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Community and Q&A

Controlling Humidity in unfinished block wall basement by using sealant

Scott Razzino | Posted in Energy Efficiency and Durability on

I have an 1100 sq ft basement in Atlanta GA and I am looking to reduce the need for my current dehumidifier. The house is about 26 years old and it is a two story with front and sides brick. I have a 65 pint dehumidifier unit that I currently empty every day. I wanted to use a product such as “dry loc” on the inside of the block walls in hopes it would reduce the humidity permeating from the block walls. I have routed all the gutters away from the house and sealed all the air leaks in the walls with mortar and concrete sealant. I have even caulked all the seams of the outside south facing wood framed wall. I plan to insulate it. I do have an HVAC unit in the basement but no supply ducts. Will this product do any good for the application? The basement does not have a sump pump. If not what do you suggest short of french drains and a sump pump (Basement Systems recommendation)

Thanks Scott

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  1. Robert Hronek | | #1

    Have you tapped foil to the wall and floor in several places to see if the moisture is coming through the concrete. If the water is trapped between the wall and foil then it is coming through. If there is condensation on the outside of the foil then the moisture is from air leaks.

    This is your first step in determing what to do.

  2. Hunter Dendy | | #2

    Have you talked to the guys at Energy Vanguard there in Atlanta? There could be any number of things going on and a good field inspection by experts will go a long way. Preferably someone who will look at your house-system, instead of just an isolated condition. Unless you have standing water issues, I'm not sure what good a sump pump will do.

  3. Scott | | #3


    No standing water just some spots with white power residue on the blocks. If I do not keep the gutters clean I will see water permeate the block in the front from water runoff.


  4. Riversong | | #4

    If the water is coming through the block walls, then sealing them with two coats of UGL Drylok latex masonry sealer will make a major difference.

    Drylok is vapor semi-impermeable (perm 0.92, a class II vapor retarder) and very water resistant.

  5. Expert Member
    Armando Cobo | | #5

    A 26 year old house in Atlanta, with all of its air leaks, poor insulation and sealing or lack of moisture management during design and construction will always need a dehumidifier even after you install air supplies and a return in the basement, and even after you semi-seal the concrete walls, etc. Concrete block walls in wet and humid climate are a recipe for disaster unless extreme attention to moisture management details are in place.
    Probably the only way to stop all that moisture from coming in the basement is to trench around the foundation, waterproof the walls and install a drainage system; but I’m sure you'll still need some dehumidification in your climate.
    Peter Yost once wrote about his own remodel in his basement with similar conditions... check it out.

  6. James Morgan | | #6

    "A 26 year old house in Atlanta.... will always need a dehumidifier..."
    I suspect Armando is being unduly pessimistic. Here in central NC where we have a broadly similar climate to Atlanta I can attest to plenty of CMU basements which have been totally cured of humidity issues. The key most often is good stormwater management on the outside. This means taking all roofwater leaders at least ten feet from the house in buried non-perforated pipe to discharge to a properly drained swale, it also means adjusting the surface grade to slope away from the house, with special attention to the uphill side if the surrounding grade is not level. We have successfully dealt with many basement water ingress issues with these interventions alone. I have no experience with the Drylok product: I have heard good things about it but I prefer to address the upslope issues first and have always found that to be effective. I do not generally recommend trenching out on the exterior of the foundation wall to install a drain and apply waterproofing. This operation is often performed incompetently with inadequately compacted and graded backfill, even by specialist contractors. The drain performs as intended for ten years or so until it clogs with sediment and then the problems miraculously reappear. By this time the original homeowner has moved on and the 'specialist' happily returns to repeat the same mistakes.

  7. Riversong | | #7

    Though I've never put it to the test, Drylok has been ASTM tested to withstand 22' of water head (10 psf hydrostatic pressure). Outside water sources, obviously, should be addressed first, and all penetrations through the block sealed with hydraulic cement, as well as the wall/floor interface.

    Drylok is the only foundation water-proofer I will use, and it's excellent for a capillary break between footings and foundation wall on new construction. I've used it to seal the interior of site-built CMU composting toilet chambers (over surface-bonding cement) as well as the exterior of exposed chimney block.

  8. Riversong | | #8

    "The drain performs as intended for ten years or so until it clogs with sediment and then the problems miraculously reappear. By this time the original homeowner has moved on and the 'specialist' happily returns to repeat the same mistakes."

    I agree that Armando is being unduly pessimistic about sealing CMU foundations, but aren't you being a bit pessimistic about the value of an exterior perimeter drain and the many fine contractors who do this work? ;-)

    Or are NC contractors still into the moonshine?

  9. James Morgan | | #9

    "aren't you being a bit pessimistic about the value of an exterior perimeter drain and the many fine contractors who do this work?"
    I am. I've seen many fine examples of the genre displaying uncompacted organic backfill and negative surface grade at the foundation wall. In our neck of the woods you can do this kind of work without a permit or a license so it's open season for the cowboys. And it's easy enough to get a glowing recommendation from the homeowner because the problems don't show up for several years.

    By the way, every detail I've seen for the approved position of a foundation drain shows it alongside the base of the footing. Every single installation I've ever seen however has the drain on top of the footing alongside the base of the foundation wall, laid to falls so mostly slightly above that critical junction of foundation wall and slab. This would not seem to matter too much unless it was actually expected to function as intended, i.e. as a drain rather than just to relieve hydrostatic pressure. Any comments?

  10. Robert Hronek | | #10


    I think you need to define your problem. Is that correct that it is 65 pints/8 gallons of water that you are dumping every day.

    I would advise you to look at the sill plate. Does it cover the openings in the CMU blocks. Check by reaching up and feeling for the openings. If the top plate does not cover the opening then sealing the block will not do. If you think about it the inside of the block is hollow, except at the webbing there is no direct path from outside to inside. Since there is a open cavity the moisture can evaporate to the air in the block and through convection loops be carried in to the basement air.

    I would think that if you are emptying 8 gallons a day and its coming through the block then the ground must be saturated. If it is the case I would start looking for the reason why.

    What is the landscaping like. Do you have bushes, wood mulch or rock next to the foundation? Have any shrubs or trees been removed from near the foundation? Is there a porch or patio that allows water to go down near the foundation? Are you near a bottom of a hill or do other properties slope toward yours?

    To me proper drainage keeps the pressure off the foundation as well water out of the basement. I think many times we symptom and not the cause. Although you may be able to keep the moisture out of the basement with drylock you may miss a bigger concern. Wet soil both pushes in on the foundation wall and does not provide adequate support to footings. I have been in many homes where the owner has tried to seal the block but in the long run ended up with bigger problems - foundation walls that need straightening and footings that have sunk.

  11. Riversong | | #11


    Just because there are some foundation drainage contractors who do a sub-standard job is no reason to avoid installing what every foundation should have: a perimeter drain. Just because there are carpenters and builders who build substandard houses is no reason to give up on having a house built.

    In my area, it's excavation contractors who perform sub-grade drainage work and every one of them knows the proper way to do this.

    The purpose of a footing drain is to remove ground-water or relieve a rising water table. Surface water is dealt with by gutters and downspouts and grading. With gravel backfill as a capillary break and drainage medium to relieve hydrostatic pressure and move sub-surface water to the footing drain, and a perforated drain pipe protected by filter fabric and brought either to daylight or a sump pump, such a system should not fail. And, while it's better to install the drain tile next to the footing, as long as the wier of the pipe (hole or water level) is below the top of the slab (which is often on top of the footings), the wall/footing junction is sealed with hydraulic cement, and the foundation wall waterproofed, this should work as intended.

    It's not necessary to dig down to the bottom of the footings and risk undermining them.

  12. James Morgan | | #12

    "Just because there are some foundation drainage contractors who do a sub-standard job is no reason to avoid installing what every foundation should have: a perimeter drain." Robert, I am in total agreement. All new houses should have foundation drains and the excavation contractors we work with are extremely capable and competent at this work. My comments were not concerned with new construction but with the many inept attempts at invasive, expensive and often counterproductive remedial and retrofit treatments I have witnessed for below-grade water problems which are not caused by groundwater or a rising water table but by a lack of simple surface-water management. On a consult which includes a damp basement or crawl space I am often told by the homeowner that they do not understand why there is a problem because a previous owner had a foundation drain installed. We then walk around the uphill side of the house to where the backfill dirt has subsided into a shallow depression right next to the house, which in wet weather forms a handy-dandy reservoir to feed the saturated soil below. This situation is common in our local soil conditions and topography: I would not presume to extend this analysis to all subgrade geologies but I wondered if this could be a factor in Scott's situation. Robert Hronek makes a similar point.

  13. James Morgan | | #13

    "It's not necessary to dig down to the bottom of the footings and risk undermining them." I agree, so why is it almost invariably shown this way in drawn details? Why have I had drawings rejected at plan review for showing the drain on top of the footing but the field inspector never has a problem?

  14. Riversong | | #14


    For new construction, where the site is excavated to bottom of footing level, the perimeter drains absolutely should be below the top of footing, bedded in 4-6" of washed stone, surrounded by an additional 6" of washed stone, all of it wrapped in a burrito of HD landscape fabric. And it should be rigid PVC or HDPE perforated pipe (not the flexible pipe which won't lie flat), laid level and with the outlet sloped at ¼" per foot to daylight or sump.

    This website ( - scroll down) depicts alternative pipe locations relative to footings. They show flexible pipe laid on top of footing to keep it level to avoid siltation and flow restriction.

    But this site ( depicts the ideal location for a footing drain.

    But for retrofits, it may be fine to excavate only to top of footing (if the slab is on top of the footing) and lay the drain pipe there, as long as the waterproofing steps I delineated are performed.

  15. James Morgan | | #15

    Robert, I'm well aware of the typical detail in your link. I can only tell you from extensive personal observation that your 'should absolutely' location is simply not observed hereabouts. I have never seen any problems arise from this, nor have I seen problems with older homes in which which foundation drains have been completely absent, except those arising from poor surface water management. As I have great respect for your knowledge and experience as well as for the builders I regularly work with I can only suppose that something about our heavy clay soils, our subsurface geology or our climate that protects us from the problems this detail is designed to prevent. In nearly two decades of designing both new construction and renovations here in central NC I can recall only a single wet basement problem, in a 1960's split-level, that was not fixed by attention to egregious surface water issues. Just sayin'.

  16. Riversong | | #16

    Well there's an old New England saying that building a full basement is like building a swimming pool and trying to keep the water out.

  17. James Morgan | | #17

    Good one. I've also heard it said that either your basement leaks or your house floats.

    It occurs to me that's another major difference in regional practice - you almost never see anything but a walkout basement here, so more of a headwall than a swimming pool (or a boat). That cuts us some major slack on water management issues, gives us fewer excuses for poor performance too.

  18. Scott | | #18

    Mr. Hronek,

    I checked the sill plate and it fully covers the open section of the block but there is no caulk between it and the block. I also see some likely air leakage from the canterlevel floor of my bay window in the room above. Any suggestion for sealing the inside extension of the bay window without fully sprayfoaming it? I currently have just batt insulation tucked under there. There is airflow I observed strands of fiberglass movement. The outside of the baywindow is sprayfoamed and metal flashed. The outside ground contour slopes from the left side of the house to the right which is a low point. I do have a front stoop which pockets water on its left wall side. The 8 gallons of water is during dry periods. We had little rain until this week. Any suggestion on the bay window air leakage would help.

  19. Robert Hronek | | #19

    IF you can spray foam the inside of the exterior surfaces of the bay window, then fill with fiberglass and cap the interior end of the fiberglass. The entire sill plate and rim joist (not just the bay window)should be foamed or otherwise sealed and insulated.

    Did you check to see if you are getting moisture through the block by taping foil or Saran Wrap to it? The Drylok may help you but look for why the ground is so wet and how you can dry it out. Think of it this way when you walk on soggy ground is squishes nder your foot. Think of what happens if there is squishy ground under the footins.

    Also block wall can hold the downward pressure of the house but it can not hold the inward pressure cause by wet soil.

    You may stop the leak into the house but over time foundation problems may be you main concern.

    Like many issues you need to look at the big pictures. Some of the of the other posters have made good suggestions about site drainage, etc. You should consider that if it applies.

    I will say that when you call a company they send out a salesman. His job is to sell you there services and products. It is the consumers responsibilty to search out all options and decide what is in thier best interest.

  20. Cynthia Freeney | | #20

    It will all really depend on how often you will want to go over the same job, to fix the same problem.

    Basements get wet because the soil around the foundation gets over saturated with water and the resulting pressure pushes water against the wall. Concrete is porous, water gets in. So the only way to really keep a dry basement is to keep that soil as dry as possible with proper foundation drainage.

    If you use a sealant, like the one named in some of the replies, keep in mind that you are not doing anything to fix the drainage problem. You are only trapping the water behind it. Give it enough time and pressure, the sealant will peel off or the water will find another way in.

    But don't take my word for it, just look at the warranties and when they expire. Usually 10 years. That is, hopefully, how long it is going to take before you have to strip down your basement and re-apply the coating.

    In addition, the U.S. Department of Energy, in its "Building America" Best Practices series, recommends that no vapor barrier of any sort be applied to basement surfaces. According to them, the moisture that seeps through concrete, should be allowed to dry into the inside of the basement. This is the link to the pdf brochure on basement insulation talking about moisture control.

    Apparently you also took all the necessary steps to keep the soil dry from the outside: working gutters and extended downspouts and I am assuming your land is properly graded, sloping away from the house.
    That said, there are two ways to provide adequate drainage:

    1 - The "French drain", "weeping tile", or drain tile buried by the footing.

    The problem with typical French drains is that they are known to fail overtime, no matter how well installed they were. They clog, collapse, crack, and because they are buried so deep in the ground they are very hard or, in many cases, impossible to service unless you dig out the foundations. So, you can have one installed but there is no saying how long it will work. Actually, chances are that you already have one installed, but clearly not working as intended. Since there is no sump pump there is probably no way to tell where it is discharging the collected water.

    2 - Internal perimeter drainage systems tied to a sump pump, which is what Basement Systems actually does, rather than conventional French drains. These systems, installed along the interior perimeter of the basement walls, were developed as an alternative to conventional French drains and they do the exact same thing: intercept and collect ground water. And then, divert it to a sump pump. They have however, the advantage of remaining serviceable for the life of the structure, which is why these systems carry a Lifetime Transferrable Warranty, that will cover you, and the next owners should you ever sell the property.

    But the bottom line here is that, if you have a basement, and you plan to use it in any way, a good sump pump system is a must, no matter what kind of drainage you have in place. Consider that basements get water from more than just the ground. There are plumbing leaks, broken water heaters, backed up drains, running faucets.

    Simply put, it is the sump pump now, or a shop-vac later, and some expensive cleanup.

    As for the relative humidity in the basement, even after installing proper drainage, you might still have some moisture problems, because of the area you live. Mainly during summer, as differences in temperature between basement and surroundings may cause RH levels to rise. You should monitor the RH levels closely and run a dehumidifier every time you see them rise above 60%, to prevent mold growth.

    I would also strongly recommend that you consider upgrading your dehumidifier to an Energy-Star rated, self-emptying model that draws much more water than the model you currently have for a fraction of the cost.

    The problem with dehumidifiers that need to be emptied is that, when the tray is full and until you get around to empty it, they are still running and costing you money, but they are not drawing any moisture from the air.

  21. Riversong | | #21


    Are you on the payroll for Basement Systems, since you seem to be a flak for their band-aid approach? And, if so, why didn't you reveal that?

    Every legitimate designer and builder knows that intercepting ground water outside the foundation is far preferable to intercepting it after it gets in. A properly installed perimeter drain should last the life of a house and a site that allows daylighting of the perimeter drain does not require a sump pump, which is just another technology prone to failure (and always fails when the power goes down, often during a severe rain event).

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