Question for all you Civils out there

OK, I need some advice. My driveway has been separating from my garage slab for *awhile* now... after months of staring at it and thinking I should do something about it, I've decided to get off my duff to fix the gap between the two. Luckily the rain here has been very infrequent!

The gap is a little over an inch wide now (maybe ~1.5"). Its about 6" deep, and my driveway is 16' wide. Driveway is concrete BTW.

After a little Google searching and talking to some friends who know more about this than me, I've found that this fix should be fairly simple. Fill the gap with backer rod up to about 1/2"-1/4" to the top of the gap, then fill the remainder with self leveling sealant.

So I have two questions.

1. Is this the correct way to fill this gap?

2. Can I fill the gap with sand first, then put in backer rod and the sealant? The reason for this is that 6" is pretty deep, and will take a LOT of backer rod. The largest size I can find is 3/4" dia.

Any help you can give would be most appreciated!

With the gap being 1.5", I think you're going to have a tough time filling that with backer rod. I would suggest using a non shrink grout to fill in the gap.

My question is, what caused this gap? Improper compaction of the subgrade of the driveway? Do you have swelling/collapsible soil? If you just fill the gap, and have more movement in the future, you will be chasing a problem again in a few years, IMHO. The gap is a syptom of the problem going on.

^^ That's what I was gonna ask. Have you perhaps got a problem with water running in the soil beneath the driveway? If the whole driveway has moved, you can get the mudjack guy to come pump his stuff in the void and pick it back up.

^^ Agreed. But I don't envision him jackhammering the slab just yet.

Fluvial said:

^^ That's what I was gonna ask. Have you perhaps got a problem with water running in the soil beneath the driveway? If the whole driveway has moved, you can get the mudjack guy to come pump his stuff in the void and pick it back up.

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Hey, he asked a serious question and you have to come in here with your filth...



Is the driveway on a slope?

My entire driveway/sidewalks around the house have moved. I had a mudjack guy come out and take a look, but he said it had moved too much (~2") to mudjack. I may have an expensive/time consuming fix on my hands. But I would enjoy doing it myself.

2" too much to mudjack ?! What a wimp.

The driveway is on a slope... I don't know anything about the soils unfortunately, I am but a lowly mechanical type. Energy I understand, soils and subgrades not so much.

So, should I call a mudjack guy instead of doing this myself? (BTW, what is a mudjack guy? I am completely clueless here.)

I have a similar situation at my house. My driveway is ok, but the sidewalk that wraps around from the front of the driveway up to the front door (including 6 concrete steps) have dropped a full 2". There's no way mudjacking would work in this situation. I know the subgrade has either washed out or just created a sinkhole (I know there's a significant void because it takes about 5 minutes with a hose pouring water into one of the cracks to get the hole filled). The only way for my walkway to get fixed would be to jackhammer, fix the subgrade, then replace the concrete. Luckily there isn't any indication the adjacent garage foundation is in any trouble.

The biggest thing I'm happy about is that I rent the house, and have no intention of buying it. I'll leave that beast for the landlord to deal with. He's aware of the problem, but since it seems to be ok for now, he's not doing anything.

The slab in the basement has also settled about 1" on one end (the opposite end of the house from the sidewalk issue). In that case, I would probably just pour a skin-patch to level it out and replace the carpet.

MechGuy said:

So, should I call a mudjack guy instead of doing this myself? (BTW, what is a mudjack guy? I am completely clueless here.)

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If you don't really know what's causing it, I'd be hesitant to get him out there 'cos he's gonna be a little expensive. You might be just as well putting the non-shrink grout in there and watching to see what happens next.

The mudjack is a kind of a slurry mixture of water, red sand, and cement (that's what they use here anyway). Our mudjack guy in the area is a really insane big redneck dude who will talk your ear off the whole time his crew is working.

I've seen him pump a void full of about 5 yards of slurry; I've seen him pick up trees and even move a driveway slab vertically 4 to 6 inches. He's a wild man.

So I should fill the whole gap with the non shrink grout? Anything else I need?

Is this the type of stuff?

http://www.quikrete.com/ProductLines/FastS...ShrinkGrout.asp

That looks like the right stuff. I would also suggest a sealant for the grout after it cures.

When installing the grout, I would recommend using high-pressure air to clean out the groove as best as you can (especially each face of exisiting concrete). Then moisten both faces of the crack. The moisture will help remove any additional dust and will help the grout to adhere to the existing concrete as well as helping the grout cure properly.

MechGuy said:

OK, I need some advice. My driveway has been separating from my garage slab for *awhile* now... after months of staring at it and thinking I should do something about it, I've decided to get off my duff to fix the gap between the two. Luckily the rain here has been very infrequent!
The gap is a little over an inch wide now (maybe ~1.5"). Its about 6" deep, and my driveway is 16' wide. Driveway is concrete BTW.

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Can you mebbe provide a picture? Not that I am disagreeing with recommendations offered but a pic might reveal something to the group that might not be obvious in your description.

JR

I'll see if I can get a picture when I get home... then you can all shake your fingers at me for not taking care of this sooner!

How long has this gap taken to form? Mudjacking will be expensive. You will not get any return on your mudjacking investment. Most potential buyers will look at the separation and not know any better.

If this is a slow process (10+ years) this is what I would do. Fill the bottom 5 to 5.5 inches of grout. Then to top it off I would use some concrete joint sealer: Fox industries FX-66 Joint Sealant (or equal).

If this is a fast process then most likely you have a water issue where your subbase is being washed away. If this is the case you have to find where the water source is and where its going. Hopefully its not from a water main.

yes post a picture, backer-rod or something similar is used on bridge joints so it shouldnt be a big problem to do, but its going to be required to be done again and again.

unless you want to dig up the whole thing get some low slump concrete (i.e. mix the concrete a little on the wet side) and fill in the voids, to be effective you really just need to pressure grout it, but its probably just the result of residential contractors not compacting the earth beneath your driveway...

I had one on a slope at my last house and I was yearly filling cracks..

Road Guy said:

...but its probably just the result of residential contractors not compacting the earth beneath your driveway...

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GCs taking short cuts? Blasphemy! That NEVER happens.

/sarcasm

they think that since they parked there while they built the house that its compacted!

Road Guy said:

they think that since they parked there while they built the house that its compacted!

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Sad but true.