Back in (we think) 1906, they simply dug a hole, formed 6 inch walls, and poured concrete over the dirt for basement walls in Maryland. Lousy concrete, with an occasional stick and large cold joints. In specific areas with really bad mixes, as moisture gets into the concrete, it flakes of in powdery chunks. I scraped and cleaned several areas back to solid material, then completely sealed thjose areas inside with concrete sealing paint, and 10 years later the paint is all that’s holding many of those now powdery flakes of concrete in place.
I doubt the foundation is going to fall apart in my lifetime, but I’d still like to figure out if I can remedy the problem.
Some external, above grade areas of the foundation have been porriged years ago, but that’s not sticking to some areas either.
The only real solution I can think of is to excavate outside, clean everything, and spray shotcrete, then waterproof the heck out of it. Very expensive.
Any other ideas?
Replies
Hi, Dave. Welcome to BT.
Need to ask you a few of questions first. And it would help us if you'd fill out your profile, too. Just click on your name in the message header above this answer and a pop-up will appear with self-explanatory instructions.
So, can you tell us:
Is there any sign of heaving or bowing in the basement walls at the present time?
Is the concrete degradation still limited to the surface, or is it now through-and-through the entire 6" wall?
Is there any water infiltration?
Is the wall solid concrete or concrete poured over rubble?
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
1: Walls are true. No cracks or movement.
2: Only the surface is visible, of course. However, there is a thinner wall under a back porch, which is now, in one area, completely perforated.
3:Water table hereabouts is high. There's no drainage inside or outside the wall. Basement floor is very thin concrete poured over the original dirt. Water seeps in regularly on the uphill side of the foundation, from under the base. Remember, no footers below.
4: Wall is entirely poured...no big rocks identifiable. But the aggregate is of poor quality, including sandstone or shale or some other very soft stone. Just what was around, it seems. When I scraped and wire flailed the interior wall to clean off the loose material, I found entirely solid material below. I'd guess less than an inch of thickness has flaked away. And some sections of the wall are entirely solid, original surface. I'm confident this is just a bunch of bad concrete batches.
Makes me wonder if beach sand was used in the concrete(not uncommon in older homes such as yours).
The high salt content of beach sand can do bad things to concrete.
Would have had to ship it, which is possible, I suppose. I'm 3 hours from the nearest beach by Interstate. Who knows how long by truck in 1906.
The powdery deposit is efflorescence -- caused when water wicks through the concrete [or masonry], dissolving any salts as it goes. When it reaches the surface the water evaporates, leaving the salt as a powdery deposit.
The problem area is just below the surface where the salt is still in solution and is so concentrated that it will attack the cement in the concrete. This is what causes the crumbling away.
The only effective long-term solutions are to prevent the water infiltrating the wall in the first place or to seal the exposed surfaces of the wall to prevent evaporation [which is what pulls the water through the wall].
Concrete comes to no harm merely by being wet -- think of bridge piers or sea defences which are below water -- but the wicking through brings fresh, oxygenated water to further rust any rebar and salts to the surface to degrade the concrete.
IanDG
I'm familiar with efflorescence. I should have mentioned this, because that's not what I'm seeing. Efflorescence is new material on the surface of the concrete. This is a change and eventual shedding of the concrete itself.Which is not to say that salt isn't somehow involved in my problem, attacking the concrete. The inside was is as sealed as it could conceivably get, and the concrete continued to break down under the multiple layers of primer, concrete sealer, etc. Almost certainly made possible by water travelling through the wall from the outside.
It is very difficult to seal the inside of the wall effectively, especially against hydrostatic pressure, but if you were still getting
water wicking through then the inside wasn't sealed satisfactorily enough to stop evaporation.
The problem of sealing against water infiltration is made worse by the fact that it can still wick up the wall from the foundation below.
IanDG
I'm afraid you're probably going to have to excavate, Dave. You need to give the ground water an easier way to get where it wants to go--which is always downhill in the final analysis--than by percolating through your walls. Otherwise you can spend your life patching and 'sealing' the inside of the walls and you'll still have water in the wall, which isn't doing the foundation one bit of good.
You need an exterior perimeter drain at minimum. For a complete job you need to bust out the floor, too, dig out a foot or so of the dirt, and shoot a foot of ¾" net washed gravel in there before you pour a new slab. That will give any water that gets by the French drain an easy way to run under the slab and go about its business downhill without coming in to say hello....
Obviously, while you've got it dug up, you should reinforce the wall. Since the walls are true and not cracked, I'd consider setting up a perimter form two to four inches outside the existing wall and pouring a new 'skin' two to four inches thick. (Paint the whole foundation with Gelcrete first so you don't get a cold joint.) Then waterproof that up to state of the art, which is actually pretty good these days with the new membranes that have come out in recent years.
You might even consider jacking the house up and demo-ing the existing foundation and pouring a new one with footings, footing drains, and the whole nine yards. Hard to say from here which would be more cost-effective in the long run. A lot depends on the value of the house itself.
Wish I could see an easier way, but I don't. Sorry.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.