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-   -   Aggregated Stucco? (http://www.diychatroom.com/f105/aggregated-stucco-144864/)

mwpiper 05-25-2012 10:15 PM

Aggregated Stucco?
 
3 Attachment(s)
I have two gables that are covered with ancient stucco long overdue for replacement. I was thinking of replacing the stucco with siding. However, at my daughter's school, I saw an interesting finish. The dark areas around roof in this picture
Attachment 51401
and detailed here
Attachment 51399
Attachment 51400
got me thinking that it would be a good texture for the gables. It looks like the gravel finish is adhered to cement fiber board.

Is anyone familiar with the technique for applying aggregate to cement board? Is the aggregate attached before the board is put up or after?

stuart45 05-26-2012 02:42 AM

Looks look pebbledash, which is done by throwing them on while the stucco is still wet, and then pushing them in with a wooden float.

mwpiper 05-26-2012 07:56 AM

So it's done by putting up the cement fiber board up first, laying on a layer of stucco, throwing the stones at it and then tamping it with a float? Is there any special type of stucco required? Single layer of stucco on the cement board? How large an area is normally done at a time? If a wall can't be completed in a day, is working from a dry edge a problem?

I've read that the stones need to be screened for uniform size. Does any size work as long as it's uniform? Case in point. The hotel we were staying at (Grand Plaza in St. Pete's Beach if you're familiar with it) has three inch stones cemented to the walls (sorry, no picture). Of course, I doubt they threw them into place.

stuart45 05-26-2012 11:11 AM

Quote:

Originally Posted by mwpiper (Post 929007)
So it's done by putting up the cement fiber board up first, laying on a layer of stucco, throwing the stones at it and then tamping it with a float?
Is there any special type of stucco required?
I use a 1/1/5 lime/OPC/sand for the top or butter coat, and 1/1/4 for the scratch coat.
Single layer of stucco on the cement board? How large an area is normally done at a time? If a wall can't be completed in a day, is working from a dry edge a problem?
It's best to the lot in a day, as edges tend to show up, as can often be seen with patch repairs. The size you can do depends on how good you are with the laying on trowel.

I've read that the stones need to be screened for uniform size. Does any size work as long as it's uniform?
Normally use small stones. There is a special trowel known as a Harling trowel used to throw them with. You need to stand back a bit to make sure you get an even spread. Go over the wall a few times to build up the stones.

Case in point. The hotel we were staying at (Grand Plaza in St. Pete's Beach if you're familiar with it) has three inch stones cemented to the walls (sorry, no picture). Of course, I doubt they threw them into place.

I doubt if they threw those on.

mwpiper 05-27-2012 04:54 PM

Many thanks stuart. I will try some samples at ground level to see how it works.

Willie T 05-27-2012 06:09 PM

One method that produces good results, and also helps the aggregate to adhere better is to do the spatter-dash as described above. Then trowel a smooth, solid layer of stucco over the stones, just covering them.

As that second covering of stucco begins to set up (usually within an hour or so), wave a stiff, but fine spray of water across the surface.... removing about two thirds of the stucco in smooth, even passes. This produces a less-harsh, cobble stone appearance, and also locks each stone into place better than just slinging the spatter dash up there and pushing the stones in.

stuart45 05-28-2012 06:13 AM

Thanks for that info Willie T. I've never seen that done before, but it seems a good method. One of the problems with pebbledash is that the stones tend to fall off over the years.
Another method used here is called Roughcast, where the stones are put into the mix first and then trowelled on as a form of concrete. This produces a very strong and waterproof finish, although not everyone likes it's appearance.

mwpiper 05-29-2012 07:19 PM

2 Attachment(s)
a site from the UK also called them "wet dash" vs. "dry dash" techniques.

When I first saw the pebble finish in the pictures I was thinking exposed aggregate concrete where the upper layer of cement is washed off a horizontal surface like sidewalks or driveways. My problem with that is the walls I want to put this on are gables (2nd floor level) over brick on the first floor. Dry dash would probably spill a bunch of gravel on the ground. If I did a wet dash, I would probably drape a drop cloth over the first floor wall to prevent staining.

This is what the old stucco looks like:
Attachment 51643
Yeah, when big chucks like this are peeling off, it's in pretty rough shape.
This is the back side:
Attachment 51644
The stucco was put on grooved wooden planking. No water proofing. Where this chunk came off, the sheathing is shot. I suspect that every place there is a crack there will be water penetration, so the sheathing will probably have to be replaced too.


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