Replacing garage floor, how to drain floor?

[zzErik]

Hello everyone!
I'm new here, but I was hoping that I could find some help. I've done some searching, but haven't found anything to help my situation, mainly just new construction.

I'm having my garage floor replaced (major cracks + sinking) for my attached 2 car garage (the previous owners had piers put under the foundation). There is currently a drain in the floor, but it's plugged, and I wouldn't be surprised if the pipe is crushed from the floor sinking. In 1960 (when the house was built), where would this drain normally have led to (sewer system, a drain in the yard, etc)? When I have the floor replaced, I want to have the floor drain working properly. I am also putting some thought into adding a small utility sink and having the drain tie into the garage floor drain. I think this would be easy to do, since the floor will be already be torn out. I think it would be fairly simple to run water pipes, but this would be about the only time I could add a drain.

Would this be legal, regardless of where the drain goes to, as long as I'm not putting anything besides water and hand soap down the drain?

Also, when I'm having a contractor replace the floor, is there anything that I should make sure they're doing? The current guy that I got a quote from said he would do 4 inches thick, with 4000 psi, with rebar. He would make the 24*24 area in one big piece, then cut it into four. (I don't know if any of this is normal). Is there any way that I could make the new floor "better", or make it have less of a chance of cracking/sinking?

(Not like it matters, but I will be using the garage for personal use, turning wrenches, and storing lawn equipment. I'm extremely careful, even without a drain, to not spill oil and other chemicals on the floor.)
Thanks!

 

[matt_i]

I can't answer your floor-drain question, its probably up to the locality where you live, and is probably on the outer fringes of legal in most urban areas. You could just do a blind sump and ladle the fluid out when it gets too high. I don't like the slope of the floor and wish mine was level.

A couple of suggestions, though, on how to get a better floor.

The 4" minimum thickness, 4ksi is a good place to start. I would add some kind of wire mesh reinforcement mats (not rolls) and add a couple hoops of actual rebar set on chairs around your center drain. I believe the saw cuts around the drain should be more of a "sunburst" pattern emanating from the corners of the internal square.

As always, compaction of the subgrade is a must, I'd use a jumping jack after the old slab is broken out. I'd remove enough material to get a 4" crushed/washed limestone base with a 3/4" nominal size, some parts of the US refer to this as #57 stone. Wet the stone base and plate-compact it.

Now time for the vapor barrier. I'd go with a 10 mil, and lap at least 2ft.

Reinforcement suggestions above.

Last thing I would apply is a curing sealer.

As far as getting the base correct, I'd go with a rotary laser level on the "coarse" setting. It should help ferret out high spots which can get thin, and you'll probably need it to setup the center drain if thats how you are going to roll.

Some of this prep work you can do yourself, if inclined, to reduce the cost. Let the contractor place, finish, and saw cut (to snapped chalklines).

 

[zzErik]

Is it likely that the old floor will have gravel under it? If so, should that be replaced/added to?

How long should the weather remain above freezing before I have the new slab poured, and how long should I refrain from both returning my belongings, and parking my cars on it?

 

[Leaflessshadetree]

Here floor drains must have a grease/oil trap and be tied to the sewer or septic. In the 60s the would commonly be open air or tied to a french drain.

 

[wssix99]

Would this be legal

In general, no. But as said above, some localities will allow it. National building code requires that attached garage slabs have two features:
- A gas curb of at least 8" raising the entry door to the house above the slab.
- A sloped floor that drains to the outside of the building.

^ These features are due to the fact that all cars and gasoline equipment can leak gasoline vapors, which are explosive in a closed room. The vapors are heavier than air and sink to the floor. (Think about the warnings on the side of a water heater.) You don't want these vapors coming inside the house and when they arise, you want them to flow towards the garage doors and outside.

Having these vapors go down the drain or in to the sewer is also not good. For industrial settings where ventilation equipment is installed to deal with the vapors, you'd also need the grease trap (as mentioned above) to protect the sewer or septic system, also.

Also, when I'm having a contractor replace the floor, is there anything that I should make sure they're doing?

Is there any way that I could make the new floor "better", or make it have less of a chance of cracking/sinking?

Base Base Base. If your floor has moved, you'll want to carve out all the dirt underneath that has moved, level it out, compact it, and add several inches of well-compacted stone to give your new slab a proper base. This will go great lengths to make sure it doesn't sink on you again.

The current guy that I got a quote from said he would do 4 inches thick, with 4000 psi, with rebar. He would make the 24*24 area in one big piece, then cut it into four. (I don't know if any of this is normal).

This is a common type of slab. If you want to bring in machinery at some point, like a lift, you may want to go a bit thicker to make sure you get the 4" minimum of thickness that you'd need.

The cuts and rebar are there to control the cracking, which will occur. If done right and enough rebar is used, the cracks should form in side the cuts bisecting your 12X12 squares.

If you are going to put in a 2 post lift at some point, the cuts could be problematic because they will be right where you'd want to put the posts. If you envision this, you may want to go with 4 cuts, giving you a big 12X12 pad in the middle, with smaller 6X12 or 6X6 pads surrounding it. (This would allow you for better flexibility in placing a 2 post lift.)

 

[n20junkie]

My floor was poured level for fab work. Too hell with the building code.

 

[Jackfre]

Your floor drain plan, as noted will not work and I would suggest that you abandon it and either pour the slab flat or graded to the outside. I poured mine flat as it is more shop than garage. The inspector asked if it was graded and I told him it was exactly like I wanted it, but I had been working with this guy for a couple years on the house re-no and shop build. My 30x30 shop has mesh in it, was cut the morning after the pour into 6 sections and there has been zero cracking. I used Rustbullet on my floor and it came out nicely. The slop sink will have tie into the city sewer or septic. The recommendation of fresh fill and compaction is a good idea given that the current base has all ready failed.

 

[zzErik]

I think removing dirt, if any, is a good idea. How deep should the gravel be? If there is already gravel there, should I get new and compact it ontop of that, or remove the old to get to the dirt below? The current slab was poured almost 60 years ago.

I think it sunk due to a water issue a previous homeowner didn't take care of. I will be taking care of the water issue, then replacing the slab. I just want to make sure it's done right, because I don't know if I will live here for 5 years, or 40 years.

Also, the drain issue, I just wanted to make clear that this was for residential use, not commercial use (If that makes a difference)

 

[wssix99]

Also, the drain issue, I just wanted to make clear that this was for residential use, not commercial use (If that makes a difference)

Generally no difference because the safety/environmental issues are the same. Your local codes, may treat the two differently, though.

I will be taking care of the water issue

This is the most important thing. Nothing can stop water and you'll just end up with the same issue if the water condition persists.

I think removing dirt, if any, is a good idea. How deep should the gravel be? If there is already gravel there, should I get new and compact it ontop of that, or remove the old to get to the dirt below?

A few inches of stone should be fine. For what you are going to do with the floor, I'd think more than three inches would be excessive and less than three inches would make things difficult to get a good layer down.

If the gravel is clean, you could re-use it. You'd want to get rid of any soft dirt, dirt that was washed around by water, or gravel mixed with dirt. (Your concrete company should have experience dealing with this.)