Turning an ugly concrete slab into modern looking rectangles with grass
March 22, 2020 11:10 AM   Subscribe

The previous owner of my house decided that he needed to pour a concrete slab over most of the open space in our yard. Rather than demoing the whole thing, I was wondering if it would be possible to strategically cut parts of the concrete to create a look of concrete pavers with grass (or a creeping oregano) between them. Is that possible to do? The slab is already divided into blocks with lines on them. It is 4" thick and 30 years old.
posted by arnicae to Home & Garden (13 answers total) 2 users marked this as a favorite
Sure that's totally possible. You can use a walk behind concrete saw.

What you'll find below the slab, how fertile that is for sod, and how difficult preparing it will be is TBD.
posted by humboldt32 at 11:19 AM on March 22

I don't see why not, but it'll require the use of a big abrasive saw and a demolition hammer for busting up the pieces you're removing. If you're not comfortable with large power tools I'd hire it out. But yeah, snap lines, cut, remove strips, fill with gravel, top with soil, voila!
posted by Makwa at 11:21 AM on March 22

If you do end up taking this on, highly recommend wet cutting to avoid silica dust!
posted by Makwa at 11:22 AM on March 22 [2 favorites]

Yes, you can cut up the concrete and lift out the unwanted parts. I have done a not-dissimilar job when I needed to put in the drain for our new bathroom; the workshop floor it had to go under was also concrete, poured on sand. So I rented a water-cooled diamond-blade saw with an advertised cut depth of 10cm (4"). Spent a day cutting strips out of the floor where the pipe should go in, drilled anchor bolts into the strips (cut into sections of about a meter long) to lift them out[1] so that after laying the pipe I could just put the strips back and fill the gaps.

In your case the saw cuts would be needed to not have jagged edges on the remaining pieces of slab; the parts that you want gone can best be dealt with using a jackhammer after making the cuts.

[1] that was when I discovered the advertised cutting depth was sliiiiiightly optimistic, as the slabs. Didn't. Budge. investigating, it was found there was about a centimeter left to go, because the saw's depth adjustment mechanism was jammed. Still, the rent (including the blade wear) didn't quite entice me to repeat that job, until I found the same saw on eBay, with a fresh blade, for about double the rental I paid. At some point I had to buy a new blade, but now I have one of my own. Which has seen more use, and will see even more.
posted by Stoneshop at 11:42 AM on March 22

No blade would survive 15 minutes without wet cutting. You can only wet cut this.
posted by humboldt32 at 11:55 AM on March 22 [3 favorites]

Over the past couple of days... the concrete in-ground pool outside my apartment's front door has been jackhammered and turned into a weirdly oval patch of dirt. You might be able to rent a jackhammer and just break squares up into bits and haul them away (or bury them and call it a day. Or a sledgehammer. But yeah, a saw if you want nice straight edges and such.

OMG yay! The day long jackhammering has stopped.
posted by zengargoyle at 12:15 PM on March 22

One trick would be if they poured it with rebar or other metal. For a driveway, they use rebar to strengthen the concrete. You’d discover that pretty quickly, I’d think. I would also worry about jagged edges.
posted by amanda at 12:23 PM on March 22

For a driveway, they use rebar to strengthen the concrete.

Might use. The workshop floor (100 sq.m, about 1000 sq.ft) I mentioned didn't have rebar. As far as I can tell, there had been several pretty heavy machines installed without causing structural cracks (evidenced by the cabling for eight three-phase power outlets still present when we moved in).

As such you don't really need rebar for a 4" driveway slab, given the weight it is meant to hold, but they can have chosen to put it in depending on the state of the soil underneath.
posted by Stoneshop at 1:04 PM on March 22

If you don't care about jagged edges, you could try a demolition grout product like Dexpan.
posted by aramaic at 2:59 PM on March 22

Another option could be to put several raised beds on top of the concrete, like islands on a little sea. Some with flowers and herbs, but for an evergreen look, you can also make a raised bed with a little bit of space between the side planks, and stick in shoots of something evergreen and fast-growing like hedera* both on the top and on the sides. Within very short time you won't be able to see the planks. You can even plant small-growth trees in the beds, such as mulberry, crab-apple or Japanese cherry. It's not entirely maintenance-free, but it is low maintenance.

If you want round or organically shaped "islands", you can make them out of concrete, brick or just rocks.

Finally, I seem to be able to grow moss on everything. I really like Japanese moss gardens and some 20 years ago I started one in a shadowed part of our garden, where there was a very low stone wall/setting. I just found some different mosses in the forest and put them there. In the beginning, it went so slowly that I almost gave up, but suddenly it really moved and now the moss has covered the stones, and also spread all over the lawn, including the sunny parts and the areas I try to fertilize and clean the moss off of. Good thing I like it. Anyway, it's fine with just stone/concrete as a base.
posted by mumimor at 3:31 PM on March 22 [2 favorites]

If you don't want to cut concrete yourself, look up concrete cutting companies (yes that is really what they are called)
posted by yohko at 5:30 PM on March 22

*I forgot to put in the note for hedera: in the US, it is an invasive species. When grown in containers like this, it can do no harm at all, except if you let it flower and fruit, then the birds will eat the fruit and spread the seed. The thing is, they only flower when they are high up a tree. And you can prevent that, even if you have a tree in your raised bed, by cutting down the hedera if it begins to move out into the branches of the tree (it will move up the trunk).
posted by mumimor at 12:31 AM on March 23

What you do depends on your area and your aesthetic. Sure you could cut area up into squares, but could also do a kind of giant crazy\polygon paving, by making cuts at angles. Think about reusing the cut out pieces too - there's a guy in LA who makes walls from recycle concrete paving strips and chunks.

Make sure you choose plants than can handle high pH. If you want to expand the range of plants you grow, and as you will be making channels through to the ground, paint the sides of the channels in a natural rubber sealer called Mulseal - this reduces cement pH messing up your soil pH. I always get underground concrete faces treated like this, saves a lot of tears later on

Is the area one monolithic slab? or is it poured in sections? I had a huge one a couple of years ago where the client wanted me to do a new carpark on a beach, but there was 2500m² of rough concrete already there. I persuaded them to keep it and just take out the bad bits and make the resulting areas into gardens. The dots in the image are recently planted shrubs. The area's new use is for overnight RV-type camping.
posted by unearthed at 9:47 PM on March 23

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