I admit, this was one of the tasks I’ve been most excited about … and afraid of. I could, of course, have asked the plumbers to repair the slab they tore up when their work was done but I’ve never worked with concrete before and wanted the chance to try my hand. When I saw the size of the hole I had a few second thoughts in the end it was a really fun time to fill it back in.
With the right tools (another post) the job was really pretty simple.
First I prepped the area by dampening the soil and making sure that a) all the PVC and drain tile was fully covered by dirt and b) the depth of the new slab would be consistently between 3 1/2 and 4 inches. I capped off all the plumbers pvc just to make sure no drips of cement could get in. I also covered the new floor drain with blue painters tape that we could razor out after the pour. My dad chiseled the edges of the broken slab to make sure that our pour would often undercut the existing slab (to be firmly set in place) and, to be better safe than sorry, we also decided to apply a coat of bonding adhesive to the broken edge to ensure a good connection.
By far the hardest part of the whole project was hauling 17 bags (1020 pounds in total) of Quikrete cement mix from Home Depot to my basement. To prepare, my wonderful sport of a dad and I carried down 8 bags each, leaving the three we hoped were overage in the car. In the end, I ran back up for a last bag when we ran out just before the floor drain area. If our square footage had been ANY bigger I’d probably have ordered pre-mixed concrete delivered to pour but our total was less than a third of a cubic yard which just didn’t seem worth anyone’s bother.
Once we were set we mixed each bag of High Strength Concrete Mix with between a half and three quarters of a gallon of water (we used to half gallon milk jugs to make sure we didn’t over pour) and stirred them until wet and slurry with garden hoes in a nine gallon plastic tub. When there wasn’t any dry mix left, Dad and I dumped the tub into our hole and I worked it into position while he and mom got back to mixing another batch.
We wore masks because pouring the bags of mix out got pretty dusty. Other safety equipment was pretty much limited to knee pads and rubber gloves (wet concrete can be a skin irritant).
Getting the concrete smoothed into place was tricky, only because of the odd shape of the hole and the large number of pipes coming up through the surface. In general, to smooth concrete, you strike off the extra with a long flat object – a screed – which is often a 2×4 like the one I used. In this case, I had to keep moving my screed around to different angles to get between the various obstructions – I used three different boards of different lengths to fit each angle and in very tight quarters I smoothed it with a small trowel.
Concrete is a fun and fascinating material to work with. Dumped out of the pan it is a rocky mess, but with a little agitation – tapping or whacking it with the trowel, or jiggling the 2×4 as I moved it forward across the concrete would shake the bigger rocks below the surface and leave a smooth liquid layer at the top.
I kept the surface level – by striking with the 2×4 – in the areas that will be hallway and bathroom but the last corner of the pour was more complex – it needed to slope down in a shallow cone to the floor drain. I finished off with the hand trowel, adding just enough cement that there would be no low pockets to catch water in – any spills will roll nicely down hill to the drain. Dad is cleaning up the edges with a wet sponge.
Now there’s nothing to do but keep the new concrete damp as it cures by spraying it down morning and evening. Next step is framing the walls of the new hallway and bathroom.