| Author |
Message |
Richard Baxter, CSI (Unregistered Guest)
Unregistered guest
| | Posted on Thursday, August 11, 2005 - 02:58 pm: |    |
Does anyone know how to determine if the “breathability” (or vapor permeability) of a finish coating is adequate for installation over historic lime plaster?
All the information I have been able to attain has stated that lime plaster is very “breathable” and that it requires a very breathable coating, such as lime wash or distemper coating. I haven’t seen anything that states what that breathability is, which means I do not have a way to determine if a finish coating is sufficiently breathable to accommodate it.
We are refinishing the ceiling of the Mormon Tabernacle, a significant historic building here in Salt Lake City, Utah. A somewhat new product, Tuff-Hide manufactured by USG, has been proposed as a coating to be applied directly over the existing lime plaster. Tuff-Hide has been proposed as a less-expensive way to smoothen the existing plaster surface, hide all the patching, and provide a smooth finished surface in one application. It is usually recommended for use over plaster, but it does not specifically mention lime plaster and it doesn’t have a long performance record for me to rely on. I would appreciate any comments that might enlighten me more on this issue. |
Susan McClendon
Senior Member
Username: susan_mcclendon
Post Number: 26
Registered: 01-2005
| | Posted on Thursday, August 11, 2005 - 03:16 pm: | |
Lately, a common answer to posts like this is "google it"! "Lime plaster permeance" returns quite a lot. Permeance is vapor transmission rate; permeability is permeance for a specific thickness. |
Doug Brinley AIA CSI CDT CCS
Senior Member
Username: dbrinley
Post Number: 57
Registered: 12-2002
| | Posted on Thursday, August 11, 2005 - 04:08 pm: | |
Richard,
I think the permeability issue is premature and don't agree with a smooth finished surface in that application. It seems you're trying to conceal defects and surface irregularities, therefore a smooth finish of any type for a repair situation is problematic.
Tuff-Hide seems a poor choice - it's a 'modern' gypsum / latex product and USG does not indicate it for plaster. Has your USG rep recommended that product and will they stand behind it? How might he know what the actual limitations are without examining the substrate?
You didn't indicate how mechanical/chemical adhesion to the (underlying) lime plaster was going to be achieved. Since it has presumably been there a long time, it's not clear how the installer will get the (modern) finish coat to 'bite' into the underlying (old) material. Ordinarily you'd want a cross-hatched texture in the underlying coat in preparation for a finish coat.
See if you can find Ian Constantinides (UK) on the web. |
Richard Baxter, CSI (Unregistered Guest)
Unregistered guest
| | Posted on Thursday, August 11, 2005 - 05:47 pm: | |
Thank you all for your input.
Susan, I tried “googling” it before, but I didn’t use the words that you suggested and I ended up with too much information about too many things that didn't apply. Using your suggested words, however, I now have information on permeance of the plaster. Thanks.
I still haven’t found anything on the permeance of the Tuff-Hide product. That is the information I really need to see.
Doug, The product information I have from USG for Tuff-Hide actually contradicts itself. The Product sheet indicates it can be applied over plaster, but the website faq says it cannot be placed over plaster unless a bonder is applied first. The product rep then told us that the product needs a bonder over new plaster, but not over existing plaster. Yet, we later received a letter from the USG Support Services Support Manager stating that Tuff-Hide is breathable and can be directly applied to plaster without a bonder. None of them made any distinctions between cementitious plaster, gypsum plaster, or lime plaster. I don't know what to think about it and so I am inclined to discourage its use.
As a sidenote, I haven’t found anything in the product data stating that Tuff-Hide actually contains any gypsum. It is described only as a vinyl acrylic latex-based coating.
I am having my doubts about the product. I agree with your concerns about the manufacturer’s understanding of the actual substrate conditions. I'd be much happier if I had a list of successful installations of their product over historic lime plaster ceilings. The mockup we did with the product did look good and adhered well - but it is anybody's guess as to how long it will last. |
Doug Brinley AIA CSI CDT CCS
Senior Member
Username: dbrinley
Post Number: 61
Registered: 12-2002
| | Posted on Thursday, August 11, 2005 - 06:19 pm: | |
Latex emulsions tend to have excellent vapor permeance (ie: 'breathable') in comparision with other film-producing liquids, and it is difficult for a manufacturer to demonstrate better performance AND ease of use AND low material cost without relying on latex. (Tuff-Hide should have excellent technical performance). I'm not sure how much further you need to go with the permeance issue. It is probably a very attractive solution from the applicator's perspective.
I think you do have to figure out whether it's a good idea to apply a contemporary product like Tuff-Hide given the tech support has not explicitly stated it is appropriate over lime plaster. Lime plaster had hair and all sorts of other regional oddities, and who knows what to expect when emulsifiers and other compounds are placed on top. I think you have compatibility and adhesion issues first, then moisture vapor 'transparency'.
USG could state in writing what is not acceptable. Until you get that information, you're probably getting sales oriented information and not 'the skinny'.
Is this a dome or flat ceiling? is it in a large volume space? I've been in the Tabernacle - is it the ceiling of that space? |
Colin Gilboy
Senior Member
Username: colin
Post Number: 193
Registered: 05-2000
| | Posted on Thursday, August 11, 2005 - 06:39 pm: | |
The Mormon Tabernacle was built about 1870 and is an enormous wood framed dome - you have probably seen it on TV. I recall the tour guide pointing out where a foot went through the ceiling and was patched. I was impressed with the construction and the timeframe it was built in.
Here is a quote from the lds.org website:
"Construction on the Tabernacle began in 1863 and ended in 1875. The exterior of the completed building is 150 feet wide, 250 feet long, and 80 feet high. This unique Tabernacle was a marvel of its time. Through the bridge-building technique of Henry Grow, the Tabernacle roof was able to span its 150-foot width without center supports–an amazing achievement in both engineering and acoustics. Meetings and concerts are still held in this historic building."
I would be concerned about paint and dirt over the years and that is probably a bigger potential problem than the substrate. |
Richard Baxter, CSI (Unregistered Guest)
Unregistered guest
| | Posted on Thursday, August 11, 2005 - 06:50 pm: | |
It is the very large dome ceiling of the main assembly space of the Tabernacle. We will also be refinishing some flat ceilings below the balconies. The ceiling has been coated with dozens of paints over the years, so the plaster has been holding its breathe for a long time now. We will be exposing it, repairing it, consolidating it, and refinishing it.
Incidently, selecting a paint removal product that works has been a trial too. We want something that can remove the many coats of paint and dirt, plus the original distemper coating. But we also would prefer something somewhat low in VOCs. |
Doug Brinley AIA CSI CDT CCS
Senior Member
Username: dbrinley
Post Number: 62
Registered: 12-2002
| | Posted on Thursday, August 11, 2005 - 07:42 pm: | |
Strippers: Try Eaco Chem; www.eacochem.com. Strippers with d-limonene as the carrier (transport) solvent might be your best choice. Solvents should have a high flash point and be low VOC. You're going to have challenges with a 'water cleanup' product because you're working inside and can't exactly flood the cleaned surface as intended. That points to a piece of equipment being necessary; equipment that can handle the solvent, apply it, brush (scrub) it, and vacuum it away before it can destroy something.
AND the stripper cannot leave residue that could influence the plaster and the new finish.
IMHO you'd be money ahead to use an natural stripper (d-limonene is a derivitive of citrus oil); traditional lime plaster as the finish coat; then apply lime paint (Olivetti Mineral Finishes LLC).
Your remaining problems would be:
efficacy of stripper;
mechanical adhesion of plaster to old substrate;
finding who is motivated to do the work. |
Lynn Javoroski
Senior Member
Username: lynn_javoroski
Post Number: 250
Registered: 07-2002
| | Posted on Wednesday, November 09, 2005 - 10:42 am: | |
I just began a search for painting acoustic plaster and this thread cropped up. Maybe it's a little late, but might the lime plaster you're trying to cover be contributing to the acoustic qualities of the space? I sure would miss hearing that choir... |
Helaine K. (Holly) Robinson CSI CCS CCCA
Senior Member
Username: hollyrob
Post Number: 194
Registered: 07-2003
| | Posted on Wednesday, November 09, 2005 - 10:52 am: | |
Better find out exactly what the "acoustic plaster" consists of! |
(Unregistered Guest)
Unregistered guest
| | Posted on Wednesday, November 09, 2005 - 11:57 am: | |
The acoustics of the space were definitely an important issue. We ended up specifying a KEIM Universal Render System with KEIM Biosil finish coats. We specified Back-to-Nature's Ultra-strip to remove existing coatings. |
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