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IdahoEv 09-09-2012 04:28 PM

What is this stuff?
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Repairing a hole in the wall in my old rental, I start opening a square hole to see this weird two-layer wall material. The outer layer seems to be some sort of brittle cement. Cutting a ten inch line in it took the teeth clean off my jigsaw blade.

What is it, and do I need any special prep to patch it with a piece of normal drywall?


Bud Cline 09-09-2012 05:00 PM

It's a form of plaster.
The tiny fibers are asbestos.
You can do what you want.

IdahoEv 09-09-2012 06:47 PM

I didn't see anything fibrous, just something cement like. Is that stuff definitely asbestos? Do I need to call an asbestos pro?

Bud Cline 09-09-2012 11:16 PM

Years ago when plaster was applied over wooden lath strips, horse hair was used to bind the mix and help to unitize the cement product. Go figure!:)

Then later the lath sort of went away and after WWII they started using mostly drywall backer board like you have. Around that time the horse hairs were replaced with asbestos fibers. The fibers were basically the size of horse hairs and slightly smaller. I'm thinking the vintage I see in your photo would have contained asbestos but maybe not.

Too late now to worry about it. In most all cases any threats from asbestos would be directed at workers using the mineral and working with it over a long period of time. Some people these days freak needlessly at the mention of asbestos and they over-react. Some asbestos abatement companies like to use fear tactics to persuade consumers to use their services. I'm not saying there isn't a threat I am just saying that the danger is in the eyes and fears of the handler. Years ago when I was certified as an asbestos abatement contractor I learned a lot about the product and quite frankly I wouldn't be at all concerned doing your project. This is a judgement-call and you have to make the call.

IdahoEv 09-09-2012 11:51 PM

Okay, good to know. How do I go about cutting it? The stuff destroyed my jigsaw blade in moments, and I still have three sides of the hole to square up. I also need to cut above and below a horizontal stud ... normally I'd do those cuts with a utility knife but somehow i doubt that would do it here. Maybe a chisel for those spots.

At least discovering this stuff explains one thing. Pulling out a picture-hanging nail in this house always results in a half inch wide crater, no matter how careful I am. I though it was just crappy ancient drywall.

Bud Cline 09-09-2012 11:58 PM

There are blades made with a carborundum (grit) edge, those are your best bet but you may still gobble-up more than one blade.

I use a 4" angle grinder with a diamond blade but dust is a huge issue when doing it that way.

You could also use an angle grinder with an abrasive (masonry) blade.

I would not do too much pounding with a chisel if it isn't totally necessary. Just my thinking.:)

chrisn 09-10-2012 05:53 AM

For sure , wear a mask

bbo 09-10-2012 08:10 AM

and feel free to mist with water to keep the dust down.

gregzoll 09-10-2012 08:21 AM


joecaption 09-10-2012 08:28 AM

I use a Roto Zip with a vacuum attachment and use a tile bit.
I have also cut it with what amounts to a small ciruler saw with a vacuum attahment with a diamond blade that also has a vacuum attachment so you can hook up your shop vac.

langless28 09-13-2012 06:46 PM

I think I have this stuff too. What is the technical name for it? Would gutting a hole kitchen be a bad idea if this was the walls?

gregzoll 09-13-2012 07:09 PM


Originally Posted by langless28 (Post 1009323)
I think I have this stuff too. What is the technical name for it? Would gutting a hole kitchen be a bad idea if this was the walls?

As I stated before, Rock-Lathe, Gyp-Rock. Bad part is when you do not keep the dust from going all over the house.

langless28 09-13-2012 07:15 PM

The house is circa 1959 so I guess I will send a sample to get tested. I was not expecting this...

gregzoll 09-13-2012 07:47 PM


Originally Posted by langless28 (Post 1009343)
The house is circa 1959 so I guess I will send a sample to get tested. I was not expecting this...

And it will come back as Gypsum, maybe some lead paint, cellulose and nothing else.

langless28 09-13-2012 07:49 PM

Well that would be a terrific result! So there's no chance of asbestos? Id rather be safe then sorry?

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