For protection against rain, I'd say metaldeck roofing is the best because it has less joints.
As far as I know, there is no permanent cure for cracked concrete roof.
Consider doing a layer of metaldecking over it.

Cement roof tiles depend on the overlap between tiles and the roof pitch, whch must be at least 20 degrees. Other factors can also cause leakage - flashings, structure sagging, cracked tiles, etc.

P.S.
There is one method of repairing leakage whereby holes are drilled at close intervals on the concrete slab. A liquid is pumped under high pressure into the holes. The liquid finds its way into the pores of the concrete, expands into a foam material and clogs up the pores thus preventing leakage through the slab.

I don't know what material that's called. I believe it is still in the market.
It worked to stop leakage through my bathroom floor slab so that I did not have to hack out all the tiles and redo the waterproofing.

This post has been edited by tehtmc: Feb 18 2012, 11:58 AM

[quote=sn4,Feb 18 2012, 12:37 PM]its called PU grouting

[/quote]

OK, polyurethane the foam packing material.
But I'm not sure whether it will work with deep cracks.[
[/quote]

This post has been edited by tehtmc: Feb 18 2012, 12:53 PM

What 400mm thick wall?
We are talking about a car porch roof which is under direct sun and rain.

Car porch roof slabs are typically 100-125mm thick. Wouldn't a thinner slab be more difficult to waterproof than an thicker slab?

The question is also, how long will it long under outdoor conditions?
The same job can be done using sealant or flexible coatings but they don't last.

The question is still whether it can take all the expansion and contraction(thermal movement) due to weather.

Here's something I found:



Source: http://www.waterworld.com/index/display/ar...filtration.html

This post has been edited by tehtmc: Feb 18 2012, 01:49 PM

That's true, it's not as if you have other choices though it may not be 100%.

How much does it cost?

Yes, this is the best solution and it is permanent. Have to spend more though.

If it is for bathroom I'm sure it will work as I have tried. For outdoor, I don't think it is 100%.

Can't imagine a room having a concrete slab over a room. Contractor's suggestion?
Isn't it hot?

This post has been edited by tehtmc: Feb 21 2012, 11:04 AM

If that is the case, my advice is to have metaldeck roofing over - the factory-type roof.
The slab is not wasted as it provides the support for the metal roof.
You need to have insulation for the metaldeck to overcome the noise problem or it would be noisy when it rains.
You not only solve your waterproofing problem, your room would be cooler and more livable.

You need to have a few steel C purlins on the slab to receive the roofing and lay it with a gradient(few degrees)

steel purlins (4"x2" abt 5 ft spacing) ---> a layer of chicken wire netting---> rockwool insulation ---> 0.48mm metaldeck Zincalume roofing

I don't know how your flat roof joins the existing roof. Any picture?

Get a roofing contractor to give you a quote. Probably a 1-day job.

This post has been edited by tehtmc: Feb 21 2012, 11:35 AM

The 2-3" clearance between the old roof and slab is not enough to have the new metal roofing underneath.
You need to modify the end of the existing roof to do a valley gutter. /\/\
What is the depth of the extension?

No, I don't have contact in Penang.

P.S.
Another way to do it, the simplest way:

Forget about purlins and insulation. Lay the metaldeck roofing sheet directly on top of slab, tilt it to fall to back as much as you can (2"-3").
The edge of the roofing sheet below the existing roof eave should be turned up ___]
Roofing sheet to project 1 ft beyond the edge of slab on all three sides.

This post has been edited by tehtmc: Feb 22 2012, 12:20 PM

No, how far to the back you extend from the existing wall.
You need some kind of frame underneath the sheet to tilt it at any angle. You can use timber battens.
And the gaps at the sides?

It will also also look unsightly.
You don't have much of gradient for water to flow (3" over 96"/8ft)

It will. Use Lysaght Kliplok which can take go down to 1 degree pitch.

http://www.lysaght.com/product/lysaght-klip-lok-406

With small job like that, it's hard to get a quote based on sq ft.
If I were to give a guesstimate, I'd put it at abt RM3.00 psf.

Not under the circumstances as discussed in earlier threads. Can you guarantee?
I guarantee no more problem with another layer of roofing over.

This post has been edited by tehtmc: Feb 29 2012, 10:14 AM