Umm. Why would you want to parge coat that foundation? Did you try to do that on the outside or the inside?
Do you have concrete slab against ground? Cellar? Or is there unused airspace between the floor and the ground?
Do you have concrete slab against ground? Cellar? Or is there unused airspace between the floor and the ground?
The foundation is structurally fine (home inspection passed, earthquake retrofitters didn't seem bothered by it even though in at least one spot a installing foundation bolt blew through the concrete), but it's noticeably disintegrating. I presume the previous owner attempted a parge coat on the internal walls to hide this. My motives are both esthetic and practical. Practical because, theoretically, a proper parge coat can act as a sacrificial layer, slowing the disintegration. Whether a parge coat would actually extend the useful life of the foundation as practical matter is something only someone with real in-depth experience and knowledge of SF construction would be able to tell me. I just don't know how to find such a person.
If you tour SF homes[1] you'll notice that most have remodeled the garage to include one or more bedrooms. The strip foundations are trapezoidal--slightly wider than the sill plate at the top (which is about a 1 or 2 feet above ground), expanding to much larger as it goes down 3 or 4 feet under the ground. Older remodels often parge and paint the foundation or box it behind wood molding; newer ones might actually hide it behind the refinished walls. But because of the awkward dimensions, whatever they do you can easily spot it if you pay attention.
What I find crazy about this is that they're enclosing foundations which are (or will be) nearing their useful life. (SF homes are technically detached, but usually only have a few inches of gap at the most so the side walls are inaccessible.) Moreover, the refinishing is probably wrong. Either it'll pop off, or if they used a chemical binder they're (theoretically) accelerating the disintegration (the moisture and salts will create pressure behind the binder, pulling on the face of the older concrete). Likewise for impermeable[2] paint. Yet you won't even notice any of this because it'll be completely hidden.
I'm happy that the home we found was (all things considered) both relatively well-maintained and unmolested. The garage was never refinished except for a parking slab poured circa 1970s. I'd like to keep it this way.
[1] Which typically sit over a garage with a parking slab poured decades (or even a century) after the foundation. The garages were serendipitous. Most of the homes were built before cars were so common; what are now invariably garages were unfinished first floors intended to be used and finished (if at all) however the owner wanted--storage, workshop, in-law, extra living space, etc. When cars exploded most were turned into garages. Now in-laws and extra bedrooms are becoming much more common, either replacing the garage or reducing it to a size that would barely fit a lawn mower. Occasionally you'll find the odd house where there's still just sand at the first floor.
[2] Permeability of paint is a whole 'nother can of worms. Like the foundation, the typical stucco finishes on homes on the west side of SF were designed to be semi-permeable. The external walls need to breath. But idiot painters (including whoever the previous homeowner hired) commonly use a low-permeability latex paint. (Latex comes in all kinds.) Moisture accumulates behind the stucco and the paint quickly bubbles and peels. In some cases (like ours) it can be bad enough to cause moisture damage inside the house because vapor barriers were either non-existent or primitive (our house was wrapped in tar paper), and in any event both the inner and outer walls were designed to be semi-permeable as compared to modern construction.
Of course, ask most painters about these permeability issues and many or most wouldn't really understand what you were talking about, even in SF. Contractors who do a good job often do so because they've inherited a workable process (proper types of paint, etc), not because they understand why. But often times you still need that deeper knowledge to be able to debug or solve certain issues. Good luck finding somebody capable of doing that. I think that, like with modern network security, the saving grace is that most people end up dodging bullets by replacing whole systems before the consequences are realized.
https://www.rakentaja.fi/keskustelukanava/img/20157/295425.j...
I live in Finland. Here if the walls of a room are not completely above ground, you risk molds and therefore it's never advisable to have living quarters in such rooms.
If you do have living quarters in such rooms, the proper way to do it is to install non-permeable membrane between the soil and the concrete. The renovation looks like this: https://www.vastavalo.net/albums/userpics/13316/normal__MG_1...
If it's just a garage or storage space with no white leaks, I would just wait it to crumble to a degree that justifies changing the whole foundation. I don't see how internal coating could help anything. And external coating helps only very little if it's above ground.
I'd guess SF is so arid that people don't really notice that stuff. It's different in a country like this that has swamps and rain all over.
SF is coastal and foggy. Most of the western half of SF is built on sand dunes. Drainage is excellent but the ground is nonetheless perpetually wet. One of the things I've always noticed about typical first floor remodels is that they always feel very damp. They may be fancy and expensive but they always feel like jail cells to me. We recently toured a house around the corner from us with a 1990s- or 2000s-era first floor remodel and, indeed, you could both smell and see mold. Unless you pour a new, modern foundation (or somehow manage to install an external barrier) I don't think it can be avoided. It's crazy to me that people pay premiums for such remodeled houses. Like I said, I'm glad the house we found was relatively unmolested.
You're probably right that the reasonable thing to do is leave it alone and replace it when it gets too far along. But then I'd have no excuse to learn an old-school masonry skill. :)
You should be good if you keep there good ventilation and avoid putting any wood dust or wood structures directly in contact with the concrete. Wood and concrete combined are breeding ground for dry rot and that fungal nightmare can tolerate more arid environments than any other.
One trick you could try is to put some asphalt outside right next to the wall. It won't solve any underlying issues, but it can help a little bit.
I think the crumbling comes from something else than moisture in your case. Probably oxidation of cement accompanied with temperature variations. You can treat that in some cases by injecting cement into the cracks in the wall. But that is very expensive.
I think the crumbling comes from something else than moisture in your case. Probably oxidation of cement accompanied with temperature variations.
In Italian it is called "scannafosso", this is the "modern" (and cheap and "wrong") way:
https://www.coffeenews.it/wp-content/uploads/2010/02/scannaf...
and this is how it was done traditionally (as said since Romans times) and "right":
https://www.coffeenews.it/wp-content/uploads/2010/02/scannaf...
The idea is that the walls must be permeable and areated, the membrane keeps the outside rain/water/humidity outside BUT it also keeps the internal humidity/vapour inside which is a good start for moulds and similar, and in any case it is definitely not healthy.
BTW the effect is not entirely dissimilar to what happens (hopely happened as nowadays it is more rare that new houses are built without appropriate ventilation) in modern houses built along "energy efficient" rules, any house in an energy class better than D (C, B, A and A+) without a mechanical air ventilation system is simply and plainly unhealthy for its occupants.
...Proceeds to give lesson :P
If I'm understanding it correctly its basically a space dug down and left empty to keep the walls ~60cm away from the foundation? In most places, but especially SF, there isnt space for an extra meter on each side of the houses
Exactly.
There is no actual need of 60 cm, which is only a "sane" width to allow inspection, the external wall and "air chamber" can be much smaller, see as an example:
http://docplayer.it/docs-images/41/9277133/images/page_8.jpg
and if there is not enough space for the above (25-30 cm) a wall of porous/hollow bricks (thickness 10-15 cm) will still do better than waterproof membrane alone.
>In most places, but especially SF, there isnt space for an extra meter on each side of the houses
I know, and I am not at all saying that it is a universal solution, and - besides - it costs a lot more than plainly applying to the house foundation and earthed walls this or that kind of non permeable membrane (there are bitumen based, PVC based, synthetical/chemical liquid compounds, bentonite, etc.).
Still if you are building a house and have the needed space, it is money well spent, I have seen tens or hundreds of recently built houses using membranes notwithstanding the availability of space (because it is easier and cheaper) with humidity/mould problems that cannot simply be resolved without mechanical ventilation (besides when needed repairing the waterproof layee(s)).
But you might be pleased that the most modern system at least in Finland actually has little of the same features than the romans had. If you look at the same membrane I posted earlier, it has little knobs that hold it little bit away from the wall:
https://monosilla.files.wordpress.com/2014/11/screenshot-201...
I don't know the English word for it. It's not perfect, but lot better than couple decades ago. They used to paint the concrete with tar. This "patolevy" is cheaper, easier to install and allows little bit of ventilation.
Besides - usually the "top" of the layer is not properly sealed/protected so - over time - the space (at the bottom)is filled with fine sand/dust brought by wind/rain, of course preventing any ventilation where it is more needed.
"Bigger brothers" do exist, like:
https://www.youtube.com/watch?v=dnxj9mTN9NE
still they are usually placed over the waterproofing layer, this should guarantee:
1) that the actual waterproofing is not punched by a stone or whatever when filling the excavation
2) that the waterproof membrane is not "immersed" in humidity