Concrete slab questions...

[IBCRUSN]

My wife has to have a slab replaced on the side of our garage due to it sinking and allowing quite a bit of water into the sump. I'm in Afghanistan and can't offer much help however I do have a few questions.

The two smaller slabs (5'x5' & 4'x4') are slowly sinking and I'd like to replace both with one 9'x9' that is tied to the garage foundation.

1. Is it permissible to drill the foundation and epoxy rebar into it so the future slab stays tight to the garage?

2. Is 4" of concrete adequate for a garage exit slab?

3. Is a 1" drop for every 3' from where the foundation meets the wall too steep to ensure water drains away from the house?

Are there any other tips or considerations I should pass along to the wife? Thanks for the help.

UPDATE....

 

[Capt. Jim]

My wife has to have a slab replaced on the side of our garage due to it sinking and allowing quite a bit of water into the sump. I'm in Afghanistan and can't offer much help however I do have a few questions.

The two smaller slabs (5'x5' & 4'x4') are slowly sinking and I'd like to replace both with one 9'x9' that is tied to the garage foundation.

1. Is it permissible to drill the foundation and epoxy rebar into it so the future slab stays tight to the garage?

We do it frequently here in Florida. Check with your local codes.

[/QUOTE]2. Is 4" of concrete adequate for a garage exit slab?[/QUOTE]

I would thicken the edge to 8" and ass a #5 bar.

[/QUOTE]3. Is a 1" drop for every 3' from where the foundation meets the wall too steep to ensure water drains away from the house?[/QUOTE]

!/4" per foot is more than adequate under normal rainfall conditions.

[/QUOTE]Are there any other tips or considerations I should pass along to the wife? Thanks for the help.[/QUOTE]

You need to determine what is causing the settling or it will just continue. If you dowel one side of the new slab into the edge of the garage slab, some differential settling may occur. i.e. The doweled side remains in place, the opposite side continues to settle.

 

[IBCRUSN]

The cause of the slabs sinking was the previous owner and how he routed the sump pump discharge, right out onto the slabs from a 6" tube on the side of the house. Since we moved in we've been using a piece of trash pump hose so the discharge is about 10' away from the foundation.

What I'm looking for from the contractor is backfill next to the foundation with gravel and earth (we have a lot of clay in KS) to aid any future drainage issues. The sump pump discharge will be routed under the slab and discharge through a grate into the yard approximately 10' away from the foundation and ~18" below the existing slab grade.

Thanks for the tips on the rebar and edging.

Is there a means to alleviate or reduce the the differential settling?

 

[osagecruiser]

compaction of the subgrade and proper drainage away from the slabs/house will be key the eliminating the problem of settling in the future...be sure unsuitable material is removed and new material compacted and sloped

osagecruiser

 

[Toyo FJ40]

The only problem with tieing it into the garage foundation with no other foundation under the slab it can lift if you get frost and lift the garage wall as well. If you don't get frost than it should be fine.

 

[titanpat57]

Pictures would be helpful...

 

[IBCRUSN]

The only problem with tieing it into the garage foundation with no other foundation under the slab it can lift if you get frost and lift the garage wall as well. If you don't get frost than it should be fine.

Is there a good means of preventing the slab from pulling away and leaking between the slab and foundation?

Pictures would be helpful...

I wish I could but distance prevents that at the moment. I'll have the wife take a pic, email me and I'll post it up.

 

[nspctr1]

If it were mine I would demo the existing pads,Buy some 4" perforated PVC pipe and pea gravel. Make a french drain for the sump pump to direct the water away from the house.Excavate approx. 1' of the existing soil, compact the material in place, Place a minimum of 6" crushed limestone and compact it in place. Set your forms and tie #4 rebar on 12" centers each way (criss cross pattern) You do not mention what the slabs are used for so kind of hard to determine how to design the new slab. If for driving then 4" would suffice but for a little more money have them pour a 6" thick slab for extra stability. As mentioned earlier, if used for driving, then at the end of the approach dig a 6" wide by 12" deep grade beam, you could do it around the whole perimeter but not necessary unless you are storing heavy objects on it or driving heavy vehicles on it. You can dowel into the existing house foundation with no problem, use a asphaltic expansion joint between the house and the new pad to allow for a little movement. Not really necessary to epoxy in the dowels but if you do, only epoxy ONE END of the dowel. that way the dowel can respond to the movement of the slabs. Choose your finish for your concrete, light broom or heavy broom or slick. If possible, keep it moist for the first week after placing the concrete. What I mean by that is after the first 24 hours, start to water it at least once a day. It will slow down the curing of the concrete and give you a better product. You can drive on it after 3 days or so but nothing real heavy. To be on the safe side, stay off of it for a week. Lastly, do not pour the concrete within 24 hours of a freeze.....

GL, post up more ? if you have them.... Also, for driveway details, check your local municipality's website and they should have engineered drawings of driveways that meet their standards.....

 

[Capt. Jim]

Set your forms and tie #4 rebar on 12" centers each way (criss cross pattern)

A 4" thick slab is too thin to place #4 rebar in, as it requires a minimum of 3" concrete cover when the concrete is against soil, and a minimum of 2" cover when the concrete is exposed to air. A 6" slab would place the steel at or above the neutral bending axis, thus providing no structural enhancement.

Use fiber-mesh concrete, or regular concrete with 6x6 10/10 welded wire fabric (road mesh) at the middle of the slab thickness to control temperature cracking.

 

[IBCRUSN]

Added pics.

Nice to know the rain makes the paint look worse. I'll have to repaint once I get home....yay!!

At any rate...I wanted to dowel the slab to the foundation and use the mesh stuff (looks 1/8"-3/16" rod in a grate pattern) for the main part of the slab.

 

[Michael Hanson]

I would not tie in. Mike

 

[Capt. Jim]

My wife has to have a slab replaced on the side of our garage due to it sinking and allowing quite a bit of water into the sump.

By sump I assume you mean a perimeter drain building sump. (Something we don't have here in south Florida). I don't think the current conditions of the slabs you pictured are the cause of this water in the sump. Doing what has been prescribed in this thread will have little or no effect on the water entering your sump. Based on your photos only, I do not believe the current slab condition is contributing to your situation.

This is based on what little experience I have in sump drainage systems. I do know that water will seek its' own level, even underground, unless you have a clay-type soil. How did you determine the slab conditions were contributing to the water/sump issue?

 

[IBCRUSN]

The houses in Wichita generally weren't built with the French drains as nspctr1 recommended as a solution. There are four drains that are plumbed into the main sump, the only one that has any water running into the sump is from the side of the house with erosion under the slabs. Since the original owner never addressed the sump pump discharge and did a poor job of installing the middle slab I just assumed that his poor execution coupled with erosion. The awful caulking was my attempt at a stop gap measure before I shipped out in April because I didn't have time to address it properly then (been away from home since January '11). Without breaking up the slab to see if there is any soil remaining beneath it there's no way for sure to tell if it's the cause. Strange though since that side of the house has the best grading on the property for water to drain away from the foundation.

 

[IBCRUSN]

I would not tie in. Mike

Can you provide more of an explanation? I'm open to all ideas but I just want to have as much info as possible to make the best decision, I only want to do this once and don't want the next owner to deal with it either.

 

[Koffer]

With pixs I can see what the problem is right away , You used a Gov surplus jet engine to fix your drier and all the power is pushing the slab down or your water hose is too heavy

Its going to need to come out and see if the builder got cheap and dumped scrap and other stuff when back filling and now its rottening away

 

[IBCRUSN]

I'm pretty sure there isn't much backfill left. The original owner left the sump pump discharge the 6" exposed from the house (green), the white fitting and hose what my white trash temp fix until the slab was to be replaced.

 

[titanpat57]

I'm with Mike...I would not tie it in.

Remove the AC

Remove existing concrete

Form and allow at least 4" of 3/4" gravel or stone, compacted under the slab, install 6" x 6" wire, or use concrete that has fiberglass reenforcement fibers in it, as mentioned allow a minimum of 1/4" per foot of drainage, away from the garage

Install, or allow, for expansion joint against the wall, between the garage foundation and new slab

Pour a minimum if 3000psi concrete, 4000 psi would be better, and probably about a $100 more for a small job like that. Float it, steel it, and broom finish

I would allow it to set a minimum of 24 hours, saw cut the slab, perpendicular to the garage, strip forms, wash down, let dry, apply sealer


Thanks for your service!! You want me to fly out and do the job?!...;p

 

[IBCRUSN]

You want me to fly out and do the job?!...;p

That would be great. My dad's in Upstate NY and if he picked you up and visited KS rather than going to FL for a month it would be done already.

Thanks for the info. One question about not tying the slab to the foundation.

What can be done to ensure that water doesn't get between the foundation and the slab and cause this mess again?

 

[titanpat57]

That would be great. My dad's in Upstate NY and if he picked you up and visited KS rather than going to FL for a month it would be done already.

Thanks for the info. One question about not tying the slab to the foundation.

What can be done to ensure that water doesn't get between the foundation and the slab and cause this mess again?

The proper pitch away fro the house, and the gravel.

I'm not sure what your freeze /thaw cycle is out there...but it isn't real severe is it?

The freeze cycle can "heave" concrete, the gravel will promote drainage, helping to eliminate water freezing directly under the slab.

 

[IBCRUSN]

We're south of NY latitude wise and I think our normal frost level is around 24" but may be slightly less.