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Concrete block veneer wall over original brick foundation to control moisture?

cocteau3's picture

Sounds crazy, but I recently saw an old, restored house that has its original brick foundation. The foundation was in good shape structurally, but the renovators built a new single course concrete block wall around the perimeter, in front of the brick on the inside of the cellar walls. The attempt is to reduce the transmission of water vapor and reduce any mold issues. It looks good right now, but I am concerned the vapor will continue to pass through the brick and build up either behind the concrete block, or pass through the concrete block. It seems either scenario will cause the mortar to fail between the two, and possible cause the concrete block to give way.

Mold is the main concern of the renovators (a non-profit, grant receiving entity) but I feel they should have dealt with the issue by installing membrane waterproofing on the outside, but this is too late to do now, as the water mains and gas mains run along one side, with sidewalks on the other side.

Any thoughts on the success or failure of this concrete block veneering method? I realize painting the block or brick before, can cause blistering, mold growth, and/or choke off the vapor and cause original mortars to crumble, etc. Latex will provide minor help...

 

What's between the block wall (post #207767, reply #1 of 17)

What's between the block wall and the brick wall?

Potential failure of internal walls. (post #207767, reply #2 of 17)

Mold needs both food and water to grow.

The World is covered in mold spores, but if you look

around mold doesn't grow in most places, because

either there is no food or no water.

Mold doesn't grow on clean brick or concrete - no food.

If water is seeping though the brick wall, it will also make

its way through concrete block or the mortar between

the blocks.

Condensation only forms on a surface that is below the

dew point of the surrounding air - the temperature in an

unused basement will be stable. If the basement is lived

in then condensation is more likely to form, but its also

likely that the only input of water vapor will be from

peoples breathing and sweating and these amounts are

very small and one would expect them to be delt with by

the ventilation system.

Neither of these alternatives will bring down the inner

walls.

However, if the water table outside is high and there is a

high rate of water ingress at some time, then the wall

could come down.

It is more likely that provision has been made for the

water to run down the original brick wall, with it being

lead to a sump to be pumped out safely.

This type of provision is quite common.

I'm with Perry.  So long as (post #207767, reply #3 of 17)

I'm with Perry.  So long as provision has been made to drain the space between, there should be no problem.  Mold doesn't grow on concrete (unless it's "fiber-cement" or some such).


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

not sure (post #207767, reply #4 of 17)

I'm not sure what is in between them. I think there is simple mortar applied to the brick as the concrete block was laid, with no air space between. Would that make it fail due to water vapor? Before adding the concrete wall, there was not much, if any, liquid water coming through the brick, only vapor from absorption of ground water passing through as vapor. Wicking action is large on it. LIke a sponge.


Would an air space have been best, and if so, how would the vapor condense without making the wall fail? Vapor barrier leading to drain system at the floor? Might work in the future on another brick foundation if such a barrier would prevent the concrete block from wicking vapor from the brick.


My impression is an air space of several inches with plastic barrier on the foundation side of the concrete block, with a drain system at floor level to collect condensed vapor, leading to the sump via subterranean drain. Would this function, or is this unheard of craziness? The idea was to prevent mold, and the original brick had a "tooth" of organic matter for mold to grow on.

If they had scrubbed the brick and bleached, etc. to clean off the tooth, I wonder if that would have sufficed, but in this area such humidity in cellars inevitably leads to mold due to the dust, efflorescence, passed through water during storms, etc.


The photo shows the brick foundation wall before the concrete block was added. Lots of build up of crap to grow mold.

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I doubt that they mortared (post #207767, reply #5 of 17)

I doubt that they mortared between the two walls to any extent -- the CMU wall is most probably self-supporting.  This is similar to brick veneer over sheathing, where the brick stands away from the sheathing by an inch or so.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Basement (post #207767, reply #6 of 17)

There is no way that water vapor will cause a concrete wall to fail, except where the water vapor gains entry through cracks and then freezes causing spalling. This unlikely to happen in a basement where the temperature basically remains steady around 40F. Condensation on/in a concrete wall only happens when the wall is below "dew point" and as I note above, the basement temperature is steady

Where a block wall with gap or plastic sheet with bumps is used to prevent water seeping through the brick wall and entering the concrete blocks there has to be provision at floor level for the water to drain away. A ceramic or plastic drain usually collects and channels  to a sump.

Condensation only happens when warm wet air meets a cold surface. Warm and wet means that the air is above "dew point." Cold means the surface is below "dew point."
These temperatures can be from 32F upwards.

High humidity as an expression is usually used to express how we feel about our environment, as the temperature rises  and moves closer to our body temperature we feel hot and uncomfortable as  our bodies cannot get rid of our sweat that we use to control our temperature. 

High relative humidity can mean 100% relative humidity at 100F and above which feels hot and sticky or ,100% relative humidity at 70F which feel perfectly normal, or 100% relative humidity at 40F and below which feels cold and dry.

Writing about high humidity without adding the relevant temperature is meaningless.

The salts we see on walls are the result of water seeping through the wall carrying various minerals, usually minerals that were in the clay when the bricks were made.

Got it (post #207767, reply #7 of 17)

Yes, understood on the weather science. What i do know is that the old brick cellar walls transmit very large amounts of water vapor through them, which can condense on objects such as metal, or get soaked up by anything stored. I've seen mold growing even on rocks on the floor that has not been poured with concrete. That aside, I'm not concerned about my body temp, just controlling any and all water vapor (NOT SEEPING WATER) that is transmitted. The original wall is very high amounts of water vapor.


My thoughts are that a concrete block wall will hold up with an air gap, and that the vapor would inevitably condense onto the plastic sheet on the inside face of the block, and a drain system could carry away the water. My concerns are possibly building up more mold than currently exists onto the inside face of the brick wall.

 

I want to address the vapor because I sense it may pass through the concrete block (if there is not a vapor barrier system with drain) and create similar amounts of mold over time as dust, organic matter, and objects are present in the cellar.

 

My questions are for how to deal with a similar house in the same neighborhood that doesn't yet have any block wall system.

 

Thanks for inputs!

Evaporation. (post #207767, reply #8 of 17)

There is no water vapor inside the wall.

The water seeps through the wall picking up salts as it moves.

When the water arrives on the surface it runs down the wall,some of it evaporates into the air, leaving the salts on the surface.

As there is no food in brick, it is merely baked clay, mold will not grow on it. The same applies to the concrete - no food = no mold.

Yeah, I've seen people using (post #207767, reply #9 of 17)

Yeah, I've seen people using Clorox solution to try to scrub "mold" off of CMU.  It doesn't work very well, but hit it with weak acid and it wll wash right off.

You will occasionally see dark-colored mold on paint on CMU, but it's very superficial.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Muriatic (post #207767, reply #10 of 17)

Nice, muriatic acid dilution? Haven't thought of that.


So back to vapor.... let's talk about the effects . . . sure, the water passes through brick, and becomes evaporated in my case since the cellar looks, feels, and Is damp and moldy and humid. Fact. Kentucky/Indiana area. Humidity central most of the year. I've seen houses with poured concrete, concrete block, limestone cut block, rock, brick and all are prone to mold growth in conditions where the moisture is high and passes through. (Poured concrete when cracks happen)..."food" is the dust, and other organic matter that collects over the years.

In my picture, there is old paint on the wall, lots of surface mold in areas.


I suppose I could buy a drum of acid and spray the wall every month . . . then I'd check myself in to the hospital (mental and physical)

 

The purpose of the concrete wall was/is to block the evaporation of the water passing through brick from entering the cellar, and thus prevent build up of evaporated water into the cellar. Make sense? Only if the moisture barrier idea works.

Question (post #207767, reply #11 of 17)

Is that stone as the floor of the basement?

Any vapor barrier under there, taped lapped and sealed to the foundation?

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The reason the acid works is (post #207767, reply #12 of 17)

The reason the acid works is because it's not mold, it's efflorescence.  Basically a buildup of lime-like minerals.  The color will generally clue you -- generally efflorescence deposits will be white or grayish.  Sometimes bluish, and on rare occasions a darker color, depending on the types of dissolved minerals.

Mold will occasionally be blue-gray, but most often a darker gray tending towards black.

Efflorescence will have a rough, spiky appearance/texture, whild mold will be smooth and slightly fuzzy.  Efflorescence will appear near cracks in the masonry where water comes through the fastest.  Mold will appear where the surface gets damp, but where fresh water isn't constantly coming through.

It's really quite hard to confuse them once you learn how to recognize them.

Acid will generally loosen/dissolve efflorescence, but have only modest effect on mold.  Diluted Clorox will usually turn mold a much lighter color (almost white) instantly, but will have little effect on efflorescence.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Back to mold (post #207767, reply #13 of 17)

Efflorescence will have a rough, spiky appearance/texture, whild mold will be smooth and slightly fuzzy.  Efflorescence will appear near cracks in the masonry where water comes through the fastest.  Mold will appear where the surface gets damp, but where fresh water isn't constantly coming through.

It's really quite hard to confuse them once you learn how to recognize them.

 

Yes, reminds me of the info I got from materials class way back in 1981 about efflorescence and what it is.... thanks for the additional clarifications.


As said above, what is in the cellar is mold. Mold will appear where the surface gets damp, but where fresh water isn't constantly coming through.

Exactly.

So back to the wall technique, maybe it is so wrong nobody has anything to say about it??? I can accept that answer, as I'm skeptical myself about trying to eradicate a moldy original foundation with a new wall and vapor barrier. Seems inevitable to end up with an unwanted air space or still have some exposed brick and such.

The question (post #207767, reply #14 of 17)

I'm not sure of something. Where is the water coming from? Is it from soil moisture, or is it from humid air condensing on the cold foundation?  The solution depends on the answer to this question. In neither case can I imagine the inner block wall making any contribution except to the pocketbook of the mason.

Andy Engel

Never try to teach a pig to sing. It wastes your time and annoys the pig.

soil (post #207767, reply #15 of 17)

The moisture migrates from the soil. There is no membrane waterproofing material etc, I grilled the renovation contractor about that, it wasn't in their scope . . . poor excuse. Should have had a membrane to even begin to control the moisture. That aside, thus the concrete block wall... I'm thinking the vapor barrier idea would cause more complicated issues with unseen moisture, mold, etc.

 

Saw a house yesterday with limestone block foundation construction, built in the '20s. Corners of the basement were black with mold. Apparently, in the real world, materials gather organic matter over time, and provide the 'food' for the mold. Goes without saying here.

I'm curious how you know it's (post #207767, reply #16 of 17)

I'm curious how you know it's migrating from the soil? Is the soil around the foundation particularly damp? You could be right, but moisture migration into basements can be more complicated than we think. Particularly in climates with humid summers, condensation can be a huge contributor, and is often exacerbated by attempts to control moisture through ventilation. That's not to say that soil moisture won't also contribute.

Andy Engel

Never try to teach a pig to sing. It wastes your time and annoys the pig.

Oh geez.... I quit (post #207767, reply #17 of 17)

Ok, this thread has become digressive! Come on already< I know what mold is and isn't and I know how moisture enters buildings, etc. I will sign off of this thread, it's been minimally interesting to talk about cocrete block walls and how nutty they are in front of defective, old, brick foundations which soak up water from the:

 

Rain which falls from the sky and soaks into the ground and soaks into the brick; passes through the brick and creates mold on filthy surfaces of the painted brick. I've seen it hundreds of times... I'm not sure what the benefit of tossing around unrelated ideas really is....condensation will come later, for now, it is and always has been infiltration. Duh....

 

 

I have gotten much better information from this site about 10 years ago. I'll be signing off. Thanks, got answers from a foundation company backed up by two other contractors, etc.

 

J