My garage is built into the hillside... the reinforced concrete roof is nearly 400mm thick....

However... every time it rains, water percolates through a couple of very very tiny cracks in the concrete and drip inside the garage...

We tried sanding back the top of the roof and brushing on a bitchumin type sealant,...this reduced the water for a bit, but it still comes through..

Are there any other higher tech alternatives to brushing bitchumin paint stuff on the surface?

Its tempting to seal it, and then backfill the hole above so we have a level garden.....That has to be the reason the slab is so darn thick!

If it has a simple curved inner surface, how about fitting thin plastic sheeting next to the surface to take the water away. Or when its dry soaking it with an epoxy resin?

Have a look at www.curon.co.uk

we have used a two pack product called 'Cromapol'
link

Throughout my career of 38 years I have had huge success in solving leaks in concrete with a cementatious product called "Vandex"

Just mix the powder with water to form a slurry and paint it over the cracks (as long as they are hairline cracks) When moisture is present crystals grow into the cracks and seal them so if the crack moves the crystals re-grow. They great thing about this product is that you can use it on the downstream side of the crack as it grows against the flow.

If they are large cracks or holes you will have to chip them out and seal them with a cement vandex mixture using a small pipe to bleed the water away until set and then plug hole where pipe was with cement Vandex.

I have never been disappointed with Vandex or had a failure.

what about fibreglassing the roof? not sure how well it sticks to concrete though

sika do a mastic thats sticks like poo to a blanket..and can be applied to damp concrete
it remains flexible.. its what we use on water reservoirs.. if its good enough to keep it in....
will try to remember to find the part number tommorow

[Edited on 17/12/08 by dave r]