[Ferro List] Mearlcell Problems Fixed

[Doug Lacy]

Just going over my notes from the project completed last week and I have some important info for all the people eager to aerate their low-water mortar to turn it into a nice creamy plaster for overhead plastering, here is an issue that needs attention.

Foaming the Mearlcell 3534 using a drill paddle and window screen has been implicated as a cause for inconsistencies in the mix.   These inconsistencies are an occasional loss of aeration resulting in a difficult mix that contrast sharply to the smooth meringue mixes we like. This problem has been hard to pin down.  I have done 18 or so projects and it was only the very last mix during a free patio shell I was doing for the neighbor in exchange for letting me use his driveway for the mixing of the next-door project, that I found this one out.  I suspected so many other causes and tried other solutions with mixed results but I have it now.  

I happened to run out of SPJ on the last mix so I had an ultra clean bucket to use for aeration.  Wow, what a contrast in the mix.  It expanded very slowly and worked so much better.

  In order for the Mearlcell 3532 to be do its wonderful magic in making a creamy low friction mix out of a dense low-water mix, it must be aerated properly.  Sometimes, if there are frayed wires on the mixing paddle window screen, or their is a roughness on the inside of the bucket it will cause the mix to fluff to quickly and never form the proper aeration or bubble size.  This is because the dilute of Mearlcell 3532 and water is held in a suspension of improperly aerated bubbles and it often will not pull back out no matter how long you mix it.  It is difficult to impossible to tell if this has happened or not so sometimes we just had to deal with a difficult mix that rolls around in the mixer like hairy clods of a dry sandy chunks that cling to the paddles instead of the creamy flow that the paddles cut through and churn through and is very easy to pour out of the mixer while it is mixing.

 You could take precautions and make sure your 10 inch by 10 inch window screen that is rolled up and attached to the bottom of the paddle has folded edges and flares out like a cone but their is only one final solution that I feel will eliminate aeration problems for good.  

I have decided that the nifty bucket aeration or expansion of the Mearlcell 3532, is a thing of the past for me.  From now on I will drag the 1.5 HP electric motor to the job site that powers the foam generator.  The foam generator is a precision way to generate the exact foam density and bubble size needed.  It injects the air and the diluted Mearlcell 3532 into a carburetor chamber in the exact proportions needed and then into the wand that is crammed full of the "Chore Boy" style kitchen sink dish scrubbies.  The spiral flat ribbon stainless scrubby is important.  Maybe if we tied the "Chore Boy" brand scrubbies onto the mixing paddle instead of window screen.  Very likely to work but I am not even going to chance it.  I have a foam generator so I might as well use it so every 25 dollar mix I throw is sure to be right.  I would recommend just buying one from Cellular Concrete Ltd because you get good customer support for making whatever it is you are making.
If you have the right mix, the rushing around in a big hurry stops.  You have time left to take good care of the shell section you have just plastered because it went on so much more quickly and smoothly.   

This closed cell aeration protects the mix from ice damage and progressive oxidation or steel reinforcing damaging rust.  It helps the steel form a stable coating of oxidation that stops further oxidation because it gives the rust a place to reside, in the spherical bubbles, so its expansion cannot crack the matrix to let in more moisture and a path for more air and rust.  The small amount of rust in the closed cell aerated shell near the steel acts like an electrical buffer zone that protects against more ionic reactions closer to the steel.  This style of closed cell aeration hinders moisture intrusion rather than creating open pores for moisture movement.  This aeration provides a space for ice crystals so they can grow without damaging the shell either by wedging into tight spaces that are not spheres.  This aeration translates to longevity because the two mechanisms of ice and rust are how concrete usually decays.  With their effect removed...  

Rushing around to take care of a problem shell and a problem mix can comprimise more than just quality.  It can comprimise safety as well.  I tend to lose my gloves pretty quickly when mix problems start.  Any other hidden problem on the job site will surely rear up when things start to get rushed because of a tough mix.

I am very glad for the progress I have made with this system and very glad for what the mistakes have taught me.  Mixing and plastering is tough work.  When everything is right the challenge feels good instead of exasperating.  It must be like surfing.  All that hardwork to get it right but it pays off when you do and everything is just smooth.

Doug
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Back to work after baby–how do you know when you’re ready?
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