4specs.com    4specs.com Home Page

Plastering Tolerances Log Out | Topics | Search
Moderators | Register | Edit Profile

4specs Discussion Forum » Archive - Specifications Discussions #3 » Plastering Tolerances « Previous Next »

Author Message
Dave Metzger
Senior Member
Username: davemetzger

Post Number: 181
Registered: 07-2001
Posted on Tuesday, January 16, 2007 - 11:12 am:   Edit PostDelete PostPrint Post

We have a theater renovation project, where we are building an interior partition consisting of three-coat gypsum plaster on metal lath on cold-formed metal framing.

Because the plaster will be used for a projection surface, the architect wants a very flat plaster surface. The only tolerance that I can find in ASTM C 842 is for the finish coat thickness to be between 1/16 and 1/8 inch thick. In the Plastering Manual, all I can find is "Finish all plaster, interior and exterior, true and even, within 1/4" tolerance in 5', without imperfections..." Which is a long way from the 1/8 inch in 8' we usually specify for plumbness of a gypsum board partition.

So my question is, what tolerances has anyone had experience with successfully specifying for flatness, smoothness, and plumbness of a plaster partition?
Nathan Woods, CCCA, LEED AP
Senior Member
Username: nwoods

Post Number: 153
Registered: 08-2005
Posted on Tuesday, January 16, 2007 - 11:29 am:   Edit PostDelete PostPrint Post

I think the application of this material in this location is a bit ackward. How are you going to hide control joints? Is your "screen" area less than 10'-0"?

There are a few options I can suggest.

1. There used to be a company called Flexirock that made a really good smooth plaster system. I think they got bought out and I don't know what the system is called anymore, but I'm sure it still exists. However, you still need control joints!

2. EIFS - this would seem to be a more ideal surface for you. Larger panels, much flatter & more square, with smooth texture available.

3. Precast or tilt-up concrete.

4. Prefabricated plaster walls, built flat on the ground, troweled with laser screeds, and then hung in panels. still have those joints though...

Ultimately, you can specify what you need for tolerances, and call attention to it so that the Contractors really see it and factor that into their bids
Richard Howard, AIA CSI CCS
Senior Member
Username: rick_howard

Post Number: 107
Registered: 07-2003
Posted on Tuesday, January 16, 2007 - 12:35 pm:   Edit PostDelete PostPrint Post

Assuming that no one will be viewing this "screen" at a wide angle from perpendicular, I wonder how critical the actual flatness would be to the apparent flatness. I think that smoothness would be more important.

You could improve the levelness of the plaster the same way you get a flatter floor; ask that longer than normal screeds be used for leveling the brown coat.

By the way, USG's spec for plaster work calls out a tolerance as follows: "Do not deviate more than plus or minus 1/8 inch in 10 feet from a true plane in finished plaster surfaces, as measured with a 10-foot straightedge place on the surface."
John Bunzick, CCS, CCCA
Senior Member
Username: bunzick

Post Number: 637
Registered: 03-2002
Posted on Tuesday, January 16, 2007 - 01:50 pm:   Edit PostDelete PostPrint Post

It would be useful to know how flat a standard projection screen is as a comparison. Maybe one of the screen manufacturers can shed some light on this.

I would think good plasterers, using screeds and other techniques, could get a pretty flat wall, particularly if there's only one area requiring this extra effort.
Dave Metzger
Senior Member
Username: davemetzger

Post Number: 182
Registered: 07-2001
Posted on Tuesday, January 16, 2007 - 05:13 pm:   Edit PostDelete PostPrint Post

That's true, Rick and John. When you look at typical projection screens, except maybe for the tab-tensioned type, they aren't all that flat.

Thanks for all the help, people.
Marc C Chavez
Senior Member
Username: mchavez

Post Number: 181
Registered: 07-2002
Posted on Tuesday, January 16, 2007 - 05:44 pm:   Edit PostDelete PostPrint Post

Once you plaster it. see the attached site for "Screen Goo". I have spec'ed this once - no complaints. But have not seen it work.

http://www.theaterthings.com/
Colin Gilboy
Senior Member
Username: colin

Post Number: 71
Registered: 09-2005
Posted on Tuesday, January 16, 2007 - 05:51 pm:   Edit PostDelete PostPrint Post

Suggest you go to the manufacturer. Just added them to 11-5200

http://www.goosystems.com/
Ron Beard CCS
Senior Member
Username: rm_beard_ccs

Post Number: 163
Registered: 10-2002
Posted on Tuesday, January 16, 2007 - 06:48 pm:   Edit PostDelete PostPrint Post

Dave:

The wall (projection) surface is only one of the many issues that one should address when dealing with “theater” projecting. As appropriate to any good design process, basic questions should be asked and determinations made. In the case of media projections, the following questions should be among the first to be asked:

1. What is the size(s) of the image intended? Be sure to confirm whether the size given is the horizontal width or the diagonal dimension.

2. What is the type and technical specs of the projector to be used? ....high-def, pixel count, light output, cinematographer's control (tonal reference) chart, focus, etc. Is the Owner expecting to use leading-edge technology?

3. Prime seating distance (from the torso of the viewer)?

4. What are the overall lighting conditions in the space? Is it a multi-purpose room with windows to the outside which might use a projection system occasionally or a dedicated theater projection facility? Light output and light scatter will adversely effort the projected image. Generally, it is best to frame the area to be projected with darker colors.

Once the brightness of the scene, luminance of the electronically converted signal, and the ability of the projection system to transfer images fast and without losses of color or distortion, then the surface onto which the images are to be shown can be fully determined. The level of smoothness of a surface viewed for a distance can be a lot different than one viewed at close range.

As mentioned by Mark, www.goosystems.com is a good source to consult.
Gerard Sanchis (Unregistered Guest)
Unregistered guest
Posted on Tuesday, January 16, 2007 - 07:51 pm:   Edit PostDelete PostPrint Post

Dave,

I believe that there are misconceptions regarding gypsum plaster. It's like brick which expands after it's installed. Plaster expands when it cures - therefore it doesn't need "control joints" in most cases.

As to how flat it can be made, the beauty of gypsum plaster is that it can be sanded and re-plastered many times making it very flat; 1/8-inch in 10 feet is easy to get and it's all you'll need for a projection screen. Make sure to specify a projection screen paint.

I would not use portland cement plaster because it's difficult to get a flat, smooth surface that doesn't crack - FlexiRock, by the way, was a pre-mixed portland cement plaster, it's now called EnRock and is marketed by Parex.
John Regener, AIA, CCS, CCCA, CSI, SCIP
Senior Member
Username: john_regener

Post Number: 255
Registered: 04-2002
Posted on Friday, January 19, 2007 - 02:31 am:   Edit PostDelete PostPrint Post

Coming from the land that fills megaplex theaters every night (I lost count at 250 screens within 10 miles of home --- in Orange County CA), it should be noted that large screens are not flat but are curved. Even in high-end home theaters, the viewing surface is sometimes curved (projected images rather than LCD or plasma HD-TVs). Also, the sound system should be considered. There are often speakers behind the acoustically-transparent projection screens in commercial theaters.

Topics | Last Day | Last Week | Tree View | Search | Help/Instructions | Program Credits Administration