Concrete buying and mixing.

cormie

Following on from this thread, the time has come to go and get some concrete for the job.

I've seen prices of cement in woodies, I think it was €12 for a 25kg bag. I'd say I'd need about 4 bags of cement and about 6/7 of gravel. I'll also need a wheelbarrow for mixing. I don't want to buy a wheelbarrow as I'm trying to keep the shed as empty as possible for the turning and this is the only time I can see me using a wheelbarrow in the next 5 years or so.

I think I need a 2(gravel) to 1(cement) mix for this job. Is that all I should put in? I've seen tips about adding a drop or two of washing up liquid and sugar if it goes wrong? What exactly will the sugar do? I've mixed concrete in a barrow before quite a lot, I just forget the exact details. I think it was 2 to 1 also and of course, mix the gravel/cement well before adding the water so you get an even spread. I've heard the less water the stronger it will be also. Is this right?

So basically I need cemenet, gravel and a wheelbarrow I don't want to buy. Is woodies my only option or is there anywhere else I should try? Chadwicks/Brooks or even Roadstone? It's only a small job, probably 3/4 full barrows.

Any idea if it would be worth my while scoping out some building sites at 4.30 see if there's any they wont be needing:D

Any feedback appreciated:)

Alun

Cormie,

You can borrow my wheelbarrow of you like?

As far as getting concrete ... your idea of scoping out a building site sounds like a good idea, or find a readymix concrete truck at the end of his daily deliveries (they always have some left over). Beware, though ... wet concrete is heavy!!

For small quantities, you can also get ready mixed concrete mix ... just add water! B&Q do it, I know, but other's might as well.

patrido

you should be able to get cement for much less than that. i got 2 bags for 4 yoyos each the other day in a small place in slane. i think my local builders merchants is a few cent more.

try chadwicks, etc.

JohnBoy

wow, I know woodies aren't cheap, but 12 euro for a bag sounds steep to me, I thought it was 4.50 last time i bought it in the local co-op.....

2:1 is way overkill too, 4:1 would be a strong mix for that job

check out http://www.irishcement.ie/tech_supp_adv_leaflets.htm for more useful info from the people that know

Drag00n79

Homebase charges around €5 for 25kg cement.

cormie

Maybe I'm a bit off the mark with the €12, then again, maybe not. Had a look at the Irish Cement PDF file on mixing and everything. Few handy hints.

So you reckon 4:1 (gravel/cement) is good enough? What about all that 20N etc, do you buy 20N/30N cement or is say a 7:1 mix 20N and a 5:1 mix 30N using the same cement?

Is ready mix cement much dearer than buying cement and gravel seperate? What if I can only find ready mix with a rating of say 5:1 or 3:1, which should I go for? Or should I just buy them both seperate and mix it at 4:1 myself?

On that pdf it says "Strip foundations for garden walls should always be at
least three times as wide as the wall being supported." Does this mean if the legs of my wood lathe are say 1ft wide, I'll have to dig a foundation 3ft wide:eek:

Alun, thanks for the offer of the wheelchair:) I'll probably get one off my friend across the road but if not I'll surely take you up on that, thanks:)

Thanks for all the replies.

JohnBoy

five to one will be fine.

without meaning to demean your machine too much, it's only a wood lathe, don't worry.

as regards the foundations point, a four inch wall should have a 12 inch base, a 9 inch wall should have a 27 inch base, but thats because walls crack and move, cos they're big, heavy and hold roofs up, you'll be fine.



buy a bag of cement and a few bags of gravel, divide em in two (unless you get the mega wheelbarrow of death) and then mix away, you'll be grand

cormie

Great, didn't even think about the wall supporting a roof, the first thing that popped into my head was the boundary wall we have in our back garden:o

Thanks for all the replies:)

endplate

Depending on what you are using the concrete for will depend on the strength. For hard wearing surfaces like footpaths a 3 : 1 mix is required but generally a 4:1 mix is sufficient for most jobs ie securing posts and fences. If a salesman tells you a 2:1 mix is required remember he's only trying to sell more cement than you really need.

Are you aware of the danger of frost to setting cement? Just in case considering the time of year sprinkle a lot of loose sand on top of the concrete and brush off next day

cormie

Cool thanks, it's just to support a wood turning lathe in a wooden shed, there would have been far too much vibration if I just kept it on the raised wooden floor. So 4/5:1 should be fine for it yeah? Thanks for the tip of the sand sprinkling:) How long does it usually take to dry? How long should I wait before compacting (getting the air bubbles out) it says allow sufficient time before compacting so all the water doesn't go to the top. What's sufficient time though? And how long should I wait before bolting down the lathe and how should I bolt it down? Just mark where the holes are when the lathe is laying on the concrete with a pencil, then drill holes where the pencil marks are?

endplate

Once it's set usually 24 hours there is no risk of vibration bringing water to the surface. A wooden lathe should be well balanced so vibration shouldn't be a big issue. You will only need sand if the concrete is at risk of frost to prevent it from cracking. Inside a shed shouldn't be a problem. I might be corrected here but I'd give it about 5 to 7 days to dry out before drilling holes and exposing it to vibration. Also do you have a solid base of compacted stone? Recommended before putting down concrete surfaces.

BTW for your job i wouldn't go any weaker than 4:1 mix for your concrete

Alun

endplate wrote:

A wooden lathe should be well balanced so vibration shouldn't be a big issue.

You're obviously not a woodturner then Whilst the lathe itself may be well balanced, the pieces of wood we put on them (at least to start with) are often far from well balanced! And, even when they're turned to completion, differing wood densities throughout the piece (dense heartwood vs. lighter sapwood) can cause quite a bit of wobble.

cormie

Ok so 5/7 days I should brush the sand away and drill it down:)

How long after I pour the concrete should I wait before I compact it (you know the way you get a piece of 3x2 or whatever and flatten and smooth it down?

I'll be laying about 3 inches of hardcore under the concrete. Is 5:1 weaker than 4:1 or is it the other way around?

endplate

Your right Alun not a woodturner forgot about the potential big blocks of wood.

Cormic you have to compact while wet so do it immediatly after laying each barrow load. If you mix say a 3:1 mix you will have a higher concentration of cement to gravel and the mix will set quicker than compared to a 4:1 mix. I'm wondering if you should consider reinforcing the concrete by running metal rods through the concrete. It won't cost you much extra but it'll add a lot of extra strength to the concrete esp if excessive vibration is common.

You can mark the concrete with a pencil several days after it's set. But leave the drilling of the holes for about a week

cormie

Cool thanks for that.

Do you reckon I'd need a big piece of metal like this:

########
########
########

or just two bits like this:

---

---

And would I just lay them half way through the pouring of the concrete?

endplate

get lengths of 1/4 inch diameter rods they should be strong. We might need somebody with experience in reinforcing concrete to answer this cos it's a long time since I was working with concrete.

And yes lay them somewhere in the middle of the concrete

cormie

Ok, I have everything I need now. I got a 20ft length of steel, so is it ok to just chop up say, 4 5ft lengths and pop them in in different stages? say a 2 layers of 2? Would a 2 to 1 mix deal with vibration better?

cormie

I started digging today anyway. I've got as far down as I need to I think and have put some plastic down between the ground and where I'm about to lay the concrete. I was talking to a neighbour and they said not to use gravel, just use sand and cement, a 3:1 mix (3 sand, 1 cement) as this will ensure the vibrations will be taken care of, I've also cut up the steel rod and will lay that half way between pouring it. The trouble is, I have 16 bags of gravel (pebbles) that I now have to bring back to B+Q and exchange for sand. He rang up a guy who does cementing full time and he confirmed all the info with him. For a wood lathe, don't lay hardcore or gravel, just pure sand and cement into the hole.

Does this sound ok?

cormie

Just got off the phone to a guy called Martin who I was put in contact with through boards thanks to another guy called Martin:D

Anyway, he told me 3:1 sand/cement would be fine so I'm going bring my gravel back to B+Q tomorrow and get some sand. He knows his stuff alright for sure, got some great tips for woodturning too:)

Corkey123

Us Martin's know everything!!

cormie

Haha, thanks again:)

rooferPete

Hi cormie,

Before you fit the lathe I am wondering if heavy guage rubber mountings similar to the engine mountings on a car might help to absorb the vibrations ?

I am not a wood turner so I haven't a clue about your machine, I have done maintenance work in factories with big machines and they always have rubber pads between the machine and the floor.

The idea being the machinery is not damaged by having to absorb all the vibration because the concrete does not allow for movement.

Just a thought

.

cormie

You're bang on roofer, this is what Martin suggested too, insertion rubber with a weave going through it, maybe 6mm thick under the legs. He was also saying I could use an apoxy resin, kind of putty if I wanted to really make sure of proper contact between legs and floor. I wouldn't really know what I'd be doing with that though so I think I'll leave it. Thanks for the tip, who knows where I'd be without all this knowledge being passed on to me:)