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  1. #105
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    Apr 2017
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    oh man, i am NOT an electrical engineer. lol man i barely passed 3rd semester physics which was all... magnetic flux this, and right hand rule that... i am terrible at that stuff. i remember exploding a capacitor in my face during this lab were we were trying to build a super crude diode rectified power supply... if i recall right the diode was just chopping off the bottom of the ac wave form and the capacitor was sort of bridging the gap between the voltage peaks... may have been a resistor in there too idk. i suck at electronics in a serious way.

    no im a civil guy, and as all engineers will tell you... we are at the bottom of the respect totem pole. mechanical guys, chemical guys, electrical guys all dump on us lol. within the engineering discipline we are basically the equivelant of a communications major. anyway i dont consider myself smart at all, i just know what i know... ask me anything else and i probably wont have any clue. and i dont take offense at anything you said what so ever because its very true lol.

    i understand what you are saying regarding the wall, but i just wanted to chime in regarding the liquid permeability of concrete because its an often cited thing thats just not true. the LIQUID permeability of concrete at normal temps and pressures can actually be in the same ball park as a monolithic granite with the right grain size and water to cement ratio and maby some admixtures.

    i was not trying to say that his wall IS water tight or even that it could be water tight. i actually suggested the opposite earlier on in the thread, and i think we actually agree in how the solution should ideally be addressed.

    yes, like you were saying concrete does indeed have vapor permeability issues, and the coeffieicnt of vapor permeability is usually a few orders of magnitude lower than for liquids( lower = more flow), so water vapor trapped inside the concrete will indeed slowly dry to the interior if allowed, and when one side of the wall is dryer than the other, you will develop a vapor pressure difference or gradient that will further drive moisture through the wall. this is why i suggested the waterproofing membrane and drainage composite earlier. i agree that a drain will partially address the issue, but again it may not solve it satisfactorily. the wall ideally should isolated from the surrounding soil completely with a vapor impermeable and water impermeable barrier or coating of some sort. as i said earlier though it will cost a grip to do all of this.

    and regarding engineers and building codes, with the exception of MEP guys and structural guys, YES i totally agree. when i started out...i once spent hours and hours calculating the aeration requirements for a treatment plant only to find out that the state required X cfm as a function of a very rigid and very conservative calculation. what we are even worse at though... is designing stuff that is impractical, wasteful, or even possible to build. its little things that you have to learn to look for... like welds that are impossible to make in the field, designs that waste huge amounts of steel sheet, speccing bent bars that would require a 10k hydraulic bending machine rental, or speccing products that have like a 6 week lead time etc.

  2. #106
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    Jan 2015
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    Thanks for clarify I hope your afternoon goes welll

  3. #107
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    Feb 2016
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    Louisburg Kansas
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    On a house if the foundation wall is only 4' tall the hydraulic overturning moment is small and is not a factor. Very few house foundation walls are designed to be water proof and as a result the walls do not have enough re-bar to minimize crack size to the point that coatings alone are 100% successful over the entire structure. That doesn't mean they will not work but their effectiveness depends on crack location and size.
    This is illustrated clearly if you look at the difference between the design of a standard above ground house foundation and a totally underground house. If you build an underground or earth contact house like a standard foundation all you end up with is a soggy basement and that is just the start of your problems.

  4. #108
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    Apr 2017
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    lol are you sure about that? have you done the math? i admit that i have not...

    assuming 100% saturated soils all the way to the top of the wall... and assuming magical cohesive and permeable soil that would contribute 0 lateral earth pressure... you would develop around 2psi gauge pressure at the bottom of the wall. the centroid of that force triangle would be 1/3rd of the way up the wall or 4/3 feet from the top of the footing.

    the average pressure over each 1' x4' wide vertical strip of the whole wall is = to (F sub 0elevation+ F sub 4' elevation)/2 *area

    F = yh ( where y = specific weight of water in lb/ft3(62.2lb/ft3) , and h = height)

    Pave = ( 0 + 62.2lb/ft3 * 4')/2 * ( 1'wide x 4'tall)
    pave = 497.6lb/ft2 per 1' wide vertical strip.
    let pave ~ 500lb/ft2.

    moment at the intersection of the wall and footing = 500lb/ft2 * 4/3ft. = 666.6lbft per unit of wall length.

    can a 4 or 6" wall resist that? it would depend on a number of factors, but i would not bet my livelyhood on that considering most of these walls are pissy no. 4 bars in a crappy 1.5" trapazoidal keyway. most of the time they are not even installing bonding agents or water stops... so they act almost as a leaky hinged joint which is why you will always see contractors putting in drainage and overhead joists on the foundation wall before they backfill lol.

  5. #109
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    Feb 2016
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    Louisburg Kansas
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    Drainage is very important for several reasons. The hydraulic moment is 1/3 up from the bottom of the wall which on a 4' high wall is a lot less than an 8' wall. Block and rock walls are more vulnerable than concrete but once the weight of the house is on them normally stay put even without re-bar. Shifting earth moves more walls than anything else.
    My main point was in support of the statement made here that the concrete walls were not designed to be waterproof. They are better thought of as water resistant but vulnerable to water infiltration mainly due to cracking.
    I haven't run calcs on concrete structures in several years and don't care to do it now. That isn't meant in any way negative toward you I just don't have the desire to do it.

  6. #110
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    Aug 2006
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    If it's a concrete block wall you can carefully cut a hole in one of the blocks above ground. Work two or three pieces of rebar into the wall cavity down to the footer. Pour concrete down inside the wall while wiggling the rebar to get the air bubbbles out. Brace a piece of plywood against the wall and pour concrete in to form the cap, while pushing the plywood against the wall. The Structural Engineer always had us use mixed concrete off a truck or use a mechanical mixer. No pan mixed concrete was allowed. BTW it took three of us to do a good internal pier build.
    Retired, after 43 Years

  7. #111
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    Feb 2016
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    A wall mix is good for getting inside block. That works well especially where you put anchor bolts.

  8. #112
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    Sep 2014
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    NW Arkansas
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    Thread Starter
    This topic has made some good conversation.

    For clarification, on this specific house, the concrete wall in question is non-load bearing, is poured, is about 4" thick x 4-5' tall x 85' long. The slab has a retaining wall which is cinder block construction but that is on the other side of the house. No known details about construction quality or design.

    I am going to pull all the dirt back away from the poured wall this week. I have a few questions. The guy doing it want to use a silicone roofing material (black jack premium) and lay 30lbs felt over it once the second coat becomes tacky. Then we will put the 2" foam against the felt.

    I suggested going almost to the top of the wall (leaving enough for either clay or plastic for runoff) with the 3/4 washed gravel. He is suggesting just going up 1-2 feet above the perforated pipe then using regular dirt for the backfill. He said the rock wasn't necessary all the way up and would cost more than needed.

    Anyone have any suggestions?

    Also, I can't have the 2"foam on the top part of the concrete wall. Will this make a big difference?

    Sent from my SAMSUNG-SM-G891A using Tapatalk

  9. #113
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    Sep 2005
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    Atlanta GA area
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    Question on the solution above...

    What is the purpose of the foam? Does it actually hold the water out... or does it provide a mechanical barrier to absorb potential physical impact that could damage the coating on the concrete wall?

    IMO: The gutters and french drain (and possibly a yard drain) are the major thing.
    Having said that... given how much work it is to dig out the wall... I would NOT go cheap on the wall once it is dug out...
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *Cheap is not good, good is not cheap; however expensive is not a guarantee of quality!
    Choose your contractor wisely!

  10. #114
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    Sep 2014
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    Thread Starter
    The foam is for insulating mainly. Help with preventing condensation on the inside of the wall. It also provides a protection for the water proofing.

    Sent from my SAMSUNG-SM-G891A using Tapatalk

  11. #115
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    Apr 2017
    Location
    Houston, Tx
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    2" closed high density closed cell spray foam is a very very good vapor barrier, but its not proven to last more than 10 or maby 15 years.

    if you go on the building science website you will see advocates of this technique touting it as both good insulation, and as very good vapor/ water barrier. however even they admit its only been done in the last 10-15 years. the oldest installations appear to be doing fine though, they foam just discolors from soil contact.

    if you want to spend more for the foam, thats fine. its probably the best of both worlds, but just be aware that its going to require prep work and its not like... age old tried and tested? does that make sense?

    foam kits are about a dollar a board foot... so take your total wall area and multiply it by 2, and that is what it will cost in foam kits... i think you will find that its not economical to do with kits, you will probably want to hire a contractor as they have access to much cheaper bulk drums of the foam monomer and blowing agent/activator stuff. make absolutly sure its high density CLOSED cell foam not the cheap open cell stuff.

    cheap open cell is good for interior walls and especially against a roof deck where you have a hot humid climate... but its going to be close to worthless when in contact with soils.

    also investigate one of the many coatings you can spray against the foam. most of these coatings are for extra fire rating... like say to get to a 60 minute wall with the foam exposed. but maby there is a coating geared for water proofing? IDK, but it might be worth looking into.

    also regarding your question of only washed stone up a few feet? it depends on your soil.

    if your soil water table is very, and remains very high after a heavy rain, then you need stone all the way up the wall to drain off the water against the wall and drop the water table.

    if your soil water table is not terribly high after a heavy rain, then stone only a few feet up would be fine. just make sure the stone is wrapped over with geotextile AND make sure you get a proper drainage composite up against the wall to drain off the water above this stone.

    if you waterproof all the way up, and put stone all the way up... you could probably omit the drainage composite, but its an extra barrier that could be useful in the long run as your stone collects super fine sediments. your corrugated pipe will also colellect fine sediments too btw, especialy if you have alot of alluvial soils you are excavating through. you should put in a cleanout at the end runs of these pipes so you could gently jet them out in like 10 years or so.

  12. #116
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    Sep 2014
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    NW Arkansas
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    Thread Starter
    Started taking the dirt off the side. They did have some crappy drains put in (guessing 5-8 years ago) but they were clogged. Has a PVC pipe on top of footer but wasn't downhill so not doing much.

    No water sealing on concrete wall.

    Having to jackhammer the excess concrete to install a pipe next to the footer.

    Sent from my SAMSUNG-SM-G891A using Tapatalk

  13. #117
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    Apr 2017
    Location
    Houston, Tx
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    oh wow man. nice work.

    i wish i knew how to run an excavator =(.

    how is your system shaping up? do yo have it all worked out now?

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