Does a weak mix for slabs mean problems?

[cdorling]

I want to put a greenhouse (aluminium, so lightweight) on top of an existing paving slab patio. As the slabs were not completely level & some were loose, I thought I'd re-lay it. The foundations are concrete (of varying height) from a previous building. I used the 5 spot method, and sand & cement. When finished it looked the business.

Next day I went to check, and noticed (from the edge and from the left over cement) that it wasn't solid. I thought I'd used a 1 in 5 mix, but I guess I measured it out inaccurately, or didn't mix it enough. Today (2 days later) its a little more solid, but I can still scratch a bit off with my nails.

So, what to do. Do I just relay the slabs which will take the greenhouse base and point it, giving it all a more solid edge around the sides (I'll use readymix next time)? Do I re-lay it all, yet again. Or do I leave it alone, as its fairly solid & as it is it is doesn't look like it will collapse. Could rain get into it, & freeze, & cause collapse.I don't know if the wet will causing freezing (there are a lot of gaps between the 5 blobs of mix).

My old dad was a builder, I wish he was here to ask. I'm an office worker (maybe thats why I'm now aching), but I always like to have a go. Thanks for any advice.

 

[masona]

A ratio of 5:1 mix does take a lot longer to harden compare to for example 3:1 mix, it will harden eventfully but a lot longer in this weather as well!

Try and use 3:1 mix round the edge to seal it and strengthen the side.

 

[Thermo]

firstly give it a little time to go off properly and reach its hardness. It takes more than a few days as its subject to a damper atmosphere under the slabs. The five spot method should be ok for what you are doing. If you do re bed any use a 1:3 mix or a 3:2:1 sharp sand, soft sand, cement. The thing to remeber is that gravity is a rather good help in keeping the slabs in place. Once pointed up it will be locked together. You dont need to worry about water and freezing

 

[notb665]

Your sand and cement were fresh and new I take it?

 

[countygardens]

Concrete continues curing to full strength for ages (months I think ).

So I'd say that your probably ok once pointed as Thermo says

 

[Thermo]

i think its 28 days to reach optimum strength and then it continues to slowley harden over time. A bit like glass continues to flow

 

[masona]

I've been told that concrete footing take over 50 years to harden because of the moisture in the ground

 

[countygardens]

I've been told that concrete footing take over 50 years to harden because of the moisture in the ground

Thats gonna be my excuse if I get any problems with previous jobs.

Customer: 'Hello, countygardens, that wall you built has a massive crack going up it, and its only 5 years old!'

Me: 'Sorry Mr/Mrs ...... but did you know it can take up-to 50 years for concrete to finish hardening? You should never have sat on it, you fat useless ****!'

 

[notb665]

A bit like glass continues to flow

POPPYCOCK!

 

[Thermo]

If your interested read this and youll see its not poppycock!

http://math.ucr.edu/home/baez/physics/General/Glass/glass.html

 

[notb665]

If your interested read this and youll see its not poppycock!

http://math.ucr.edu/home/baez/physics/General/Glass/glass.html[/QUOTE]

Apart from reminding me of when I was at university, the whole article is about how glass does NOT flow over time, isn't it?

 

[Thermo]

its about how its all a bit inconclusive so its neither one nor the other....rather peculiar really!

 

[notb665]

OK - look at this one:

http://www.glassnotes.com/WindowPanes.html

 

[Thermo]

nah......im not that bothered and i DONT want to be reminded of school!

 

[cdorling]

Thanks everyone, its definitely a bit harder today, so I'm really glad I didn't rip it all up and redo it thevery next day, which did go through my mind. So, just the pointing to do before I start on the next job. And thanks for the stuff about glass, I'll double check what arrives with the greenhouse