May I ask what kind of interior finishes people have used on Durisol ICFs (whose forms are made with 80% recycled wood chips and 20% Portland cement, rather than with foam)? Their website has an Australian guide on plasters for Durisol (http://www.durisolbuild.com/Webdocs...URISOL.pdf ) and I wonder if anyone has tried their method for gypsum drywall mud as a plaster.

They suggest a single coat of 0.6" or more, embedding fiberglass mesh after applying 2/3 of the plaster.

Thanks for your thoughts.
...Terry

Drywall mud will re-emulsify if the exterior wall is not 100% sealed. One house near Austin TX. (Rastra) has a stucco leak that creates a mess on the interior because the architect specified "sheetrock mud" for the interior plaster. The exterior stucco is a sto product without mesh which developed hairline cracks along the joints of the blocks that allowed moisture penetration. There is a thread on this issue on GBT that was started several years ago.

Sheetrock mud in my opinion is far from traditional plaster in terms of the durability properties, it is not very abrasion resistant. You should look into plaster products possibly by visiting the walls and ceilings website (i believe it is wc-online.com) or look into hybrid products such as Gigacrete (www.gigacrete.com) and ask the particular manufacturers if they feel the product will work on Durisol. Either way you go, your success will be based on the ability to insure the exterior is sealed for the long term.

Sheetrock mud, or drywall compound, is NOT gypsum plaster - they are two different materials.  I don't recall from my reading that they are suggesting to use drywall mud as a finish.  I have not attempted gypsum plaster but have seen many Durisol projects with that finish.  Call Durisol and ask to see projects in your area with gypsum plaster (or a lime plaster) finish.
I use drywall (costs less $$) and plaster finishers are hard to come by in Ontario. (not exterior stucco - different again).


http://www.limes.us/projects.php?catID=13
(there are some durisol projects in their list)

Posted By JakeG on 12 Apr 2010 11:55 AM

I use drywall (costs less $$) and plaster finishers are hard to come by in Ontario. (not exterior stucco - different again).

Hard to come by in Idaho too, I found out when I was getting ready to build my ICF house. As I recall the estimate I got from the one plasterer I did find would have been double, if not upwards of 4 to 5 times the cost of drywall.

Hi Terry,
I hate chemistry, but here goes:  Joint compound, or drywall mud, is mostly comprised of limestone (calcium carbonate) and additives to make it into a slurry.  Plaster is a little more complicated.  It is comprised of plaster of paris (calcium sulphate hemihydrate), lime and gypsum.  I guess technically they are very different materials.  If you read through Durisol's downloads on indoor air quality, they show some differences between various finishes for vapour permeability.  You are correct that the paper does add some vapour resistance, but overall I would not say that much when compared to "normal" construction with a vapour retarder within the wall assembly.  I have seen finished Durisol with just a stain.  I'm not a big fan, but to each their own.  Of course the exterior must have some weather barrier, unless its a shed or garage on the back 40 somewhere.  Many Durisol basements are left unfinished on the interior - almost normal practice.
Hope this helps.

Terry, Where are you located? The summer/winter humidity cycles and levels have a lot, if not almost everything, to do with what you should have in your wall assembly. You seem to be quite concerned about moisture travel through the wall. What is the reason for this concern? Even with conventional construction, vapor travel is not a real issue as long as the wall material and attendant permeability and insulation values are selected properly. This includes drywall. Drywall, even with latex paint, is vapor permeable. Nearly all, if not all, wall assemblies discussed at BuildingScience.com have gypsum drywall as the interior finish.

If you haven't already, go to http://www.buildingscience.com and click on the Information link. Particularly go to the Designs That Work page and look at the document for the city closest to your climatic conditions. That link is http://www.buildingscience.com/doctypes/designs-that-work.

What your wall design needs to balance is the exterior humidity levels, interior/exterior temperature ranges, the vapor permeability of each component in the wall, and where the dew point is most likely to occur either inside or outside the wall. You may even find that Durisol will allow too much vapor travel thus causing problems you wouldn't have with a less permeable wall. You will need to plan on either an HRV or ERV to ventilate the living space, and here again all the factors I just noted will come into play in your HRV/ERV selection.

I'm in central Ontario north of Toronto, Dmaceld. So on your www.buildingscience.com link I chose the Minneapolis design and found lots of useful info -- thanks!

It isn't that I'm worried about moisture travel through the Durasol ICF (I have a good bitumen membrane on the outside), it's that I want to take advantage of it. I will indeed have an HRV with a built-in dehumidifier to handle overall humidity levels, but one benefit of Durasol over foam ICFs is that it absorbs temporarily-high humidity like a sponge and releases it back into the internal air as that air dries out -- it balances overloads. So I don't want to seal off this functionality with a vapour-retarding drywall or latex paint. It's good to know that common drywall and latex paint are just vapour retarders, not vapour blockers, but an earthen or lime or gypsum plaster instead will allow greater permeability.

Thanks again,
...Terry

terrynew, I would be very interested in learning more about the"temporary-high humidity like a sponge and releases is back into the internal air" benefit. Any data you can provide would be appreciated. Regards.

Check out the Durisol website - they have their detailed report on this topic that was conducted by J Straube of Building Science Corporation. The link is

http://www.durisolbuild.com/Downloads.shtml

Click on Indoor Air Quality for the document.