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I've got a load of rubble sat in the garden and a trials bike so I want to make some fake rocks to place in the garden to ride it on rather than buying some big old rocks (or filling the garden with any more palettes).
Going to wrap the rubble in chicken wire etc, and then cover it with concrete/cement, but I don't really know anything about concrete/cement etc.
What mix of cement/sand/ballast/etc would be recommended to make a good tough fake rock to take the weight of me and my bike repeatedly falling onto it?
The standard ratio seems to be 1:2:3
1 cement
2 sand
3 aggregate
It'll be pretty tough.
If it's only meant to be decorative and to take the weight of a bike or person, probably just 1 part cement to 10 parts sand would be fine. Once you have the concrete poured, sprinkle sand over it. That way it won't look quite so much like concrete. It'll be easier to smash up later with a pick if it's just weak mortar than if it's proper concrete.
Two extremes there, one mix pretty strong concrete and the other will take ages to set let alone harden and will just crumble to powder
Does the bike have an engine or not ?
You'll need a reasonably strong mix to avoid surface wear from repeated landings in the same spot. It's also surprising how much material you need - a 1m cube of concrete is 2.4 tonnes.
If only Jennifer Lopez were here.
She's an expert on fooling people with the rocks that she got.
You can add colorant to the cement mix. Make a change from grey.
No engine on the bike no.
Using the rubble/hardcore (the usual bricks/breazeblocks/broken concrete/etc) wrapped in chicken wire as the bulk of each fake rock to reduce amount of concrete needed.Hoping concrete would seep in between to hold it firm, with a thick coating on the outside.
For the first recipe, 1 sand, 2 cement, 3 aggregate - leaning away from ballast as those type of stones would be a nightmare for grip, could just use crushed hardcore instead?
You can add some cloth rags into the final few layers to create 'features' rather than just a round rock. A bit like these bowls but on a bigger scale and obviously you don't need to paint them.
I bought sharp sand and cement the day before the snow came, so after a hop about on the bike today, in shorts & t-shirt in glorious sun, today seemed like the perfect day to make some fake rocks!
Started with some chicken wire and wrapped some rubble. It was a delight for my hands. Used molgrips (no not him) to grab the wire and twist it together to try and pull everything close.
Of course I ignored most of the advice here about concrete and just mixed 1 part cement, 2.5 parts sharp sand with some slop of water. On the kitchen lino we ripped out when we moved in. I was assisted by my 4 year old son, he had a great time! Decided that I should dollop some of the mixed up cement on a polythene bag and place the rubble bundle on top.
Next we slapped it on top and discovered I hadn't mixed enough.
My boy was still enjoying it but I was starting to loose a little patience and the mixture became a little too wet perhaps.
Slapped it on anyway!
I'd put too much cement on and the polythene bag too small, so removed some with a spade and then used straps to just pull it altogether a bit around the bottom. Covered with a bit more polythene.
With the left overs filled a flowerpot lined with old t-shirt (for texture).
size 45 510 Freerider EPS High for scale.
I tried to push the cement through the chicken wire and between the rubble inside, but I doubt it will have got far in so I wouldn't be surprised if it falls to pieces. Hope I'll be proved wrong. And it will definitely be fairly heavy.
The next one I make I might try building a rough mould out of offcuts of OSB & MDF and line with an old bed sheet or something and dispense with the chicken wire. Throw the rubble inside and pour the cement on top and then mix it all together.
Cement is highly toxic and can give nasty burns, so I'd keep your nipper away.
What you mixed is a mortar. no aggregate, just sand and cement. Which is a bonding agent or render so won't have great inherent strength.
As long as the rubble inside is well compacted and won't jiggle, the render coat you applied may work, or may crack and fall off. Interesting experiment though, good luck!
Cement is highly toxic and can give nasty burns, so I’d keep your nipper away.
Yes I told him to stand well back while I was mixing the dry cement & sand together so it didn't blow all over him. Was quite windy. And warned him it was bad for him etc. Obviously a four year old, so won't really understand. Was nice to have something to do with him he was showing enthusiasm for, can be difficult sometimes.
What you mixed is a mortar. no aggregate, just sand and cement. Which is a bonding agent or render so won’t have great inherent strength.
As long as the rubble inside is well compacted and won’t jiggle, the render coat you applied may work, or may crack and fall off. Interesting experiment though, good luck!
Think that was part of my fear once I'd started slapping the stuff on. While my Dad had taught me years ago how to mix it on a board, I haven't worked with it at all over the years other than filling a big bucket to use for locking bikes to.
Do you think the idea of making a mold and filling with concrete rather than mortar, and then adding the rubble to it would work better?
The more water you add, the weaker the concrete/mortar will be. To make the mixture workable, add some washing up liquid to the mixing water, you'll end up using less water and it will be stronger. Plasticiser from a builders merchants would be even better.
If you’re inclined to use a mould, and it the final rocks are intended to be of a size that you can shift around then I’d look at digging a hole and filling that.
Partially fill the hole with concrete and then drop the rubble in and top up as needed. Leave it overnight and then pry it out of the ground and do the next one.
That's a good idea, I like it and seems so obvious now you've mentioned it. Though prying out the ground sounds less like fun.
Going by the weight of the one I made yesterday; it's heavy enough I can lift but unlikely to be able/want to carry it. Maybe for anything larger I'll only put broken breeze blocks in to reduce some weight.
For strength, you need as much hard material as possible, provided you can fill all the gaps with cement paste. If there any holes, water will get in over winter, freeze and split it. So your rubble should be broken up into a variety of sizes. Mix it all in, don't pour mortar onto it or you will get gaps. You can push the biggest lumps in afterwards provided the rest will flow round them. Use a length of 4x2 to compact it; just keep pounding the surface until the mortar rises to the top. If you use a hole as a mould, line it with cloth or something or you'll have a really rough surface. Once it's set, keep it wet for a week - concrete doesn't 'dry' it's chemical cure process that needs water to work. It won't reach full strength for while - maybe 90% after a month.