concrete roof

[couchie]

Hi.

My garage has a concrete roof, because of the lay of our house this is also our back yard. It's 8.5 x 4.5 mtrs, block beam constuction with concrete over, & a large RSJ, well supported, halfway along. Done in the mid 70's I think.

The problem is it leaks like a sieve, no cracks, just very poreus. The garage ceiling is covered in small stalegtites. At the moment to stop my tools & stuff getting soaked I have suspended polythene underneath, when it rains I empty it, gallons of it.

It's flakey & every frost just degrades it more.

I would like to put a new layer of crete over, about 75mm, with dpm, a better fall & then a good floor paint. The structure itself is sound enougth, just bad concrete over it & only about 50mm thick at present so I don't think the extra load is a problem.

Access is bad so I've ruled out readymix, cost is also an issue so it's going to be diy.

Can anyone advise me on the best mix to use, ie size of ballast, ratio of opc etc. Also of any admix that would be good to use. Would I need to reinforce it & put in expansion joints?

If anyone can advise or maybe come up with a better idea, it takes a lot of wear & gets hosed down & brushed because of our dogs, I would be gratefull.

Regards, Chris.

[welsh brickie]

I would lay a 50/75mm screed over the roof,then tile on top ,this will provide a hard wearing area for your needs and stop damp getting through.
You dont need expansion joints but put chickenwire in the screed for added strength.
Mix course sand with cement for your screed 4:1 ratio. 2.5 ton of sand and 10 25kg bags of cement should do.