concrete slabbing in the African bush.

[vackie]

Hi all, I am brand new to DIYnot (thankfully found this wonderful site). I'm building fairly remotely in Mozambique and have a question about applying a screed to my current slab. The slab is 150mm thick, steel reinforced and been in place for 3 months as I build the house on top. Am building on a sand dune so the dpc membrane is under the slab. I need to put a screed layer on top which will then be acid stained and sealed. Size is 50 sq/m.
The question is what will be the easiest way to bond the thinnest screed to the slab. This is a problem of logistics as getting materials to where I am is tricky and expensive. I have a couple 20l tins of bonding liquid which I was considering using to bond the screed. Or is it better to use a slurry mix just prior to throwing the screed? I'd prefer to keep the bonding liquid if i could but will use it if it's a safer bet for securing the screed. How thick/thin can I go here?
Any thoughts greatly appreciated.

 

[dann09]

Why do you need to put a screed on top?

Why should it be so thin?

Can you explain a little more ref the acid and sealing?

What will your finish floor material be?

AAMOI: scrubbing a slurry of sand and cement will provide a good key for a sand and cement screed.

 

[vackie]

Hi Dann, thanks for your reply. I'm putting a screed on because that will be the floor finish. And I was asking how thin I could go because of the difficulty/cost of using more cement where I am building. My understanding is that a 50mm screed would unlikely cause any problems with regards delaminating, but it can be considerably thinner if correctly bonded to the base slab. Correct?

Regards acid staining, that give the aesthetic finish to the floor. I'm not sure if it's a big thing in the UK, they do a lot of it in the States and its becoming very popular here in Southern Africa. Basically, you take a solution containing a metal oxide such as Iron Oxide or Copper Sulphate, and mix that with Hydrochloric acid. When this is sprayed onto the concrete, the acid reacts with the lime in the concrete and the the result is a very cool marbled effect with the overall colour of the metal oxide used ie. Reddish/Brown with iron oxide, greeny/ blue with copper sulphate. There's others but these are the two I've used with good results. The sealing is done with a solvent based polyurethane which brings out the colours a bit more and gives a very hardwearing surface.

Anyway, you think it best to scrub in a slurry mix before throwing screed down? And safe thickness?

Thanks again

 

[ban-all-sheds]

Interesting.

http://images.google.com/images?q=<acid+stained+floor>

 

[dann09]

Thank you for the pics BAS.

I had heard of the technique, but the idea of applying and cleaning up an acid slab surface does not appeal to me.

Thing is vackie, the process is applied, TTBOMK, to the concrete surface (a polished surface by the look of things) not to a sand and cement screed surface.

I still dont understand why you would want to apply a screed to a properly finished slab? Modern residential slabs are typically finished level, flat and lightly polished.

If you do screed, then slurry first, and while the slurry is just tacky get some screed mix rubbed in.
50mm would be best practice for you.

 

[vackie]

Thanks dann. Unfortunately I'm not in the modern, residential world here. Where I am is still pretty raw Africa so all concrete work is mixed onsite by hand, and the slab is thrown rough. My guys here, bless them, just blink curiously at a spirit level.

I had some reservations about the acid staining technique when I first saw it but actually it's a very quick and clean process. The acid is just pool acid HCL that you get in 5l container. After spraying the surface with the mix, you neutralize it with a diluted ammonia solution to fix the reaction at the effect you've acquired. Wait till morning, then seal it. Job done. Obviously, this is DIY job and the pics Bas posted are professional outfits who are much more intricate and do apply on a polished slab, though we still get some great effects. I'm progressing with it and hope to get some diamond polishing discs on one of my rare trips to the real world!

I'll try post some pic of the latest project when it's done.

Think I'll go with the 50mm screed. Thanks again.

 

[vackie]

Oh, what is TTBOMK???

 

[ban-all-sheds]

My guys here, bless them, just blink curiously at a spirit level.

The people who built my house would have nothing to do with them, nor plumblines, straightedges or measures - tools of the Devil, the lot of them, appears to have been their attitude.