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  1. #1
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    Default Finishing interior side of exterior brick walls

    We have an interesting building from the 1920s that is brick construction, built as a two-storey bank building. All good-looking brick on the outside, well tuck pointed. Inside, the applied stucco?/mortar?/plaster? is chipping off in some places (about 10% surface area) and the rest of the 90% is just roughly done in the first place. I'm wondering if the best thing to do is knock off the loose stuff, and repair and restore 100% of the walls using drywall mud. I've done this before on brown coated plaster in good shape with minimal problems. Is mortar or stucco actually used to skim and finish brick walls in the first place?

    Also, it may be best to furr out the walls with 2" wood strips, insulate with 2" rigid foam, and apply drywall. Using a vapor barrier before installing drywall is my choice. Will this cause any moisture issues to use rigid insulation? I've heard the mortar used on older buildings (certainly from the 1920s) may not be moisture hardy like Portland cement is these days, and using a vapor barrier could cause moisture to "backflow" to the exterior, passing through the old mortar joints twice instead of evaporating to the inside, and causing accelerated mortar joint failure. Is this a concern?

    Thanks much for any help with this subject.


  2. #2
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    Default Re: Finishing interior side of exterior brick walls

    Yes mortar / plaster was applied to the interior of many structures it was very common in the 1800 & early 1900's.
    As for repairs you would need to match the existing material that is now applied to the brick.
    The use of a dry wall product over a brick & plaster substrate will fail.
    If the exterior mortar joints have been repointed and the wrong material was used it will cause failure to the older mortar.
    See if you can find the following report Paul H. Shipp, PhD,P.E. What you ought to know about air barriers and vapor retarders. This report will let you know where to place the barrier in your weather zone.
    If the failed areas of interior stucco / plaster seperates from the brick and some of the mortar joints come off with it you have a moisture problem,

  3. #3
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    Default Re: Finishing interior side of exterior brick walls

    Found the article, it reminds me of what I learned in school about vapor barriers, and helps define how moisture migrates and why to avoid a "double barrier". I think in my brick structure example, it would suffice to use rigid 2" foam insulation directly against the inside surface of the brick, and in between the furr strips placed 24" on center, and then apply a plastic 4mil or greater sheet barrier directly on the foam and furr strips. That way, if any moisture wanted to travel from the outside brick into the wall cavity and through to the rigid, the rigid could stop it and keep it mostly against the brick, where it could hopefully migrate back to the outdoors, as with a normal wall? I know the original builders, pre-vapor barrier technology, just enjoyed having the moisture travel in, then evaporate, or travel out and evaporate.

    Not sure how to address the mortar questions, but I suppose if the moisture traveled through the mortar joints from the outside to the inside (as it has been doing since being built) it can just as easily travel out again without any abnormal deterioration...?


  4. #4
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    Default Re: Finishing interior side of exterior brick walls

    Wikipedia has some good articles on mortar types and how to identify and deal with old 'lime' mortars. Read them and you'll understand why you must never use anything but lime mortar to re-point or replace lime mortar. They also have the proportions for the mixes if you plan on doing this DIY.

    As to vapor barriers in general, they are normally placed as close as possible to where the conditioned space begins. If you place one on the inside of these walls, then the entire wall will have to be seen as 'unconditioned' which means unheated as well as not being ventilated on that side. This may lead to excess moisture within the masonry wall and deteriorate the brick and the mortar. I'd stay with the traditional approach of a directly applied plaster or stucco finish done with compatible mixes- it's worked pretty darn good so far!

    If you do drywall, treat the installation as if it were similar to balloon framing by having open airflow across the wall from bottom to top. This will allow for enough ventilation so as to not degrade the masonry. This is easy enough to accomplish by having a gap below the baseboard and the walls extending above the ceiling line remaining open. A vapor barrier directly behind the sheetrock would be a good idea so long as it doesn't inhibit the airflow beneath it. There's really little to recommend this approach unless interior space is at an absolute minimum and the walls can't be stuccoed.

    Sheetrock can also be done as a free-standing wall with insulation, again being sure that the masonry can breathe. This approach is easy and cheap to do with metal studs so when space is available that's how I do these. It hides any aesthetic problems with wall and is fire-resistant to boot. The vapor barrier here will belong on the back side of this wall, separating the moist unconditioned area of the masonry wall from the dryer conditioned interior one. Though not totally impervious to airflow, use Tyvek here because it's easy to fasten securely to the metal studs whereas plastic is troublesome- and it works well enough. Narrow track and studs are made for this purpose though with them you don't have space for insulation, wiring, or pipes.

    All will be based on what the masonry type is and what options that leaves you.

    Phil

  5. #5
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    Default Re: Finishing interior side of exterior brick walls

    I think the mortar in the structure is fine. That aside, I may opt more for trying to patch and smooth the existing material. I like the idea of the fake wall, wall inside a wall, etc. I had thought about that earlier. Leaving a space at the top would be easy since it is a 16' ceiling with tin ceiling, so I would opt out of framing through the ceiling to an attic because it is a two story. It would require some sort of attachment bracket from the metal stud top plate to the brick. I assume leaving a gap at the bottom is essentially raising the base molding up a couple of inches - would look strange, but provide bottom to top ventilation for each stud bay.

    Did people actually take mortar perhaps and smear it over brick? What is the difference between stucco and mortar products? Keeping the patchwork and skimming the same material I understand since it is an exterior wall essentially. Is there a compatible product that is easier to work with for skimming?

    Also the wall is currently painted. Would it help to prime it before patching?

    John

  6. #6
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    Default Re: Finishing interior side of exterior brick walls

    Just raise the base 1/2" or less and that coupled with thermal flow will ventilate the space well enough. Leave a similar space between the lower drywall sheet and the bottom track of the metal stud system or the wood sole plate- the base will cover that visual gap but be open to ventilation. Bracket the top plate to the wall as needed.

    Stucco can be "natural" or "synthetic". Many old (and some new) stucco jobs were done with regular mortar, but that doesn't always adhere as well as it should. Proper natural stucco is a different mix than mortar and includes different things for better bonding. All of my experience and most of what I know about stucco is with synthetics so I can't help you with the mix. Find an older stucco guy in your area and have him look at it- he will know what to do to make the mix right and match the finish. If you want to learn about it and save some money, offer to be his helper- maybe he will allow that if he's not union. If you want to take this on yourself, research on the web about it- I have seen practically everything you'd need to know out there but I don't remember where any of it is at- google is your friend as is youtube. And always verify what you find through several sources before proceeding- nobody prevents idiots from posting bad info on the web.

    I like the idea of a tin ceiling, they have so much more character compared to the usual boring flat plaster or drywall ones. I'm glad they're coming back in style now.

    Phil
    Last edited by Mastercarpentry; 01-12-2014 at 06:57 PM.

  7. #7
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    Default Re: Finishing interior side of exterior brick walls

    As for the question of mortar applied direct to brick on thr interior yes it was & is a very commond pratice.
    As for the mix Any of the following will work for a stucco mixture.
    1 part type N mortar 1/2 parts type 1 portland cement & 4.5 parts sand

    another would be 1 Part type 1 portland cement 1/2 to 3/4 parts lime and 5.25 parts sand.

    Also 1 part White Portland Cement 2 parts Lime and 9 parts sand

    You can also purchase premix that will meet the above mixes.

    Structolite or Gypso lite plaster will also work for interior over brick.
    For a smooth finish use a veneer plaster finish.

    If yoy select to fur the wall out for venting at the bottom check out FRY REGLET Reveal Base DRMB or " F " Reveal FDM and use the vented

  8. #8
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    Default Re: Finishing interior side of exterior brick walls

    So if my existing wall finish is mortar, I should use mortar. If it is plaster I should use plaster . . . or can plaster go over mortar? I am interested in trying to create a smooth, drywall-esque finish. I'm very good at using drywall compound to skim, but have never used mortar. I fear it is too viscous and difficult to manipulate as a finish product. Any advice ?

    J

  9. #9
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    Default Re: Finishing interior side of exterior brick walls

    Correct if it is a cement product than use a cement lime mix.
    If plaster use plaster.
    To determine what existing is , If it is grey it is a cement product and if it is a light beige it would be a lime plaster product.
    To skim coat look for one of these.
    Master of Plaster
    American Clay
    Variance
    Any of the above will work better than a Joint compound or drywall product.

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