Concrete!

[Alie Barnes]

Well i have been having vibration issues with my lathe but now i am able to put a concrete fllor in my shed which im very happy about and will bolt my lathe stand down.

My question is what is the best type of concrete to make?

Just sand and cement or should it be a gravel and cement mix?

I was thinking about 4/1 mix would this be suitable?

Thanks again.

Alie

 

[Doug B]

Alie.

It`s ballast you want, which is a mix of sand & gravel.
6 to 1 is a strong enough mix, 6 ballast, 1 cement.
Making the mix to strong (adding more cement) could lead to the concrete cracking.

 

[matt]

Also do not let it dry too quickly (or allow the surrounding surface to suck all the moisture out). Also leads to cracking and weakness. If in doubt keep it covered with damp cloth - the longer the better.

(I'm not a concrete pro - just someone who has used it quite a lot and learnt quite a lot from a very dry and dusty floor repair on one occasion :evil: )

 

[Turn It In]

Hi Ali,
I have just installed a heavy milling machine in the workshop and the floor concrete mix we used was 3 sand, 2 gravel, 1 cement which is very similar to the premix ballast recommended by Doug. I recon you will be fixing the stand down to the concrete floor so you might consider an interface of a commercial carpet floor tile cut to a suitable size between the concrete and the stand, and this will damp out any vibration.
I have four pieces under the miller base without the machine bolted down and that weighes 1200kg so it won't move anyway.
Hope that helps,
Regards
Ian

 

[Doug B]

Another thought, a plastic membrane under the concrete would be a good idea, to stop any damp rising, also it would prevent the concrete drying too quickly, as Matt pointed out.
If it`s going to be a large area & not very thick a sheet of steel reinforcing mesh wouldn`t go a-miss.

 

[MikeG.]

Doug,

you are dead right with your advice, but there is a regional thing going on here. In some parts of the country you buy ballast, as you described, but in other parts it is sold seperately (sand and stone), and you have to mix it together yourself. When I moved to Essex I had to ask what ballast was!

Mike

 

[Steve Blackdog]

this is the web site for concrete advice - if you've not looked here you haven't lived!

http://www.pavingexpert.com/

 

[RogerB]

5 to 1 Ratio is as weak as you should go.

You need to dig out deep enough to lay some hardcore in the base blind this of with sharp sand or ballast you may need to form some kind of shuttering round the hole to get to your shed base level.

lay a thick polly membrane over the hardcore / blinding and then lay your concrete.

To stop it setting to quickly lay damp sacking or simular over it to keep it out of the direct sun / heat.

I would leave it at least a week, longer if you can before trying to stand/ fix the lathe on it as only the top surfacxe will be set.

All most forgot the concrete needs to be 4" thick and so should the hardcore .

Hope this is of some help.

Roger

 

[Doug B]

Hi Alie.
This site http://www.bellegroup.com/en/support/mixingHints.html will clear any doubts on mix ratio, you only need the ordinary concrete mix, 1:2:4, cement, sand, gravel, i wouldn`t go weaker.
But if you buy the sand, gravel pre mixed (ballast) as sold in Wickes B&Q etc then its 1:6 cement, ballast. You can also get ballast in ton bags from builders merchants, depending on the amounts needed.
If you need to work out how much material you need there is an online calculator, but the address eludes me at the minute.

 

[Alie Barnes]

thanks for all the advice.

All i shall be doing is laying a concrete square on top of the shed base (slabs) and then mounting lathe on that.

I shall go for a gravel mix and about 4:1 ratio.

 

[MikeG.]

Alie, (is that enough "L"s?)

It is almost pointless pouring concrete on top of your slabs. Take 3 or 4 of them up, dig out properly, whack down some hardcore & blinding, and then pour your concrete. Otherwise you will expend time and money for no great gain at all.

Mike

 

[Alie Barnes]

Alie, (is that enough "L"s?)

It is almost pointless pouring concrete on top of your slabs. Take 3 or 4 of them up, dig out properly, whack down some hardcore & blinding, and then pour your concrete. Otherwise you will expend time and money for no great gain at all.

Mike

this is not an option for me sadly, ive had to fight tooth and nail just to get permission to pour concrete ont he slabs.

Its so its considered "removable" in future and isnt permanent

 

[matt]

Why not fix straight to the slabs in that case? Alternatively (and I don't use a lathe so I don't know if this is practical), but how about buying some bags of sand and just drape them over the stand on some cross members very low down?

 

[user 5053]

You might want to consider hiring a vibrating plate to compact the sub base and also you may wish to concrete in some threaded bar to bolt the lathe to.
Some modern lathes are of such cheap lightweight quality that you might be better getting a better engineered and heavier machine.