How do you waterproof an exterior wall?
October 4, 2023 8:35 AM Subscribe
A mason repaired a section of the brick on the front of my house. Another contractor ripped out the plaster on the opposite side because it was moldy. I'm worried that it's not waterproof and the mold will come back. How do I prevent that? Pictures of the wall from the inside:on google photos. Same pictures on imgur 1, 2, 3
Should it look like that from the inside? Should I be able to see the back of the brick from the inside? Is it already messed up beyond repair? Or is it supposed to look like that and all I need is a competent contractor to repair the inside wall?
Or is it something in between? Like, the state of the wall isn't ideal, but it can be adequately corrected? What should I look for in the repair of the interior wall? What does that contractor need to do besides replace the plaster and paint it?
Should it look like that from the inside? Should I be able to see the back of the brick from the inside? Is it already messed up beyond repair? Or is it supposed to look like that and all I need is a competent contractor to repair the inside wall?
Or is it something in between? Like, the state of the wall isn't ideal, but it can be adequately corrected? What should I look for in the repair of the interior wall? What does that contractor need to do besides replace the plaster and paint it?
That looks like a single skin wall, ie there is only one skin of bricks whereas most modern brick/block house walls would have a one wall, then a gap (or an insulation filled gap), then another wall. Its hard to tell from the angle but looking at the thickness of the window opening, it is probably single skin.
If it is damp coming through the wall then the cheapest solution is to paint the exterior of the wall with a damp proof coating, search "water seal brick wall" for products. That isn't a great solution but it is very easy and very cheap. Also check for any holes in the mortar or place where the wall has been drilled or cracked.
If it is damp coming up from the ground then you are better getting professional advice. But this is rarer than people think. You may need to have the bricks injected with treatment, or the ground drainage improves, or any number of other things. But as I say... thats not very common these days.
However it is more likely the problem is condensation and not damp coming through the wall. The rooms you live in are probably warm and humid - humans, cooking and bathing all heat the air and add lots of moisture. If the wall is old then the living area it borders it probably a LOT hotter and more humid than when the wall was put in.
A single skin wall is very bad at thermally insulating so it will tend to be close in temperature to the average between the outside and the inside, which is often colder than the inside - but it depends on the local climate. If you touch the wall and it feels colder than your fully internal walls then that is a sign of this problem. When the air hits the wall it cools and will dump moisture on it and into that air void within it. So the wall is always a bit damp, and that leads to mould.
The best solution is to add installation and then seal it internally. So you would add fibre insulation between the upright wood supports. The insulation has to also stop air movement, as air carries moisture, so make sure the voids are totally filled and not just part filled. Try to minimise "bridges" where cold can pass between your layers, so minimal things going across layers horizontally. Your trying to make a series of vertical skins that wrap around the living space. Next you add a layer called a vapour barrier, which is needed as everything else (plaster and brick etc) are all porous. Then you add plasterboard (sheet rock, wallboard, gypsum panel, it has many names). Then you add the plaster (mud) and decorative finish.
Or just watch this video, Steve Maxwell explains things really well with no padding. Quicker than reading this.
Search youtube for "vapor barrier wall" if you want to see loads of guides. It's a REALLY common problem and its the reason building codes don't allow single brick walls like that in most places these days. Its extremely fixable and nothing to worry about.
If you have black spots on the inside of any other external walls, or in the corners of ceilings, than you have condensation causing mould and that is dangerous to health. Looks t better ventilation (extractor fans) in bathrooms and kitchens and better insulation on all external walls.
(I am not a builder. I have fixed a similar problem in a garage space we were using a living space. Your local climate, codes and whatever may be very different)
posted by samworm at 9:34 AM on October 4, 2023 [2 favorites]
If it is damp coming through the wall then the cheapest solution is to paint the exterior of the wall with a damp proof coating, search "water seal brick wall" for products. That isn't a great solution but it is very easy and very cheap. Also check for any holes in the mortar or place where the wall has been drilled or cracked.
If it is damp coming up from the ground then you are better getting professional advice. But this is rarer than people think. You may need to have the bricks injected with treatment, or the ground drainage improves, or any number of other things. But as I say... thats not very common these days.
However it is more likely the problem is condensation and not damp coming through the wall. The rooms you live in are probably warm and humid - humans, cooking and bathing all heat the air and add lots of moisture. If the wall is old then the living area it borders it probably a LOT hotter and more humid than when the wall was put in.
A single skin wall is very bad at thermally insulating so it will tend to be close in temperature to the average between the outside and the inside, which is often colder than the inside - but it depends on the local climate. If you touch the wall and it feels colder than your fully internal walls then that is a sign of this problem. When the air hits the wall it cools and will dump moisture on it and into that air void within it. So the wall is always a bit damp, and that leads to mould.
The best solution is to add installation and then seal it internally. So you would add fibre insulation between the upright wood supports. The insulation has to also stop air movement, as air carries moisture, so make sure the voids are totally filled and not just part filled. Try to minimise "bridges" where cold can pass between your layers, so minimal things going across layers horizontally. Your trying to make a series of vertical skins that wrap around the living space. Next you add a layer called a vapour barrier, which is needed as everything else (plaster and brick etc) are all porous. Then you add plasterboard (sheet rock, wallboard, gypsum panel, it has many names). Then you add the plaster (mud) and decorative finish.
Or just watch this video, Steve Maxwell explains things really well with no padding. Quicker than reading this.
Search youtube for "vapor barrier wall" if you want to see loads of guides. It's a REALLY common problem and its the reason building codes don't allow single brick walls like that in most places these days. Its extremely fixable and nothing to worry about.
If you have black spots on the inside of any other external walls, or in the corners of ceilings, than you have condensation causing mould and that is dangerous to health. Looks t better ventilation (extractor fans) in bathrooms and kitchens and better insulation on all external walls.
(I am not a builder. I have fixed a similar problem in a garage space we were using a living space. Your local climate, codes and whatever may be very different)
posted by samworm at 9:34 AM on October 4, 2023 [2 favorites]
I think the window above is the source of condensation moisture, in any case all the advice so far is very good. I would add insulation to that space under the window, maybe think about upgrading the windows in the future.
posted by hortense at 9:40 AM on October 4, 2023
posted by hortense at 9:40 AM on October 4, 2023
I am not your architect, but will provide my opinion. The brick face should not be exposed at the interior wall cavity as shown in your photos, unless the brick is protected by some kind of exterior cladding (I am assuming it’s not). Brick is a “reservoir” material, meaning it absorbs water when it rains and releases it slowly. Brick exposed to the interior of the house (as you have) will release water vapor to the interior. If you seal this up, it will mold - like definitely for sure will mold, and quickly. Insulation may make it worse since it’ll get wet and won’t dry well within the cavity. It’s possible there are other sources of moisture (window, foundation, etc.) but the brick is absolutely a source of moisture in this scenario and I would not recommend leaving the wall like this.
In terms of solutions, this is an archaic construction method that would not meet modern codes. Given that, any solution that is not “rebuild the entire wall” will be a bit of a stop gap. The way to think about it is like so: the brick will get wet and hold water; it will then release the water vapor as it dries. You can either stop the water getting into the brick on the outside in the first place, or you can stop the vapor from being able to travel inside past the brick once the brick is wet.
Painting the brick to make it impermeable from the outside is probably easier, but it will (a) require a ton of paint (brick will suck it up quickly) and (b) will require frequent maintenance as the paint will tend to crack and create pathways for moisture. Someone more expert in these coatings than me may be able to recommend something appropriate.
I can’t think of a good way to solve the vapor issue from the interior without rebuilding that wall, but the way a modern brick wall should be built is as follows: brick exterior (“cladding” layer), small air gap so water weeps down, air/water/vapor barrier (like a Tyvek), sheathing (plywood or similar material), then studs, insulation, and interior drywall.
I’d be interested to know how the existing wall is constructed - I’m assuming it’s similar to this? If you open up a couple more bays of studs beyond where your mason did the work is it still exposed brick? If NOT then you’re likely missing sheathing and waterproofing that should be there and the mason just… did really shoddy work. If it looks the same, then you have a bigger problem of a wall that will be prone to damp that is difficult to solve without rebuilding it :(
Please do be aware though that just adding insulation will not solve this. You’ll just get wet insulation, although you’d probably be warmer…
Quick edit: the suggestion above to use a foam fill insulation that can act as a vapor barrier has potential. You’d need to engage a professional to do it and it’s very important the ENTIRE stud cavity is filled completely with a vapor impermeable foam, but that would probably work to solve the issue if the entire wall is constructed like this. To be clear, you’d need to foam the entire wall to effectively stop the water vapor intrusion.
posted by annie o at 3:19 PM on October 4, 2023 [2 favorites]
In terms of solutions, this is an archaic construction method that would not meet modern codes. Given that, any solution that is not “rebuild the entire wall” will be a bit of a stop gap. The way to think about it is like so: the brick will get wet and hold water; it will then release the water vapor as it dries. You can either stop the water getting into the brick on the outside in the first place, or you can stop the vapor from being able to travel inside past the brick once the brick is wet.
Painting the brick to make it impermeable from the outside is probably easier, but it will (a) require a ton of paint (brick will suck it up quickly) and (b) will require frequent maintenance as the paint will tend to crack and create pathways for moisture. Someone more expert in these coatings than me may be able to recommend something appropriate.
I can’t think of a good way to solve the vapor issue from the interior without rebuilding that wall, but the way a modern brick wall should be built is as follows: brick exterior (“cladding” layer), small air gap so water weeps down, air/water/vapor barrier (like a Tyvek), sheathing (plywood or similar material), then studs, insulation, and interior drywall.
I’d be interested to know how the existing wall is constructed - I’m assuming it’s similar to this? If you open up a couple more bays of studs beyond where your mason did the work is it still exposed brick? If NOT then you’re likely missing sheathing and waterproofing that should be there and the mason just… did really shoddy work. If it looks the same, then you have a bigger problem of a wall that will be prone to damp that is difficult to solve without rebuilding it :(
Please do be aware though that just adding insulation will not solve this. You’ll just get wet insulation, although you’d probably be warmer…
Quick edit: the suggestion above to use a foam fill insulation that can act as a vapor barrier has potential. You’d need to engage a professional to do it and it’s very important the ENTIRE stud cavity is filled completely with a vapor impermeable foam, but that would probably work to solve the issue if the entire wall is constructed like this. To be clear, you’d need to foam the entire wall to effectively stop the water vapor intrusion.
posted by annie o at 3:19 PM on October 4, 2023 [2 favorites]
Further edit to above - I would not recommend trying to insulate with traditional batts and applying an interior vapor barrier (brand name often Visqueen); these types of barriers are notoriously difficult to seal and have been associated with lots of mold problems. Also, water would still get into the batts of a fiberglass insulation in that scenario and grow mold. A closed-call foamed in insulation (like this: https://www.energy.gov/energysaver/types-insulation#sprayedfoam) will make it so water cannot penetrate the insulation layer, limiting potential for mold growth.
posted by annie o at 3:29 PM on October 4, 2023 [1 favorite]
posted by annie o at 3:29 PM on October 4, 2023 [1 favorite]
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posted by Jane the Brown at 9:02 AM on October 4, 2023