Concrete Mixes

[Roberto2019]

Does anybody have a definitive guide to the different strengths of concrete, and the ratios of how to mix?

Online searches are confusing to say the least.... C20, C30 etc... M20, M35 etc... Gen 1...??

For what it's worth, I am after a mix for C35 for a cast in-situ padstone.

 

[^woody^]

You don't have the controls to make concrete to a standard at home.

2:1, not too wet, and vibrated.

Or use a concrete lintel.

 

[jks7492]

Why does it need to be cast in-situ? What size padstone has been specified?

 

[Roberto2019]

300x300x215... or thereabouts. Can't find one that size anywhere, but also the access is a right pain so I was thinking it might be easier to just shutter up once the beam is held in place and then pour the concrete in under it.... still getting my head around it to be honest.

When you say 2:1 Woody, you mean all-in ballast to cement, correct?

 

[jks7492]

300x300x215... or thereabouts.

Thats a big one..
Is it a 215mm solid wall or 300mm cavity wall?

 

[Roberto2019]

300mm cavity.

So will sit 300mm over cavity, 300mm long, 215mm high.

I should be able to get at least a 200mm bearing on it with the beam...

 

[Diver Fred]

Are you using premixed (bags of) ballast or are you going to mix it yourself?

Mixing your self
1 cement, 2 sharp sand, 3 20mm Stone. just enough water to ensure mix is stiff and 'flumphs' (noise) when dropped from about 12inches.

Premixed Ballast
1 cement, 4&1/2 ballast, water as above. If the mix is to grey add up to another 1/2 of ballast.

Vibrate into mould.

 

[Notch7]

these people do them £44.24+vat

https://snsbp.co.uk/shop/330x300x215mm-concrete-padstone-sns022/

no idea how much delivery might be -at todays diesel prices probably about £800

 

[^woody^]

LOL

Unless you have a 300mm wide single beam, then you would use two padstones - one per leaf/beam, as one padstone spanning fresh air does not spread the load down the cavity.

 

[John D v2.0]

If you want to keep it simple you can get a sack of dry 40n mix from Wickes, just add water. It's not too expensive either.
I used a couple for an infill drain cover

 

[noseall]

Unless you have a 300mm wide single beam, then you would use two padstones - one per leaf/beam, as one padstone spanning fresh air does not spread the load down the cavity.

Says a bloke that angrily waves his surveyors licence at anyone who dares to install a pair of beams without a few bits of threaded bar between them.

 

[Roberto2019]

The beam is 203mm UC - with a 280mm plate welded on top to hold up both sides of the cavity wall. Hence I assume the correct way is one big padstone sat across the cavity, with the beam sat in the middle.... that is certainly what I have taken from the SE calcs (although they could be clearer)....

 

[^woody^]

Says a bloke that angrily waves his surveyors licence at anyone who dares to install a pair of beams without a few bits of threaded bar between them.

You should get your own licence to chill.

 

[noseall]

You should get your own licence to chill.

Ironic that you champion the importance of connecting the beams so they behave more as a 'unit' then scoff at single pad.
Bizarre and no continuity.

 

[^woody^]

Bizarre and no continuity

.... across a cavity you mean. Yes, that's right.

The performance of a beam and of a padstone are completely different things.