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mfiore 05-01-2008 07:45 PM

Slope to foundation slab
All of the directions stress how level to make the foundation slab. Can this have a slight slope to it? Couldn't the above block stand be leveled properly with a little mortar below the first course? I would like to avoid rain from running into the wood storage area.

Obviously, I've not poured concrete or put down brick before.

gjbingham 05-01-2008 08:24 PM

Re: Slope to foundation slab
I think that is valid. You don't need much slope of foundation to direct water runoff. 1/4 - 1/2 inch over an eight foot length of concrete slab will drain the water away. I'm not a mason by any means. I recommend you wait for a couple other answers.

Dutchoven 05-01-2008 08:31 PM

Re: Slope to foundation slab
I actually would say that it is not a bad idea at all...the paramount concept being a verrry level hearth slab and that could be reached as you said by leveling the first course and continuing...the slope of the ground slab for our restaurant oven has a slight fall to it and is almost exactly what george said...about 1/2 inch on 8 feet
...good luck mfiore

james 05-01-2008 10:16 PM

Re: Slope to foundation slab
Or, you can pour your foundation level, and then use mortar to add the slight final slope after you are finished you stand. If the natural run-off slope of your foundation doesn't make it easy to slope the area under the stand, that might be easier.

That's how we did it.


RTflorida 05-01-2008 11:51 PM

Re: Slope to foundation slab
I used James approach. Level slab, built the stand, and made a thick slurry of type S mortar, sand, a bottle of acrylic bonding agent. coated the entire inside of the stand block then floated about 1/4" of slope on top of the slab. So far, so good (its been a year) we have horizontal rain every day in the summer, have never had water get more than 3-4 inches past the doors on my wood storage area and it runs back out under the doors - never reaching the wood.
The type S slurry has held cracking or damage from tossing wood on top of it. My only expense was the bonding agent ($8 or $10), as I had plenty of type S and sand at the time.


DaveHI 05-02-2008 01:38 AM

Re: Slope to foundation slab

My pool area has a 1/4 inch/foot slope to get the water to flow where we wanted it. I built a CMU wall and leveled the first course as you thought.

But be warned. It's a bit of a pig once the mortar bed gets more than about an inch thick. Or at least it was for this rookie mason.

mfiore 05-02-2008 07:58 AM

Re: Slope to foundation slab
RT, James,

Intuitively, I'd worry that a think skim coat of mortar on top of a slab of concrete would chip away or be very difficult to uniformally apply the slope. Do you think this is more of a concern with freeze/thaw cycles (Michigan)


james 05-02-2008 08:48 AM

Re: Slope to foundation slab
We tiled and sealed on top of the mortar.

In our case, it was too thick to do in a single coat, so we pour the slope and let it dry, the came back with thinset and the tiles on the hard mortar.

Mike, mortar is basically concrete with a finer aggregate. Plus, it sits under your stand, which will give it some weather and cold protection.

If your layout works where you can get the right slope with a single concrete pour, go for it!


Mojoe 05-02-2008 11:24 AM

Re: Slope to foundation slab
I sloped my foundation slab, dry stacked the cmus, and leveled the hearth slab. If you're building your stand with cmus you need to cover them or water will penetrate through. Winter set in before I could put on the stone veneer and my wood has been damp as a result.

david s 05-02-2008 01:16 PM

Re: Slope to foundation slab
Had the same idea about moisture in the bottom of the wood storage and also came up with the same solution of adding an extra layer with a slope. When making a thin layer it is really difficult to do if you have course aggregate. Use fine aggregate or course sand. I find that I never use the wood right on the bottom. It must have been there for about three years. Who cares what happens to it. Dont be too fussy. I find that leaving two bits of wood just inside the entrance to pre heat it before it goes on the fire works well and would dry off any moisture. Hardly ever rains here in the dry season. Have not had a drop of rain for two months, but everything still green.

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