We are graveling the basement floor of the cottage this weekend 4″ high and would like to know if it is necessary to poly the gravel once we are finished or can we use tarps for the winter. We have alot of black tarps and wondered if we could use this instead of the poly.
We will not be pouring the floor until next year and thought if we gravelled it it would help with keeping the heat in and the moisture down. We will also be pink insulating /vabour barrier the front wall which is the only wall that is not block.
We are in Ontario so the freeze thaw is an issue.
Replies
No idea if the tarps are okay, but whatever you put down,place it down before you install the gravel. The vapor barrier won't be liable to tear up this way when you do pour the floor.Personally, I would buy 6 mil poly and install it before I would use the tarps, unless I knew the tarps were okay to use.
mike
We have been advised that the poly goes down after the gravel not before.
Now you are saying it goes down before the gravel. Won't the moisture be trapped if we do that.?
yep, and that is one reason we don't poly beneath slabs!
OK so it does go on top of the gravel.
If you use it!
Well, theres the next question..... Do we need to use it.?
Bingo!
I live in upstae NY and have framed literally several thousand of homes in Syracuse.
It has not been done for years. The reason I have been given, is it retards the curring of the cement for a long time.
I've been involved on ONE job where sand was used between poly and concrete. The floor in question was a High School Gym floor. The sand was there as a cushion, and yes, after the pour ( and finished to within 1/8" FLAT all the way around, PITA) the concrete was wet down and covered for two weeks to cure. Any water in the sand is used up by the concrete as it cures, the poly keeps any more water from coming up into the sand "base". After the floor had "water-cured", a maple hardwood gym floor was installed with rosin paper between the concrete and the wood floor. After about 10 yrs., still no "call-back" to fix this floor. Floor is located at Sidney Lehman High School, Sidney, Ohio." Although I have the right to remain stupid, I try not to abuse that right"
The water cure made that a perfectly cured job. My best slabs have been water cured.
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>>The reason I have been given, is it retards the curring of the cement for a long time
And that is a bad thing?
Most slabs that are poured directly on stone or the gound looses moisture quickly and the results is shrink cracking.
To much water in the mix will weaken the test strength of concrete and is the biggest reasonmany concrete contractors don'y want poly under a slab. they incorrectly think that the moisture drawn out of the mix by the stone or dirt will compensate for thier poor judgment in adding to much in the first place.
More on this later.
I gotta go.
Maybe BB will enter the discussion.
Most slabs that are poured directly on stone or the gound looses moisture quickly and the results is shrink cracking>>>>>>>>>>>>>>>
Something I personally have never witnessed.
We can go back to the old discussion on which way moisture is driven in any structure. It is going to move from higher to lower areas. In walls with the RH insides a house is generally higher than outside the structure so we place a vp inside to keep the moisture out of the wall assembly. For a concrete slab without a vp directly under it, you can think of it as a large very hard spong that will wick any moisture in the ground up and through it into the relatively lower humidity environment of the building envelope.
Even with a vp under a slab the same thing will happen at any point the vp is compromised by holes, tares, untaped lapes and unsealed edges. Taping a 2x2' square of plastic on top of basement slab is a common test used to determine how much moisture is moving through the slab and into the house. The use of a sand layer between a vp and the slab does nothing to prevent the mechanics of water moving and according to Building Science may excaberate the problem.
As far as slabs poured directly on dirt or crushed stone you can think of the same mechanics working in the opposite direction durring the cure cycle of the concrete. The stone or dirt are dry in comparison to wet concrete. Moisture will wick out of the mix to the drier stone or dirt andgive you an uneven cure. the bottom is setting faster than the middle and top of the slab so it is shrinking somewhat as the matrix is formed while the middle of the slab is building the same crystaline structure at a slower rate, and the top maybe going at an even different rate. The results is an amorphous stratification of stresses developing in the slab which will eventually cause stress cracking. Even in the best if conditions you get some of that going on and it is the reason for cutting or placing control joints in the slab as much as the normal expansion and contraction of a cure slab is.
Gotta go to work.
I'll finish later if brownbag doesn't come along and do it first.
When the crew I worked with poured directly on compacted gravel bases, we'd spray the gravel down with a water hose before the pour. We wanted the gravel to as wet, or wetter, than the concrete being poured. Just a thought..." Although I have the right to remain stupid, I try not to abuse that right"
I've done that to on exterior slabs and driveways.
Mostly I've done large commercial pours and poly was always speced. I even did one job where the sand layer was called for by the design engineers. I think it was one of those things making the rounds about 98 or so.
We always cut our slabs early and often as well as using cure and seal soon after the trowel machines came off of them. In the summer months we would also place sprinklers on them to keep them wet.
I'm not sure how much any one of those things helped but overall we managed to greatly reduce the early stress fracture on large pours.
When watching some residential flat work guys I am appalled at the amount of water they add. It sure make placing easier but I hate to think what the test strenght would end up being. I've probably only known only three or four residential guys that truely know the whats,whys and wherefores of good concrete work.
Last year I helped out on a driveway/sidewalk pour. By "helped out" I mean acted as a consultant/boss. Turned out that I probally forgot more about pouring concrete than the crew I helped even knew about the subject. Order for the concrete was 4 yards off, rebar was wrong and just laying on the gravel, no water handy to sprinkle on the slab so that it wouldn't set up too fast ( we almost lost it), no "rakes" to help the screed guy (me). Yep, residential work is a whole nother world. Now, what would happen if they (the residential guys) had to do a Tilt-up wall panel type of structure? Now that would be scary!
" Although I have the right to remain stupid, I try not to abuse that right"
"When watching some residential flat work guys I am appalled at the amount of water they add. It sure make placing easier but I hate to think what the test strenght would end up being. I've probably only known only three or four residential guys that truely know the whats,whys and wherefores of good concrete work."I asked one flatwork contractor what water content he prefers to use, and he replied a 5" slump. I've seen his results, and it does look very good. Your opinion on the 5" slump?
The 5" slump is usually the best to work with. Lower slump numbers (4" and below) are a bit "stiff" to place, and need more vibration to level out. The "high slump" numbers are more for wall pours, where you need the concrete to "flow out" in the forms." Although I have the right to remain stupid, I try not to abuse that right"
One point about laying gravel in the basement was brought to my attention while visiting a friend in Vermont last week. He put a layer of gravel on the basement floor, I forget why, but after a few days he discovered the house cats were using the floor as a giant litter tray......
It won't hurt the concrete one bit.
There was a basement I was involved in one year, the contractor did things as cheap as he could get away with. Basement had poured concrete walls, house was frmed, sided and roofed, and then he remembered to pour the basement floor! We backed the trucks up to the garage door, ran the chute inside and over to the stairwell to the basement. Poly was in place over the gravel, but no mesh of any kind was laid down. Couldn't get it in the basement anyway. Two "screed" guys worked the pour, with three guys running wheelbarrows from the chute to where the concrete was needed. The last three yards were held up while we "bucket-brigaded" about 100 gallons of muddy waterup out of there. What we had poured was just a "rat-slab" of a floor for a $98,000 house's basement! Within a year, that floor had buckled up in the middle, and was slowly turning into a gravel floor. Also, NO expansion was used around the walls, so the basement had no where to go but up. No control joints were ever cut in this floor, so cracks went any( and every) where. Whenever someone talks about pouring a basement floor, I will tell the RIGHT way to do it, and that way was NOT the way. Now, IF one wants a basement floor down RIGHT, here's a little "How-to":
When ordering a house with a basement( with poured concrete walls), 1) have a "water-stop" ( a strip of rubber, ridged to lock it into the concrete) installed between the footer and the walls, 2) poly on top of well compacted gravel ( NOT pea gravel), 3) 6x6 Welded Wire Mesh, install on either "dobies" , small rocks, or those new plastic "standees", and tie the sheets of mesh to each other, 4) leave about 2-3" of space between the walls and the mesh, 5) install foam expansion strips along the walls, with the top of the foam matching the height of the finished floor, 6) IF there is an "inside corner" in the plans, install two #4 rebars, about 2-3' long, as diagonals at the "point" of the corners, 7) pour and finsh the floor, add "cure and seal" when done, 8) come back the next day and cut "control joints" about 1/2"-1" deep. Divide the floor into "squares" about 12'x12' when laying out for these cuts, clean up the mess when done and pay the bills. Done.
" Although I have the right to remain stupid, I try not to abuse that right"
Edited 9/19/2009 10:01 pm ET by whitedogstr8leg
house was frmed, sided and roofed, and then he remembered to pour the basement floor>>>>>>>>>>>>>>>>>>>>
In my experience, this is how floors are done in new construction. As far as the rest of your story, sounds like a bad job.
4-5" is what I want
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A 5 slump is good.
Depending on the ready mix plant location and weather, we ussually ordered on a 4 and then could add a little water.
I like a 4 for footings and walls if I have a good tuck driver. A good crew and a good driver can make all the differance in the world to how hard you end up working.
A 4-5 slump is right for footers, but for wall... a little bit more water is nice. Vibrate the wall forms and watch the "excess" water run out from the bottom of the forms. I want the concrete to "flow" down along the forms, past the rebar, and other "items" in the wall forms. I used a 6-8 slump on wall pours for this reason. Too "thick" of a slump will move things out of it's way, driving rebars to the sides of the forms ( been there, done that) and it needs a LOT more vibration to "settle" the concrete in place. Of course, when one pours and finishes 75' to 125' of wall a day, anything to help with the pour is welcomed. It also gives the crew time to set another 75' to 125' of forms for the next day's pour. As for "flat-work" slumps, it will depend on the crew. And the most important part of that crew would be the "rakers" behind the screeders. A good "raker" will help even a bad screed-man by keeping excess "mud" away from the screed board. Of course, if one has a powered screeder, even a 4" slump is easy to do. " Although I have the right to remain stupid, I try not to abuse that right"
I just had 47 yds. poured in my foundation wall.
9' walls on stepped footings that took it to 12' in two places and couple of steps in the wall down to 6' and 3'-8". Wood forms with a wall tie and round bar locking system I've never seen. High walls had #5 vertical on 16" centers to 7' high and #4 's @ 16" o.c. The low walls had #5's @ 2' o.c. vertical and #4 @16" horizontal. We pumped it at 5 with a water reducer added on site. These guys didn't vibrate at all. Instead the rodded the whole wall with 2x2's and beat the forms with a rubber mallet.
Wildest thing I ever saw. We poured last Monday and I did'nt let them wreck the forms untill Thursday. I was expecting a spitpot full of honeycombs but was very pleased to have onl two small spots (cover them both with my hand). All in all it was a slick job and I'm pleased with it.
These were 8" walls with all that steel and no vibration to move the mud or keep it from honeycombing. Both the company owner and his Dad liked the water reducer i had added. Said it made the pour so much easier.
Like I said, I did commercial work. A vibrator in the right hands is a great tool. In the wrong hands, it is a catastrophy waiting to happen.
"I've probably only known only three or four residential guys that truely know the whats,whys and wherefores of good concrete work."YupI almost got into a knock down, drag out fight with a guy on a slab where he wanted to keep adding more water. He was crying that it was too hard to push/pull. I had to get right in his face and holler
"NO
MORE
WATER!
If you're too much of a puss to do it right, I can handle the job alone."He went back to work doing it my way and muttering the whole time about how this guy and that guy and somebody else all pour it with more slump...But all their slabs have excessive shrinkage cracks from too much water. All they are intersted in is making it flow easy
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"The reason I have been given, is it retards the curring of the cement for a long time."That is pure baloney!Concrete cure is a chemical reaction that begins the minute it is mixed with water and continues near infinitely, tho for all practical purposes, 30 days gets over 90% at normal temperatures.The only thing that is retarded is that the crete guys who use too much water in the crete to make their slump screeding go easier have to wait for it to seep into the soils below or to evaporate. The problem is guys adding too much water, not the fact that the plastic lets it float to the surface.The strongest concrete comes from having the right amt of water and then keeping that water in the mix until it cures as a part of the slab
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Sure go ahead and use tarps for the interim. And make sure you do use 6 mil poly lapped and taped before you do pour the floor. Don't forget to provide a floor drain at the lowest point.
Edit: There was a point several years ago when it was suggested that the poly should be placed under a layer of sand to help the concrete cure. But recently it has been found that, as you suggest, quite a bit of moisture is trapped there. Pour your concrete directly on the poly and end up with a nice dry floor.
If you want a more detailed explanation of the issues involved you might want to go to the BuildingScience website.
Edited 9/16/2009 4:09 pm ET by fingersandtoes
If the winters are severe in your area the freezing and thawing action on footers and any plumbing must be considered. By tarping the whole area as you mentioned this will help but where footers are not below the frost line I would supply further protection. Things like laying some rigid insulation on the areas where footers are before tarping might be in order. Others might have some thoughts. Also keeping the area as dry as you can will help.
I think you meant to send that to poorgirl.
Yes winters are severe, we did use straw for 2 years, but last year we put hydro in and had 2 4800W construction heaters tied into the panel going full time and we are still paying for the hydro bill. But it did keep the place dry. Our neibours did not heat their basement they just left it alone and they did end up with large cracks in their cement floor, they have never heated it and it's 5 years old. Who knows what other damage they have done. We don't ask since they think we are nuts to heat it.
So if we lay the gravel and insulate the exposed wall then we are hoping we only need to use one heater and use the other as backup.
Yes, we will heat the basement for the entire winter and insulate the exposed wall
Thank you, I will check out the web-site
"There was a point several years ago when it was suggested that the poly should be placed under a layer of sand to help the concrete cure. But recently it has been found that, as you suggest, quite a bit of moisture is trapped there. Pour your concrete directly on the poly and end up with a nice dry floor."
Where does this moisture come from and why does eliminating the sand eliminate the moisture? Does the sand somehow cause the moisture?
From buildingscience:
"A sand layer should never be installed between the sheet polyethylene vapor barrier and the concrete slab. Sand layers located between the slab and the vapor barrier can become saturated with water, which are then unable to dry downwards through the vapor barrier. In this scenario, drying can only occur upward through the slab which typically results in damaged interior floor finishes (Lstiburek, 2002)".
All I asked is where does the water come from. I could say water in fiberglass wall insulation is bad.... doesn't mean we should dump insulating walls does it???? No we keep the water out.
So I'll ask again where does the water in the sand on top of a vapor barrier under the concrete come from?
Rather than my having to paraphrase the whole article I have already posted one paragraph of, and considering I have twice said where it was from, couldn't you go and read it yourself at the Buildingscience site?
The "water" is in the sand itself. IF done right ( NO holes in the vapour barrier) once the concrete has cured, using the excess water IN the sand, no more water will come up through the vapour barrier. We are talking about an inch or less of sand on the poly. If the "system" is good enough for a High School Gym floor, covered in Maple hardwood flooring, I would guess that it would be good enough for a basement floor." Although I have the right to remain stupid, I try not to abuse that right"
That would be from the soil - groundwater. in a lot of places, there is hydrostatic pressure from below. I learned that here at BT, it is not something I often see in places I have lived.
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Gravel it now, place the tarps over the gravel for now. When you are ready to pour the concrete, first add another 4" of gravel and compact the gravel down , and level it out to "grade". Then add your 6 mil. poly on the gravel. Add some small concrete "dobies" ( small concrete "bricks") to keep the 6x6 Welded Wire Mesh up off the poly ( no holes in the poly, that way), and TIE the sheets of WWM together. THEN pour your floor. Note: add some foam "expansion joint" strips around the perimeter of the floor. This will help "seal" the area between the floor and the walls. These strips come with a perforation along the edge, after the pour, you can "strip" off this 1/4 x1/4 strip, and epoxy-caulk the small gap. Nice and weather proof basement.
Thank you, I will print your instructions and give it to my DH
What are doing to keep the footings from freezing/heaving?
In MI, we used to use straw. It's not very pretty in the spring though. The builders used to lay poly, then straw. Then, after they got heat to the basement, they'd toss out the straw with pitchforks and roll up the poly with the nasty messy rotted straw juice and toss it out.
You can avoid this mess if you put the frame on the basement and keep a little heat down there but that is expensive too.
I've seen builders try to skip the straw process. The stanchion pads would heave as much as two inches. They eventually settle back down but then the carpenters have to come back and retighten everything.
We did the straw bales for 2 years and yes what a mess to clean them up, but they did work. I wasn't looking forward to the spring since that was my job to clean up .
bump