Foundation - thin stone veneer project
#1
06-03-21, 07:34 AM
Foundation - thin stone veneer project
I'm going to be installing thin stone veneer (real stone, approx 11lbs/sq ft) on an exterior foundation, and need to decide between durock or metal lath. I have to do 100 linear ft, 18" tall on two sides, the other sides taper to 12".
I'm on the fence about which method to use. It feels like the lath will require more work (mixing) to install, and might end up costing more as well since the price of the lath is a bit more than durock (or equiv). I don't mind the extra work but I'm concerned that it will make this project take longer than it "should".
Also, the manufacturer doesn't mention anything about expansion joints in their literature, but I have two runs of 35' and I've read online that long continuous runs of masonry need to have breaks to avoid cracking.
Finally, the distributor is a branch office of the manufacturer - General Shale. They sell/carry a different mortar than what the manufacturer lists on their website... I presume I can trust the local branch office?
I've done stone work before - I installed a wood stove stone "shield" to protect a wall - and it's held up for over 10 years
, so this should be doable... just trying to get the project off to a good start!
I'm on the fence about which method to use. It feels like the lath will require more work (mixing) to install, and might end up costing more as well since the price of the lath is a bit more than durock (or equiv). I don't mind the extra work but I'm concerned that it will make this project take longer than it "should".
Also, the manufacturer doesn't mention anything about expansion joints in their literature, but I have two runs of 35' and I've read online that long continuous runs of masonry need to have breaks to avoid cracking.
Finally, the distributor is a branch office of the manufacturer - General Shale. They sell/carry a different mortar than what the manufacturer lists on their website... I presume I can trust the local branch office?
I've done stone work before - I installed a wood stove stone "shield" to protect a wall - and it's held up for over 10 years
, so this should be doable... just trying to get the project off to a good start!
#2
06-03-21, 07:46 AM
They sell CSE4 mortar because it's half the price of Laticrete (which the mfg recommends). I guess I'll go with the mortar they sell - but would appreciate any thoughts regarding the durock vs lath.
#3
06-03-21, 08:07 AM
Group Moderator
You never mentioned the wall's construction. Is it a wood wall and you are adding cement board or lath to support the masonry? Or, if it's a masonry wall there must be a reason for the extra step of cement board???
#4
06-03-21, 08:47 AM
Member
So be aware there are a lot of technical requirements for installing faux stone on an exterior structure, layers of water proof barriers, weep screed, not just a simple slap it on a piece of cement board.
Id confirm with your material manufacture or the MSV guideline, it was more than I expected when I did my shed last year!
https://ncma.org/resource/msv-installation-guide/
Id confirm with your material manufacture or the MSV guideline, it was more than I expected when I did my shed last year!
https://ncma.org/resource/msv-installation-guide/
#5
06-03-21, 02:45 PM
I have.... a unique project/application. I have a poured foundation wall with 12-18" showing above grade. It is covered in 2" XPS foam (25psi I think), concrete is 4000psi. I would like to retain the insulation - I cannot move the insulation to the inside, unfortunately.
From what I've researched, since my foam is a WRB (taped/sealed) and in front of concrete, I do not need an additional wrb or other form of water barrier. The material is real stone - cut thin - at about 11lb/sq ft (not including cement board or mortar). The mfg has a pretty simple install guide:
https://generalshale.com/resources/f...39b46f166e.pdf
However they don't provide details on more complex assemblies. I'm evaluating:
2" thick pressure treated furring strips touching the foundation wall and screwed to the concrete every 16" using tapcoms, durock or lath screwed into these (issues: material can rot, bugs infest, and fasteners need to be compatible with treated wood, wood might split with screws all in alignment)
Heavy-gauge (18?) z-furring channel screwed directly into the wall every 16" using tapcoms, durock or lath screwed into these (issues: steel can rust, might conduct heat more than wood). Several manufactures show foam insulation being held to a concrete wall with these z-flashing strips, but they do not list weight bearing capacity for these strips.
4" or 5" Tapcons screwed directly through the lath/durock foam at some spacing interval (16" oc, 6-8"), using flat lath washers to prevent pull-through and spread the load (1.5" recommended). A clerk I spoke with at a local masonry store said "people do this all the time" but he couldn't provide anything specific. I also spoke with someone who sells said washers and it was a similar response. A study done for the EPA has a report that indicates this method may work - but long term there may be some creep. Boral stone has a technical paper that says "it can be done": https://f.hubspotusercontent40.net/h...%202020pdf.pdf Which confirmed my calculations using a 1/4" - 4" Tapcon, but it doesn't specify spacing requirements between screws.
When all is said and done I'd like to install steel z-flashing (2" deep), and screw durock to that to keep things simple. If I do this or the wood framing I'd likely use a WRB to provide drainage and prevent excess moisture from harming the materials.
Finally, a 16" x 18" section of wall will weigh about 30 pounds... assuming 15psf. I don't have enough experience with Tapcons to really evaluate whether this assembly will hold, even if the fasteners (depth, and quantity) clearly will support it.
From what I've researched, since my foam is a WRB (taped/sealed) and in front of concrete, I do not need an additional wrb or other form of water barrier. The material is real stone - cut thin - at about 11lb/sq ft (not including cement board or mortar). The mfg has a pretty simple install guide:
https://generalshale.com/resources/f...39b46f166e.pdf
However they don't provide details on more complex assemblies. I'm evaluating:
2" thick pressure treated furring strips touching the foundation wall and screwed to the concrete every 16" using tapcoms, durock or lath screwed into these (issues: material can rot, bugs infest, and fasteners need to be compatible with treated wood, wood might split with screws all in alignment)
Heavy-gauge (18?) z-furring channel screwed directly into the wall every 16" using tapcoms, durock or lath screwed into these (issues: steel can rust, might conduct heat more than wood). Several manufactures show foam insulation being held to a concrete wall with these z-flashing strips, but they do not list weight bearing capacity for these strips.
4" or 5" Tapcons screwed directly through the lath/durock foam at some spacing interval (16" oc, 6-8"), using flat lath washers to prevent pull-through and spread the load (1.5" recommended). A clerk I spoke with at a local masonry store said "people do this all the time" but he couldn't provide anything specific. I also spoke with someone who sells said washers and it was a similar response. A study done for the EPA has a report that indicates this method may work - but long term there may be some creep. Boral stone has a technical paper that says "it can be done": https://f.hubspotusercontent40.net/h...%202020pdf.pdf Which confirmed my calculations using a 1/4" - 4" Tapcon, but it doesn't specify spacing requirements between screws.
When all is said and done I'd like to install steel z-flashing (2" deep), and screw durock to that to keep things simple. If I do this or the wood framing I'd likely use a WRB to provide drainage and prevent excess moisture from harming the materials.
Finally, a 16" x 18" section of wall will weigh about 30 pounds... assuming 15psf. I don't have enough experience with Tapcons to really evaluate whether this assembly will hold, even if the fasteners (depth, and quantity) clearly will support it.
#6
06-03-21, 03:52 PM
Group Moderator
Thank you for elaborating. That is a tough situation. My house's foundation is bare concrete on the outside, the foam is on the inside, so mortaring stone to the exterior was relatively easy.
#7
06-03-21, 04:24 PM
The stone wall I built on the inside of the house was screwed into wood studs, about 8' tall by 4' wide, and supported by furring strips in the back to create an air gap of about 1". But... I used non-compressible pieces of durock for the spacers. Not sure I want to cut strips of that stuff to make furring strips for this project! That way I'd feel like creep would be lessened since the Tapcon could (theoretically) be tightened against a non-compressible block as opposed to foam.
#8
06-04-21, 06:40 AM
I linked to the wrong install instructions, so metal lath it is:
https://generalshale.com/resources/f...439dbe0b22.pdf
They don't specify durock - or even list it as an option - although I have seen it specified elsewhere for exterior and real stone - I'd rather not risk it. Note page 7 shows them cleaning the rock off with a metal wire brush and they state "Do not use a wire brush to clean rock"
https://generalshale.com/resources/f...439dbe0b22.pdf
They don't specify durock - or even list it as an option - although I have seen it specified elsewhere for exterior and real stone - I'd rather not risk it. Note page 7 shows them cleaning the rock off with a metal wire brush and they state "Do not use a wire brush to clean rock"
