Aircrete is collapsing

  • Water chemistry has a lot to do with concrete! Ignoring your water chemistry when mixing any concrete is an invitation for disaster. Sulfates in your water or aggregates in any portland cement mixture are really bad. Here's a link to more information on concrete and sulfates:

  • @FoamAir I followed this recipe with my own foam that weighs 85g / ltr made with reverse osmosis water and 7th gen foam. My slurry seems thinner and runnier than yours but maybe that is the pictures not showing up well. Also, there is sand sitting in the bottom of the mix. The cement mixes but there is sand at the bottom in the slurry and after the foam is added as well. Did you have a bit of sand sitting at the bottom too?

    I have formed it and can hear my foam reacting one in the form, it is gassing off and collapsing. I will go buy a small foamer and try. I have Drexel on the way. This is all with reverse osmosis water, foam and slurry. Thoughts?

  • Major Contributor

    @chuckj sand? Portland cement has no sand. Are you using the correct cement?

  • @HandyDan hi. Yea I was wondering if I was using the wrong mix. I am using concret mix. 10.5lb bag of quickrete. So it is a mix of cement and aggregate. Wrong stuff I guess. No wonder. I have anothe idea too. I am going to mix in crusaded scoria (lava rock) to add strength and still give good insulative value and light weight. Off to get the correct mix now :). Thanks!!

  • Major Contributor

    Experiments are great. However, it will not be true air-crete and will cost more.

  • My first test batch did something similar, I lost an inch or two after an hour, before it could set up. I'm using the drexel soap. I weighed it and it was in the proper range. I thought it was my mix at first because I calculated out a 5 gallon bucket test run. But then I noticed the test foam on the ground had deflated too by same amount.
    My thought is the well water is effecting the soap, in my case, our well has a lot of rust from old well pipe removed years ago. Could also be inorganic mineral salts in the water. Glad to hear that cleaner water worked for you, I am by a river and will have to test if that water will keep the soap foam stable better than the well water. One other note, I do have a coarser stainless scrubby in my tube, not sure if that would matter?
    If anyone wants to know if their water is good, just make some test foam and let it sit around for an hour or so and see how stable the foam stays. That will be my next test before another batch.

    After my hunch on the reason mine had deflated, I found this complicated info that seems like it could explain why :
    "There is a critical salt concentration above which the salt acts as a defoamer."
    "We report unexpectedly strong ion-specific effects of counter-ions on the stability and the rate of drainage of planar foam films from solutions of 0.5 mM sodium dodecyl sulfate (SDS) as a function of concentration of a series of inorganic salts (MCl, M = Li, Na, K). We found that the counter-ions can either stabilize the foam films (up to a critical concentration) or destabilize them beyond it."

  • @hajjargibran After my hunch on the reason mine had deflated, I found this complicated info that seems like it could explain why :
    "There is a critical salt concentration above which the salt acts as a defoamer."
    "We report unexpectedly strong ion-specific effects of counter-ions on the stability and the rate of drainage of planar foam films from solutions of 0.5 mM sodium dodecyl sulfate (SDS) as a function of concentration of a series of inorganic salts (MCl, M = Li, Na, K). We found that the counter-ions can either stabilize the foam films (up to a critical concentration) or destabilize them beyond it."

  • Greetings all,

    I'm just about to make my very first test block.
    Came here looking for how much foam to add to cement slurry.
    I made my own foam generator and tested it using Dawn Ultra.
    However, I too have a well water here in Florida, USA.
    My first foam test made lots of foam but it did seem to collapse rapidly.
    But here at my house I harvest rain water off my roof!
    Rain should be free of any hardness and minerals.
    And it is free and readily available to me. I generally use it for my garden and greenhouse.
    So I'm about to go out to my garage and try the cement slurry and the foam mix with rain water.
    Seems to me easier than going to buy distilled water.
    Thanks for the discussion.
    Pappy the Sailor Man

  •  Okay, I'm finished making my very first test block of AirCrete!
     First I measured 1/2 gal US of water from my rain barrel in plastic pitcher I use for iced tea. After weighing it on my kitchen scale just to be sure it was about 4 lbs I poured it into a 5 gal bucket.
     At this point I would like to apologize to those readers who are on the metric system. I can and do use metric, but all my utensils are imperial.
     Next I weighed out 8 lbs of type I-II portland cement from the 94 lb. bag I bought yesterday from a local Home Depot store for $9.20 and put it aside. 
     Then I measured another 1/2 gal of water from my rain barrel and mixed 1 Tbs (tablespoon US) of Drexel F.M.-160 foam / marker concentrate I purchased from local Rural King store. 1 gallon cost me $22. The directions said mix 1 gallon with 160 gallons of water. Apparently it is used in large sprayers for pesticides on crop fields to mark where the spray has been dispensed. The container does not say what the active ingredients are. Only that they are exempt under CFR-40 (code of federal regulation). However, because it will be stabilized in the cement when it sets I feel it is not an environmental issue. And more over it is used on crop fields so hopefully our government is making sure it is not toxic.
     Next I mixed the cement into 5 gallon bucket with the ½ gallon of water using an electric drill with a joint compound type paddle mixer.
     After that I started my compressor and poured the foam concentrate mixture into my foam generator and connected the air hose and started shooting the foam into the bucket of cement slurry, all the while using my other hand to run the drill and mix the foam into the slurry. It was awkward but I managed.
     I added foam until the bucket was almost completely full and then continued mixing it with the drill until it was uniform texture.
     At this point I should mention that I have been doing construction for over 40 years and 30 years of it included building concrete forms and tying rebar and pouring and finishing concrete. So when the Aircrete mix was finished I braced myself and grabbed the bucket. I couldn’t believe how light it was!
     Previously I had built a 16 in. square form from wood and I now filled it up which took the whole bucket.
     So now I am just waiting for it to set up.
     I didn’t caulk the formwork but only screwed it down to a piece of plywood I had in the yard for a base. It looked pretty tight. But as I was admiring my work I saw some but not a lot of the cement leaking out. 
     My whole purpose of doing this is to prepare for making preformed slabs about 4 inches thick and 2 feet wide and 6 or 8 feet long to use in setting up a raised-bed garden. Instead of stacking blocks I will just set these on edge and fill them with mulch and compost.
     Good luck everyone and safe voyages!

    PS. I'll give an update later when it is set and hard and try to upload some pictures also.

  • It is now the next morning and my test block is still not set hard. I can poke my finger right into it. I am thinking I used too much foam. I am going to give it another day to set. This morning I gently poured water on it and covered it with plastic sheeting to help with the cure process. Hopefully it is not the foaming agent that is retarding the cement. As for the bubbles collapsing I did not observe any. And it is surprising because it stayed wet a very long time. I have a picture to upload but I am not sure how to do it.
    Safe voyages,
    Pappy the sailor
    PS. my apologies for the previous post that published in mixed colors and dark background. Not sure how that happened and I have not been able to remedy it.

  • @leroy That is a good thing to know when making those blocks Thank you very much.

  • @Davy-Oneness Hello my friend, last weekend I made a test block, and had a few problems from the start. First when I weighed out my foam at 3oz/qt, I noticed right away that the soap and water started separating, within about 1 min I had about an 1/8 inch of water in the bottom of my clear container. So I went ahead with my test block. My block size 9.25"x 9.25"x 20.0" approx (1 cu ft) for simplicity. Using 2x10 lumber. I used plastic under the form and wrapped it up to top ridge of the form and stapled it down. After about 15-20 mins after the pour, I noticed the plastic was bulging on the outside of the form and after about an hour the pour collapsed about 2 inches and water was leaking out from the plastic. I really think I have a problem with the water quality. So this weekend I am going to use some deionized water for my next soap solution and aircrete mix then see what happens and try to seal up the form a little better. Oh by the way I used Drexel for my foam solution. I will keep you posted.

  • Major Contributor

    I have never had the problem of foam collapse my self. I have seen poor foam that turned to light and airy quickly though when the water pump is priming. Personally I don’t trust the foam weight method so much. I tend to test my air pressure with displacement ratio. I have found that if you can expand 1 gallon of water/ foaming agent to 10 gallons of foam you will typically be at the desired weight.. I could be wrong, but I feel there is a point where a bad mix can weight the same as a perfect one.. With practice you will notice the amount of water used will vary largely by batch with very small air pressure changes. I just happened to notice the strongest batches all have that 10:1 ratio when complete

  • we witnessed this during the feb 1 day workshop here in Kalapana. That can happen when the mix is not right - usually with the foam density when mixed, not mixed evenly enough, or if it is not poured quickly enough when setting. What kind of soap are you using? There is a specific concentration of a chemical needed that varies greatly depending on the brand of soap used.

  • @mundane9 I am using Drexall 160. The directions call for a 160:1 mix however I did go to a 120:1 mix @ 3.0 oz per qt. but noticed a rapid separation of soap and water in the 1 qt weigh container. I think I may have a water quality problem to be honest.

  • Hello again!
    I'm happy to report my second aircrete pour went pretty good and I am quite happy with results.
    Here is how it happened:
    I built a new 18" x 72" form using nominal 1x4x8' on top of a scrap piece of plywood. I laid a piece of plastic on the plywood. Then I screwed my 4 pieces of the edge form together and set the form on the plastic, squared it up, and screwed it to the plywood base. Then caulked the bottom of edge form to the plastic.
    Next day after the caulk had time to dry I set up my tools and materials. Doing my calculations I figured I needed 20 gallons of aircrete so I just cut Domegaia's recipe in half.
    So I put 3 gallons of rain water into a 20 gallon galvanized trash can I bought for $20. Then I mixed up my foaming agent using the Drexel F/M 160. Using a bathroom scale I weighed out my portland to approximately 48 lbs. (1 gal. H2O = 8 lbs. X 3 = 24 lbs. With 1:2 ratio cement weighed 2 x 24 = 48 lbs.)
    When I bought my 1x4s I also purchased some bamboo tomato stakes. There were (6) 6 ft each in a pack and I bought 2 for $3.17 ea. I wanted to use them for reinforcement instead of steel rebar. So I cut them to length where they would fit into the form both transverse and longitudinal.
    Having everything set up poured the 3 gallons of rain water into the trash can and added the 48 lbs of portland cement while mixing them together. The trash can leaked some but not enough to make a difference. Next I started my compressor and made the aircrete, mixing and adding foam and mixing and adding foam. It is a little tough when you do not have a helper. But I managed.
    Having everything mixed I filled my form up. I ran a little short so the panel ended up only 2 1/2 inches thick. I put my bamboo reinforcement in and troweled the surface. And cleaned up.
    Next morning it was set and pretty hard. I could not poke my finger into it like the first test block. I poured water on it several times that day and also the next three.
    Fourth day I unscrewed my form boards and tilted the panel up and lifted it and took it out to my garden where it is going to be the walls of my raised beds.
    I think it was a great success and I want to thank everyone here for the knowledge and expertise shared to help make this a better world to live in.
    Safe voyages!
    PS. I have a cousin who lives about an hour away and earlier this year she offered to give me some bamboo plants out of her yard. So I think I am going to take her up on the offer! :- D

  • @kimo How do you measure that, how do you know your gallon of water is getting you 10 in foam? Are you using the little dragon and mixing inline, as the foam is produced, or do you produce the foam into a 10 gallon total and pour it into the cement mixture, and blend?

    My wife and I are getting amazing foam with the Drexel but it is frustrating as we blend with the cement mixture. There is a point where we are trying to pump the foam in to get the recommended quantity for a bag of cement, but it won't quite get there. It seems to start to collapse while mixing, especially when trying to finish up the mixing by blending some surface remnant foam in, while not infusing fresh foam. Just plummets.

    You're right, the tiniest adjustments in air pressure drastically change the weight. I feel like the "shaving cream" like foam I am most proud of weighs only 2oz/qt or so , not the recommended 3oz/qt. So we keep adjusting until the weight is right, but that foam is less thick, more watery.

    The foam itself, you can see it separates to water some in a clear bucket and does some collapsing in a relatively short time. Maybe this foam quality is why my experience is so bad when blending into cement. We just can't get a batch that resembles the lightweight but dense concrete we want...all are far too airous and brittle. You can poke your finger right into it after several cure days.

  • Major Contributor

    Yeah that’s not right at all... any time after the 2nd day it should be pretty difficult to stick you finger in a block... the way I check my foam expansion ratio is by just checking the amount of water I have left after a batch, but that’s more because I have it dialed in already. If I end up with 1 1/2-2” of water in my bucket I assume I’m still in the ball park for the next batch, if not I make a small adjustment for the next one ;)

    Starting from Zero.. fill your foam generator bucket 1/2 way, make a mark.. then add 1 gallon of water and make a new mark.. prep 2 empty 5 gallon buckets for foam filling.. after filling the 2 five gallon buckets with foam see where your foaming agent bucket is in relation to the starting mark.. my guess is that your air pressure is too low and you will be using over one gallon of solution to fill these buckets..

    There is certainly a point where the water content is too high and it gives an indication that your mix is correct by weight.. This is why I moved to the expansion method. There is only one pressure that makes a 10:1 expansion :)

  • Major Contributor

    Oh! And as far as what I do with the test foam.. toss it out, wash the car or something.. foam that’s not injected directly into the slurry will not ever be as good.

  • @kimo Thanks, brother. Super helpful. I was just about to try my test with Cement All last night and the little dragon pump jammed... it's toast. Magnet around the copper coil is cracked and broken. Nice.
    I'm pretty sure the cement all is going to work well. They have a set time increasing additive as well as a thinning flow additive and they work well with the product. Add foam and a lightweight, strong and fast curing product should be the result. Expensive, sure...but when you're making furniture, who cares. I'm normally buying 6 dollar a board foot Black Walnut for my designs.
    I ordered a new pump this morning, but it looks like they have the little dragon one made just for them, and I can't see how to buy another from them. The one I ordered should be the same only with a max psi of 70, not 90. Should be alright as 70 is where we seem to be in our Drexel foam production.

    Any input on this? Thank you again, Kimo, for your expertise.

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