Fine concrete for casting foot partially outdoors by garage?

[Grillen]

Last year, I replaced the garage door and now need to level the floor under the door as the garage slab slopes. There is a gap of 5mm to 40mm from left to right, and I will need to cast a "step" to create a flat surface so the door will be sealed.

I have a few unused bags of fine concrete in the basement and am now considering whether I can use them to cast the step even though they are labeled for indoor use. Or will it crack or have some other issues if I use this?

 

[Claes Sörmland]

The tricky part here is getting the new casting to adhere to the old slab. To increase the chances, it's advisable to chisel the old concrete with a sledgehammer and chisel to remove the carbonated and dirty surface, allowing you to get a clean rough surface that the new concrete can grip onto.

Why it says "indoors" on the fine concrete, I don't know. Fine concrete can be used outdoors; the difference from coarse concrete is the size of the aggregate, which means it is usually used for thinner castings.

 

[Grillen]

Assumed that was the case. But might as well ask since krauta just goes "if it says indoor, then it's for indoor" but they're useless at knowing things about what they sell.

Remove a few cm from the existing slab and bend some rebar which I drill into the existing slab and we'll see if it holds

Thanks for the answer.

 

[Mogg]

You can also "slura," i.e., swab on pure cement mixed with water to a consistency of filmjölk before pouring onto the old cement. The surface must be clean, though!

 

[Grillen]

You can also "slura", i.e., swab on pure cement mixed with water to a consistency like buttermilk before casting on the old cement. However, the surface must be clean!

Planning to try a casting this weekend now that the temperature is becoming stable. But if I "slura", should it set before I put on the normally mixed concrete, or should it just be a layer at the bottom at the same time as I cast?

I plan to grind off the dirty top surface with an angle grinder so that it’s clean concrete to slura/cast on.

 

[Grillen]

Since the weather has been completely terrible with 0 degrees and below until now at night, I haven't dared to pour until now.

But I'm planning to pour sometime during the week.

How do I clean the floor, is there a specific cleaner I should use? And do I need to sand the surface beforehand?

Also, how do I "slura," should it dry completely before I pour on top, or should it be moist?