Hand mixing cement

[Dana]

 I am putting in the slab for my Central Boiler today. The question is what is the ratio of cement, sand, and gravel?  I know that the trucks call it 4 bag five bag ext. mix but that dosent help get the shovel ratio right.

[GareyD]

For a low strength general mix...

Use 6 parts gravel, 3 parts sand and 1 part cement.

For a medium strength general mix..

Use 4 parts gravel, 2 parts sand and 1 part cement.

I use a bucket instead of trying to estimate the heap on a shovel...seems to give me a more consistent mix..

YMMV  ;)

[Dana]

Thanks Garey, I will use the medium strength mix ratio.

[SwampDonkey]

Been 20 years since I helped do that around the farm. I can't remember the ratios, so go with what Gary said. Don't even have the mixer any longer. ;D

[Corley5]

We're lucky to have a Great Lakes Redi Mix plant 5 miles from here.  The slabs for all three of our outdoor boilers have been balances on loads coming back.  Each 4'X12' slab cost $50.00.  Dad's was leftover from a garage approach, mine is curb mix from Petoskey and Grandma's new slab was leftover from parking lots being poured at the Coast Guard Station in Cheboygan.  That load was HOT.  I had to work pretty fast on it.  It was poured and screeded by 5PM and at 6:45 PM I could walk on it with out leaving a mark.  If you're close to redi mix plant it'd be worth a call

[maple flats]

For using crushed stone or washed stone the ratio of 1 cement, 2 sand and 3 stone will give you footer grade concrete (3500 psi). I hate working with concrete!

[Jeff]

Dana, dont use round stone or washed gravel in Michigan for a slab. Your concrete will pop in the winter as the small water bearing rocks freeze. Use only crushed limestone.

[Jason_WI]

Usually flint in the gravel will cause the cement to pop in the winter. My grandmas cement steps have pop holes in them and at the bottom of every hole is a flint stone.

Jason

[DouginUtah]

Since no one has mentioned the fourth ingredient, I will.  ;D

The most important consideration in making concrete is the water:cement ratio. You want the mix ( I have always heard 1:2:3) to be as dry as is reasonable. If it is soupy there is a good chance that you will not be getting the strength you would if it had a good stiff slump.

-Doug

[sawguy21]

Boy, this thread brings back some memories. OOOH, my aching back. ;D I have not done it since 1973 and still remember how. Footings and floors were not too bad but running that wheelbarrow while pouring basement walls was DanG hard work. No ready mix in those days and I don't know that my dad would have used it anyways. He was fussy about his mix.

[SwampDonkey]

My dad wouldn't use ready mix on his fix up jobs. Gravel and labor was cheap so, grab the shovel, wheel barrel and bale the water from the trough. He always thought us young fellers needed something to do, even if we thought otherwise. ;D :D

[Dana]

Jeff, I went right to work yesterday and poured the slab with pit run gravel. I hope she dosen't pop. I have seen many old barn foundations and floors that didn't break apart that used pit run so we will see. Corley, we have a redi-mix company within five mile but they take the cement back home and use it to make those moveable poured wall blocks. I got the cement for our pole barn from Grreat Lakes in Gaylord and also from Alden. Nice guys to work with. I plan on giving the cement a week to harden since the boiler weighs over 2,000 lbs empty.

[etat]

just a suggestion, after it fully cures if you spray it with watersealer it won't soak up as much water

[sawguy21]

Good point.

[Dana]

Cktate, do you mean something like Thompsons's water seal? Sounds like a good idea.

[etat]

  They make a water sealer especially  for concrete but all of the contractors that I know just use plain old Thompson's water seal.   That's what I used on my shop floor too.  Just be sure to let the concrete  cure  good first, I 'think' about three weeks.  I put it in a  pump up sprayer and spray it.  Also I often use it on older chimneys on houses.  Sometimes in a blue moon there will be a leak caused by the bricks or mortar joints cracked or from the bricks being too porous and letting water get behind my flashing from somewhere higher up on the chimney, even though my flashing  is cut into the bricks themselves.