Flat Concrete roof, sealer ?

stackerman

I have some out buildings and attached to one is an toilet. The roof is a flat concrete one, and has started to draw damp through to inside (after many years with no prob). Because of this mold is starting to show on the plasterwork.

Could anyone recommend an external concrete paint that could be applied to stop water passing through ? The water does run off, but seems to be be a prob mainly when there is alot of heavy rain or if snow lies on top for a period of time.

I would be most greatful for any advice or tips

ART6

Concrete waterproofing solution from a builder's providers or PVA adhesive (from the same place) mixed with water should do the job. B&Q also sell the PVA. I have always used the latter and put on two coats for best effect.

Martron

the pva being water solouble..... would this not matter on an exterior roof?

ART6

Martron wrote: »

the pva being water solouble..... would this not matter on an exterior roof?

Don't know -- I haven't made a study of it. But as I understand it once the PVA has set in the concrete (it penetrates rather than setting on the surface) it is no longer water soluble. If it was then using it in mortar mixes and as a primer for cement rendering would mean the mortar would crumble and the rendering would fall off I imagine.

kierank01

try thompson's water seal.

or General Paints in Celbridge, Co Kildare should have a similar product (they have stockists all over the country).

Martron

ART6 wrote: »

Don't know -- I haven't made a study of it. But as I understand it once the PVA has set in the concrete (it penetrates rather than setting on the surface) it is no longer water soluble. If it was then using it in mortar mixes and as a primer for cement rendering would mean the mortar would crumble and the rendering would fall off I imagine.

Thats very true.

I was not questioning your suggestion more curious for myself

ART6

Martron wrote: »

Thats very true.

I was not questioning your suggestion more curious for myself

No probs Matron.

neilthefunkeone

Lads and ladies...

im gonna drag this thread slightly off...Similar question but not concrete..

Its a flat roof actually 2 of them.. one is an extension and 1 is a garage looks similar to pic below.. Its a felt of some sort, smooth.. Any suggestions for a seal for that.. They are not leaking but gf is moving into the house soon so just want to get everything tip top for her!!!

Martron

you could rrefelt it easily enough.

but as the old saying goes ........ If it aint broke, dont fix it