Guest Alphonsox Posted June 28, 2016 Share Posted June 28, 2016 Help needed please - SWMBO has reported that a strange brown stain has appeared in the newly plastered ceiling. (12.5mm plaster board + skim). It seems to be a long way from any possible point of water ingress. Any ideas ? Link to comment Share on other sites More sharing options...
daiking Posted June 28, 2016 Share Posted June 28, 2016 Screw? I had a couple of blooms that eventually faded. Will put some Zinsser over before final decoration. Link to comment Share on other sites More sharing options...
Guest Alphonsox Posted June 28, 2016 Share Posted June 28, 2016 My guess would be a screw or nail as well, but its difficult to see how it's any different to the other screws in the ceiling. Link to comment Share on other sites More sharing options...
DeeJunFan Posted June 28, 2016 Share Posted June 28, 2016 8 minutes ago, Alphonsox said: My guess would be a screw or nail as well, but its difficult to see how it's any different to the other screws in the ceiling. Rust potentially? Link to comment Share on other sites More sharing options...
Declan52 Posted June 28, 2016 Share Posted June 28, 2016 Tap where it is to see if there is a joist there. If there is no joist it can't be a screw. Never seen that one before . Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 28, 2016 Share Posted June 28, 2016 Dig it out and get rid first as last Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 28, 2016 Share Posted June 28, 2016 Could well be a duff plasterboard screw, one that missed the corrosion proofing. I noticed that our guys found the occasional "blind" screw in a strip, where the head hadn't been formed, so there's always the possibility of there being one that missed out on being passivated. Link to comment Share on other sites More sharing options...
Guest Alphonsox Posted June 28, 2016 Share Posted June 28, 2016 Thanks for the thoughts - I'll get SWMBO to do some tapping and see if its on a joist - Unfortunately my metal detectors are all in England, Link to comment Share on other sites More sharing options...
Construction Channel Posted June 28, 2016 Share Posted June 28, 2016 get a magnet, i carry a relatively big neodymium (?) magnet for finding studs at work Link to comment Share on other sites More sharing options...
daiking Posted July 8, 2016 Share Posted July 8, 2016 Did you sort this? What's above the plasterboard? cjard (formerly of the last parish?) has posted on GBF about oily knauf wool insulation causing marks like this. Link to comment Share on other sites More sharing options...
Guest Alphonsox Posted July 8, 2016 Share Posted July 8, 2016 The plasterer was also of the opinion that this was a result of the insulation - I guess its possible that the insulation had dropped at that point come in contact with the plasterboard. I can't say I find this argument particularly convincing the patch is the size of my hand so any oily substance would have had to soak through 12.5mm of plasterboard and 5mm of skim. That would imply a reasonable amount of oil I would think. The mark is on a joist but I am informed the mark is the wrong colour for rust (I haven't been on site recently so haven't seen this for myself.). The patch hasn't grown any larger and we haven't seen any other marks developing elsewhere. We have covered it with a couple of coats of Screwfix stain sealer and will see if that is the end of the issue. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted July 8, 2016 Share Posted July 8, 2016 4 hours ago, daiking said: Did you sort this? What's above the plasterboard? cjard (formerly of the last parish?) has posted on GBF about oily knauf wool insulation causing marks like this. That's a very good point about the insulation. I used Knauf insulation above the ceiling downstairs and found the occasional stiff bit of what look like black, oily, bitumen, and smelt a bit like it, too. I've no idea how this stuff gets into a roll, but I can see that if it was left there (I tore the black bits off) then it could cause a stain, and it may well be that the black stuff melts when it gets warm, making it run and drip on to the plasterboard. I was just intrigued at the time as to where this black stuff came from, because it seemed to be very like tar or bitumen, and I can't see why something like that should be used when making rockwool/fibreglass insulation. Link to comment Share on other sites More sharing options...
daiking Posted July 8, 2016 Share Posted July 8, 2016 1 minute ago, JSHarris said: That's a very good point about the insulation. I used Knauf insulation above the ceiling downstairs and found the occasional stiff bit of what look like black, oily, bitumen, and smelt a bit like it, too. I've no idea how this stuff gets into a roll, but I can see that if it was left there (I tore the black bits off) then it could cause a stain, and it may well be that the black stuff melts when it gets warm, making it run and drip on to the plasterboard. I was just intrigued at the time as to where this black stuff came from, because it seemed to be very like tar or bitumen, and I can't see why something like that should be used when making rockwool/fibreglass insulation. To paraphrase cjard and I am just repeating from his other place post, he says its used to reduce dust but must congeal/lump in some parts. Link to comment Share on other sites More sharing options...
Guest Alphonsox Posted July 8, 2016 Share Posted July 8, 2016 The insulation is Knauf rockwool so this sounds like it may well be the problem. I guess the question now is whether we can expect other patches to appear or whether this will stabilise now its fully exposed. Link to comment Share on other sites More sharing options...
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