Sloping Top of Slab Via Cementitous Fill

[marinaman]

I’ve got a question for you guys:

I’ve got a project where I have a mat foundation. The mat is 12” thick concrete. Off of the mat, there are several very short concrete walls (4’ Tall or shorter). The walls create planters atop the mat foundation.

Inside the planters, the top of slab needs to slope to drains. The mat foundation is fairly large, and as such, we do not want to try and slope the top of the mat slab itself because this would be very difficult to do, given the size of the mat slab, the number of planters, and the difficulty in locating all the planter extents while trying to pour this mat slab. In fact, we’re going to allow the short wall dowels to be epoxy anchored into the mat slab, following the pouring of the mat slab, because laying out the dowels, via a surveyor, post mat slab pour, will be easier for the contractor to do.

All that said, we need to slope the bottom of the planters to drains. The bottom of the planters is also the top of the mat foundation.
The idea is, once the mat foundation is in-place, the dowels are epoxied into place, and the planter walls poured....the planter bottoms can be poured by a thin thickness of flowable fill or gypcrete.

Have any of you guys tried to slope-to-drain via a cementitous over-pour before? Do any of you guys have any recommendations on a product for this purpose that worked well for you?

 

[cvg]

just use a troweled stiff grout (not poured) and slope and shape it to drain

 

[RickyTickyTavi]

Just roughen the surface to 1/4'' amplitude and place a thin-set pre-bagged concrete or mortar to the slope you need. I like using BASF, Sika, and Euclid all have several products that would suffice. Repair products will be a bit more expensive, but I'm guessing youre not talking significant volumes of material.

You could also use your planter waterproofing system to achieve the slope required, a lot of times they have built in drainage backing. Punt it to your architect.

 

[jayrod12]

You could also use your planter waterproofing system to achieve the slope required, a lot of times they have built in drainage backing. Punt it to your architect.

Most definitely this comment. However the architect wants to deal with the slope. If they want to have the contractor do it with cementitious grout, then by all means the contractor can provide that. Either way it doesn't really matter you you.

 

[JAE]

Don't use Gypcrete. OK for indoor floors, etc. but not for wet environments.
Gypsum doesn't like water.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[marinaman]

Thank you for your input guys.

I've got a good contact with Euclid. He's telling me that the Versaspeed 100 is probably the best product.

Here's a wildcard for you:

The architect emailed me today and told me that they have decided to waterproof the walls of the planters, but not the bases. The bottom of the planters are just my concrete mat with a topping.....sloped to drains.

Seems weird to not waterproof the bottom.

 

[dik]

If the bottom is not waterproofed, the walls will be damp by capillary action... no point in waterproofing the walls... Maybe an epoxy or polyurethane coating.

Dik

 

[RickyTickyTavi]

yeah, I respectfully disagree with the architect on the waterproofing detail. Dik is correct. And I'd also add that two things will occur over time. Water will find its way to the cold joint between the bottom of the planter and the wall. In addition, depending on the plants within the planters, their root system could also find the cold joint.

 

[dhengr]

Marinaman:
Why not precast the planter floor/tubs in place, on top of the mat found. Slope the tub fl. as needed, install all of the rough plumbing for the drains, and build 6” high curbs around the tub. Then build the planter walls on top of the curbs, with vert. rebar, water stops, waterproofing, etc. as needed. That will give the Arch. a couple more construction steps during which he can change his mind again.