Rusting corner mesh on internal walls

steamdave

The steel corner reinforcing mesh in several rooms is rusting and staining the wall paint. The "correct" way to fix it is probably to cut out the old mesh and install new and replaster. Messy and expensive!

Are there any suggestions on hiding the rust marks that don't involve plaster surgery? I have tried oil based paint under the water based emulsion, but that only delays the stains coming through a short while.

Dave

Dave

Lenar3556

I have struggled with this externally and didn’t find a very effective solution. Plastic corner beads are a better solution - not must help saying that now!

But I didn’t think this would be as much of an issue internally. Is dampness an issue?
In terms of a blocking primer, Zinsser BIN (either the original version or new water based might be good)

Calahonda52

You need to raise the rom temperature above the dew point and reduce excess humidity in the room.

else consider fitting a 50 mm by 50 mm triangle or 1/4 round

eg

https://tjomahony.ie/4-8m-75mm-x-75mm-angle-fillet-1-to-give-2-en14081-16-3-x-3-03af757548.html?utm_source=googleshopping&utm_medium=cpc&utm_campaign=googleshopping&gad_source=1&gbraid=0AAAAAClBc6YRD_BJ2k1KYI7-tZLaxXoY7&gclid=Cj0KCQiAoJC-BhCSARIsAPhdfShgUh18kmu3xSeCz3Qyzfg-7UIbnLyHMFN3HH6l2mNAQQFW-d0ltd4aAvw4EALw_wcB

this one is 75, make sure it dry to avoid shrinkage. once painted SWMBO wont even see it

steamdave

Thanks, gents for your suggestions. This question was meant to go in the DIY forum!

Dave

10-10-20

https://www.boards.ie/discussion/comment/123225181#Comment_123225181

Just one comment - the room temperature will always be above the dew point except where the air is saturated (RH = 100%). So I'd correct it to say to reduce the dew-point by lowering the relative-humidity, but also increase the room temperature at the same time (which will also reduce the RH - but only for the duration of the increase in temperature).

Back to the original poster's question - steel corner beads are supposed to be galvanised so that they resist rusting, but this protection can only last so long before it breaks through and stains the wall. The fact that the beads are made from metal means that they are the first object in the room to release their thermal energy, therefor becoming colder quicker than the surrounding air. The problem then is that if the relative humidity in the house is high then the dew-point (the temperature that water condenses on a surface) will also be high, so the moisture will gather on and around the coldest surface in the room - in this case it's the beads.

The overall solution is to ventilate more, isolate and eliminate internal sources of humidity (run bathroom fans more, use lids on pots, dry clothes outside or in a dryer, etc.), increase the ambient temperature and dehumidify where appropriate. Beyond that you could consider increased insulation to keep the house warmer, but be aware that by adding heat you also increase the ability of the air to hold more moisture, so when it cools down, it all has to condense somewhere!

To fix the rusting beads, the best option is probably to replace them as their protection has gone so they are susceptible to further corrosion if the conditions dis-improve again.