Preventing mold in a fieldstone basement

November 4, 2005 9:14 AM

Our 100+ year old house has a fieldstone basement with no mortar between the stones. Water doesn't flood or drip in, but the walls are always a little damp. Black mold is beginning to grow down there, and we'd like to stop it.

We've been told that actually waterproofing the basement is not an option. (Although if that's wrong — if there's a cheap, reliable way of waterproofing it — I'd love know know.)

If there's always going to be a little moisture down there, how can we deal with the mold?

posted by nebulawindphone to Home & Garden (15 answers total)

Scrub it down with bleach. It will come back, and you scrub it down again. It's a lot like weeding, you're just keeping it at bay. I don't think there's a permanent solution, moisture in a dark place is going to produce mold.
posted by doctor_negative at 9:38 AM on November 4, 2005

Ditto on the bleach & scrubbing. Make sure you get a mask/respirator that is for fine airborne particles (don't know the particular ranking here...but they are all marked as such clearly on the package).

Unfortunatly, the dampness is going to keep the mold coming back...so, unless you seal the basement (somehow, and I imagine this is always going to be quite pricey), the scrubbing is just going to get rid of it for a little while.

Have you tried a placing a dehumidfier in the basement? That might lower the humidity enough to keep the mold from...molding up the place all the time (but it depends on size of the basement, etc etc etc).
posted by tpl1212 at 9:51 AM on November 4, 2005

An Ozone generater on a timer may help keep the mold under control.
posted by hortense at 10:22 AM on November 4, 2005

Response by poster: Hmm. According to the EPA, that might not be such a good idea.
posted by nebulawindphone at 10:38 AM on November 4, 2005

You can fight the mold, but it shouldn't be there in the first place. There could very well be poor drainage outside leading to moisture in the basement. There could also be a ventilation problem if the basement is too airtight. Why is waterproofing not an option?
posted by lazy-ville at 12:38 PM on November 4, 2005

A dry stacked stone foundation is just that: a pile of rocks. Short of digging a foundation deep trench around the complete permitter of the house and applying a dampproof membrane to the outside there is no way to stop moisture migrating in.

Better ventilation can help. If the stone is below the dew point heating your basement will help cure the problem.
posted by Mitheral at 1:00 PM on November 4, 2005

A dry stacked stone foundation is just that: a pile of rocks. Short of digging a foundation deep trench around the complete permitter of the house and applying a dampproof membrane to the outside there is no way to stop moisture migrating in.

Well, that's how you waterproof basements. I was asking why this is not possible.
posted by lazy-ville at 1:33 PM on November 4, 2005

Digging a trench around the outside of the foundation to waterproof it is usually not feasible because dry stacked foundations can become unstable if they're open to the air on both sides. These aren't the most stable structures and the earth on the outside is providing it with some support. Remove that earth to waterproof and part of the foundation could collapse.
posted by HiddenInput at 1:43 PM on November 4, 2005

Can't you plug the spaces between the stones with mortar? And then skim over the whole wall? Don't you hate AskMe answers that end with question mark? But wouldn't that work?
posted by stupidsexyFlanders at 4:03 PM on November 4, 2005

Try a space heater to dry it out the best you can, then spray
few ounces of tea tree oil mixed with alcohol and wet the surfaces of the stones.Mold hates tea tree oil and may stay away for months. side note, Don't use the ozone without the timer.
posted by hortense at 6:11 PM on November 4, 2005

forgot the link for the side note
posted by hortense at 6:20 PM on November 4, 2005

Send email to the folks at "Ask This Old House." Maybe they'll send Tommy Silva to help solve your problem.
posted by ilsa at 9:29 PM on November 4, 2005

I had this problem, and we ran a nice french drain down along the offending wall, about 8 feet off the foundation maybe? it drained out away from the house, and worked like a champ.
posted by Joseph Gurl at 11:51 PM on November 4, 2005

I second any recommendation to look at drainage. When it was built, the basement probably did not leach enough water to grow mold. If it is now, you could have problems or could have changed the environment of the house. Do you have a new, more efficient furnace that doesn't radiate as much heat into the basement? That could reduce drying, and then once you get water into the foundation, it freezes and cracks stones. So yes, this could be serious and you could need a really good expert to look at it.

Old barns used this type of construction, and they depended on the heat of animals in the basement to maintain the environment needed for this type of wall to remain stable. With changes in farming, the barns that remain rarely have those animals, so the foundations collapse, and the walls collapse, and the old barns disappear. I don't want you to panic, but the same type of problem could be happening here in slow motion. I would look very carefully on the wettest walls for any type of settling, and check things with levels and plumb lines.
posted by dhartung at 12:14 AM on November 5, 2005

Definitety consider any changes that might be leading to this. Anything that leads to more moisture (irrigation system? new gutters?), less heat (new furnace?(as suggested above)) or less ventilation (new weather stripping? change in building airflow?) could lead to this.

If you can narrow it down, that should suggest a remedy.

Barring any guess at a potential cause I'd set up a vent that is controlled by a moisture meter.

Best luck.
posted by deanj at 10:28 AM on November 5, 2005