plastering on metal


Old 11-04-02, 02:06 PM
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plastering on metal

I have what looks like plaster over the metal lintels which are above windows. The plaster is broken and I need to repair, but have no clue how to do it. Also behind the radiators are brick walls and then plastered. Some of the plaster is loosening. How do I repair this? If I just replaster, I run the risk of it breaking somemore.

Any thoughts?
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Old 11-05-02, 03:57 AM
Join Date: Nov 2001
Location: Taylors, SC
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The old bugbear is why is the plaster failing? Around a window, it may be moisture. If that be the case, then any repair will eventually fail unless the moisture is eliminated.

I usually use lightweight joint compound to repair my plaster. Clean off the damaged material and appply mud to the area. It may take more than one coat to fill the open space to level over the metal. If this is a thin fill over something as stable as metal, taping may not be necessary. If the plaster cracked along a line and failed, then tape it. If it pulled away from wall in a sheet, taping won't help the cracking. The same applies to the area behind the radiator.
Old 11-08-02, 08:03 PM
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I've seen your first problem, failing plaster on lintels, addressed many ways. In my opinion the best way was done by a company that repaired, restored, and/or reproduced old windows for the restoration of antiquities. They informed me that the main reason this type of plastering fails is because metal lintels and plaster expand and contract at different rates. They do not want to patch with a third material and introduce another expansion and contraction rate, so it is their practice to very carefully remove all the plaster from the lintel, usually by hand with a hammer and chisel, then screw or power fasten expanded metal, and then replaster carefuly matching the textures on the other lintels.
Old 11-09-02, 04:30 AM
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Join Date: May 2002
Location: Alabama
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Chfite - I am curious. Why do you use drywall mud rather that patching plaster for plaster repair. It seems that you would have shrinkage which would require subsequent coats of the compound, whereas the patching plaster doesn't shrink and sets in minutes.
Old 11-09-02, 10:03 AM
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Second thoughts - my sixth sense tells me that both these conditions, the cracks and failures on the lintels and on the bricks behind the radiators, that it's a very old 100+ home and that it isn't plaster, it's cement. If so, don't use anything but cement. The mix used in those good old days was 1 part portland cement to 3 parts of sand and hydradate lime equal to 10% of the portland being used. That formula is still used today, but redimixed bags are easier. Just chop out the bad plaster/cement/stucco and replace it with new. Don't patch. Do it right - once.
Old 12-27-02, 12:06 PM
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Nuts and Bolts is Right!

What you described is exactly what I have. I have done some patching in the front of the building which is the living room, but there are areas like around the radiator that keep crumbling. The building has been tuckpointed so I know there aren't any obvious holes, but it is constant repair from the hot / cold changing.

The pre blend mix, is that an exterior repair material? The only preblend I have seen in the drywall section at H.D. is the blend of joint compound. you were right, the building is 100+ years old. Repairs in it are a real pain - nothing's ever easy!

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