This is the second post in our short series on a concrete pathway repair job. You can read all about the basis for the repair in our Part 1 of the post (link below).
Anthony Painter
Prepping, Prior to Pour
More prep photos (found later)
After saw cutting the old concrete into roughly 400mm square blocks, we used a crowbar to lever them out between the cuts, then hand carted them to the site skip. We got a 4.5m³ skip instead of the budgeted 3m³ to allow for variable concrete thickness and the spoil to be removed. The maximum weight for a 4.5m³ skip of concrete and spoil is 3 tonnes, which adds up quickly when concrete weighs 2.4 tonnes per m³.
We dug out 150mm below the old path, because the original contractor had done no subgrade prep beyond scraping off the topsoil.
After excavating and breaking up the existing subgrade, we set our path heights (fall) by flicking a level chalk line across the existing house footing, then setting the fall we wanted across the path to the height of the edge form (red timber). With those two heights set, we know water will run away from the house.
We then placed around 0.3m³ of blue crusher dust to a depth of 50mm and screeded it level. This keeps the concrete thickness consistent and to scope, and makes it easier to order the right amount of concrete.
We then laid 200µm black polyethylene plastic, taping the joints where there were any. We now had a level, solid working platform.
Next we installed Ableflex (a self-adhesive foam isolation joint strip) against the house, in line with the chalk line, and around the downpipe, to isolate the house from the path.
We wanted to install three dowels into the existing concrete paths but found they were less than 50mm thick. If we had drilled 12mm or 14mm diameter holes, we might have broken the existing paths, which we would then have had to replace too, increasing the scope and cost.
Note: if dowels were installed you would then place bar chairs under the ends of the dowels sticking into the yet to be poured concrete, bend them to ensure the chair is supporting and maintain cover, then tie the dowel to the chair with tie wire.
After this we cut and placed the F or SL92 mesh on top of the plastic, keeping 50mm clearance off the edges all round (for reinforcement cover).
Next we tied the sheet laps with tie wire, so the mesh doesn't move during the pour and keeps its edge cover.
After this we installed 50/65 plastic bar chairs. We had the standard bag of 100 bar chairs so we went a bit crazy adding chairs to make it easier during the pour by better supporting the wheel barrows running and placing concrete.
We then marked the edge form every 1.8 - 2m with a nail and spray painted the nail to show where we would form control joints (tooled joints) into the slab post pour prior to surface finishing.
After this we then cut the mesh every 2nd bar where the control joints were located, across the width of the joint. You do this to create a "weak" spot in the concrete to help promote the concrete crack in the preformed joint (under it).
Before the pour we lightly wet the plastic and mesh, and sprayed down the house walls and windows. We didn't put up plastic protection on this job because we had to work around the AC unit, so we thought it was easier to clean as we went rather than deal with flappy plastic 😄
Post Pour Photos
Completion Photos
BEFORE
AFTER
We really like Soudal Soudaflex 33SL self-levelling polyurethane for sealing isolation and expansion joints. You can't buy it from Bunnings, but you can get it from trade retailers. The other way to source it is to call Soudal customer support, get in touch with your local rep and ask who buys from Soudal regularly. Then call that retailer and order a box. You'll have to buy a box of 12 from retailers who don't keep it in stock.
https://soudal.com.au/productlist/soudaflex-33sl/
Why we love it for this job: you don't need to tape up or tool the joint after applying it from a sausage gun.
Just fill the joint slowly to the level you need, and once you get to the end you're done! No clean up, no sealant all over your hands, shirt and shorts.
I really do not understand why more people are not using this here in AU.
Why you should seal isolation and expansion joints?
Because the Australian Standard for residential pavements (AS 3727.1) shows sealed isolation joints (see the detail above), and because it will save you time, money and maintenance. If water gets between your concrete and a structure, it will undermine the subgrade over time. There's a really good YouTube video explaining this visually below.
Why Seal Expansion Joints
PS: Yes, we polished the air-conditioning unit all round as well.
What to check if someone is pouring your path
Base: firm, prepared subgrade with a compacted crusher dust layer, not just scraped soil.
Plastic: a polyethylene membrane under the slab, with joints taped.
Mesh: reinforcement on bar chairs with about 50mm cover to the edges, and laps tied.
Isolation joint: a foam strip against the house and around downpipes, sealed once the concrete has cured.
Control joints: evenly spaced every 1.8 to 2m.
Fall: the path slopes away from the house so water doesn't pond against it.
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