# homemade self leveling skim coat



## archibaldtuttle (Apr 19, 2009)

I have to level a slab that was compromised in one corner by failed downspout and drainage. It was a slab on grade with a kind of mortared stone grade bar. I poured a new foundation just outside and insulated and corrected drainage. Of the 35o sq. ft. slab less than 100 sq. ft. settled and needs to be leveled from 0" to about 3 or 3.5 inches deep.

For various reasons, including long stability and lack of further cracking or piecing of this one large settled piece since drainage was corrected some years ago, relatively low yardage even with rip out, experimenting with new materials and skimming techniques and because my finished product here will be covered with insulation and then osb secured to the existing slab so I'm not really worried if my experiment results more in flowable fill rather than a well adhered crack resistant final subfloor, I decided to go over existing slab rather than break it out.

I have PVA fibers from Nycon that they tell me are designed to chemically bond with a standard concrete mix and essentially intend to mix some loose sand mix with Planicrete AC instead of water and the fibers as an admix.

I'm wondering if it would be advisable to pepper the slab where it will be skimmed with concrete screws sticking up so that the new mix will have some hold down or whether you think it would be better to just let the new mix float on the old slab. 

Given that I'm using the fibers , would additional reinforcing mess in areas where the depth is sufficient to allow for it be advisable, e.g. hardware cloth or some fiber product. Would it be advisable to try to introduce some batches with 3/8" stone into the deeper fill areas first and then skim in with sand only mix on top.

Any other ideas appreciated. I've used self leveling and nonshrink cement products for these approaches in the past but the expense for the volume of fill is pretty serious. I've never tried the fibers with those products and maybe I should have, but didn't get absolutely crack free performance I was hoping with overbuilt doubled subfloors and the nonshrink quality. The quick curing is an advantage and a hazard.

I could certainly introduce a portion of these mixes along with standard portland as an alternative.

Thanks for any suggestions.

Brian


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## tjetson (Jul 28, 2010)

i would run a bushing hammer over the area and use a proper product for the job


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## archibaldtuttle (Apr 19, 2009)

tjetson said:


> i would run a bushing hammer over the area and use a proper product for the job


That is actually the thrust of the thread. What do you consider to be a "proper produce" and what particular chemical make up and resulting properties together with mechanical approaches (such as the bushing hammer you suggest and/or raised anchoring screws which is my idea for additional grab) are suitable. Could those properties be approximated with a mix I can make myself?

I've made a number of differently batched underlayments myself in the past and been reasonably satisfied but I'm trying to go thinner and less material with advanced fibers available and just checking to see what approaches any others may have used successfully. So this is really more of job where I can experiment with a new mix. It is a little different than my usual job where I am commonly going over tongue and groove plywood subfloor with radiant tubing attached and between 1.5 and 2.5 inches of concrete over.

While the two applications are also markedly different in terms of substrate, I'm just interested in moving towards a skimming mix that might be a little more self leveling, or easier leveling mix with some anti-cracking properties that might allow thinner install than what I'm currently using. I've had remarkably good luck with just standard floor mix with pumice aggregate for a lighter dry weight at 2.5" over sub floor polished finish without cracking whereas I used non-shrink concrete products for some smaller jobs that I hand batched and got cracking. 

The previous success with more or less standard concrete is why I'm working at modifying a standard portland mix. Most of what I do, the cost has to be shaved. If I want infloor radiant it's got to be on a budget. That's why I'm always trying to find cost effective skim mixes. I'm also experimenting with sandwiching radiant tubes between 1/2" foil faced insulation over subfloor and 1/2" hardoibacker with cut strips of the 1/2" insulation between the tubes (using 3/8" nom pex tubing which is 1/2" OD). 

Brian


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## stuart45 (Oct 7, 2009)

Our floors here are often 4 inch concrete with a 2-3 inch sharp sand/OPC 3/1 dryish mix screed to level. I have known people go down to an inch, but any less needs something like polymer emulsion or epoxy resin screeds for a decent job.


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## archibaldtuttle (Apr 19, 2009)

*polymer emulsion?*



stuart45 said:


> Our floors here are often 4 inch concrete with a 2-3 inch sharp sand/OPC 3/1 dryish mix screed to level. I have known people go down to an inch, but any less needs something like polymer emulsion or epoxy resin screeds for a decent job.


Are you saying that the whole 4" of concrete are a stiff mix with 3 parts sand to one part Portland?

By polymer emulsion are you referring to the various "latex milks" usedd to replace water in the mix and sometimes painted on to surfaces which you want cement or plaster products to adhere well to?

I do plan to use one of those produces, Planicrete AC to replace 1/2 the water although I could go heavier. I've got it in 5 gallon jugs at a good price.

Or am I mistaken as to what a polymer emulsion is?

Sounds like the expoxy screed is applied afterwards -- while still actively curing (well I mean while still wet, i guess curing goes on for the milennia if you get technical)

thanks,

brian


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## stuart45 (Oct 7, 2009)

archibaldtuttle said:


> Are you saying that the whole 4" of concrete are a stiff mix with 3 parts sand to one part Portland?
> No, the wet concrete is laid first near the start of the job, and then the dryer screed is put on top later after the walls have been plastered near the end..
> 
> By polymer emulsion are you referring to the various "latex milks" usedd to replace water in the mix and sometimes painted on to surfaces which you want cement or plaster products to adhere well to?
> ...


Probably done like this as our concrete finishers are not that good for a finished floor.


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## stuart45 (Oct 7, 2009)

Found this site with some info.
http://www.ppscreeds.co.uk/Data Sheets/Screeds/Isocrete Floor Screeds/Isothin.pdf


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## archibaldtuttle (Apr 19, 2009)

stuart45 said:


> Probably done like this as our concrete finishers are not that good for a finished floor.


interesting. so how much time between setting the 4" concrete floor and the sand mix screed.

I would think if it were on the dry side it wouldn't be that easy to float it level, but it is a 'soft' mix.

what finish for the first concrete before the screed, e.g. bull floated and rough broomed?

do you use polymer in the sand mix for adhesion. Are you saying the sand mix might go as thick as an inch?

thanks,

brian


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## tjetson (Jul 28, 2010)

I just know going from a feather edge on a slab or patch always ends in problems. what will be the final finish over the concrete be? 

call lafarge and price out Agilia screed i know in some american states its really cheap like 85 a meter. I just paid almost 300 a meter for it here in canada


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## archibaldtuttle (Apr 19, 2009)

*interesting isoscreed*



stuart45 said:


> Found this site with some info.
> http://www.ppscreeds.co.uk/Data Sheets/Screeds/Isocrete Floor Screeds/Isothin.pdf


this seems to essentially say you make a sand mix with polymer and use a polymer primer. They are really selling their brand of polymer but the rest of the mix sounds just like what I had in mind making (except for the PVA fibers that are supposed to be the cats meow -- maybe they are just cat hair who knows)

brian


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## stuart45 (Oct 7, 2009)

archibaldtuttle said:


> interesting. so how much time between setting the 4" concrete floor and the sand mix screed.
> Could be a couple of months. It would be one of the last jobs. Nowadays the insulation is sometimes put on top of the concrete, so the sand/cement screed is laid on top of the insulation. Myself, I prefer to put it under the concrete.
> 
> I would think if it were on the dry side it wouldn't be that easy to float it level, but it is a 'soft' mix.
> ...


The flooring sand used is normally very sharp like used for concrete without the gravel.


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