How to repair ceiling damaged by rat urine

There is a downward bulge the size of a tennis ball (thanks Benjamin Moore) next to the ceiling light in our kitchen. "Water" damage runs the length of the drywall joint. How do I fix this? Our attic has been free of rats for almost a year after I had plugged the visible entry points below the roof with hardware cloth. It's been raining hard here in the Emerald City and I thought the damage may be due to a water leak (the roof is overdue for a repair and is going to be recovered in 2 weeks). When I went up the attic, I saw at least two fat rats scurrying and there were tell-tale signs of fresh droppings, the insulation had been moved and urine had run along a rafter. The rain did cause the damage I suppose by driving the rats inside and keeping them there. The junction box must attract the rats due to it being warm when the light is on. They had lifted up the tar paper too. I opened a fresh bag of poison and left a rag to soak up the urine. Time to look around to check how they get in..
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KublaiKhan wrote:

The answer to your question depends a on what the existing ceiling finish is. You're in luck if it's a textured or swirled finsish as you can just cut out the damaged plasterboard fit in a patch, and moosh over it to duplicate the original finish. There are thin metal clips available to hold a patch in place in a cutout for locations where there's nothing to nail or screw into behind the patch.
Or, you can hold the patch in place by fitting a strip (or two) of wood up through the hole with glue on its ends so it adheres to the upper surface of the existing plasterboard and then fasten the patch to the wood strip with a couple of screws.
Then, use patching plaster to fill in the gaps between the patch and the cutout. If the patch is small and well secured, you won't have to tape the joints and use drywall compound.
To restore the textured or swirled finish, you can use some "textured finish", which is a dry powder to be mixed with water and applied with a coarse brush or roller to duplicate the original finish. I've had luck using white latex ceiling paint with a little ptching plaster mixed into it for the same purpose. You may have to repaint the whole ceiling to get a good color match.
If the ceiling finish is smooth, the repair is pretty much the same, but you'll have to tape, compound, and sand the patch joint lines, and then repaint.
Good luck,
Jeff
-- Jeff Wisnia (W1BSV + Brass Rat '57 EE)
"If you can keep smiling when things go wrong, you've thought of someone to place the blame on."
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snipped-for-privacy@hotmail.com (KublaiKhan) wrote:

Ummmm...EEEEEWWWWWWWWWWWWW!
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Any chance the rats are getting in along the foundation? I know it's possible that rats can climb wires, siding, etc., but after checking with a pest control person, he said that although it's possible they can climb up high to get into your house, it's not real likely, particularly if you have more than one rat in your house. Most of the time they get into holes along your foundation ... and in your case, they may be climbing up your insulated walls into your attic. I'd go inch by inch along where the ground meets your house's foundation, and reach up under your siding to check for holes. We did this to get rid of mice, and I found a number of gaps, such as where the siding met the chimney, and on corners, were the building materials (i.e., sheathing) used under the siding don't quite meet tightly.
Once you find the holes, fill them with foam and steel wool or hardware cloth.
Of course, it does pay to look for other holes up high, like the one you already filled, because even if rats aren't getting in there, bats could.
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