older walls built out of concrete masonry units sometimes called concrete block or cinder block can be deceptively challenging to insulate properly the concept behind these concrete masonry units is that they're lighter weight they can be grouted or filled with concrete at the location of reinforcing bars without having to fill the entire block wall while this provided some economical benefits the ungrounded cells have the potential to accumulate water if the block wall is exposed and unprotected in uninsulated concrete block walls this isn't a big issue since that water can dry out easily either to the interior or to the exterior however insulating a concrete block wall on the interior can pose a bunch of potential moisture problems as insulation slows the flow of heat and reduces the drawing potential of the assembly keeping the wall assembly wetter for longer in this video we're discussing strategies that you can use to insulate your old concrete block walls from the interior the right way while keeping them dry and durable let's get into it so the first strategy that we can use to avoid moisture problems in a concrete block wall is to install a taped dimple m right up on the interior side of the block wall and what this does is that it provides a drainage space and a capillary break between the damp concrete block and the framed interior so any water that's driven inside through cracks in the block or mortar is just drained down the drainage space keeping this framed cavity nice and dry and preventing any moisture from being distributed to the interior it also allows us to insulate the interior space with whatever insulation strategy that we want here in this detail we have taped extruded polystyrene which is specified here to prevent condensation on the back side of of The dimple mat if you're located in a warm climate you don't necessarily need this but this XPS provides a nice thermal break and it prevents air leakage and Vapor diffusion that could deposit moisture on the back side of the dimple mat in colder and more temperate climates then we're able to install our framed wall which we can insulate with any air and Vapor permeable insulation of our choosing my preference is mineral wool but you could use fiberglass wood fiber or cellulose but the point is we want to make sure that the stud cavities can dry out freely to the interior we don't want to trap moisture in the cavity now the SLE mat strategy is the gold standard if we're insulating from the interior we want to uncouple the wet concrete block walls from the wood framed insulated interior this is really important to preventing mold and rot in the wall cavity especially with the addition of insulation now if we're unable to install a dimple mat on the interior side of the block wall we need to limit the amount of moisture being absorbed into the surface of that CMU wall so what we're calling out in this detail is a stucco rendering or a parge coat with an exterior grade mineral silicate paint and what this does is that the stucco or the parging helps to fill in any cracks or gaps in the block wall and it provides a smoother more uniform surface so that water can drain down the wall more easily without being absorbed and collected at the bottom of the CMU cells the surface of that concrete block tends to be highly porous especially if it's split-faced where it has an extremely rough and uneven surface and so we want to make sure that we're addressing this then the mineral silicate paint acts as a vapor permeable hydrophobic or water repellent surface that chemically bonds to the stucco or the parge coat so it's not going to Bubble or blister off like some other paints which simply form form a coating and it's going to provide some Superior durability to that final finish since mineral silicate paints don't really Fade Out its Vapor permeable quality is also allow the walls to dry out if they get wet so this mineral silicate paint is a really important consideration from both a functional and aesthetic perspective so the whole goal of this strategy is to reduce the amount of water being absorbed into these walls to be distributed inwards because if we can't rely on a diplomat to provide a capillary brake to prevent hydrostatic pressure from driving water inside we need some way to manage that water we're reducing absorption and we're providing a water repellent surface with that mineral silicate paint then on the interior side of the CMU wall we have a fluid applied negative side waterproofing which gets applied directly to the block wall and this serves as our final barrier against water getting inside if you're controlling bulk water on the exterior a negative side waterproofing like this can work in above grade walls to prevent water from finding a path inside this fluid applied waterproofing system also provides the benefits of an air barrier so it fills in all the cracks and gaps it's coating that entire surface on the interor side and it's that final line of defense so any water that happens to get inside will hit that waterproofing and make its way to the bottom of the wall and we'll talk about what we're doing at the bottom of the wall to address water in a second here but that water isn't ending up in the framed wall cavity that's the whole point then we're insulating with that same strategy using the taped XPS to prevent air leakage and condensation on the block walls since we don't have the dimple mat layer here so we don't want any condensation forming on the inside of the wall and then we have a 2x4 insulated framed wall and then the gypson board is installed right over it we want the cavity insulation to also be air and Vapor permeable so that moisture can dry out of the wall assembly to the interior we don't want any vinyl faced or foil-faced insulation the taped rigid insulation serves as our air and Vapor impermeable layer everything inwards of those insulation boards needs to be permeable now as I mentioned earlier we need to address water that accumulates at the base of the wall and so we need to install a drainage mat or a dimple matat at the base of the wall to uncouple the CMU from the slab at this location so any water that leaks inside through through the cells or through cracks or from groundwater rise it's going to be uncoupled from the slab and the framed wall assembly and it's going to drain to a new interior perimeter drainage tile that's discharged to a sump pump or directed to Daylight because technically this would be above grade and that drainage mat is serving as an uncoupling layer it's a capillary brake and it provides drainage so that any water that makes its way inside just drains to the drainage tile now we do need to excavate part of the slab in order to install the drainage mat and the perimeter drainage tile so after the concrete has been cut and removed at this location we install the new drainage tile in a crushed stone bed that's been wrapped in Filter Fabric and then we can install the small strip of drainage mat or dimple mat at the bottom ensuring that it extends over the drainage tile and then we patch the concrete at this location after everything is in place the framed wall assembly is bearing on a seill gasket which is acting as a capillary breake because remember this concrete patch is coupled to the existing concrete slab so moisture can still technically Wick in there's no Vapor Barrier underneath and we don't want to take any chances so we want to uncouple the framing from the concrete with the doesn't require any cutting or excavation of the concrete except for maybe a sump pit if you choose that option making it suitable for these types of structural monolithic slabs so we seal the joint between the baseboard drainage Channel and the slab with an epoxy sealant or another waterproof sealant that's compatible with concrete it can also be beneficial to tape this joint with flashing tape if we're expecting a lot of water leaking through these block walls as sort of a belt and suspenders approach now we're not done just yet water can still Wick through the slab and be distributed to our interior flooring and finishes so we want to uncouple The Damp slab from the finished floor with a taped dimple mat to provide a capillary breake and a vapor barrier and prevent any water that potentially leaks through the flush Port from flooding or seeping into the interior space this way if the sealant at the flush Port leaks the water stays in the wet slab it doesn't get distributed inwards because the finished floor is raised above the slab I have a whole video on why this strategy Works in damp slabs which you can go and watch right here if you're looking for a complete guide on how to remodel your old home properly get my moisture management guides residential remodels where we discuss how to control moisture and safely insulate a wide range of existing building conditions that's only available at A-D designs.com shop links will be in the description below we've also got over 150 free building science articles many of which cover topics that we discussed in this video except at even greater depth make sure to give this video a like if you haven't already and subscribe for more weekly building science content for now good luck with your projects [Music] cheers [Music]