1950s Garage Slab, Below Grade, Moisture Issues. Help?

[cash68]

Hey guys,

Haven't been on here a while. I finished my last project thanks to a lot of your help, you can see it here:

Album

It was great! However, **** changes, new job, new location, and I recently bought a house. It was built in 1958, and it has two garages. One is about 2 cars deep, attached, and below grade. It's 30'9" x 15', and I'm having a fair amount of moisture issues, the surface itself is pitted, and I really need to finish the floor and build up the shop before this winter, as I'm planning on rebuilding my 911 engine.

Here is a pic of the house and garage in question:

Here's some of the moisture happening, it seems like it is coming up through the slab, and along the edges. No puddles, but definite moisture.

Closer look at the floor, and the pitting in the concrete:

So. There you are. I don't know where to start. I've done a lot of reading, and I'm going to wager a guess I don't have a moisture barrier. The ceiling is already relatively low, so I can't install one and pour over it, and I don't have the liquid to break this up and pour a new one.

I know I need to fix the pitting before anything, but what should I be using? Do I etch before patching to get better adhesion for the patches? Have any good links or suggestions on patching? Some places say don't use concrete, it will pop out, so I'm sort of lost.

Then I'm guessing I will rent a diamond grinder, and grind the **** out the floor. Then ... ???

Do I seal it? What would work? Really need your help, I have to get started on this asap.

 

[DougWil]

Hmmmmm........ I don't see any pics?

But anyway, doubtful that much of any kind of durable finish will adhere to damp, soggy concrete.

I would first try and install a drainage system outside the building with a pump (since it would be well below grade) to reduce that pond under that slab.
The foundation would appreciate it too, if it hasn't already sunk and cracked up.

 

[DougWil]

OK, now I see the pics.

That cratered surface is probably from the concrete having low strength, no air entrainment, road salt dripping off 60 years of cars and a billion freeze-thaw cycles.

Live with it, or tear it out.

 

[cash68]

It's actually relatively dry most of the time.

So far I have cleaned the gutters, and regraded the land around the house. It helped a ton. The last rain we had was about 2 days straight of rain, hence the moisture.

Have any other options? I can't blow that kind of cash on it.

Also, what I really don't understand is the rest of the basement is finished, and I have no moisture problems in any of the other parts of the house. I have ripped up the carpet to put in LVT flooring, and there is no sign of moisture anywhere else at all.

Why would the garage get wet like this, but not any of the rest of the house?

 

[DougWil]

Also, what I really don't understand is the rest of the basement is finished, and I have no moisture problems in any of the other parts of the house. I have ripped up the carpet to put in LVT flooring, and there is no sign of moisture anywhere else at all.

Why would the garage get wet like this, but not any of the rest of the house?

Because that slab is the lowest part of your house and rain/surface water is simply saturating it. The rest of your house is many feet above that point.

And latex paint makes a pretty good vapor 'retarder', so if the garage is well finished without a bunch of holes, cracks, etc, in the drywall and paint the humidity would be contained in the garage where it leaves through the open door or drafty door.

And if the garage isn't very warm, the air doesn't hold much humidity to infiltrate the rest of the house.
Pretty much just stays a cold puddle on the floor.

However, I expect if you were the gut that garage, you would find black mold on some of the floor framing above.

 

[skylar1692]

Maybe look into Sika products such as their Sika Bond Moisture Barrier to use before epoxy flooring or some of the Westcoat systems which utilize a polymer or sand base to allow moisture to breath or escape the floor. Maybe something like a Redgard product which is a waterproofing for shower pans/floors can be used as the water/vapor barrier then another product installed on top of that. I agree with DougWil with the fact that once the garage is closed the moisture has nowhere to go in the sealed room. It might be beneficial to add a vent and small exhaust fan in there to draw out the moisture.

 

[theoldwizard1]

• Remove existing concrete floor.
• Remove an additional 6" of soil.
• Install "weeping tile" system around the inside perimeter. Connect to existing sump and pump or install a new sump and pump.
• Back fill with gravel. Compact it.
• install vapor barrier.
• Pour new concrete.

Anything less is a "band-aid" and will truly solve the problem.

 

[DougWil]

[*]Install "weeping tile" system around the inside perimeter. Connect to existing sump and pump or install a new sump and pump.

Yep, that level of 'moisture' is way beyond a simple vapor barrier controlling.
The current slab is sitting on a mudflat.

 

[cash68]

• Remove existing concrete floor.
• Remove an additional 6" of soil.
• Install "weeping tile" system around the inside perimeter. Connect to existing sump and pump or install a new sump and pump.
• Back fill with gravel. Compact it.
• install vapor barrier.
• Pour new concrete.

Anything less is a "band-aid" and will truly solve the problem.

I don't have a sump pump. Like I said, I have no other moisture issues anywhere in the house, which is all below ground on the same level as the garage.

 

[cash68]

Because that slab is the lowest part of your house and rain/surface water is simply saturating it. The rest of your house is many feet above that point.

And latex paint makes a pretty good vapor 'retarder', so if the garage is well finished without a bunch of holes, cracks, etc, in the drywall and paint the humidity would be contained in the garage where it leaves through the open door or drafty door.

And if the garage isn't very warm, the air doesn't hold much humidity to infiltrate the rest of the house.
Pretty much just stays a cold puddle on the floor.

However, I expect if you were the gut that garage, you would find black mold on some of the floor framing above.

Nope. I have a full finished basement on the same level. That's what I don't understand. As far as I know it might even be the same slab.

 

[cash68]

Maybe look into Sika products such as their Sika Bond Moisture Barrier to use before epoxy flooring or some of the Westcoat systems which utilize a polymer or sand base to allow moisture to breath or escape the floor. Maybe something like a Redgard product which is a waterproofing for shower pans/floors can be used as the water/vapor barrier then another product installed on top of that. I agree with DougWil with the fact that once the garage is closed the moisture has nowhere to go in the sealed room. It might be beneficial to add a vent and small exhaust fan in there to draw out the moisture.

Would I seal it before patching? Or patch and then seal it?

 

[Zeke]

Don't put lipstick on a pig. Until you solve the moisture problem and can count on the floor not being damp, I think anything you do will be in vain.

I know there are some exceptions, but generally speaking, sealers are to prevent moisture from getting underneath, not holding it below the surface. Used to hold the moisture down, in the end the water will win.

Minor soil moisture would be one of those exceptions.

Look at it this way, you can seal below grade vertical walls from the inside but there better be a really good drain system on the other side of that wall. Most would prefer the waterproofing be done on the outside of that wall.

 

[cash68]

Don't put lipstick on a pig. Until you solve the moisture problem and can count on the floor not being damp, I think anything you do will be in vain.

I know there are some exceptions, but generally speaking, sealers are to prevent moisture from getting underneath, not holding it below the surface. Used to hold the moisture down, in the end the water will win.

Minor soil moisture would be one of those exceptions.

Look at it this way, you can seal below grade vertical walls from the inside but there better be a really good drain system on the other side of that wall. Most would prefer the waterproofing be done on the outside of that wall.

Is it still a problem if this only happens twice a year? It stays pretty dry most of the time, most of the time it rains it doesn't get a drop and stays at maybe 50-60% humidity in there. It only happens when it REALLY rains.

I've already graded the exterior of the house. I have giant lannenstone planters on the side of the garage, so removing them would be a pretty huge PITA.

 

[DougWil]

Nope. I have a full finished basement on the same level. That's what I don't understand. As far as I know it might even be the same slab.

Well is runoff running into the garage from the driveway?
Broken water pipe?

Because it does seem odd you don't have issues in the basement yet practically an artesian well percolating up under that slab.

Did the house have a drainage system at the footing perimeter to drain water away from those basement walls?

 

[cash68]

• Remove existing concrete floor.
• Remove an additional 6" of soil.
• Install "weeping tile" system around the inside perimeter. Connect to existing sump and pump or install a new sump and pump.
• Back fill with gravel. Compact it.
• install vapor barrier.
• Pour new concrete.

Anything less is a "band-aid" and will truly solve the problem.

Did you see I have a classic 911 that needs the engine rebuilt?! I have no money for that solution.

 

[DougWil]

Did you see I have a classic 911 that needs the engine rebuilt?! I have no money for that solution.

Maybe it is time to sell off a few of the projects and toys so you fix up a place to work on the remaining ones.

 

[PugetDude]

95 S6 Avant, 77 911S, 00 Insight, 77 Sleekcraft, 68 Czech Bike, Sleds, Bikes... **** I have too many toys

Priorities.

 

[zeeway]

Okay...you need more suggestions...

Water is very logical...it flows downhill unless you have a natural artesian well. So your grading and all was good. You should remove those planters too...sorry.

A medium cost solution would be to dig a 12 X 12 trench on the uphill side, and fill it with gravel and one of those sleeved drainage pipes to create a French drain. This pipe would need to drain away from the garage. This may necessitate cut a similar trench across that driveway, a major pita...sorry.

Then if the pitting is not too bad, you could cover the garage floor with racedeck tiles or equivalent. You could actually do this without doing the French drain, if you wanted the higher risk solution.

Good luck.

Ps - one of my past favorite cars was a 912 - rebuilt that engine with bigger pistons and cylinders. It was one of favorites.

 

[MagKarl]

You need drainage below the elevation of the slab. It will be a ton of work, but not too expensive for materials. I'd dig a trench outside against the garage wall and install drain tile and backfill with drain rock. If you have downspouts in the area, reroute them so they don't add to the groundwater problem. Hopefully you can gravity drain, if not put in a sump pit and pump.

 

[DougWil]

A medium cost solution would be to dig a 12 X 12 trench on the uphill side, and fill it with gravel and one of those sleeved drainage pipes to create a French drain. This pipe would need to drain away from the garage. This may necessitate cut a similar trench across that driveway, a major pita...sorry.

The OP didn't give us much info, but looking at that pic it appears the garage slab is at the lowest elevation with zero retained soil. And the top of grade rises substantially from that point.

So I am guessing that behind the garage is many feet of retained soil, as in getting a backhoe or more, to dig down to the bottom of the footing and put in a drain line.

 

[machsnell]

You need drainage below the elevation of the slab. It will be a ton of work, but not too expensive for materials. I'd dig a trench outside against the garage wall and install drain tile and backfill with drain rock. If you have downspouts in the area, reroute them so they don't add to the groundwater problem. Hopefully you can gravity drain, if not put in a sump pit and pump.

What he said...if you have graded to drain away from garage above and still have the problem it is time to go below grade of the slab.

I would dig a hole on the low (grade wise) side of one of the walls. Get to bottom of footing if you have one or bottom of turndown if that style. See if it fills up with water. Maybe do this a day or two after a rain so the purged water is still under slab. If it fills at all then you can probably remove to daylight at lower grade away from garage.

You just have to hope that the water isn't sourced under the slab. If it is then you have to hope that it can make its way to your drain tile outside the footing/turndown.

If it gets out then trench around the exterior seal your vertical concrete and install dimple board (vertical drainage board) install perforated corrugated plastic pipe (draintile) and fill with 57 stone and pipe to daylight water at lower grade.

Water will travel down easier than up but will go against gravity if it is the path of least resistance. Your concrete is a portion of that path. You just have to hope opening up a theoretically easier path outside doesn't have a roadblock (clay) for the water to get to it. Sounds like you have a vein or a path where water is coming up through a path of least resistance right under your slab. Otherwise you didn't do as good a job with your surface drainage as you thought or your dirt on the exterior is too permeable allowing water to drain and saturate under you slab wicking through.

Sent from my SM-G900V using Tapatalk

 

[cash68]

Ok. Did some more grading. No water for about three months now. I'm getting ready to do the floor, but it has all that pitting. Do I patch the floor, then grind it flat? Or do I grind the floor then patch? Sorry for the news questions.

 

[Chief919]

Ok. Did some more grading. No water for about three months now. I'm getting ready to do the floor, but it has all that pitting. Do I patch the floor, then grind it flat? Or do I grind the floor then patch? Sorry for the news questions.

That is the same question I am looking at right now with my floor that is in similar shape- did you ever figure out an answer?

 

[Dr Stan]

Ok. Did some more grading. No water for about three months now. I'm getting ready to do the floor, but it has all that pitting. Do I patch the floor, then grind it flat? Or do I grind the floor then patch? Sorry for the news questions.

If you grind it, you'll probably find it necessary to patch the floor. Get it as dry as possible, then use a latex patching compound to repair the floor. Top that with tile.

I had water infiltration at one corner of my shop. Drove me nuts until I finally found the problem. The backyard neighbor's backyard slopes down toward my shop and the soil was not low enough. On top of that I have a down spout at that corner.

I dug a fairly small ditch starting at the down spout and around the end of the shop. I used some guttering covered with grating then used PVC piping to direct the water away from the corner. I'd hoped to run it out to a grate that is part of the city's storm drain, but with 1/8" per foot of drop that just was not going to happen.

So backed up & regrouped. I bought a 55 gallon plastic barrel, buried it in the ground with 2" or so still above the lawn and put some dense grade in the bottom of the barrel to keep it from popping up out of the ground. Ran the PVC pipe to the barrel, and installed a sump pump. The discharge is directed away from the shop and I've never had a wet shop since then.

Another thing; is the garage sloped from the back to the garage door? Around here that's part of the building code.

BTW, what about a dehumidifier in the garage?

 

[skipnay]

The french drain works very well. On the side of our property where the driveway is. Once you pass the house it would level out and then towards the end it would go down hill. Even in July or August when we have went a month or more without rain the dirt/grass area would still be very muddy. I did a french drain about 4 feet in the ground. The reason I'm finding we were having a problem is because in that area was full of slate and water just can't go through it. Since I have done the french drain we haven't had any problems even if it rains for days. Money well spent because you couldn't get down to the garage without going through a bunch of mud.