Thread: Exterior Cement Block Walls

Hey,

Here in our tropical Panama, almost all visible constructions (residential/commercial)have exterior walls which are cement/clay blocks, finished with cement plaster and painted. That's it. There is really no wood framing here becuase it rains 8 months out of the year, leading to quick and excessive rot. However, since the climate here is tremendously hot/humid and of course movement naturally occurs, the paint and plaster crack, eventually leading to water intrusion into buildings causing tremendous damage indoors. So owners and builders are spending thousands of $ constantly repairing with sealants, grouts, and repainting. I'm wondering why building wraps that can act as vapor barriers and drainage planes, are not installed on exterior walls over cement blocks and under the cement plaster? Wouldn't this prevent water intrusion into buildings as the paint and plaster deteriorate with the climate? Would this be at all advisable?

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I think a rain screen/ drainage plane would be the way to go. That way water never actually makes it to the structural blocks.

Originally Posted by Roni Litmanovic

So owners and builders are spending thousands of $ constantly repairing with sealants, grouts, and repainting. I'm wondering why building wraps that can act as vapor barriers and drainage planes, are not installed on exterior walls over cement blocks and under the cement plaster? Wouldn't this prevent water intrusion into buildings as the paint and plaster deteriorate with the climate? Would this be at all advisable?

That could work, but it also could lead to more directly forcing water in where it is not wanted with less-than-good-quality-careful workmanship.

Concrete block with stucco is a get-wet-storage-and-dry-out system. Stucco *is not* water proof, no matter how much some people want it to be.

You are thinking of adding a get-wet-and-drainage system, and any failures in that drainage system simply puts you back where you are, in possibly even worse conditions in localized leak areas.

Instead of "owners and builders are spending thousands of $ constantly repairing with sealants, grouts, and repainting", why not grout the walls solid? My guess is that the cost at the time of original construction will be no more than they spend in a short time "spending thousands of $ constantly repairing with sealants, grouts, and repainting".

If your concrete blocks are made like ours are, they will have a 1-1/4" face shell inside and outside, that is only 1-1/4" of storage capacity before it is saturated and can hold no more. You really can't count on the inside face shell for adding much to the storage capacity as the water typically runs down the inside of the outer face shell, runs across the tops of the webs, then seeps in through the mortar joints, or, simply runs down to the bed joint of the first course and then inside.

Making the walls fully grouted gives you 8" of storage capacity instead of just over 1", and, it blocks the flow of water running vertically down for that full 8". The storage capacity may now well exceed what is required and necessary for the storage-and-dry-out function to function properly. I say "may well exceed" because I don't know, an engineer would need to address that, but I think it would work.

At the cost of all those continuous repairs, it seems to me that a few 'experimental homes' could be constructed that way and see what the results are over the period of several years, can't be any worse than you are describing.

My home in Thailand is built very much the same as in Panama except, Block walls are made of what they call SuperBlock which is a lightweight solid block glued togertaher at the jisnts with an epoxy type cement. Then the exterior surface is screened with lightweight mesh and surfaced with mortar. The mesh inhibits cracking of the surface coat which is where the leaks start. Even so keeping up with minor cracking by applying silicone(vinyl) heeps the water out. The main problems I see in Thailand are the home designs. Western style structures with minimal roof overhang at the soffitts do not work in a hot wet climate as there is just too much water cascading down the exterior walls for anything to control.
3 to 4 foot overhangs, steep pitched main roof sections to lower pitched soffitt sections create shade and keep the side walls dry.
So I would say start with design and then look to new methods or products but remember. You can't beat mother nature.
As in Thailand I am sure Panamanians are not typically maintenance orientated. Finally, when the $hit hits the fan the laborers come out and make repairs. These guys get about 5 dollars a day so thier attention to detail is minimal. Also if the guys fixiing your house live in a bamboo hut how can you expect them to understand why a leak is a problem?
Attached is my home which shows the style that I know works.

Originally Posted by wayne soper

Block walls are made of what they call SuperBlock which is a lightweight solid block

"solid block"

Precisely what is needed. That, in and of itself, makes a huge difference on 'storage capacity' and the time needed for (allowed for) drying out.

"Solid block" or fully grouted, end result is the same, except that a fully grouted wall will have far fewer horizontal breaches in the "solid" wall structure, resulting in far less horizontal movement of water to the interior surface.

Follow that up with a more water-tight 'mortar' joint and many of those problems go away.

For existing homes, why can't they just install siding with a rain screen system over the blocks to keep the blocks dry? Of course, I don't know whether they have access to the same materials as we do.

Once the stucco is painted it retards the drying out.

They don't use moisture barriers on cmu in the southern USA because they have not figured out moisture goes to the cool side of the wall yet.

Let alone when the HVAC comes on it sucks the moisture into the walls.

And it might cost the builder more money than just stuccoing over the CMU.


IMO

I have a question about stone veneer on concrete block construction for a hot humid climate (Florida). I don't know if I should start a new thread, but it seems relevant to this discussion.

My question is that most manufacturer's specifiy directly adhering the thin stone to the block, thus creating a get-wet-storage-and-dry-out system (borrowing your term, Jerry). Sometimes this doesn't work the best when pounded by continuous rain, like tropical storm Fay.

What do you think about painting the concrete block with an elastomeric paint and then attaching metal lath and adhering the thin stone to the lath? This would create a screen/drainage system. Here is a link to some install instructions indicating this may be acceptable. I attached an excerpt from the document so you don't have to read the whole thing.

http://www.robinsonbrick.com/product...stallGuide.pdf

My question is, do you think this would be better or worse for long term water control?

Thanks, Tim

If it were my house, I would use something like this:

WaterWay Weather Barrier 9714.

Of course, I'm a West coast guy.....

Tim,

Seems to me that those installation instructions only permits 1a under one basic condition:

1a. Concrete/Concrete Block/Stucco needs to be clean and in its original, untreated condition. If the surface has been treated, light sandblasting or waterblasting can be used to restore the wall to a smooth, clean surface. Remove all form-release agents, dust, etc., that may inhibit the mortar bond.

"and in its original, untreated condition", i.e., bare, raw, concrete block, no stucco, no paint, no nothing

Otherwise, you have no choice but to use 1b.

Thus, if this is not a brand spanking new concrete block wall ... there is only one option available to you - 1b.

If you have that brand spanking new concrete block wall ... then you can use *either* 1a or 1b - your choice.

Thanks,

I was wondering if 1b with a painted block wall would give better protection against water intrustion and not cause any ill effects.

That WaterWay Weather Barrier that Brandon posted looks like it would work great with a 1b install.

Originally Posted by Tim Voss

I was wondering if 1b with a painted block wall would give better protection against water intrustion and not cause any ill effects.

Tim,

"better"?

Don't know.

However, if the concrete block is anything but (from the installation instructions) "clean and in its original, untreated condition" or is in a condition in which "light sandblasting or waterblasting can be used to restore the wall to a smooth, clean surface", then 'the only' option is to use 1b.

But ... is it "better"?

It it was "better", I would think the manufacturer would have them do it that way anyway.

Wait, no, the manufacturer does give that option anyway, it just allows the short cut 1a.

Wait ... ... if 1b was preferred, the manufacturer would make 1b 1a, and make 1a 1b, making 1b the optional, but less preferred, method.

They didn't, they made that option 1a. Does that indicate that 1a if the 'preferred option'? Usually, yes.

I'm sure 1a is the preferred option from an installer point of view. Much easier.

I'm not so sure 1a is the better option from a water intrusion point of view.

1a is a storage wall, 1b is more of a rain screen/drainage type wall.

I would think 1b would be better, but there might be problems with it that I don't see.

I think standard brick veneer with the 1" air gap is definitely better than directly adhered brick. But stone veneer is too thin to stand on it's own and has to be adhered to something.

Originally Posted by Tim Voss

I'm sure 1a is the preferred option from an installer point of view. Much easier.

Agreed/

I'm not so sure 1a is the better option from a water intrusion point of view.

1a is a storage wall, 1b is more of a rain screen/drainage type wall.

Agreed - sort of, but not necessarily.

I would think 1b would be better, but there might be problems with it that I don't see.

That's the "sort of, but not necessarily" part.

Let's start here:

Stucco on frame, a drainage system:
1 - old way which did not work well: paperbacked metal lath over sheathing
2 - old way which did work well: sheathing covered with paper, paper backed metal lath over paper
3 - new way WRB over sheathing, paper backed metal over WRB

In 1, the paper of the paper backed metal lath served as a bond breaker over the sheathing, with the sheathing serving as the drainage plane. We all know what happens to sheathing when used as a "water drainage plane".

In 2, the first layer of paper over the sheathing acted as the drainage plane, the second layer of paper (the paper on the paper backed metal lath) served as a bond breaker between the stucco and the drainage plane.

In 3, the first layer of paper is replaced with a weather resisting barrier (better than just being wrapped in paper), which serves the purpose better than building felt.

In using option 1b, you would be creating 1 (from my 1, 2, 3 above) over block (instead of frame).

Not sure that is better that 1a.

Now, if you wrapped the house in a WRB, then used option 1b, you would be treating the CMU wall as though it were a frame wall, and turning a storage and dry out system into a drainage system.

But ... that is not one of the options shown, thus, unless an engineer specifies that way, you would be improperly installing the fully adhered veneer.

Haven't poured through the whole thing, but there's a white paper on the BuildingScience.com web site, (RR-0503_Rainwater_Management_Performance.pdf - 2997Kb)

Originally Posted by Terry Beck

Haven't poured through the whole thing, but there's a white paper on the BuildingScience.com web site, (RR-0503_Rainwater_Management_Performance.pdf - 2997Kb)

Here is a clickable link.

http://www.buildingscience.com/docum..._download/file

Wow, nice report. We have been applying many of the recommendations for years, even in our dry climate. Not sure where it applies to stone veneer over block, except for the "seat" recommendation, but should be required reading for all...
I don't really like the "mass storage" theory of water management, it seems far better to keep the moisture out in the first place. There are too many edible materials beyond the block(for mold) to risk the mass being overwhelmed in extreme weather cycles. I do see the cost advantage to subscribing to this tho, simply put, drainage systems are far more expensive, and you really do get what you pay for.

Originally Posted by John Carroll

Wow, nice report.

John,

We, at FABI, were fortunate enough to have had our winter meeting scheduled such that Dr. Joe presented that report to us on Saturday and Sunday before he presented it to the people who paid for it the next day, Monday.