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Community and Q&A

Rigid foam on basement floor and support posts

reimhagen | Posted in General Questions on

What is the recommended way to deal with support posts when following the recommendation to cover a basement floor completely with rigid foam?  I have several 6×6 pressure-treated posts supporting the central beam of my house that make contact with the concrete slab.  Do I cut the foam around it and th en seal it with caulk/canned foam?  Are there concerns of moisture being sealed in in that case?

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  1. onslow | | #1


    I am surprised that the posts would be in direct contact with the floor slab. There should be steel standoff bracket much like you would see in deck construction. Are there footing pads under these posts? Is the slab cast over the footing pads and around the post bottoms?

    How the water management has been done under the slab will play a large part in what to do next. Before doing anything with foam over the main floor area, I would do the plastic and bucket test to see how much moisture drive you have in the slab.

    Take a square of clear poly sheet and place it on the floor cleaned of all bits. Place a plastic bucket upside down on the square of plastic and weight the bottom to ensure the bucket lip is sealing the plastic to the slab. Wait at least 3 days, preferably a week. Remove the bucket and observe how much moisture is trapped under the plastic sheet. Check back in after this and more GBA people can help. I will keep an eye out as well.

    You do not want to be trapping a lot of moisture under the foam, which I assume you intend to cover with subflooring toward the goal of making the space livable. Even if the floor test is good, I would not seal up the post sides given their unknown status re the slab. Pressure treating does not make them waterproof, only rot resistant. Soggy post bottoms are not a good thing.

    1. reimhagen | | #3

      Thanks. I set up the plastic sheet today, will report back in a few days.

      I've added a photo of the post detail. There doesn't seem to be a steel bracket, although the concrete has been built up underneath the post so that the post connects to concrete about 2" higher than the surrounding slab.

      1. Patrick_OSullivan | | #4

        I think that the concrete being built up under the post helps you. How much foam are you putting down? I suspect the concrete/post intersection will still be above foam, won't it? I would live with that little bit of concrete that's proud of the foam not being covered and move on.

        This is one of those things where there are numerous straightforward ways to reduce the risk of this becoming a problem in the future (e.g. replace the wooden post with a steel post right now), but where the expected value (in a probability sense) of that improvement is perhaps low. If, in 10 years, you realize the bottom of the post is rotting, so what? You replace it then and are thankful you didn't spend the money 10 years earlier. Of course, this is presupposing you're not covering everything up entirely and then having to dismantle it for a future repair.

      2. Expert Member
        BILL WICHERS | | #5

        I agree with Patrick that the raised concrete under the post is a good thing here. You really want a capillary break between the end of the post and the concrete though, and there doesn’t appear to be one from what I can see in your pics. The rigid foam makes the need for a capillary brake more important, so I’d try to add one as part of your project.

        Are those tack strips around that post? Carpet on basement slabs is bad news. You’ll be much happier with your new insulated floor!


        1. reimhagen | | #6

          Yeah, I'm demolishing the old slipshod finish work. He had adhered thinset/tile directly to the slab, as well as carpet. The carpet smells very musty, but we had a couple water leaks in the past year as well that contributed to that (not water from outside, but a leaky water pipe in the ceiling). Can't wait to get a better floor that's not moldy/freezing all the time :).

  2. Expert Member
    BILL WICHERS | | #2

    If you need some drying around that post, leaving the rigid foam an inch or two out from the beam all the way around and filling the gap with mineral wool would probably work. This isn’t ideal though, you really want the beam on top of a bracket like roger mentioned, and only the bracket penetrates the rigid foam — the wood column would end ABOVE the rigid foam where it rests on the bracket.


  3. reimhagen | | #7

    As for the floor assembly itself, I'm considering 1-1/2" XPS. I know it's not exactly an environmentally friendly option, but I appreciate its greater compressive strength (looking at the 25psi option). Instead of two layers of 1/2" plywood, will 3/4" T&G plywood suffice in this application? With the tongue and groove I don't think leaving a 1/8" gap will be possible, unless I don't interlock them. Will I need to do anything special where the laundry machines, water heater, and bathtub go? Also, I saw that polyiso doesn't perform well in cold conditions. I'm in the Seattle area; should I stick with EPS/XPS for the walls, or will polyiso work where I am?

    1. JRoyal | | #8


      The question of two 1/2" layers vs one 3/4" T&G is an often asked question, by myself recently for example. From the answers I got, there doesn't seem to be a right answer, and depends somewhat on what your finished floor will be. If it is any help, I am proceeding with a single layer of 3/4" T&G OSB over 1" of 25 psi XPS in Climate Zone 3A. The anchoring of the subfloor to the concrete absolutely sucks, but it does provide a satisfyingly solid floor.

      I'm not sure I understand your statement about not leaving a 1/8" gap. The gap is at the butt ends of the plywood/OSB panel, and is required for expansion and contraction. The tongue and groove side self gaps, so there is no need to do anything special there.


      1. reimhagen | | #9

        Thanks for the info. As for the gaps I was referring to the original guidance in the "no mold stay dry finsihed basement" article that's linked often on these forums. The author of that article set down the plywood (non-t&g) and left gaps between them. I just wanted to verify I wouldn't need to do that with the T&G.

        One more thought -- I really have no reference or idea as to how R-7.5 will "feel" underfoot. Right now my basement floor is constantly freezing (the tile is adhered directly to the slab, and the carpet was as well). What sort of comfort difference should I expect with R-5 or R-87.5? Is losing the additional 1/2" to get 2.5 more R value worth it?

  4. onslow | | #10


    If you can spare the 1/2" of head room loss, go for the nominal 7.5 and keep your flooring and plywood that much further from dew point danger. The feel under your feet will be more related to the flooring choices. If you choose ceramic tile it will always feel cold as the conduction rate of tile is very high. That cold feeling can only be overcome by having the tile at least 80+F. (This is a constant issue in radiant floor discussions) Cork floors are quick to feel warmish under foot since it is essentially an insulator. Carpet generally will feel "warm" though the style of the yarn will make a difference as to how warm.

    For walls, there is no reason not to use polyiso over eps or (recycled) xps. You will be starting above the danger point of the bottom edge getting wet, if the T&G foam floor goes all the way to the foundation. Setting the wall base plate to the floor deck will be fine as long as you are tagging the plywood down to the cement slab. I will not say anything openly libelous about Tapcon screws beyond I recommend other choices. I am not alone in this opinion and yet I have many leftover Tapcons from my basement ventures. Slow learner, I guess.

    I will assume you completed the moisture load test on the floor. A similar test can be done on walls by simply taping a plastic film square to the wall and waiting. I personally would UGL or Thoroseal on a cement or block wall before putting foam over it. Cement walls will transpire moisture pretty much no matter what. If the outside of the wall is prone to ground water, even if not constantly, the chance of a moisty condition building up behind the wall is there. Taping and sealing the foam from the basement side will go a long way toward heading off the room humidity from getting behind the insulation, but that is a separate concern. You want the wall to be once and done.

    You spoke of laundry, water heater and a bathtub being down in your new area. If you are certain of the location, I would insert some blocks under the T&G. Yes the load per sq. inch is small despite a full water heater weighing over 500lbs or more if an 80 gallon, but time and all that. It won't affect the R value much and belt and suspenders can be a good thing. I am bit puzzled about the bathtub. How are your going to drain it? Same for laundry. Are you sure about the hook ups? Do you have plans for overflow pans on the laundry and water heater. Be a bummer to have water get under the new floor. It will be a very long time drying.

    1. reimhagen | | #11

      Thanks for the informative reply.

      Flooring type -- I'm considering doing engineered wood for the common areas, tile for the bathroom, and wall-to-wall carpet for the room that may be a bedroom. I'm aware of the risk that carpet poses should any dampness ever enter. I'll be using a lower-priced carpet with the awareness that replacement will need to occur if/when the water event happens. For the tile I will likely use some sort of heating system like schluter ditra-heat or something similar. The engineered wood I would like to nail down, so that precludes the use of most heating systems. It was this that I was concerned would feel "cold". If it will be similar to the feel of the hardwood floors on my main level (above the basement), then I'm fine with that. But I understand that's unlikely to be the case as the main level is over a heated basement.

      Walls -- the article shows the foam going from foundation wall to foundation wall, but the plywood only spans from the foam against the foundation wall to the foam against the foundation wall. The wall foam makes direct contact with the floor foam, and the seam is caulked/sealed with can foam. In this assembly, should I use the same foam type for both floor and wall?

      Floor -- I did the plastic sheet test. It's been four days so far and there is no visible moisture accumulation on the plastic sheet yet. I still have it set up, but I am doubtful any will show up in a couple more days. Can i consider my slab to be somewhat dry if this is the case? For attaching the plywood, what do you recommend in the place of tapcon screws?

      Laundry/etc. -- the existing basement already has a bathtub, as well as the laundry. Currently there's no floor drains in the laundry area, however. It may be a good idea for me to plan to get one put in, as a washer pan without a drain sounds somewhat useless.

  5. Expert Member
    BILL WICHERS | | #12

    I would reconsider your choice of carpet in that one room. Use the same hard floor in there and a big area rug or carpet remnant. Much easier to change that out if you have to.

    r7.5 will be a huge difference over your current non-insulated floor. While the floor still won’t feel warm, it will no longer seem like it’s sucking the warmth out of you. That’s a plus :-)

    I’ve never understood all the anti-tapcon sentiment. I’ve installed thousands of them and rarely have a problem. Don’t drive them with impact drivers, and don’t drive them at high speed with your drill — use the low setting. If they seem to crunch the concrete going in, drive them by hand. It’s very important that the holes be straight and even, especially with the smaller size tapcons. Use a proper hammer drill and a GOOD masonry bit. I use my SDS plus drill and bits for this. Using tapcons bigger than you actually need helps give you more margin in terms of tolerance to holes that aren’t perfect too since the larger anchors seem to be more forgiving in this regard. The biggest issues I see with these anchors stripping out is holes that aren’t drilled well (usually from not keeping the drill straight as you’re drilling), or trying to drive the anchor in under power too fast. If the hole is drilled too big, the anchor can’t bite in and hold. Concrete isn’t springy like wood so it’s not forgiving. If you drive the anchor in too quickly, it tends to crumble up the concrete and strip out. Once you get the feel for these they work pretty well.


    1. Expert Member
      MALCOLM TAYLOR | | #14


      I find Tapcons are just too slow. They work alright - although not as well as the GRK Caliburns - but the time it takes to use either is out of step with that of other building tasks.

  6. onslow | | #13


    Lots to cover. Most important before you get too far, what sort of drain situation do you have in the basement? Can you verify all pipes? The wood posts tend to mean older construction, but that may only be my bias. Our 80 yr old second home had mixed wood and steel posts that were set on concrete blocks. They looked alarmingly like yours. The floor was just dirt from about 1934 to 1954. The second owner hand poured (badly) parts of the slab before getting someone to help do the rest better.

    The wood post actually was damp at the bottom for most of the thirty years we lived there while I cobbled the house into survival mode. Oddly the steel post was the sketchier of the two as it had rust blisters that were kind of scary. The floor drain just went into a stone filled pocket under the slab so we never pushed our luck. The septic was clay tile and fortunately the city forced hookups before we bought so we didn't have a tank to deal with. And they put in ductile iron the whole way from the house.

    We were not so fortunate in our first home. The floor drain was tied to the perimeter foundation drain and all were tied to the city sewer. During one major storm cycle the entire city system stack loaded so severely that the water backed up our line into the basement until it was over 2 feet deep. Despite the main sewer line being at least 8 feet lower than our basement slab, our elevation relative to most of the surrounding homes was 20-30 feet lower. Lots of homes in our area got the same surprise. Eventually the town forced all homes to sever the foundation drains from the sewer lines. A cautionary tale to suggest some research into where the poo goes in your neighborhood.

    If you don't have hook ups for the laundry, laundry catch pan, heater catch pan and the bathtub, do you have a clear plan (and a permit)? Overhead injector pumps are not too onerous to install and may be something you will need. All that said it appears that you do not have a soggy slab, so one point for Gryphendoor.

    It is good to have a dryish slab since you have already put the wall foam up. If it is polyiso there should be little cause for worry. It will wick bulk water, it will not likely suck up any more damp than other foams. I would advise against it on the floor simply because being trapped under the plywood will set up different long term moisture conditions. Plus I have always used XPS. Karma will get me yet.

    The fastener situation is a tough one. GRK makes concrete screws. Tapcon makes many concrete screws. The bits in the box of screws are crap. The type of aggregate can make your holes nice and easy or a fight to the death. Trying to set holes accurately to hang steel supports on a wall is the bane of my existence. I do have impact drivers, hammer drills, high torque low speed drills, and ratchet wrenches and bit braces. Sadly, I can't offer a known substitute that I have enough experience with. I have actually returned to lead anchors for walls and other types that expand in the holes. Neither will be practical for tagging down your floor.

    Maybe you will be like Zephyr and breeze through the whole job with every screw setting perfectly. If you do, then good show. I would at least plan on a few extra holes being needed. Maybe rent the SDS type drill, they do hold the bits better than the amateur hammer drills. Don't forget to counter sink the plywood before setting the screws. You will find forcing them into plywood risky in my experience.

    Now that that is out in the open, have you considered floating floor choices for the areas where you are planning on wood. I agree with Zephyr that carpet is inherently dicey below the first floor level. Spilled Kool aid and such tends to weld the backing and padding to the plywood and over time pets will often become the dominant flavor. But those are my problems, your mileage may vary.

    One advantage to floating floors is not having to nail down the material. The snap together types are getting pretty good and the synthetic ones set pretty tightly. I did a rental kitchen which survives splashes and spills pretty well so far. The feel under foot is not much different from the pre-finished woods with the aluminum oxide finishes in my opinion. Not as classy, but that is another issue. Some like Pergo come with a foam backing that helps reduce the clacking sound. Others offer thin foam to put down first.

    An if you go with heat under the tile, be sure to install at least one extra sensor if not two. If one fails, just swap the wires for the next one. You will be glad you did.

    1. reimhagen | | #15

      Hi Roger,

      Again, thanks for the helpful reply.

      The basement slab was originally built with a roughed-in 3/4 bath. Thus, there is some in-slab drain pipes. My house is on a septic system. In addition to this, the previous owner put a perforated-pipe drain system around the perimeter of the foundation that empties into an outdoor sump pit with a pump.

      I already have hookups for the laundry. However, I don't have a plan yet for the drain pans. I'll have to research more about how they're hooked up to a drain. I do have an overall plan for my entire house that's going through the permitting process right now. The water heater will definitely need a drain as I've put in one of the heat pump based ones that continuously emit condensate that I'm currently manageing manually with a 5 gallon bucket.

      All I've done so far is demolition. The walls are bare concrete right now. I did do some research into both the UGL DryLok product as well as Thoroseal. They seem to be very different formulations (Drylok goes on like paint, but Thoroseal is a cement-like product?). The article I read previously had the floor foam go from basement wall to basement wall, but the plywood over top that would span from the wall foam to wall foam (i.e. the wall foam makes contact with the floor foam and the seam sealed). I assume you would recommend me go with covering all the walls with one of the two?

      I've read good things about GRK screws. I'll take a look at them as well. With 1.5" foam + 3/4" plywood, I imagine I'll need quite a long screw (at least 3"). I have a rotary hammer with SDS bits, so I hope drilling the holes will be somewhat easier than your experience.

      I did consider floating floors, as the under-hardwood heating options all generally prefer floating. However, I really detest the hollow/soft/clacking feeling underfoot that floating floors that I've seen generally are like, even with a underlayment. I would prefer the very solid feeling of a glue-down or staple-down floor if given the choice.


  7. onslow | | #16


    Well at least a septic tank will pretty much save you from enjoying what the neighbors might send you. Grossness aside, it would seem that you have less reason to be presented with plumbing surprises. I would have to guess that the tank and field location puts the main line from house to tank below the footing, by which I would infer a sloping lot. If the line to the tank is mid height in the wall, I would have to question where the 3/4 bath waste lines are being directed.

    If you have an access port to the field distribution pipes header box, it might be a good time to verify the system connection to the basement waste lines. Just look in the header box while someone in the house slowly empties a 5 gal pail of water down one of the 3/4 bath lines. In a few minutes you should see a trickle of water arrive at the box. If not, better do the same check while watching or listening at the outside sump pit. Pray that you don't get water there.

    I am a bit surprised at the outside sump. You have commented on the slab being very cold and I assumed you were in an area with temps falling to at least 32F. Does the sump risk freezing? Also, where does the discharge go relative to the septic field? It would be unwise to burden the field with additional water if the sump discharge crosses that area. It would be long term concern not immediate.

    The UGL product has been around somewhat longer than I have. The version I knew back before the summer of love days may not be the same as now, but it certainly has a track record. There is an extreme version now with higher hydrostatic resistance. The Thoroseal I used about 35 years back was harder to find and more costly, but could be used to seal concrete water tanks. The very poor condition block basement I was attempting to get dry made the Thoroseal a better choice. The block surface was very nubbly, so the more paint like UGL missed all the little pits without great fussing and tedious attention. The Thoroseal was more like a brushable cement parge coat. The dry powder required careful mixing for consistency, but the Thoroseal did block the CMUs tightly. Wicked heavy brush loads, but I was younger then. For a relatively smooth cast wall, the UGL might be a good match. Plus it is pre-mixed.

    The foam placement comments were based on thinking you had already mounted the polyiso sheets. If the basement slab is pretty dry then the potential for wicking into the foam would be low. If you have the option to use EPS or reclaimed XPS on the floor, it would be best to set the wall foam down onto the floor foam as described, then do the walls and then deck the floor foam with the plywood. Pretty much what you described.

    You can go with EPS on the walls. Polyiso will give you a little bit more R value and the foil faced type is easier to tape. Some EPS brands are foil faced as well. When building the wall framing, it is fine to set the base plate on the 3/4 ply, the walls are not bearing. It would be silly and unnecessary to interrupt the foam to set them down on the slab. Plus you would lose the backing you need for paneling and base trim. Though a double height base plate is a work around if you must set to the slab for some reason. That doesn't seem to be the description you cited, just be wary of inspectors demands. Don't forget to insulate the rim pockets.

    My angst with the blue nightmares is largely born of my mainly using them for setting steel supports and other fixed hole choices. While oversizing the bracket holes can allow for some adjustment play and new holes can be made, the clock is always ticking and a botched hole costs me. So do snapped off heads and shredded holes, etc. With the floor, you will be relieved of precise placement, so one or two failures won't set you back. As others have noted, being perpendicular is key and I find counter sinking the plywood safer when snugging down the screws. Do drill deeper and blow the holes (with a vac hose next to the hole).

    I hear you on the floating floors. I own a tap dancing dog you can follow by ear wherever she goes in the house. However, the last dog ruined the lovely oak floors so Pergo was my fate. If you are drywalling the ceiling, do a joist check for planar consistency. If you are going with suspended (for pipe and wire access) mind the hang depth so you can get the panels in and out.

    1. reimhagen | | #17

      Hi Roger,

      So, I went and got the UGL DryLok stuff. Out of curiosity, how did you pretreat your walls to remove efflorescence? Seems like the most effective way to remove it is using muriatic acid, but doing that indoors in the basement seems like a foolish thing to do, due to the very harsh fumes in my home, and then having to hose down the walls and floor with (lots of) water. Part of my basement is not demo'ed yet, so I don't see a way of hosing everything down without resulting in a big sopping mess. UGL's seems safer, but it has mixed reviews as to its effectiveness, and it still requires a water rinse.

      Could I possible just use an angle grinder with masonry wheels and grind off the effloresced areas? There's not too much of it...

      By the way, did you drylok the floor as well?

  8. onslow | | #18

    Hi reimhagen,

    I just spot scrubbed the efflorescence with muriatic acid and a stiff wire brush followed with a sponge bath of baking soda in water to speed the neutralization. I have since learned this is not what to do. It was 35 years ago, and that was what I got told to do by the old timers. That statement of course puts me and my advice in a very shaky light now that I think about it ;).

    There are less hazardous methods now with safer chemistry. I have not tried any of the new ones since my basement is now dry as a bone. Eco-Etch Pro might be a good bet, and Miracle Sealants Heavy Duty Cleaner might be valuable if it really does get all manner of goo off of concrete. You will have to be the guinea pig on this task I guess. The sell points on the EcoEtch sound credible. I do know that most other choices like vinegar and coffee pot cleaner (phosphoric acid) are weak tea for concrete. TSP and good wash can also be helpful. It can be quite amazing how much film of dirt can collect on a vertical surface.

    If the walls are slightly shiny you may be facing form release agents. Sadly, some contractors use diesel fuel as a down and dirty release agent. If spritzing some water on the wall creates standing beaded dots, follow up with TSP and a sponge to see if the wall is just dirty or has oil film on it. The Eco Etch or similar might be a wise choice at that point. No sense going to all the work and not have the UGL stick well.

    The wall efflorescence fuzz is salts of various types making crystal farms. If the wall is not actively wet then you might wire brush them off (dry) and just kiss the surface with the grinder. Spot coat with the UGL and after the spots dry, just go ahead with the rest after checking for dirt and oils. Just for the record, I used the Thoroseal due to the block being so porous. My floor was a nightmare mess that never got sealed. Just keeping the walls dry enough to insulate was my only goal. The ceilings were only 6'8" at best, so not much point in going all in.

    Do check and see if the fuzzy spots are associated with the ties left in the concrete. I worked on a house from the mid 50's that had numerous rusted out round wire ties. A few even flowed water when the downspouts weren't up to the rain. I drilled out the spots with a 3/4 masonry bit to make cone shaped clean concrete spots I could then fill with epoxy. Also think about the fuzzy farms relationships with downspout locations and other places that might be feeding water too close to the foundation. Drippy faucets, patio and driveway runoff, etc.

    If you were to go ahead and UGL the floor, etching the concrete to also make it clean enough for a good bond would be wise, if a lot of work. Garage floor epoxy might be a good sealant too, but the fumes would be a definite hazard. If you are dry enough to pass the plastic on the floor test, it is probably safe to go straight to the foam. I will leave it to you to judge if the dry condition is stable. You have the old carpet and tile to judge by. If the floor was giving up a lot of moisture the carpet would be pretty funky. The tack strips in the pics didn't look rotted. You seem to have been in the house long enough to have a sense of whether you are currently in a drought or any musty smells are from humidity rather than ground water.

    I will advise against attempting to use any solvents on the carpet tape residue or tile adhesives that you may be afflicted with. First, you will probably gas yourself and if you still have a gas water heater, you could easily extend your basement project into a whole house rebuild. Additionally, you would most likely drive the problem into the concrete and make a bigger mess. The residual goo might be the main driver of whether sealing the floor is practical.

    One way to handle the water mess is to use a bunch of towels on the floor and work small sections with grout sponges. Tedious and tiring, but what project isn't if done right. If you have windows or a basement door, plan on a box fan to push the humid air out as much as you can.

    I am a bit curious if the floor drains checked out as being connected properly. It would be a pity to discover too late that they were just dumping into a rock pit under the slab. And yes I have encountered this as well. Like they say, they don't build them like they use to. Thank God.

    1. reimhagen | | #19

      Hi Roger,

      I went ahead and tried just a simple 50/50 vinegar and water scrub. I left it to dry through the day and the concrete is now dry without new crystal buildup. Does that mean the wall is safe to coat, or is there something invisible that the stronger acids clean out?

      I don't think my slab has any release agents. The surface is rough quite porous, but I don't think it's so porous that UGL wont' work. I'll put it on thick and see how it looks after the first coat dries.

      The ties are a concern; I'm grinding them flush with the surface of the concrete right now. My plan is to simply coat them with UGL and hoping it'll bond with the metal; drilling each and every one with a masonry bit and covering the remaining hole with a hydraulic cement is probably the better solution. You can see water streaking down from a few of the tie locations too. Do you think I should invest the time and effort for the drill+cement approach prior to applying the coating?

      I'll roll the dice on the floor. There has been a couple water intrusion events since I've lived here, but it hasn't been water coming up through the ground; one time a downspout came loose during a week of rain and I didn't notice. The water was just flowing to the foundation wall and got into the basement. A second event occurred when I was trenching for some electrical conduit; when the rains came it directed about 300' of trench's worth of water right up against my foundation. I categorize those two as operator error. You're right, the nail strips looked new when I pulled them out, and the carpet appeared to be fine (although it smelled musty). No visible buildup of mold, even on the pad.

      There's no floor drains in my slab; only the roughed in bathroom drains. The drain pipe he put around the exterior of the home empty into a sump pit, which is then pumped underneath and across my driveway in a 4" pipe and it then just daylights out onto the hill and flows away. (For reference, my house is about halfway up ab approx. 15% grade hill).

    2. reimhagen | | #20

      I did a bunch of research last night on DryLok and it seems that Thoroseal (now it's MasterSeal 581) is a much better product. I think I will just return the DryLok and use the Thoroseal instead. More work, but it looks like DryLok can fail pretty easily. Xypex also seems like a very good product, but Thoroseal is easier for me to obtain than Xypex.

      Unfortunately I had already went and applied roughly 75sqft of Drylok, haha. I'll have to go grind that off first.

      1. Expert Member
        BILL WICHERS | | #21

        Any interior side water sealer can fail. Drylok is one of the lower cost interior-side sealers. While drylok certainly does work, there are better products out there but keep in mind that none of them will perform as well as an exterior-side sealer would.


  9. onslow | | #22


    Bummer about the UGL. You might try and contact the Thoroseal people and see if UGL doesn't count as a painted surface before grinding all that area. I suspect they are worried about latex or oil base paints that can be pushed off the surface by hydrostatic pressure which of course what UGL is made to resist. Worth a try.

    As for the vinegar working as well as it did makes it sound like the efflorescence is not too bad. My fuzzy farms had progressed to large yellowish crystal growth that was well integrated into the block. The block wall was being fed water on one side by a hidden clay tile pipe that had gotten paved over. Once found and plugged, I drained the wall by punching holes in the lowest course of block. That was some smelly fun. If you have clean concrete showing it should be okay to proceed.

    The form ties that are leaking will not give up. Depending on the type and condition, it may be possible to drive the wires back into the wall with a drift pin. Many common type of ties are dead straight in the middle. Unfortunately, some wires had bends in the middle to facilitate the placement of rebar or just stabilize them. They won't move. Statistically, the straight kind are more common. Flat bar ones are equally mixed with some having notches that will prevent being able to drive them back.

    There are types of very liquid epoxy used to fill foundation cracks which might be a quicker way to seal up the offenders. The crack kits are rather pricey and would fill more than you likely need. Try contacting a local supplier to concrete contractors and see if they will help. One epoxy you might try is meant for marine repairs and comes in a putty form you cut and mix together. It is meant for pretty harsh environmental conditions. I did use it once for an emergency pipe repair which held for over a month under pressure. Probably would have kept going if I hadn't finished the replacement. The repair was in my own house so that's why it waited so long. Shoemakers children syndrome.

    Tampico brushes are what the directions for Thoroseal recommended and for the life of me I can't imagine why. I may have bought the wrong form, but the ones available in the masonry section look and act like large wallpaper paste brushes. Unfortunately, as you will find out shortly, the Thoroseal is relatively thick to brush and very very heavy. My first tries with the standard brush were a nightmare. I ended up cutting the bristles down about half way to make the brush stiffer. It might be worth acquiring a range of sturdy bristle brushes and see which ones can carry enough material to the wall and yet not be so stiff as to pull it too thin. Doing two coats is probably easier and will lessen the risk of thin spots. One trick to test the bristle theory is to clamp two wood pieces across the bristles such that only 1 1/2 " are exposed. If that is a good working length, go with it. Another possible idea is to apply the material with a scrub brush that looks like a mini floor broom, then smooth and even out the coat with the Tampico brush.

    I do recall wetting the block with a spray bottle to keep the material from being sucked dry immediately on contact with the porous surface. A cast wall may behave similarly. I wouldn't over wet, just give it a little misting to keep the edge from stalling. Best of luck.

  10. user_8675309 | | #23

    I too, insulated my basement floor with 1.5" of XPS and used 2 1/2" layers of plywood. When drilling for Tapcons I found it very helpful after drilling to use a can of compressed air and stick the thin nozzle/tube down the hole to get the concrete dust out of the hole. Have a shop vac handy to suck up the dust as you do it. And yes, use a countersink bit on the plywood so the screws fit flush. Speaking of belt and suspenders, I also sealed the edge where the lineoleum met the bottom wall plate with silicone - figured if there ever was a water leak i don't want it soaking into the plywood.

  11. Elizabeth21 | | #24

    If you are suffering from Herpes or any other disease you can contact Robinson buckler today on this Email address: R o b i n s o n b u c k l e r @{ y a h o o}. c o m

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