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Efflorescence = Water Damage — Building Science Podcast

The white powder on the surface of brick, block, and mortar between rocks is water and salt attacking these porous materials. In new construction you can prevent it — in old houses, you can only control it.

Posted on Mar 29 2010 by Joe Lstiburek

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This podcast series is excerpted from a two-day class called "Building Science Fundamentals" taught by Dr. Joe Lstiburek and Dr. John Straube of Building Science Corporation.

For information on attending a live class, go to

In our last episode, Dr. Joe Lstiburek compared air barriers and vapor barriers, and explained how airtightness helps keep homes free of mold and rot. This week Dr. Joe explains how water and salt move through masonry by osmosis, often causing serious damage to foundations. He also offers some solutions to this common problem.

Osmosis isn’t a problem everywhere
In new construction, it’s real easy: you coat the top of the footing, you’ve got your stone (capillaryForces that lift water or pull it through porous materials, such as concrete. The tendency of a material to wick water due to the surface tension of the water molecules.) break, you’ve got your dampproofing. You don’t have to worry about salt, and you don’t have to worry about capillarity — life is good. It’s kind of hard to retrofit this. It’s a wonderful way to do it in new construction, but it’s tough if you’ve got a 100-, 200-, or 300-year-old structure to deal with.

What’s so bad about salt and water?
The physics of the osmosis forces works like this: water takes the salt in solution to a surface, the water evaporates, and the salt is left behind. And as more water evaporates, more salt accumulates, so the concentration of salt goes up. As the concentration of salt goes up, water rushes to the concentration of salt in order to dilute it — because one of the rules of physics is that nature doesn’t like these kinds of concentrations. The action of the water rushing to the surface actually creates hydrostatic forces. This pressure from the water rushing through the pore system causes the material to flake apart, and the explosive flaking is referred to as spalling. Let me summarize this: salt is very bad; water is very bad; salt and water together — whoa!

Osmosis is powerful stuff
The pressures are extraordinary. With diffusion, pressures are 3 to 5 psi — it’s nothing. Water vapor never pushed nothing off of nothing. Capillary pressures are fairly impressive — 300 to 500 psi. It moves water to the top of a 400-foot tree. That’s a pretty impressive force. But it isn’t anywhere close to the league of osmosis pressures, which are 3000 to 5000 psi. The compressive strength of even good concrete is 2000 to 3000 psi — salt and water will beat concrete every time. Osmosis beats capillarity which beats diffusion. Wow. Bridges fall down, life comes to an end, when you have salt and water.

Sacrificial mortars are one solution
Well, old-timers figured stuff out. What these folks noticed was that the mortar was eaten away much faster than the masonry, and certain mortars were eaten away much faster than others. The pore structure of the mortar was very critical to this. And someone said, "Aha! Maybe if I get the pore structure just right, all of the salt will end up in the mortar instead of the brick. And the mortar can sacrifice itself to protect the integrity of the brick." That's when we figured out that softer, weaker mortars are actually the ideal complement to clay brick that's been fired at a specific temperature. And the solution would be to re-point the mortar as it was eaten away. You never want to have a mortar that's stronger than the brick, because then the brick sacrifices itself to protect the mortar.

That's why historic preservationists — the old ones that know stuff because they've been around a long time — go to an enormous amount of trouble in old buildings to match the mortar chemistry precisely. The general rule is: if you don't know what's going on, don't mess with the building. Or if something's been around for two or three hundred years, don't mess with the strategy. If you come up with the right mix, all of the deterioration happens in the joints, and you simply re-point them on a 15 or 20 year basis.

Parging protects the entire surface
Well, why not just coat the whole thing with a sacrificial layer? And instead of doing this on a 10-year basis, why not extend this to a 30- or 40-year basis? The way you think of this sacrificial layer is as a sort of lime-based poultice that sucks the salt poison out of the assembly. So how do you know when you have to replace it? Well, when it falls off. It's the building telling you it's time to put on another sacrificial layer.

Related topics

Read about a real-world example of water damage in a brick foundation.
And find strategies for keeping bulk water away from a basement.

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Image Credits:

  1. Rob Wotzak

Apr 5, 2010 8:43 AM ET

Efflorescence on a brick foundation
by Rick

Dear Joe,
Thanks for your article, which explains this phenomonon better than any others I have seen. I have a 120 year old house sitting one-half block from the ocean (i.e. lots of salt and water). The foundation seems to be changing from bricks and mortar to just a pile of bricks --- which is I guess what your article would predict. Two questions: Is this the same as the phenomonon sometimes referred to as "rising damp"? Can I protect my foundation from further deterioration by repeated tuckpointing of the joints (with the correct mortar of course)?

Apr 5, 2010 8:47 AM ET

Surface parging old brick
by Larry

What would be the recommended mortar for parging the surface of old brick in foundation walls?

Apr 5, 2010 9:23 AM ET

water absorbed thru brick
by t mckenzie

House pointed 4 years ago .When nor'easter wind driven rain hits front of house,water seep into two front rooms ,one on 1st floor, 1 on second . Roof and porch flashing is good ..contractor says 90 year old brick is porous allowing water to seep into brick and drip down inside brick and find a way into room ceiling and door frames,...Can water repellent be applied without changing original brick look ?

Apr 5, 2010 9:46 AM ET

Yes, Water repellants can work
by Joe Lstiburek

A water repellent will change the appearance - the brick will get a slight "shiny" sheen. And the repellent will need to be reapplied every 3 to 5 years as it degrades due to exposure to UV radiation.

Having said that, water repellent coatings do tend to work - they are about a 50:50 to 60:40 proposition of being successful. Pretty good odds given the alternatives. They are frowned upon by historic preservationists as they do have a risk of permanently damaging the brick if salt is present (see comments on efflorescence above). But this risk is now much smaller than it was two or three decades ago when the repellents were silicones. Now, most repellents are silanes and siloxanes and the risk of damage is much less.

Apr 5, 2010 9:49 AM ET

A couple more answers...
by Joe Lstiburek

Reply to Rick: "Rising damp" is the term Europeans use to describe capillarity. Re-pointing with lime-based mortar works as does a layer of parging with lime based mortar.

Reply to Larry: "Lime based mortar"

Apr 5, 2010 12:22 PM ET

efflorescence versus subflorescence
by Kristin Whiteley

My understanding of this is that efflorescence, where the salts are deposited on top of the surface, is not the problem, but rather subflorescence , where the salts are deposited just below the surface. And that the spalling is caused by the build up of salt crystals below the surface, the pressure of which causes the brick to flake off kind of like freeze-thaw damage is caused by water trapped below the surface of brick creating pressure by the expansion of the water turning to ice.

A coat of stucco/parging over brick works to protect the brick because the salts are deposited in the stucco/parging and then when the stucco comes off it can be patched and the brick stays protected.

Apr 5, 2010 2:19 PM ET

Reply to Kristin
by Joe Lstiburek

Reply to Kristin Whiteley,

You are correct. The salt is carried in solution by water and
typically migrates into the assembly from ground contact below grade.
So the salt seen on the surface comes from within the assembly and
accumulates on the surface due to the evaporation of the water phase
of the salt water solution after the salt water solution has traveled
to the surface. Where less water is available the evaporation of the
water can occur a millimeter or two beneath the surface and the salt
accumulates just beneath the surface of the assembly. This increased
concentration of salt just beneath the surface leads to osmosis
forces that can be greater than the cohesive strength of the material
and the material breaks apart leading to "spalling". The increased
concentration of salt beneath the surface is called subflorescence.
The mechanism of damage is similar to frost damage - although frost
damage is not due to the expansion of water when it turns to ice, but
due to the increased concentration of salt when water turns to ice
and leaves the salt behind. This increased concentration of salt
leads to osmosis pressures (hydrostatic pressure) similar to
subflorescence. For more information you can go to the following

Apr 5, 2010 3:03 PM ET

New brick on Superior Wall and Concrete Block
by TJ

I had a house built 2 yrs ago with a Superior Wall system. Some of the brick on the system's brick ledge, but very little, is displaying efflorescence. A retaining wall which is brick faced and capped concrete block is chalky white over a majority of its surface. What is the proper procedure for dealing with this issue? Thanks in advance.

Apr 5, 2010 4:11 PM ET

TJ: A stab at your questions
by Joe Lstiburek

You don't provide enough information about the wall assembly detail so that I can make a solid recommendation. But let me guess at what might be happening anyway.

The Superior Wall issue is different from a retaining wall issue. If I were to guess, the retaining wall is not waterproofed and drained on its back side and otherwise does not have a capillary break uncoupling it from the ground. It could be made worse by not having a water shedding and water tight cap.

In terms of the Superior Wall issue, it could be that there is salt in the mortar due to some additive that is probably coupled with poor drainage between the brick and the drainage layer.

Fixing retaining walls typically means reconstructing them. Same with poorly drained brick veneers with mortar additives. Or you could just live with the efflorescence or wash it off every now and then.

Apr 5, 2010 5:32 PM ET

What about freeze thaw damage on upper stories, where's the salt
by Kristin Whiteley

There are many old brick buildings around Toronto that have brick damage on the upper stories which I understood could be caused by a combination of vapour diffusion from a heated interior in the winter and freezing temperatures outside, and in some cases a painted brick facade. How do salts figure into that kind of scenario? Or water dripping off a roof where an eavestrough has come detached or brick facades facing east in the city that would get more wind driven moisture.

I'm not trying to be stupid. I'm sincerely interested in these issues and am trying to understand this new information you are providing. I took a couple of building science courses at the University of Toronto last year through what was then the Professional Development Centre at the Department of Engineering and feel like some of what I learned appears to be in conflict with what you are describing. It did look at the basic physics of air and moisture transfer but maybe didn't get into enough detail in this area.

I would be very happy to get a better understanding of how this mechanism of hydrostatic pressure causes spalling and would certainly read any links to research papers or books that you can recommend on the subject. I did have a look at the link you provided in your earlier reply and it was also interesting but if you have something that goes into more detail that would be helpful.

Much Thanks!

Apr 6, 2010 9:40 AM ET

hydrostatic pressure and salt water system and old cement pools
by Anonymous

If brick and cement don't mix well with salt water what about all those old outdoor swimming pool made of cement that need to be painted every two years... should we be avoiding the installation of the new salt water system to purify the water?

Apr 6, 2010 9:43 AM ET

Capillary break question
by Matt

Great article! This may be a dumb question, but where I live in Utah the brick on most houses starts anywhere from 18-24 inches above the ground, leaving that space of concrete foundation exposed. Is the point of this to serve as the capillary break from snow? And if I were to cover the foundation with stone or brick would that simply bridge the buffer zone causing problems later?

Apr 6, 2010 10:18 AM ET

Capillary break question
by Matt

Actually I think the link to provided to Kristin answers most of it.

Apr 6, 2010 11:08 AM ET

More answers...
by Joe Lstiburek

Further reply to Kristin Whiteley.
Frost damage also happens in the absence of salt but the principle is similar. Hydraulic pressure is created by differences in chemical potential and by vapor pressure differences between super-cooled water and ice. A good place to start to get a more in depth understanding is with one of the old masters. Start with the following paper:

Litvan, G., "The Mechanism of Frost Action in Concrete - Theory and
Practical Implications", Proceedings of Workshop on Low Temperature
Effects on Concrete, IRC/NRCC, Ottawa, September, 1988

In terms of the University of Toronto and conflicts with what I am describing. I doubt that we differ. Kim Pressnail is the head of the building science program there and it is first class. Professor
Pressnail did groundbreaking work there on adfreezing in the mid 1980's. His mentor and mine was Professor John Timusk. Professor Pressnail and I were grad students there at the same time. I can hardly disagree with my alma matter. I do miss my hometown though - Toronto.

To Anonymous:

The interior paint coating on the swimming pool is the capillary break. When salt in solution gets into the concrete and migrates to the other side - the ground side - crystalization does not happen as evaporation is not possible because the ground is at 100 percent RH.

With pools the problems are at the water line where evaporation is possible and at the top of the pool where it intersects with the coping and perimeter traffic surfaces. The results in ongoing
maintenance and the need for recoating.

If you cover the foundation with stone or brick, paint the above grade portion of the foundation with a vapor open, hygrophobic coating, i.e. concrete paint before installing the stone or brick. Think of it as a liquid applied building paper.


Apr 6, 2010 12:59 PM ET

Thanks for the reference
by Kristin Whiteley

Thank you for the reference. I found the paper on line and will read it carefully.

The courses for the PDC are not as in depth as the core university courses and are structured to be for anyone in any part of the construction industry to give a basic knowledge of building science. And on the whole I thought especially the introductory courses were great. But I found the section in our printed notes from my course that discusses subflorescence. It's actually very brief and upon rereading it does not describe in detail the mechanism by which the buildup of salts causes spalling, however I gave it to several other people to read and they all said the suggestion seems to be that it is the expansion of the volume of salts ("forming crystals that expand") that creates the pressure causing spalling, so I'll point it out to the instructor that the wording can be easily misunderstood.

Thanks again - Kristin

Apr 6, 2010 2:02 PM ET

Block Foundations
by Dave

I recently read an article about how to manage hydrostatic pressure on a block foundation with 'floating' basement floors. The article said to drill holes at the bottom of each space column of the blocks so the water could run out, relieving the pressure of collected water. Do concrete block foundations have similar issues as a brick foundation? It seems that since the block is fairly porus, the block would be the sacrificial element.? Is the physics different for concrete block? If there is a small amount of spalling in isolated areas of the foundation is this a reason for concern?

Apr 14, 2010 10:18 AM ET

Block foundation wall, parging flaking off after SC winter
by Luke

I have a block wall/parged foundation on my crawl space home. The parging is coming off off the above grade foundation in various areas. I painted the exterior parging two years ago with a good quality acrylic latex exterior paint. The paint is bubbling up and loosing adhesion and the parging seems loose underneath the affected areas. My crawl space is very dry with no real moisture issues, other than some slight wall staining/efflourescence on foundation wall mortar joints inside the crawl space. All of my downspouts are fully drained away from the foundation walls.

I was going to fully thoroseal the interior side of the block wall in the affected areas. Do you think this will stop the moisture transfer to the outside exterior wall/parging surface which will stop the adhesion issues.

Apr 14, 2010 12:11 PM ET

Parging over damaged brick
by Carol

I am having a problem with conflicting advice provided by contractors. I live in a condo-conversion building in Chicago. Formerly an apartment building, converted to condos in the 1970s. Three story brick building, about 100 yrs old. We've been seeking a contractor to do some tuckpointing/repair of the structure, which is showing signs of rising damp and the resultant crumbling brick and mortar. The damaged portions rise from ground level to about 4 feet. The back of the building has had parging done, presumably to cover the damaged brick. However on the side of the building that faces the building next door (no sun exposure), the brick is still uncovered, and this is the portion we need to address. One contractor suggested parging to cover the area, in order to "protect and reinforce" it. Another contractor stated that parging will NOT protect it, but will simply be a cosmetic solution, under which the damage will continue, and that the entire portion of wall needs to be replaced. In his opinion, if we are not going to replace the brick, we should leave it alone until we CAN replace the brick. What do you think?

Apr 20, 2010 1:17 PM ET

Concrete basement wall with efflorescence
by DCal

I have a poured-in-place concrete basement wall with efflorescence flaking off wall. Can I stop this process by applying some type of waterproof coating or sealer to the interior wall surface? I would like to attach things to the wall, but I am afraid to cover it up and have this building up behind it.

Apr 21, 2010 10:57 AM ET

Answers for Dave, Luke, Carol, and DCal
by Joe Lstiburek


Block foundations have much fewer issues than brick foundations due
to the different pore sizes of the block units compared to the pore
sizes and distributions of the brick. The small amount of spalling
you are experiencing is typically not much for concern. The best way
of dealing with it is to drain (control) the water.


The peeling paint is telling you two things - the paint is not as
vapor permeable as it needs to be not to peel and secondly you have a
lot of water coming up through the foundation. I don't think the
Thoroseal will help much dealing with the exterior paint issue - but
I think the interior Thoroseal is a good idea in general. To deal
with the exterior paint issue you really need to dig up the exterior
down to the footing and coat the exterior with dampproofing. Or you
can remove the existing paint and repaint with a much more
"breathable" coating such as a vapor open concrete paint (such as


The parging contractor knows what he is talking about. Check out the
"Small Sacrifices" link:


You can hide the efflorescence with something like Thoroseal, but to
control it you need an effective exterior drain and effective
exterior dampproofing. You can try an interior drain or apply some
of the strategies in the link I gave to Carol above. Or you can
ignore it.

May 4, 2010 5:32 PM ET

Efflorescence on a brick chimney
by Scott

A 20 year old home has been getting efflorescence on the interior brick facing of the fireplace since almost day 1. The original builder investigated things 20 years ago and determined that nothing was wrong with their construction - go figure they are out of business now. They have had chimney specialists come out and apply sealers to the exterior, and even redid the chimney cap - all with no results. The HO even installed a new roof 2 years ago, and the problem is still there. As time has gone on, the HO now gets water that drips down through the steel support angle as well as the flue (there are obvious rust stains where water has seeped through).

Joe, Do you have any thoughts? I attended your full day session on building enclosures at the NESEA10 conference in March, and have become quite interested in the building sciences since. This issue has been a bit lost.


May 12, 2010 5:08 PM ET

salt & concrete block
by David

I had a Rain Soft system installed about 12 years ago, and this past year we found that the relief valve had fallen allowing salt water to leak into the crawl space and it has migrated to the concrete block. We do not know how long the system was leaking. We first noticed the issue when we got spalling on the block showing in the garage. Two questions, now that we have pretty much dried the space out except for typical moisture, and heavy rain how much should we be concerned? Second, we put water proofing on the inside and outside of the affected block face, did that increase the possible damage? Any information that you can provide would be very appreciated. Thank you.

May 13, 2010 5:11 AM ET

Reply to Scott
by Joe Lstiburek

I don't want to sound like a smart ass, but the reason that the interior brick facing of the fireplace has efflorescence is because the chimney is leaking. So, you have to stop the chimney from leaking.

In my experience with chimneys they leak at the following places in order of importance:

1) Down from the very top because of a bad, poor, old, broken, whatever chimney cap.

2) From where the roof meets the wall because of bad, poor, old, broken, missing whatever flashing.

3) Through the outside face of the brick because of bad, poor, old, broken, missing mortar joints.

So the way you fix them is deal with the chimney cap, deal with the flashing and repoint the bricks.


May 13, 2010 5:13 AM ET

Reply to David
by Joe Lstiburek


Keeping water out of the concrete block is a good thing. So water proofing both the inside and outside of the block is a good thing.


May 13, 2010 3:56 PM ET

When there's a gap between wythes
by Richard

My home in Maryland has 2-wythe load bearing brick walls, built in 1938. My basement is about 6 ft below grade and 2 ft above (with some windows in this 2 ft space). I see interior efflorescence and spalling up to about 4ft. I've read through the posts and links, and am wondering if the recommendations change when there is a gap between the wythes. Looking at my walls, there is a 3/4-1" gap between inner and outer wythe in the basement ( I can see it from outside looking laterally at the basement windows). (From the top of the window up, on the other hand, I begin to see a brick on end every 5th row, which I'm told is tying the wythes together without an in-between gap; there are no bricks on-end in the basement). Would I need to have a lime based mortar sacrificial layer both interior and exterior, one for each wythe?

May 13, 2010 4:36 PM ET

Reply to Richard
by Joe Lstiburek

No, only an interior sacrificial layer on the innermost wythe is necessary. The reason is that the gap between the two wythes is almost always at 100 percent relative humidity and so evaporation
will not happen into the gap and therefore salt crystallization will not happen on the surfaces bounding the gap. It is a version of "vapor pressure equalization" described in Figure 3 of the following link:

May 14, 2010 12:28 AM ET

Differential capillary water flow up the wythes?
by Richard


Thanks for the response. (It's a privilege). I am glad to hear that the two wythes stay in equilibrium so I only need one sacrificial layer. I'm also glad I can do the internal layer, since I would like to retrofit exterior insulation with mineral wool as capillary break and to contain the thermal mass. I take it that if I dig down on the exterior I won't find efflorescence, because the soil RH is also always 100%, thus keeping the RH in the external wythe in 100% equilibrium and salt always in solution (with low salt concentration, and more to the point a low total number of salt molecules, i.e. moles, and thus low van der Waals inter-molecular adhesive force and thus low water retaining power, i.e., osmotic pressure).

I think the part I don't quite understand is what happens above the highest efflorescence line on the internal wythe. I gather that the capillary force of brick would pull the salty water 10 kilometers, but the water finds less resistance by detouring into the basement air, and does this in my particular brick and mortar within the first 4 feet or so, leaving the salt as its fingerprint. But then the salty water coursing up the external wythe will suddenly find, above this 4 ft mark, that the gap is dry, because the internal wythe is dry, and will offload its vapor into the gap. Why wouldn't I find efflorescence in the interior of the external wythe starting above where the internal wythe leaves off? Or externally when it comes above grade, and is no longer next to 100% RH soil?

On a separate note, if I may, you wouldn't know what they would have been doing for water control in the 1930s with these brick mass wall houses? I have seen some drawings where the external wythe would have a lower footing than the inner wythe, but would there be weep holes below grade? Am I right in thinking that there is no perimeter drain, and I'll need to put one in (along with bitumen and capillary break)?

May 14, 2010 4:26 PM ET

Reply to Richard
by Joe Lstiburek

You can cap the cavity at grade creating an airspace underneath the cap that equilibriates with the ground conditions. Or you can ignore it as most of the moisture flow will be inwards towards the
sacrificial layer.

Or you run a vapor barrier membrane up the inside and have the sacrificial layer on the exterior as in
If you do this you should cap the cavity. How? Inject high density foam and then over the top of the foam cap inject grout.

Joseph Lstiburek

May 15, 2010 9:11 AM ET

When the brick is paneled
by Richard


Thank you. I think I'll put the sacrificial layer on the inside and not worry about capping so long as I don't see efflorescence on the exterior.

My basement has wood paneling on 3 of the 4 walls, with a 1" gap between brick and wood. I imagine I should take down the paneling to put up the sacrificial lime-based mortar. I'd then like to put the paneling back up. I imagine the vapor coming off the sacrificial layer will course around to come out in the unpaneled (utility) area or else straight up into the attic (there is 1" between brick and plaster in the upper floors). When I see that the sacrificial layer in the exposed utility room needs replacement, I'll know to take down the paneling and repair the rest. I gather the higher up I go on the sacrificial layer, the longer between replacements.

Does that sound OK? Is there a risk of letting salt-laden spalled mortar accumulate on the concrete floor between brick and paneling?

May 15, 2010 2:36 PM ET

More for Richard
by Joe Lstiburek

Why don't you spray low density foam over the sacrificial mortar.
The foam allows vapor to pass inwards so the sacrificial layer still
works but now you don't have a mold risk with the panels. Check out
Figure 12 in the following link:
Reading the rest of the link is also a good idea.

May 17, 2010 12:43 AM ET

Spalling affecting interior foam? Foam affecting ventilation?
by Richard

I thought that if I sprayed on top of the sacrificial mortar, the day the mortar fell off I'd also lose the insulation with it. Given the rate of spalling I have now, I thought that would be fairly continuous. I wasn't sure that the article applied to masonry walls that had spalling.

The article speaks of the thermal bridging by brick veneer. But if, as in my case, it is 2 wythe brick top to bottom, what is the heat loss from the uninsulated top 2 ft compared to the externally insulated bottom 6 ft? Is it 50%, as I read for concrete? Perhaps I could have subgrade exterior insulation to allow for direct visualization of the sacrificial layer, and place internal insulation for above grade - wan't this estimated to have a modest 10% decreased efficiency to top-to-bottom external or internal?

My concern was also that placing insulation on the interior up to the joists (which are embedded in the masonry) would cover the 1" drainage and ventilation gap that lies behind the brick all the way around. For the sake of protecting the structure of the roof, on reading through Building Science, I was leaning to placing external above-deck insulation for the roof (e.g. R16), ergo also beneath the rafters to complete to R38 (I'm in Maryland climate 4), and thus have a closed attic. I have no soffits or ridge vent as it is, only gable end windows, and the roof is somewhat complex. I could thus close the attic, but keep the ventilating gap from attic to basement. Or seal off the gap at attic ceiling and basement rim. I worry about convection loops in that closed space causing wetting, as I've read in Building Science articles. What is the best solution? My wife and I are loathe to lose interior space, as would occur with interior insulation. Also, the Manual J heat and cooling calculations are almost exactly identical with the current status with thermal mass compared to adding R15 interior to all walls (Baltimore has 20 degree difference max to min average temperature every month of the year). In the future, we may consider external insulation with brick slips new veneer (with drainage gap and vapor barrier behind, per your writings). But with either exterior insulation or not, I'm not sure what would be best with the current drainage/ventilation gap between brick and plaster. What would you advise? Seal them or allow them to offer air ventilation?

My many thanks in advance

May 17, 2010 11:05 AM ET

Spalling on a post-tension concrete slab
by Eric

I live in an area of Maricopa AZ that has high sulfide levels in the soil, add water & now we have salt being sucked into the foundation. I have efflorescence, and assume sub florescence, and do have spalling in spots where the foundation has chipped away (the corners). I have been told that the foundation can/will deteriorate to an unusable state within 15-20 years. The issue is also the steel in the concrete that can rust? (although it is not exposed to air directly) Are there any fixes, repairs, etc that you can point me in the direction of? In AZ there is not a vapor barrier under the concrete, it is poured directly on top of the soil. The damage is visible on block wall fences also.

May 19, 2010 8:02 AM ET

Response to Eric
by Joe Lstiburek

The short answer is that you are "screwed."

The problems associated with sulfate attack on concrete are legion. There is no easy answer.

In theory if you prevent all evaporation from the top of the concrete slab and from the sides (above grade and below grade to the bottom of the grade beam) you could stop the process or slow the process down sufficiently for you not to worry about it in your lifetime. Having said that, in theory Communism works. If you epoxy coated the top of the slab everywhere and the sides with several coats (even under plates - good luck there) to have a zero vapor emission layer (i.e. a perfect vapor barrier) it might work. The principle being if no moisture evaporates outward, nothing will be able to get in after the slab equilibrates. This has not been tried in your neck of the woods, but as I pointed out earlier, the physics says it might.

A good paper on the subject is a paper by Lee, Seung-Tae et al.: "Mitigating effect of chloride ions on sulfate attach of cement mortars with or without silica fume," (Canadian Journal of Civil Engineering, November, 2008). There was hope some time back about lithium injection, but that hope and change thing apparently did not work out. Sound familiar?
Joseph Lstiburek

May 24, 2010 4:58 PM ET

by Joe Lstiburek

One last answer for Richard

Doing stuff on the outside is always better to doing stuff on the inside. I did not think that outside was an option in your case. Since it is, do everything on the outside, above and below grade.
Add sacrificial layer to the inside below grade and be done. Seal the gap at the top of the wall where it hits the roof framing.

May 25, 2010 5:34 PM ET

Joe, Thank you very much.
by Richard

Joe, Thank you very much.

Jun 5, 2010 3:46 PM ET

138 yr. old Victorian with basement issues
by Karen Simon

We purchased a 137 yr. old brick Victorian from a couple last year. The basement was dry, no mold and in excellent condition. The exterior walls are brick with plaster over them and there are a few interior brick walls that are bare. My father was a carpenter and I grew up knowing about maintenance. My fiance, on the other hand, is one who is more reactive than proactive! We have had a lot of heavy rainfall in this area since purchasing the home. We were told by the previous owner that the basement does flood on occasion. Well, since we purchased it and today it has taken on water at least six times. Here's what happens--we'll get an excessive amount of rain. A portion of an exterior wall area will bring in water (not coming down the wall, which is plastered, assuming from base of wall). The fiance will let the water SIT. We do have floor drains in all the areas, but the water has to get very high for that to drain. Last year I finally had to buy ONE dehumidifier on the sneak because he feels the basement doesn't need any!!! It needs at least THREE, I think 1500 square feet. Now the walls have developed the salt and they are crumbling into dust. And we have mold developing on some of the plastered areas. I'm scared...this house is listed on the local historical society and I wanted to get it on the national listing. He has NO IDEA what he's doing/not doing. Now we also have an issue with a corner outside where water is pouring down the brick exterior and causing green mold to form. We're going to end up ruining this house and I REFUSE to see that happen!! I need some guidance on who to call in the area--historic preservationists? Contractors? Oh, and the original builder of the home was a brickmason. So most of the bricks are ORIGINAL to the home and made on sight.

Please help!

Jun 5, 2010 6:42 PM ET

Reply to Karen
by Martin Holladay

If your basement has low-lying areas that accumulate water that doesn't drain -- and if you have operating floor drains elsewhere in your basement -- your first step is clear: hire a contractor to install operating floor drains in every area of your basement that has standing water after a rainstorm.

These new drains can be connected to the existing (presumably functional) drain system if the existing drains have enough of a slope for the new drains to be connected. Otherwise, the contractor can connect the new drains to a new sump equipped with a sump pump.

Good luck.

Mar 18, 2013 9:57 AM ET

salt water pool run off dumps into my cinder block garage
by Angela Doucette-Grasby

My neighbor's property is 6ft higher than mine. 5 years ago he altered his grade of land sloping it at me, he also hooked up weeping tile to his eaves trough and ran them into my retaining walls, then installed a salt water pool that runs off into my garage. It has been 5 years of water that he refuses to fix. My garage is made of cinder blocks and I have a white powder crawling up my walls cracking from the ground all the way to the top. The whole garage has shifted including doors, bricks along the front are starting to fall out. Water is present a lot and in winter months its a skating rink in the garage. One company that came in said the garage would have to be torn down and rebuilt, the other said it could be fixed without tearing it down. In your expert opinion what would you suggest? Thank you Angela

Mar 18, 2013 10:31 AM ET

Response to Angela Doucette-Grasby
by Martin Holladay

Q. "In your expert opinion what would you suggest?"

A. I suggest that you consult a lawyer.

Mar 18, 2013 9:30 PM ET

I have retained a lawyer and
by Angela Doucette-Grasby

I have retained a lawyer and we have been in court for 5 years now, the other side keeps stalling. I am just wondering who is telling the truth! The City won't help until the court is done and my lawyer is trying to talk me into settling saying that salt water won't ruin my garage. But after reading this report I'm thinking he is very wrong on that advice.

Mar 19, 2013 6:06 AM ET

Response to Angela Doucette-Grasby
by Martin Holladay

There is no way to anwser your question without a site visit.

Jul 14, 2014 10:11 AM ET

100% humidity
by scott plantier

Think I'll maintain 100% humidity throughout my basement and eliminate the rising damp. But then it would just rise until encountering the drier, conditioned, living space.

Oct 29, 2014 10:16 AM ET

1905 block basement & water damage
by Stephanie Lurk

The place was built in 1905. Basement floor was originally (probably) a dirt floor, and now has a very thin layer of concrete, which is all sorts of cracked. There are two types of walls (as I can tell from the interior): #1 is a CMU wall with parging. It gets a bit moldy when the floor seeps, but is not my main concern. #2 is a much thicker structure, the innermost surface being a parge coat. I am not sure what is behind this coat or how thick the coat is, but it may be several wythes of brick. My main issue is cosmetic (I hope) and arises from water moving through the thick structure and leaving stains on the wall, also flaking the paint and cracking the parge coat somewhat. The upper floors of the house have not moved at all; all my doors swing freely, my floors do not bow and my walls upstairs haven't shifted. For these reasons I do not think I have a structural problem. I am painting over the stains and cracks with Kilz2 Latex and it looks nice, but I fear that in the future this will just peel off. Also, and more concerning, is that when I tap the wall, there are a few areas that are most definitely hollow, as the sound changes completely. The visible surfaces of those areas have water staining on them. I am wondering if I can get away with continuing the application of the Kilz2 Latex over these areas of if I should break out the hollow areas and fill them with either new masonry or just a large mortar patch. Thanks so much for your wonderful article and helpful replies!

Oct 29, 2014 11:36 AM ET

Response to Stephanie Lurk
by Martin Holladay

The key sentence in your long paragraph is the following one: "The CMU wall with parging gets a bit moldy when the floor seeps."

You have a damp basement. It's likely that your foundation has several problems, most of which will be difficult to diagnose over the Internet (without a site visit). For a general overview of approaches to fixing damp basements, I recommend the following article: Fixing a Wet Basement.

In short, it sounds like you have more problems than loose parging and peeling paint. Your basement would probably benefit from an inspection by a contractor who specializes in wet basements.

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