Another UK oven project

[nissanneill]

Re: Another UK oven project

To improve your concrete surface, after you have screeded it and lightly trowelled ot with a long wooden trowel, mix a toppong of 1 part concrete sand (like a washed coarse river sand) with 1 part portland. When your concrete has initially set enough to walk on carefully (2-3 hours after laying), sling handfulls of the topping over the slab and work it up with a wooden trowel. It will draw water out of the cement and go to a thick slurry which can be finished with either a woodern trowel ( a non slip slightly rougher texture) or a flat steel trowel for a smooth finish. You can also use a household or garden brush to produce a non slip surface for paths/driveways. You can also add some colouring in the form of an oxide if you wish to have a coloured finish rather thanuse a lot more to colour the entire concret thickness.

Neill

[dmun]

Re: Another UK oven project

You may want to look at my concrete mixer thread, as well.

http://www.fornobravo.com/forum/f6/concrete-mixer-basics-790.html

[karl]

Re: Another UK oven project

Matt,

Maybe some help here:
Mixing Concrete, concrete, sand, cement, ballast, Calculator

regards from karl

[Les]

Re: Another UK oven project

When I poured my hearth, I brought in a yard of ready mix (5 sack). That required enough shoveling as it was.

Les...

[aureole]

Re: Another UK oven project

When I poured all my sidewalks using a mixer I used 3 sand, 2 gravel, 1 portland. Plenty of sand to float for a smooth finish. I thought that was considered 5 sack - pretty common for driveways, sidewalks, etc.

Was this the same mix you used for the hearth slab?

[aureole]

Re: Another UK oven project

Overworking a slab is a classic amateur mistake: I've yet to finish a slab to my entire satisfaction. I'm told that it's a help to leave the leveled slab to set about fifteen minutes before you try to float it.

I've read that the ideal time is just after the bleed water on the surface gets sucked back in. Patience isn't my strong point though!

[Les]

Re: Another UK oven project

When I poured all my sidewalks using a mixer I used 3 sand, 2 gravel, 1 portland. Plenty of sand to float for a smooth finish. I thought that was considered 5 sack - pretty common for driveways, sidewalks, etc.

Les...

[dmun]

Re: Another UK oven project

I mix my concrete with 1 bucket of sand, one bucket of crushed stone, and a scant half bucket of portland. That's 1 : 2.5 : 2.5, so yes, I'm using more sand than your first example. As far as the aggregate, by the time you level the concrete for the forms and smooth it out (a process called floating) all the fine stuff (and a bunch of water) will come to the surface. Overworking a slab is a classic amateur mistake: I've yet to finish a slab to my entire satisfaction. I'm told that it's a help to leave the leveled slab to set about fifteen minutes before you try to float it.

[aureole]

Re: Another UK oven project

Haha. I'm more of a wikipedia guy - bugger all practical skills but good on theory.

IIRC standard concrete is a 1:2:4 mix or so - 1 cement, 2 sand, 4 gravel, c20p meaning cement, p for portland and 20 is the compressive strength (20 newtons per mm2 I think). This is also the 1:6 standard aggregate mix used by most people here (as I understand it). C35p is a stronger concrete - 1/2/1 mix of cement, sand and gravel (or 1:3 cement:aggregate).

What I'm asking is: most people have a nice smooth hearth slab with no visible lumps in it - I don't know if this is because they polish it nicely, or if they've been putting a lot more (or entirely) sand in the mix they use for the hearth slab. I'm just wondering if I should buy some mixed sand/gravel ballast/aggregate to make it, or get some

[dmun]

Re: Another UK oven project

C35P is a new one on me: Google's no help. We're sort of bucket of this and half a bucket of that kind of folks: maybe you could re-phrase your question?

[aureole]

Re: Another UK oven project

Question about hearth slabs- do people reduce the amount of gravel in the mix for the slab? I'm wondering if I should be making a mix of C35P instead.

I've got half a bag of sand/gravel aggregate left- I need another 1/2 bag, but don't know if I should get all sharp sand instead and do half aggregate/half sand for the slab (I'm going to get calsil boards too).

[aureole]

Re: Another UK oven project

Thanks for the help and advice: I got a neighbour to go check the forms, and the plastic had blown off so he reset that and watered it for me.

nissanneill: I've got some chunky (220x220x440) hollow blocks so I'll fill the cores of those with concrete and 1/2" rebar.

[christo]

Re: Another UK oven project

I'm quater of a world away, but the clay here is not as reactive (swelling due to water absorption) as the some of the clay in Oz. As a result, we get away with pretty much the same foundation you poured. You may find the clays in your region aren't overly reactive as well.

With all that rebar in there and compacted gravel on top of clay, I think you'll be fine. It's too late now anyway - so enjoy.

Loved the pics and sorry about your hands.

Christo

[nissanneill]

Re: Another UK oven project

Yes, but late monday night here in Adelaise, Soith Australia.
You can reinfirce your walls if you are to use the 8" hollow cement blocks which can be filled with conctere forming vertical concrete sides and very strong. You might lay a course, fill with concrete and then lay the next. I have seen the ends and centre bits of the blocks ghipped out to approx 2/3 the height and a couple of reinforcing rods run along the line/ course of blocks. Wuite easy to do, just takes a little extra time. If you have a look at industriasl buildings built with theses blocks, check out the lintels oveer the wider 8 foot doorways. They are concrete filled with reinforced rebar without steel lintels.
Let's see what some of the other forum members think once they wake up to monday morning.

Neill

[aureole]

Re: Another UK oven project

Monday morning, still a bit slow at work, hence the speed of reply.

I hope the foundation is enough - sadly, there isn't much I can do about it now I think.