Anyone know anything about concrete? (should I seal old garage?)

[BrianK]

My house was built in the 20's. I can only imagine the garage was built about then. If it wasn't then, it was the 60's. Either way, it's old.

My lot is fairly steeply sloped & the garage is at the street level, so it's almost entirely underground - half way covered at the sidewalk & 3' retaining wall holds up the dirt at the back (i.e. it would be underground at the back if it weren't for the retaining wall). The majority of the the garage is unreinforced concrete (no rebar). A bit of the retaining wall was replaced a few years back & was rebarred, but that's just the top of the structure.

So here's the question:
Inside the garage, if I rub my finger across the surface, I can scrape off a decent amount of material. If I sweep out the garage, after a month or two, I see bits of the wall & cement dust on the floor around the edges. I'm about to cover the walls with drywall (or something similar), but I wonder if I should seal up the wall before I do it? If so, what's the stuff for the job? Should something else happen other than sealing? Of course, I would rather not replace the garage - I can't imagine what that would cost.

[smoseley]

Hmmm... concrete isn't supposed to degrade like that, even if it's not reinforced. All reinforcement does is add strength under forces other than compression (e.g. tension, torsion). It sounds to me like they may not have mixed the concrete well enough on the initial pour or not cured it properly. You should definitely have a structural engineer check it out instead of just covering it up and forgetting about it. That could wind up costing you a lot more if you have a failure.

Edit: I take that back... http://www.structural.net/News/Media..._concrete.html

Apparently, concrete will degrade if exposed to the elements (i.e. not sealed). Get the walls checked out to see if they're still structurally sound.

[sndesign]

The stuff is called drylock, you paint it on, it keeps the water from coming through
the concrete.

[MikeW]

As I understand, you have dirt against the wall. That will retain moisture against the wall. The dirt needs to be removed so there's nothing but air against it. Then drainage needs to be considered so there's no standing water in the future. If you have to have dirt against the wall, it can be removed and a moisture barrier can be put between the wall and the dirt. Likely the best method would be a hot applied material in the form of a thick mat with fiber. It's rubber/asphalt I believe. Anything you do to paint or coat it from the interior side won't stop it. It will just trap it and could even cause a mold problem. A barrier is the proper method. I suggest you get a shovel and start digging and see what the outside of the wall looks like.

[BrianK]

Originally Posted by MikeW

As I understand, you have dirt against the wall. That will retain moisture against the wall. The dirt needs to be removed so there's nothing but air against it. Then drainage needs to be considered so there's no standing water in the future. If you have to have dirt against the wall, it can be removed and a moisture barrier can be put between the wall and the dirt. Likely the best method would be a hot applied material in the form of a thick mat with fiber. It's rubber/asphalt I believe. Anything you do to paint or coat it from the interior side won't stop it. It will just trap it and could even cause a mold problem. A barrier is the proper method. I suggest you get a shovel and start digging and see what the outside of the wall looks like.

That's what I was afraid of. I thought I had posted a response to the drylock comment, but I guess I didn't hit "submit"

Digging eh? Those 20' tall pine trees bellied up to the back of the garage are going to cause a big problem for that. d'oh!

[James007]

I would definitely get someone out to look at your garage, maybe a concrete guy, geotech?
If I understand you correctly, there is evidence of the concrete degrading. I would expect the construction practices of garage slabs and retaining walls were alot different when your home was built compared to existing practices so getting a professional opinion wouldn't hurt -- except maybe your wallet?
I've been told that concrete is like a sponge that absorbs moisture, unless they applied some kind of moisture barrier. If you have a damp, moldy smell you may have a moisture problem.
In any event, before you cover up the wall with anything, you should seriously consider having someone evaluate that area. Like someone else said, if you cover up that area without doing anything else, you may create other problems in the future, which will probabaly cost alot more money to fix.

[milehitom]

MikeW's right on the money. Your deterioraion is caused by moisture infiltration. Concrete is porous. Moisture from the earth is getting through. But dirt against the concrete is ok; continuous damp isn't because chemicals in the water can react with the chemicals in the concrete to cause it to degrade. You'll have to address the drainage issue form the outside of the concrete walls. Drainage board, a rubberized asphalt membrane and weeping tile around the base will move the majority of water away from the structure and then you can drywall the interior to your heart's content. If you drywall it now, even after painting on Drylok or UGL, the moisture will continue to wick through and the drywall paper will eventually mold.

I'd guess the structure itself is still sound. Older concrete often has lots more Portland cement in the mix-if your concrete dust is fine and not gritty, your mix has a high Portland content and is quite strong. Check for cracks everywhere, though. They'd need to be filled with a similar strength material.

If you leave the conditions as is, you could also add a dehumidifier to garage to reduce the effects of the dampness. But I still wouldn't drywall until the drainage issue is addressed.

Tom

[MikeW]

Brian
a picture might help a bit. While you've mentioned concrete, there was no actual mention of block. I assume the walls are block at some point. You still need to dig and do some minor poking with a screwdriver or something to get a clue about the integrity of your wall. I get a bit of the same thing in my garage. I added a slab next to a wall for the car. I used a felt expansion joint. Just washing the slab and getting the felt wet will wicks enough moisture to cause efflorescense and some release of some of the bonding mortar between the wall and the foundation.

Proper drainage, gutters, additional overhang should be considered. Some soils absorb moisture and retain it more than others.

[LSUFAN]

Good acid etching, rinse and then I'd float tile with black grout and never worry about it again.

[Lotus Fury]

This sealant will help tons. Spray the outside as well as the inside. If you seal the floor as well as the wall it will help decrease the amount humidity in the garage area as well as increase the life of the concrete.

Here's a list of prices and products, there's all pretty much the same.
http://www.stonetechnologiesinc.com/specials.html

Drylock is good for walls and ends up being a white paint, the above stuff is clear & flat, not shiny. Drylock has a longer life, 10 years, the above stuff last 3-4 years.

[Z-dculus]

Civil Engineer here.....without seeing pics its hard to even attempt at assessing this. First off, concrete does degrade over time, especially if exposed to the elements and the quality of the mix (and the mix design). Second, virtually no retaining wall or concrete structure in existence should be built with out a properly designed rebar lattice and anchoring system. Concrete is phenominal in compression, but virtually has no tensile strength. It can only bridge imperfections in tensile loading to a very small point. I would definitely suggest to consult a structural engineer for a professional opinion.