What am I doing wrong with the concrete. Becomes brittle

[Axiotrade]

I have tried mixing small batches of ready-mix fi concrete from places like Byggmax. We're talking about 1kg of concrete and the water calculated based on the amount indicated on the bag. I don't remember exactly, but it was about a dl or 2 per kg of concrete.

I was supposed to fill 2 drilled holes in the foundation so I could drill again in close proximity to them.

I lightly moistened the hole before pushing in the concrete and covered it with tape to preserve the moisture while the concrete hardened.

After a few days, I checked with my finger and I could crumble the concrete with just my fingertips. I could take a drill by hand and remove the new concrete from the hole.

Does anyone know what I'm doing wrong? I've cast larger foundations before where I've used the same type of bag and they're rock-hard.

I would be very grateful for tips.

 

[Betongapa]

Just a guess now, but it could be that the ingredients in the concrete are not evenly distributed in the bag, so when you take smaller amounts from a bag, there is the wrong amount of cement compared to the other ingredients.

 

[Drburr]

Water like hell if there are smaller holes. The old concrete absorbs the moisture from what you're applying. Stupid question, but are you using something like cement mix/concrete and not a bag of pure cement? Has happened…

 

[Plupp 405730]

I have tried mixing small batches of ready mix concrete like the ones from byggmax.
We're talking about 1kg of concrete and the water calculated based on the amount indicated on the package. I don't remember exactly, but it was probably some dl or 2 per kg of concrete.

I was going to repair 2 drilled holes in the foundation to be able to drill again in close proximity.

Moistened the hole slightly before I packed in the concrete and covered it with tape to preserve the moisture while the concrete hardens.

After a few days, I felt with my finger and I could crumble the concrete with just my fingertips. I could take a drill by hand and remove the new concrete from the hole...

Anyone know what I'm doing wrong? I have cast larger foundations before where I used the same type of sack and they are rock hard.

I would be very happy for tips

Fine concrete is meant to be cast, not used to repair small holes; you need to buy concrete repair mortar if you want to succeed..
Something like this:

https://www.se.weber/betong-cement-vagglagning/reparationsbetong/weber-rep-45-reparationsbruk

 

[Nicro]

I would fill the borehole with ankarmassa.

 

[MultiMan]

Water like crazy if there are smaller holes. The old concrete absorbs the moisture from what you're applying.
Idiot question, but are you using something like cement mortar/concrete and not a bag of pure cement? It has happened…

I believe this too. I actually know nothing about concrete casting but have tried to read up and get tips. It included that if you're pouring into dry ground (in my case) a lot of water is required, otherwise the concrete will dry out before it cures properly. I used 5-year-old Finja coarse concrete for the mailbox, for example (stored dry, no lumps). Watered a lot in the dry hole, mixed by feel (usually find it a tad too dry according to the instructions), and it was rock hard after a week or so. Watered once or twice on top since it didn't rain at all.

As others have also said, it might be best otherwise to use anchor mass if there are already existing holes.

 

[Axiotrade]

Thank you very much. That was a lot of useful information.
I think I will try another product to fix this hole.