Replies

1. 
   billybatts | Sep 13, 2007 07:08am | #1

   bumpy

2. 
   woodway | Sep 13, 2007 07:36am | #2

   No significant thoughts on concrete but if you intend to heat the garage during winter, make sure you install rigid foam insulation around the perimeter down to the frost line.

1. 
   billybatts | Sep 13, 2007 09:20am | #4

   thanks, we insulated to about 18" below grade with 2" blue board and the insulation also follows the contour of the thickened edge and also the whole area of the slab. What a pain in the neck that whole deal was.

1. 
   woodway | Sep 13, 2007 07:38pm | #6

   Insulating the whole area of the slab is not necessary. Just the outside edges will get the job done, the thermal energy radiating up from directly below your slab is the ground temp which, I'm guessing here, is about 68 degrees anywhere in the North American continent. Geothermal heat pumps, used throughout the US and Canada, take advantage of this constant ground temp to function in their heat exchange processes. Caves and mines, within say 50 to 100 feet of the surface, are always at constant temperature regardless of the outside temperature, hot or cold. PS I'm guessing on the earth temp but I'm sure someone here will jump in to correct my guesstimate.

1. 
   r | Sep 14, 2007 04:46am | #8

   My guess would be closer to 50-55 degrees F.

2. 
   Billy | Sep 14, 2007 05:10am | #9

   You're missing the point of insulating radiant slab.  If he has a radiant slab then the winter temperature of the radiant slab will be hotter than the earth temperature and the ground will be a heat sink and result in wasted energy.  It is good that he insulated underneath.

   Billy

1. 
   woodway | Sep 14, 2007 11:32pm | #15

   Yes, if he's heating the slab I don't see any sense in trying to heat the ground under the slab too. I guess I was just too focused upon the cold (frozen in winter) ground temp outside the structure drawing heat out from the interior of the garage. If it were an unheated garage, I would argue for not insulating under the slab, just the perimeter as he's already done.

   Edited 9/14/2007 4:34 pm by woodway

3. 
   tom21769 | Sep 14, 2007 11:42am | #12

   >>Insulating the whole area of the slab is not necessary.A radiant slab will take time to cool down as well as to warm up. You will accentuate this effect by not insulating the center. In effect, you're creating a big thermal flywheel out of the ground under your slab. In a consistently cold winter climate, or if you have a solar system in a cold area with frequent cloudy days, this may be exactly what you want. Maybe not so desirable if you have many mild winter days or long spring/fall transitions.

4. 
   Piffin | Sep 15, 2007 04:32am | #16

   "Just the outside edges will get the job done, the thermal energy radiating up from directly below your slab is the ground temp which, I'm guessing here, is about 68 degrees anywhere in the North American continent."It is better to know than to guess when giving that sort of advice. It's not like he can ad insulation under the slab later if he decided he needed it.Here, the soil temp average at four feet down runs about 54-57°F In Alaska, which is a good sized part of the North American continent, they have this sthing called permafrost because it stays frozen.Geothermal loses efficiency after it gets below 55 degrees. I know of a place here designed by a professor - retired - for himself with in ground geothermal. he abandoned it becaue of the cold soils.We always insulate under slab. If he is heating space to 70°F using fluid at 110° while the soil is 55°, the diffential is pretty extreme to have no insulation. 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

1. 
   woodway | Sep 15, 2007 08:25pm | #21

   Take a look at my message #16 in which I agreed with Billy that since he's heating the slab it makes sense to insulate directly under the slab to avoid the endless heatsink into the soil below. As was mentioned in message #9 by "r" the soil temp is fairly constant once you get below the frost line in the soil, about 56 degrees it seems.
   I suspect they have deal with "permafrost" in Canada too so insulation around the perimeter would be a "must," as would insulation under the slab if hydronic heating is planned. Permafrost must be taken into account whenever construction in cold climates is considered. As you pointed out, once you get down below the maximum depth of frozen soil, things are constant year round. In the 40's they had a lot of problems with construction of the "highway" due to thawing of the permafrost in sections where vegetation was removed.

2. 
   Piffin | Sep 15, 2007 09:45pm | #23

   Yeah, I see you had already been corrected and changed your mind by the time I posted that one. 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

5. 
   rich1 | Sep 15, 2007 06:03am | #18

   Actually, we  have a proposed hydronic code up here that requires insulation under the slab.

1. 
   woodway | Sep 15, 2007 08:33pm | #22

   Sounds perfectly reasonable to me, see my message #16.

2. 
   Devin | Sep 14, 2007 03:19am | #7

   May I ask why ?

3. 
   shelternerd | Sep 13, 2007 07:55am | #3

   Workshop floor I think you can do 3,500 psi. Might save a few pennies.

   ------------------

   "You cannot work hard enough to make up for a sloppy estimate."

1. 
   billybatts | Sep 13, 2007 09:21am | #5

   it will have a garage door so i guess we have to get driveway concrete.

4. 
   Jeff_Clarke | Sep 14, 2007 05:11am | #10

   billy - that's around 10.5 yards ... $160/yard for 5,000 psi a/e concrete seems like a good price.

   I'd consider 4,000 psi but add fibermesh as well as 6 x 6

   Now this 10.5 yard pour ... ever done that before?  First, at a stiffer mix of 4-5,000 psi you might want to consider adding SuperP (superplasticizer) for workability or else you're going to have to add water (bad idea) because it's hard to place and finish that much concrete, quickly enough, without a minumum of 3-4 people and a power trowel.   It's a pretty big slab, maybe 24 x 40 (?) so you'll need to cut contraction joints the next day.   Have you figured out how to protect your radiant tubing when you cut the joints?   ;o)  You should also have enough plastic to cover it (moisture retention) for a few days.

   Insulating under the whole slab is absolutely required - you did the right thing.

   10.5 yard pour is a lot of hard work!

   Good luck!

    

   Jeff

   
   

   ---

   Edited 9/13/2007 10:13 pm ET by Jeff_Clarke

1. 
   billybatts | Sep 14, 2007 08:34am | #11

   it's a 22x20 slab...it has rebar placed 12 or 18 oc can't remember.
   Have not done it before but people on the crew have.
   How deep should the control joints be?
   Thank you for the advice, i will ask LaFarge to put in the superP. Lot's of old guys on the crew will thank you later :)

1. 
   Jeff_Clarke | Sep 14, 2007 08:04pm | #14

   Control joint depth should be 1/4 to 1/3 the thickness of the slab.

   The control joint product mentioned is called a 'metal-keyed control joint' - you can get them with tear-off strip for caulking.   Probably overkill for a garage - if you're careful and plan the joint locations you can set your tubing to 'take a dive' under the joint locations.

    

   Jeff

   Edited 9/14/2007 9:20 pm ET by Jeff_Clarke

1. 
   billybatts | Sep 16, 2007 04:23am | #26

   dang i should have planned my control joints before i placed my tubing. Thanks for the formula, i had no idea what depth to go to.

5. 
   STAINLESS | Sep 14, 2007 04:30pm | #13

   Hallo out west!

   Another one in the Great White North we call home EH?

   Hail & well met!

   If you can find post #93454.38 I had about $0.02 worth of advice on control joints re: "Concrete floor in garage" a while back that may be of some use to you.

   The advice on cutting without damaging the tubing is right on, in my opinion. I might even suggest it could be worth your time to form your control joints during the pour to avoid cutting altogether. I suspect that a commercial product exists that allows you to place the joints prior to the pour & just zip up a cap strip after the curing is done to allow filling of the joint later. (I have just never been able to connect with the right person to locate a product name or supplier.)

   The suggestion of a high range water reducer (Super P) is heartily endorsed by me, and I would suggest that you bring in a few vibrating pencil type devices to get good consolidation around your tubing & rebar. The heat conductance from the tubing depends on close coupling to the concrete, you don't want voids between them.

   Have you planned on pressurizing the tubing during the pour? Pressurized tubing is tougher to crush under foot and can ID a leak with a rush of air in time for you to effect a repair before the slab sets up. You might want to consider a few repair couplings to have on hand that are compatible with your heat tubing as insurance against that. Pay the big bucks for the good fittings, they may have to become permanent features of your floor!

   Your concrete mix depends on floor use and placement thickness. I happen to like 5000 PSI too. You could get to 5000 PSI if you could buy 4000 PSI & damp cure it long enough.

   If you ultimately intend on coating (painting) the floor  you might want to forgo a cure & seal product so the concrete presents a better surface for the final coating to adhere to. That makes a poly curing membrane & lots of water after initial set all that more important.

   I think my price for 5000 PSI with Super P about 3 yrs. ago was near $120. per m3 CAD, however that was Summer concrete and depending on when your pour is planned, you may have to pay the premium for Winter mix which adds to the cost.

   Sincerely,

   STAINLESS

    

1. 
   Piffin | Sep 15, 2007 04:37am | #17

   With radiant in slab and a good mix like this, not too much water, i would not even bother with control joints on such a small slab 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

1. 
   Jeff_Clarke | Sep 16, 2007 07:45am | #28

   "With radiant in slab and a good mix like this, not too much water, i would not even bother with control joints on such a small slab"

   That advice is EVERYTHING it's cracked up to be - ;o)

   He needs one down the middle as a minimum - period.

    

   Jeff

1. 
   Piffin | Sep 16, 2007 03:32pm | #29

   Well, my last garage slab was just this size as a monopour three years ago and hasn't shown a crack yet.Controls are when you assume it will crack and want to specify where the crack will happen.but most shrinkage cracks are from shrinkage in larger slabs. I would control them every 16-20'With a small slab, the shrinkage is from edge towards center.The point I was making was IF you limit water use so it does not shrink so much. Too much water is the prime cause of shrinkage in curing concrete, IMO. And too many crews use too much water to try and make their jobs easier. 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

1. 
   Jeff_Clarke | Sep 17, 2007 04:06am | #32

   ROT is 40 x slab thickness, for 4" =160/12 = 13' and change MAX>

    

   Jeff

2. 
   SamT | Sep 17, 2007 04:24am | #33

   Max doesn't work here.I wouldn't be afraid to pour a 22x20 slab without control joints. I don't know about anyone elses work.SamT

2. 
   billybatts | Sep 16, 2007 04:21am | #25

   The suggestion of a high range water reducer (Super P) is heartily endorsed by me, and I would suggest that you bring in a few vibrating pencil type devices to get good consolidation around your tubing & rebar. The heat conductance from the tubing depends on close coupling to the concrete, you don't want voids between them. Good point, never considered thatHave you planned on pressurizing the tubing during the pour? Pressurized tubing is tougher to crush under foot and can ID a leak with a rush of air in time for you to effect a repair before the slab sets up. You might want to consider a few repair couplings to have on hand that are compatible with your heat tubing as insurance against that. Pay the big bucks for the good fittings, they may have to become permanent features of your floor!Unbelievably good advice! Thanks for taking the time to write all of this, i will do those things.

1. 
   STAINLESS | Sep 18, 2007 06:28am | #34

   BB,

   The pleasure was mine, you are most welcome.

   Sincerely,

    STAINLESS

1. 
   billybatts | Sep 18, 2007 07:39am | #35

   Reserved the vibrator today.

6. 
   Matt | Sep 15, 2007 02:33pm | #19

   I don't even know if 5000 PSI concrete is available around here.   Granted I'm in an entirely different geographic region, but 5000 PSI seems entirely un-necessary to me, unless there is some reason the radiant heat effects the situation (we don't use that since it is not very cold here).    I've had 8 monolithic slabs placed in the last 2 months and we used 3000 PSI per the engineered specs.

   Further I'm gonna guess that your slab, in the thin parts, is thicker that 4" due to the radiant tubing. 

   Just out of curiosity is this a regular mono slab, frost protected slab, or a floating slab inside of stemwalls?

   On a side note, the concrete supply company we use adds a midrange water reducer to the mix allowing the finishers to add water to bring it up to as much as a 6" slump.  I know some people here are going to scoff at that, but I just went through a big pissing match with the concrete sub over this.  I lost.  I had a slab tested by the engineering firm I use, and the concrete supply company tested 2 more slabs and they all came in at well over 4000 PSI 30 day strength.   I was amazed but after the head QC guy from the concrete supply explained to me about the mid range water reducer I understood.  I forgot the name of the chemical, but he specifically told me it is not a super-P.   He also wrote me a letter saying that 2 gallons of extra water per yard was fully acceptable with this particular mix, and sent me about a 20 page FAX of articles that descried various aspects of placing concrete.  I haven't had a chance to read it yet.  That 2 gallons is on top of the 4" slump that the concrete is ordered at.  BTW - this is a big concrete supply company - he told me they supply approximately 2000 yards on a slow day... and that their goal was to supply mixes that were practically "idiot proof". :-)

   Another FYI: all concrete sold (here) is air entrained.

1. 
   SamT | Sep 15, 2007 03:31pm | #20

   If you ever feel like scanning that FAX and sharing it via email, I'ld like a copy.Thanks,SamT

1. 
   Matt | Sep 17, 2007 01:42am | #30

   The documents the guy FAXed me were part of a series called "Concrete in Practice": Look at this web site.  It looks like you can view them online for free but you gotta pay $$ to get an actual copy of them.  It doesn't look like they address admixtures though.  I don't have ready access to a scanner, so the actual letter the QC engineer wrote to me I can't easily post.

1. 
   SamT | Sep 17, 2007 02:35am | #31

   Thanks.SamT

2. 
   billybatts | Sep 16, 2007 04:26am | #27

   Just out of curiosity is this a regular mono slab, frost protected slab, or a floating slab inside of stemwalls?It is a mono-floater with fro-prot.
   I heard air entrained won't conduct heat as well.

1. 
   Matt | Sep 18, 2007 01:57pm | #36

   >> It is a mono-floater with fro-prot.<<

   Just out of curiosity, what is the thickness of the edge of the slab (footer + slab)?

1. 
   billybatts | Sep 18, 2007 03:20pm | #37

   12"

1. 
   user-144854 | Sep 18, 2007 07:59pm | #38

   Not being a mud guy myself, about all I can add to the above excellent advice is that using fiber reinforced concrete instead of mesh can make it difficult to achieve a nice finish on an exposed slab.

   }}}}

7. 
   daveinnh | Sep 16, 2007 03:15am | #24

   • I would think 5000 psi is overkill;
   • Did you install a poly moisture barrier below insulation?;
   • I'd go with a sand mix - maybe w/ pea stone but w/o coarse stone aggregate to ease placement;

   Good luck