Thin overpour

John Abbott

I have to do a thin overpour with insulation and 1/2" pex and concrete in a basement I have never done one less than 3" but this should be 2" max. Can some one with experience in this area give me some advice as to what strength concrete ,any additives to the mix etc.I am thinking adding the chopped fiberglass to it would be nescesary but what else I am not sure Any suggestions would be appreciated.

Thanks,

John

hr

Think I'd

use a smaller aggreate mix, like a pea gravel. To get some "rock" above the tube. You want 3 times the aggreate diameter over the tube.

Double the fiber to 3 lbs to the yard, typically a polypropylene of nylon is used.

Ask about a shrink reduction admix (WR Grace) as thin slabs with small aggreate will have more shrinkage.

Ask for fly ash add if the weather is real warm. Your local batch plant should have additional recomendations based on the products available in your area.

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Weezbo

This summer ......

we placed a few hundred feet of stadler ,wirsbo ,rehau of the 3/8ths variety and placed an over pour of 5/8ths"+/- 1/8th.works fine. it is a sand cement over an insulated preexisting slab. it is working fine. it was allowed to cure 28 days .no cracks. have been using constant circulation and it functions well for either heating or cooling.did i mention its working fine?:) i may not put a covering over it just yet,my "plan was for a floating floor like prego or whatever:) i will wait on that a bit as tarkett floating vynil might suit me better. my cat and dog would be less able to fine tune my work:) Next year spring this thin set will have either done didit or died:) ...all it is to do is clean the existing slab ,mix up some moose milk (acrylic)and water "Paint "the floor,let it dry, trim the room out around the exterior walls wit a dash of foam ,go get a bunch of 3/8ths and a group of those stick ums for bundeling wires with a zipp tye lay out the pipe stich the stickers down zipp tyem done deal. i Know This sounds SO Not:) ) some thin uni strut is good to lay on the top of them while you let it be for a while. as this is remodeling we are talking about dont think its like slam pipe shoot crete striker flatand split.
the area i am speaking of is only like 420sq'...three very small rooms. so there is a lot of homeowner stuff i am doing that is nothing like the way i get into new construction...first off yyou cannot get small enough fines to do the deed:) i am not terribly concerned with heavy furniture with pointy legs digging into the cement now concreteand puncturing the tubing....
I am impressed with its speed to ramp and i am happy with the no cracking going on. it is the fastest ramping slab i have ever done. i also like the supply and return temps:) and the room temps... sorry i digressed..
in your home you may not have anything like insulation under the existing slab...if not, things could be different.a thin slab needs lots of things going on as it were,my understanding is that the existing slab needs to "Bond With"and 1 &1/2 " without tubing is the thinest set slab in a garage i think id reccommend,and stand behind 3/8ths is standard with tubing unless you can find a large company with larger screened sand ,getting them to mix exotic cement is another thing. your mud shark will probably be just happy with 3/8ths minus. you prep it with acryl first.dont place tie downs more than 2'6" apart, come out with a formed bend or electrical conduit with the pipe stuffed thru it,insulate the edges at least,dont go too soupy,use clean water and make it a little Green 6 sack..use fiberglass,maybe go with a slu over the top.put poly sheating on the lower section of the wall if you use anything hirer teck than a fresno. enjoy your new radiant..

John Abbott

I'm leaning....

towards 4000 psi with 3/8" aggregate with the admix and fiber as suggested. Am I on the right track?

John

hr

What's the final floor covering?

Thin slabs, regardless of the mix and admixes will be more prone to shrinkage cracking. This should not bother a floating wood, of course, or carpet, etc.

If tile is the final covering I would wait at least a month. Cracks can be dealt with before tile is set. if you tile too soon and cracking occurs it very well may crack the tile with it or through grout lines.

On large slabs tilesetters around here generally just put the crack membrane over the cracks, not the entire slab. That stuff is pricey!

The mix sounds good to me. Don't let them water it down too much when it arrives. For every gallon of water added, to a yard, the psi rating is reduced by 200. Concrete finishers like to add water to make it easier to rake around. Better to add a plasticizer if they have to pull the mud a long distance.

If you pour on a real hot day a sealer or fog spray slows the cure by keeping water in longer and some say this helps prevent shrinkage cracking also.

Also use a foam strip around the concrete walls to allow some expansion room.

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

John Abbott

The final flooring is.......

going to be floating laminate and vinyl so I should be ok.I am going to use zip strips for control joints.Thanks for the help guys I appreciate it.

Gordy1

Hey Hot Rod where did you get all of your concrete knowledge? Coming from an ACI level 1 certified Concrete Tester.
Hot Rod is right on, also adding a plastisizer instead of water will reduce shrinkage verses adding water,when the water leaves the mix it leaves micro voids, the more water you add the more voids .Micro Silica mix is the ultimate for over pours,very high psi.You can ask the concrete company about it, but batch plants won't mess with the mix unless its a very high quanity.