This week's Ask Old Town Home comes to us from Old Town resident, Kate. Kate recently moved into her 18th century home and has been having a small issue with her basement's stone foundation. Here's what Kate has to say:
We just moved into a home on Prince Street in December and one of the things that sold us on the home was the amazing stone dining room and kitchen in the basement. According to the man who renovated the house in 2004, the house was built onto the original retaining wall of the Potomac. While they look nice, the stone walls have some issues. My biggest complaint is that they shed a lot of dust. It drives my husband nuts that I have to spend a couple of hours each weekend vacuuming the walls! But we're told we can seal the walls and that we should have it done while we're on vacation with the pets since it is toxic. My husband is still on the fence about doing it. After last night's heavy downpour, we discovered another issue... the wall is "weeping" some water. It's not pouring in, but the stone is wet. What is weird is that it isn't pouring in from the top of the wall; rather it is coming from midway down the wall. We don't even know who to call about this, let alone what can be done about it. Any thoughts? Thanks!
Unfortunately, this isn't a particularly easy one to solve. No matter the "solution," there will always be some unexpected/unwanted side effects. With one exposed brick wall in our house, and a basement that has all brick walls and soft mortar, we feel your pain on both the sandy mess and the weeping walls. Hopefully, even if we don't have a magic solution for you, we at least have some information that can help.
Old Town Home's Answer:
Basement's of the 18th and 19th century were more often created as utilitarian spaces rather than the comfortable and finished areas we've begun to expect in homes. Walls were typically constructed of rubble stone or brick to support the rest of the house, and no significant attention was paid to making those areas water tight. Back in those days the mortar used to set this stone and brick wasn't the Portland cement based hard and largely waterproof mortar we are accustomed to today, but rater a lime based soft mortar. You can easily tell the difference in mortars by wiping your finger across a joint.
Try it the next time you're out and about. If some sand comes off on your finger, the mortar is probably lime based soft mortar, if it feels gritty and hard, but it all stays in place, your looking at modern cement mortar. Color is often an indicator as well, light tan for lime and darker gray for cement, but this isn't always the case.
Lime based mortar was a very important aspect in old construction, especially with older and softer bricks. Placing the weight of a home on rocks or soft bricks that move and shift slightly over time requires a mortar that will allow this movement. If the pressure of the movement was put on the stones or brick, the end result would be a cracking and failure of the stones or brick, not the mortar.
Today, in Kate's house, the softer mortar is doing its job, allowing 200 plus year old structures in the United States, and much older around the world, to stand proudly. However, the major drawback to these types of soft mortar is the dust that it creates. This didn't use to be an issue when homes never had exposed bricks, but with the modern interest in exposed brick and rock walls, this dust isn't just a problem outside of the house.
We have the same issue in our home office. Every week we have to clean off the desk where a little bit of mortar has fallen out and collected. It's not that bad since we had the bricks repointed (old and unstable mortar removed and replaced with newer and more solid mortar), but it still occurs.
In Kate's beautiful kitchen/basement, she has a much larger surface area, which also means more dust. Take a look at her beautiful walls.
The secondary issue with this soft mortar in basement locations is the fact that the earth is just on the other side of the wall with no membrane to keep moisture away. When it rains, the mortar is porous and allows water to seep into the basement. I know some masons that call these "point weepers." They don't typical cause issues in unfinished spaces, but they are a serious headache when your basement has beautiful salvaged floors and is a livable space. Kate is having this issue when it rains heavily and the ground becomes saturated, and that leads to what we saw in the photo we showed above.
Let me be the first to say, Kate is not alone. Just look at what we were met with after the first really big rain we experienced in our house. If you were reading yesterday and saw our backyard flood and pond floating away, this was the same rain storm that caused the following in our basement.
The first reaction with something like this is to seal the wall. As you can see in our photo, the wall was previously sealed with a thick white paint sealer but has seriously failed. But in the case of Kate's basement, the wall is gorgeous, and you don't want to hide it with some sort of thick water proofing material, especially if it isn't going to work. Your only real option is to use something clear, like an oil based polyurethane. This will both seal the dust and sand into the mortar joints, giving a good sheen to the stones, and may help to keep some of the water from coming through the joints, but this isn't a true water proofing approach.
Here's Wendy applying some polyurethane to our office's exposed brick wall. You can see the difference in color that it makes, and it really made our office wall look much cooler.
While applying a polyurethane may help, you have to keep in mind that the water on the other side of a basement wall is still there, still trying to get out, and it might just find a more destructive location to come out if the first location is blocked.
What we can say is that, as you saw above, we've applied polyurethane of this sort indoors and the fumes really aren't that bad. With our old house being so loose from an energy standpoint, just leaving some windows open tends to solve the fume issues while it dries.
While covering your walls with polyurethane will seal in the dust and give a nice look to the stones, to truly solve the water issues usually requires a far more labor intensive and expensive approach. It makes sense that the water will come through the walls if you consider that any water sitting behind the walls during a heavy rain has no other place to go. Once it's in the ground, the water is stuck, and it will look for the path of least resistance. This path is almost always through the basement walls. When the water is minor, as it seems to be in the photo, you can often just let it dry and understand you'll have the occasional weeper.
But if this gets worse, and you have water collecting on the floor and not draining from the basement, your goal should shift to water removal, not water proofing. What I mean by this is to give the water that would otherwise come through your wall an alternate and easier place to go, like a drain to a sump pump that will then pump the water up and away from your house, or improved drainage on the ground around your house to take the water further from the foundation.
To accomplish this there are several approaches, but one is more straight forward while the others are going to have significant cost/labor associated with it.
- First you can install improved drainage pipes on your downspouts and burry drain tiles in the ground anywhere that you notice water coming onto your property from your neighbor's property. This will hopefully keep excess water out of the ground around your basement walls and will result in less overall saturation and leaking. This is a first step to see if you can get yourself to a point where you are keeping enough water away that it won't find you in your house.
- Second, and typically the best (but most expensive) option is to install a "French drain." A French drain installs either inside of the house beneath the basement floor and around the interior perimeter of the house, or more typically it is installed outside of the house, dug down quite deep and embedded at the base of the foundation. The drain is perforated and covered in loose fill stones that allows water to enter the drain through the holes rather than collecting behind the walls. The water then runs through the drain to a sump pump, where it is eventually removed from the house.
If you don't already have a French drain, it very well may take care of your water issues, but it's often quite pricey for the install. If you do have a French drain already installed, there's one more option.
- The final and most labor intensive option is to dig down around the foundation of your house, nearly to the bottom of the foundation wall, and apply a sheet of water proofing material to the outside of the wall before filling it back in. The material will then be affixed to the wall with some sort of adhesive and will extend above the surface of the ground. Where the material comes above the ground it will then lean back toward the house and will not allow water between the material and the foundation wall. In short, this means tons of digging and lots of labor, but it's still not foolproof. The material will be in contact with water almost the entire time and is bound to break down and let water in over time. So it seems like just about any solution will have a level of dependability issues.
Though I don't have the magic solution, I think the most important thing to remember. As much as we all want bone dry basements, your house is over 200 years old with a rubble stone foundation, so some issues tend to be expected. If your water seepage is only as bad as the photo shows, I think you're in pretty good shape overall, but if it gets much worse, hopefully this information will help.
Does anyone else out there have any great ideas on how to deal in the mortar dust and work towards a better sealed basement wall? What would you do in this situation? Drop us, and Kate, a line to give us your two cents on the matter.
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Disclaimer: Ask Old Town Home is meant simply as a friendly bit of advice and is provided free of charge. It is your responsibility to fully research any and all items related to projects or suggestions to ensure proper safety and code precautions and regulations are fully followed. In other words, any advice we provide is just our opinion, and our opinion is only worth the price we charge for it. :-)