why was my concrete "rocky"?

[SpiderTrev]

i have never worked with concrete before yesterday, but i wanted to make my own planters, so made a mold and i mixed my own concrete.
i used wickes ballast and blue circle cement and mixed it in a bulk bag using a shovel.
i mixed a ratio of 6 parts ballast to 1 part cement, as recommended on the bag and from other people here a few months back, then slowly added water.
the whole time the mix seemed very "rocky", as if it had too much ballast, or the stones were too big. i kept adding water thinking it would look better once the ratio was correct, until eventually the mix seemed to have too much water (based on the fact that it was not holding it's shape).
at that point i thought it might need more cement, so i added more, bringing the ratio to 4 parts ballast to 1 part cement, which still seemed very "rocky". i did not want to add more because from what i can tell from my research that is a lot of cement.

i used it anyway and i have accepted that the first planter is going to come out badly, but i am wondering what i can do to make my mix smoother for next time?
my best guess is that the stones were too big and i need a ballast with finer stones?

thank you for the help

 

[endecotp]

my best guess is that the stones were too big and i need a ballast with finer stones?

Yes. You might be able to add a load of sand, but that doesn’t make the big stones any smaller.

 

[SpiderTrev]

Yes. You might be able to add a load of sand, but that doesn’t make the big stones any smaller.

ah i see, thank you!
i will do some research and see what i can find. maybe i will make my own mix so i can broaden my options.
thank you

 

[Dereekoo]

As long as you have vibrated/tamped your concrete in the planter to get rid of the air bubbles I think the end result will be OK

 

[SpiderTrev]

As long as you have vibrated/tamped your concrete in the planter to get rid of the air bubbles I think the end result will be OK

thank you for the reply
i don't think i did a very good job of that either to be honest haha
a few things went wrong and i was racing against the sunset by the end of the project. i did tamp it a fair bit by kicking it on the side all over, but i was tired and frustrated by then and was convinced it was a failure. i did not even tidy the top, i chalked it off to a learning experience
i will see how it comes out in a couple of days! fingers crossed.

 

[SFK]

How thick are the walls of the planter you are making?
Asking as that will effect size of the rocks in the MOT.
SFK

 

[SpiderTrev]

How thick are the walls of the planter you are making?
Asking as that will effect size of the rocks in the MOT.
SFK

the walls are 4 cm.
the mold is a cube with a 58cm outer edge. this one is filled to about 40-45cm depth.
the ballast said it was 20mm stones at the biggest if i remember correctly, but there was definitely a lot that were bigger than that.

what is MOT?

 

[stuart45]

20mm down is too big for what you want. You need 10mm down. You could also add a bit more coarse, sharp sand. Mix it up for longer to get a bit more air into the mix and it will be workable without adding too much water.

 

[Koolpc]

You need smaller stones...

 

[Dereekoo]

MOT was a Ministry of Transport spec for grading sub grade material (63mm or 40mm to dust) for road construction, nothing to do with concrete ballast. As long as what you are filling is 2.5 x larger than the largest stones used the compaction and finish of concrete will be OK, your 1 to 6 mix is Ok just add water so its workable/compactable

 

[stevie888]

All in ballast isn't the most consistent material so you'd be better with ideally 5-10 shingle and sharp sand as separate materials. I would try equal parts first off and mix about 5:1 with cement. Dependant on how your mould is designed you may be better with a semi dry mix well tamped.

 

[SpiderTrev]

thank you all for the replies!
i will look for smaller stones and probably make my own mix. i do have a small amount left so i will probably use that with some added sand just to use it up.

Dependant on how your mould is designed you may be better with a semi dry mix well tamped.

i'm not completely sure what a semi dry mix is, but a quick search on duckduckgo says it is a less runny mix, which would probably be ideal because my circular saw is broken and i used a jigsaw to cut straight lines... badly so i have been taping the edges. maybe with a semi dry mix i could skip the tape and make separating the mold easier at the end.

thank you all so much for the responses! you are all amazing! and much appreciated <3

 

[SFK]

Duplicate.

 

[SFK]

what is MOT

No idea why I said MOT in this context - especially as I frequently use the Wickes ballast you mentioned.
SFK

 

[SpiderTrev]

No idea why I said MOT in this context - especially as I frequently use the Wickes ballast you mentioned.
SFK

haha no problem, now i have learnt something