# Forum Home Renovation Waterproofing  Reaction with waterproof membrane?

## Watters

I removed the old tiles, removed the old tile adhesive. I primed the surfaces using a dilution of 1:1 waterproof membrane and water as recommended by the waterproof membrane supplier. Then I applied the waterproof membrane which is a green coloured heavy duty modified rubber, reinforced with siliceous aggregate." In three or four areas there were small grey areas (no more than 6mm diameter) afterwards. 
Could the waterproof membrane have reacted with something on the slab? I have added reinforcing bandage (twice in one case) and more waterproofing membrane and the problem seems to have gone away, or is at least hidden. 
I'm not sure if related or not, but the construction of the bathroom's raised subfloor concrete slab is unusual, but not for the period when the house was built.
Basically, the brick supports were built, then tin sheet supported by wood formwork (horizontal wood with vertical wood supports) was used and the concrete was poured onto the tin sheet. The tin sheet and the formwork were not removed afterwards. Fast forward, probably some 50+ years, and I removed the vertical wood supports to remove temptation by termites. The horizontal supports (except for one which I removed) remain attached to the tin sheet but not to an area that has rusted much. The tin sheet below the slab had been rusting due to the shower leaking in the past. The shower has not been used in a long time, so it is dry under there. From the horizontal beam I did remove there were nails protruding. Clearly the nails embedded into the slab, not a good look. As I mentioned before, this may or may not be related to the problem of grey patches, hard to tell, but I don't think so. I will, though, at some point remove the rusting portion of the tin sheet.

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## Oldsaltoz

> I removed the old tiles, removed the old tile adhesive. I primed the surfaces using a dilution of 1:1 waterproof membrane and water as recommended by the waterproof membrane supplier. Then I applied the waterproof membrane which is a green coloured heavy duty modified rubber, reinforced with siliceous aggregate." In three or four areas there were small grey areas (no more than 6mm diameter) afterwards. 
> Could the waterproof membrane have reacted with something on the slab? I have added reinforcing bandage (twice in one case) and more waterproofing membrane and the problem seems to have gone away, or is at least hidden. 
> I'm not sure if related or not, but the construction of the bathroom's raised subfloor concrete slab is unusual, but not for the period when the house was built.
> Basically, the brick supports were built, then tin sheet supported by wood formwork (horizontal wood with vertical wood supports) was used and the concrete was poured onto the tin sheet. The tin sheet and the formwork were not removed afterwards. Fast forward, probably some 50+ years, and I removed the vertical wood supports to remove temptation by termites. The horizontal supports (except for one which I removed) remain attached to the tin sheet but not to an area that has rusted much. The tin sheet below the slab had been rusting due to the shower leaking in the past. The shower has not been used in a long time, so it is dry under there. From the horizontal beam I did remove there were nails protruding. Clearly the nails embedded into the slab, not a good look. As I mentioned before, this may or may not be related to the problem of grey patches, hard to tell, but I don't think so. I will, though, at some point remove the rusting portion of the tin sheet.

  Yes common practice back then, the sheet iron was only to support the slab till it cured, so harm done. 
It does sound like a reaction, but overlapping should be ok as it ends outside the effected area so bonding should be a problem. 
Good luck and fair winds.   :Smilie:

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