Concrete recipe

[Ali]

I want to cast a couple of these drain surrounds, it seems possible to buy them but none of the yards near me stock them and I can at least make it to match the size of the cover if I do it myself. In the past I’ve used cut up kerb stones but I thought it might be a bit of fun to make a form.

I’ve got red sand, sharp sand, cement. What gravel? I can get 10mm, is that small enough?

Add reinforcement? Something painted on the form to aid release? Frostproofer? A bit of steel reinforcement?

Any advice welcome, just a little weekend project, will post some pics.

 

[gaz1]

river sand 5mm pebbles and cement advice test on your colour of mix you want

yellow sand is better to a degree on colour but riversand is finer just uses more cement for the colour

so if i used b&q riversand and pebble mix with normal cement 3-1 ratio its too dark so you need more cement

whilst with yellow sand the mix is fine

however the more white you want the more cement is needed

if you want smoothe to the top then you make the mold to the bottom it needs vibrating but your sds drill will do so on forms

 

[knighty]

10mm is perfect

1 cement : 2 sand : 3 gravel

Can go a bit heavier on cement if you want, I normally get pre mixed sand/gravel and do 1:4 to make it nice abd strong

Rub some veg oil on the wood as release agent

A bit of rebar... or any other bar bent into a U shape will help

 

[Agroshield]

Frostproofer?

Frostproofer is only to protect the concrete between the time you mix it and the time it sets if doing so in cold weather. It does nothing long term once the concrete is set.

The key to good concrete is low water/cement ratio.

 

[Ali]

river sand 5mm pebbles and cement advice test on your colour of mix you want

yellow sand is better to a degree on colour but riversand is finer just uses more cement for the colour

so if i used b&q riversand and pebble mix with normal cement 3-1 ratio its too dark so you need more cement

whilst with yellow sand the mix is fine

however the more white you want the more cement is needed

if you want smoothe to the top then you make the mold to the bottom it needs vibrating but your sds drill will do so on forms

I’m not too fussed on colour to be honest. Do you mean the open end will be smooth or the bottom of the mould?

Rub some veg oil on the wood as release agent

I imagine that would soak right in, throw some old paint on it first?

Frostproofer is only to protect the concrete between the time you mix it and the time it sets if doing so in cold weather. It does nothing long term once the concrete is set.

The key to good concrete is low water/cement ratio.

I didn’t know that, I’ve been wasting frost proofer for years

 

[Agrismith]

For such a small quantity then you might be better of using bags of c40 pre mixed.
The reinforcing on items like that is at most high tensile wire. But most items like that won't have any in them. Mould release agent stops it sticking but have seen vegetable oil used before. Use an SDS drill on chisel mode to vibrate it on the sides. Enough to get the air out but not so much that all the aggregate sinks to the bottom

 

[Martin Hocking]

Place I used to work at making paving slabs* etc used 10mm all in/ pre mix sand/ballast and heating oil as mould release applied with a sponge in the plastic moulds. It’ll soak into a wood mould so you might need a bit more, didn’t seem to hurt the slabs and posts at all.

Bend a little thin rebar to the shape and push it gently into the concrete at about half full and another bit once it’s full for reinforcement.

Agroshield is right about the keeping the water down but I have to say the place I worked at seemed to prefer a slightly wetter mix than I would go for in a pad for example. The reason being a drier mix is harder to vibrate air bubbles out of. Which is the crucial bit for making them look nice.

The other thing to look out for is the strength of cement. I bought some Hanson stuff the other day which looked identical to what I had already except it was 32,5 instead of 42,5 I don’t really know what that actually means long term but at point of use it makes a leaner mix. Slab place used to use ‘high strength’ bags not sure what they are at 4:1 with the all in.

*not a big factory or anything but have been doing it for the best part of 40 years

 

[voipio]

Once it's cast, leave it to age and gain strength. I remember seeing the concrete running beams, for the guided busway in Cambridge, being cast on site, and then left for several weeks before being laid in position.

 

[roofman]

I want to cast a couple of these drain surrounds, it seems possible to buy them but none of the yards near me stock them and I can at least make it to match the size of the cover if I do it myself. In the past I’ve used cut up kerb stones but I thought it might be a bit of fun to make a form.

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I’ve got red sand, sharp sand, cement. What gravel? I can get 10mm, is that small enough?

Add reinforcement? Something painted on the form to aid release? Frostproofer? A bit of steel reinforcement?

Any advice welcome, just a little weekend project, will post some pics.

i would buy 5 off you Ali..great idea

 

[gaz1]

i will get you some photos uploaded of a cast wall capping tomoz

thats with wood framing and floated up

 

[arther dailey]

for white add titanium dioxide.

 

[Erie Fred]

Local precast place uses a very low slump (watery) mix for the reasons above, air bubbles.
However, they add Super P so the water is not as much as you would think (and they don't
have as much strength loss either)

 

[gaz1]

the capping photos

 

[knighty]

that's something I forgot to say.... hit the side of the mould with an sds drill / hammer drill / sander / something that vibrates

veg oil will soak in but it's no big deal, it'll still work


do you need many?

 

[Onoff]

This as the additive. It de-aerates as well.

https://www.amazon.co.uk/Everbuild-ILW5L-Integral-Liquid-Waterproofer/dp/B00133HA1A

 

[daleyd]

Soap oil was the traditional release oil - my dad was a shuttering joiner and my childhood stank of the stuff! If you know the smell you know it gets into everything - his work van smell was a heady combination of soap oil, shuttering ply and golden Virginia roll ups!

 

[Smallfry]

You can buy mould release stuff for concrete. Not very expensive.

I would use a vibrator on that too, to get a nice finish and all air bubbles out.

 

[gaz1]

@Ali can you float plaster ?

as it helps to build a standared form mold for the concrete

 

[Onoff]

Pretty sure I used veg oil as the release agent.

One thing I did do was silicone the internal corners of the mould then go over it with a Fugi Cramer radius tool.

Some minor imperfections I filled with a tiny mix. Cap stones came out as good as you buy I think.

 

[Ali]

that's something I forgot to say.... hit the side of the mould with an sds drill / hammer drill / sander / something that vibrates

veg oil will soak in but it's no big deal, it'll still work


do you need many?

I'll see how I get on, I might make a few

This as the additive. It de-aerates as well.

https://www.amazon.co.uk/Everbuild-ILW5L-Integral-Liquid-Waterproofer/dp/B00133HA1A

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Nice work, I can get that stuff at Toolstation

@Ali can you float plaster ?

as it helps to build a standared form mold for the concrete

Yes, I was planning on knocking something up with plywood though

Pretty sure I used veg oil as the release agent.

One thing I did do was silicone the internal corners of the mould then go over it with a Fugi Cramer radius tool.

Some minor imperfections I filled with a tiny mix. Cap stones came out as good as you buy I think.

Good plan