waterproofing a flat concrete roof

[TMC]

Hi All

ex council house outside store roof 100mm thick concrete area about 4m x 3 metres

has rasied front and sides (a lip about 25mm high)

Never been felted

Looking at the fibrous paints or other low cost solution

any recommendations

Regards

[Dean Heighington]

Is there any provision for the rainwater to drain off or does it just puddle up and stay trapped? is there a fall?

[TMC]

yep slight fall to the back with gutter and downpipe

Regards

[Steve Firth]

The usual solution in places like Italy where flat concrete roofs are normal is to lay a waterproof screed on the roof. This requires the roof to be clean and dry before you start.

example.

[Lobster]

Sounds identical to one I did myself once. IIRC I used bitumen paint as a cheapo solution, as I knew I'd be selling the place not long afterwards.

Seemed to do the job well enough; I can't vouch for it's longevity but think if I'd been intending on keeping the property for a long time I'd have chosen something more durable. Indeed, the purchaser's surveyor flagged it as a future maintenance issue.

David

[The Natural Philosopher]

yeah. Concrete itself is pretty impervious, depending on the grade.

Anything that soaks in a bit of a plasticky or tarry nature will improve it immensely.

Probably one of those render waterproofers will do.

[TMC]

[Phil L]

having atempted all of the suggestions in this thread over the past thirty years, I have found only one solution and that is to use a product called 'cromapol'

've done a few concrete rooves with this and had no problems at all, it's expensive, because it works.

Don't bother with anything available from B&Q et al, they also have expensive sealants, but none of them work on cracked concrete

It's available in black, white and grey

[Dean Heighington]

Having read all the other posts since my reply this am, I would also recommend the cromapol product or there's another called aquapol, I think... Check out JJ Roofing supplies or Wedge roofing, but again, it's not cheap- about £90 a tin retail, £60 trade. For a cheaper way of remedying it as a trial.... If you can find the crack get a tube of Sika Flex

use that to fill the joint, it's great stuff.

Hth Deano

[The Natural Philosopher]

Cracked is different from porous, sure. I'd probably use epoxy mortar on cracks, but that stuff looks a useful thing to know as well

[Jim K]

cracked?

Jim K

[Phil L]

TMC mentioned it was cracked at 16:48 yesterday