follow your trench, and the ends are made to snap together - no gluing needed for this type of piping.

    Hope that helps get you started - the guys at the supply house answered all my questions the first time I put one of those drains in.

  2. Guest_ | May 28, 2000 09:03pm | #3

    *
    I am a competant handyman and am very comfortable with many aspects of home renovations. However I have been asked to do a couple of things that are out of my comfort zone of abilities and need a few pointers. There are two related jobs. 1. Pour a slab in a 20 by 20 garage. It is currently just gravel over sand. I intend to rake off the gravel, dig out 4 inches of sand and them replace the gravel. Questions: Do I need mesh? Plastic or steel? Should there be crack lines made? At what spacing? I intend to put a center drain that slopes back to the driveway as there is no basement/sump pump. Job 2. The driveway slopes towards the house and water builds up there after heavy rain and during spring melting. My plan is to cut out a 12" wide strip across the front of the garage sill and install a box - into which the garage will drain - put in a pipe and then concrete a shallow dip to catch and direct the water, and then run a drain pipe down hill to a ditch. The client has had a trench dug already from the corner of the house to the ditch. Questions: What sort of pipe should I use? 4" perforated with cloth? Solid ABS or what? If perforated, what goes under it? Sand/Gravel? Same question - what goes above it, before filling the trench back in. If I can't get a bit of a handle on this I will decline the job, but would like to give it a go. Any help would be appreciated. Thanks Derek Nayler, Montreal

    1. Guest_ | May 28, 2000 08:51pm | #1

      *Hi DerekThe concrete part is easy. 4" of concrete, 25mpa with a 3" slump, 6 x 6 mesh. Cut a control joint in the center between the two cars.The drain part is another thing.With a drain trench in the front of the garage, it will freeze in the winter and will only thaw after the spring rains start. You will have to install a heat cable to prevent this.Better to install 2 floor ( one under each car) drains when you lower the gravel and drain under ground, below frost ( 5 ft.)into a ditch with a vermin screen. If you can't go 5 ft. because of the elevation allowed, then you can go as shallow as 2 ft. if you cover with SM 2" for 4 ft. wide.Gabe

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