Comment by vlehto | Hacker News Reader

Comment by vlehto | Hacker News Reader

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Is the concrete seemingly leaking some white powder? If it is, then you have something to gain from external non permeable layer. Something like this?

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.

There's a little efflorescence, but nothing out of the ordinary for the area; it's more uniform and nowhere near as severe as your picture. I suspect installing a barrier wouldn't make any sense. Because of how houses (and foundations) abut, largely limiting access to within the property's footprint, I imagine it would be easier to simply pour a new foundation. New foundations are increasingly common, but I'd rather not drop $30,000+ before I need to.

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. :)

Sounds like the water comes just from capillary action. That is very good situation compared to actual ground water pressure pushing moisture through the walls.

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.

Interesting. Thanks!

Not at all to try giving any lesson on the matter, but using membrane is a modern (and cheap) way to solve an issue that the Romans some 2000 years ago had solved in a much "cleaner" way.

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.

>> Not at all to try giving any lesson on the matter, but using membrane is a modern (and cheap) way to solve an issue that the Romans some 2000 years ago had solved in a much "cleaner" way.

...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

>If I'm understanding it correctly its basically a space dug down and left empty to keep the walls ~60cm away from the foundation?

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)).

That was interesting, thanks.

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.

Yes, I know those, though - technically - they are not a waterproofing membrane, they are intended (at least here) to be only a mechanical protection and a separation layer, and the height of the knobs is anyway too small to have an actual ventialtion.

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

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