Clay bricks

[ajk1]

For normal 4" wide clay bricks used a sface brick on exterior building walls, is the composition of the brick relatively constant throughout, or is the portion closest to the face of the brick more dense and impermeable than the portion near the centre of the brick, given that the face of the brick is perhaps more highly heated when it is fired then the interior of the brick. Specifically, is the permeability relatively constant throughout, or is the portion near the surface significantly more impermeable?

 

[Ron]

ajk1....in my experience with cross sectioning and checking the "hardness" of brick in the cross section, there is typically an outer "firing" crust and the inner portion is softer.

See attached photos of cross-sections of old brick. Newer brick is better, but still has same gradient hardness.

 

[Ron]

Pushed the button too fast...no, the permeability will not be consistent throughout the cross-section.

 

[ajk1]

Thanks Ron.

Is the denser layer in the photo the slightly darker layer near the surface?

The issue I am dealing with is spalling of brick in 50 year old building of solid wall of 2 wythes of brick.

What tests should be done on the brick?

Is RILEM tube water uptake test the only test to be done? This is the only test that the engineering firm investigating the brick spalling has done to-date.

Should some form of freeze-thaw durability testing be done on the brick?


The interior of the building is very dry in winter, ranging from 15% on very cold days to 30% when the outside temperature is around zero Celsius. The spalling is mainly on the east wall(the wall is 2 wythes on 4" brick and a 1/2" colalr joint), above the interior ceiling level of a periodically (once a week) used auditorium (1.5" insulation on the interior of the wall), but there are some other areas as well, such as a mechanical room with no ceiling and no moisture generating equipment (brick and block wall). Driving rains in this city are mainly from the east, so I feel that any moisture penetration of the brick is most probably mainly from the exterior.

Is a thermographic scan of the wall likely to be of any help determinin g the casue of the brick spalling or would we be better spending our money on other tests?

What tests should done of the brick (and the mortar and the wall)?

 

[dik]

The outer surface (fireskin) is generally harder. Moreso, with old masonry. Just a caution... concrete shrinks, clay brick generally expands a tad.

Dik

 

[ajk1]

Does the firing crust occur on both faces of the brick?

Are there any tests that should be done on the brick to determine its durability (particularly its resistance to surface spalling)?

 

[concretemasonry]

ajk1 -

This may not be a structural question.

If you are looking for compliance, you may be a little late in the process to question the testing procedure since the products, specifications may have already been decided (usually based on type, exposure and appearance) since brick is a highly variable product when it comes to specific tests and properties.

To answer you last post, the question of durability is based on sets of samples of the brick for a test. Durability is a very complex property to determine by single set tests.

Brick is a highly variable product depending on the available raw materials, manufacturing process in a plant to create what makes the product specified. Rarely is brick a structural concern since 4" brick are usually just a veneer.

As an example, given a clay to be used, the process of molding/extrusion can be different to achieve is already determined. The firing consists of staking bricks and running through a kiln for a long period of time and then for cooling down before being stacked for storage or delivery. The clay in a brick has significant thermal inertia and warms and cools differently that affects the appearance. The rate of temperature change affects the colors of the surface. Not all brick in a firing actually have the same condition because of the exposure (orientation and spacing).

Masonry is designed as wall and not separate materials or properties of specific areas of a material. Where else would you find a material specification saying that you should use the lowest strength possible to carry the loads?

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[hope9010]

Thank you concrete masonry. The brick that I am investigating is the outer wythe of a solid bonded brick wall (4" brick, 1/2" collar joint, 4" brick) of a 50 year old building, and the outer face of the outer wythe of brick is spalling. I was wondering what tests could be carried out on samples taken from the wall, that might identify if the brick has an inherent durability issue, such as a lack of proper resistance to freeze thaw cycles.

 

[madmantrapper]

The building is fifty years old and this is a new issue?

 

[hokie66]

Why do you find that surprising, madmantrapper? There are deterioration issues with most buildings, whether new or old. This may have started some time ago, but the OP is trying to figure out what to do about it now.

 

[dhengr]

I’d investigate water getting into the middle of the wall from above, in the areas of the spalling problems; leaking copings, flashings or joints and caulking , etc. immediately above the problem areas. The brick has worked pretty well for 50 +/- years, and all of a sudden you have this problem. That doesn’t sound like a problem with the brick itself. The fired shell around the brick might vary, and it will tend to keep moisture in the brick, as well as try to prevent it from getting in. Although, there are ASTM tests, and the like, for brick performance characteristics, but I don’t know the std. numbers off the top of my head. Also, look at the “Technical Notes on Brick and Tile Construction” by SPCI ( that’s the BIA, now. Google BIA/tech notes).

 

[dhengr]

That’s SCPI (Structural Clay Product Institute), not SPCI, and BIA (Brick Industry Association). Sorry about that. I rather dislike the over use of acronyms, particularly when I shoot a bull on one. You generally don’t impress people with all your smarts, by using a bunch of acronyms, when they have to look up every other phrase/word to try to determine what you are talking about. Why should they waste their time, they don’t have the problem/question?

 

[concretemasonry]

hope9010 -

Regarding your building -

I don't think running long term tests(slow and costly) tests on existing brick that were exposed for many years will be valuable since they cannot be correlated to laboratory tests of new products.

Durability is a long term process up in different places because of exposure (wind, water, sun and temperature maximums of minimums. Fortunately, the massive wall thickness provides good stability of conditions.

When you look at older structures from a durability standpoint, it muddies the water when looking at the microscopic details.

Unfortunately, looking closely at samples of new products does not allow you any real comparison to predict durability for the future. All you can do is look at existing performance and the material types used in a global view.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[ajk1]

Looks like I have done a poor job of outlining the issue. Let me have another try at describing the issue.

1. The 50 year old brick has had spalling problems over the last at least 30 years that I have knowledge of the building, perhaps longer. The last major repair of spalled areas, was carried out in 1997, at a cost of about $50,000. The areas of the 1997 repair are performing well, but other nearby areas of the original brick in the same wall, are now severely splalling. This is one fact that leads me to belive that the properties of the original brick are worth investigating.

2. The wall is a total of 8.5" thick. It is a solid bonded wall of the type common in the 1960's before the widespread use of cavity walls. I would not describe this as a massive wall, but anyway I am not worried about its structural stability.

3. The wall in question is the east wall of the building, and the problem predominates above the level of the interior ceilinig, perhaps because the wall may be colder there.

3. We and another engineering firm have investigated all the more usual causes, including flashing at the top of the wall (in conjunction with a roofing specialist inspector). We have considered sun, wind, water, moisture egress from the interior and of these, only wind is a factor because it is the east wall and the wind driven rain is almost always from the east in this city. The wall has a vaour barrier and the interior is not a high humdity area, although we may put a data logger in the ceiling space to see if the humidity is higher there and what the temperature is there.

4. My opinion is that the only thing not investigated to-date is whether the brick is more subject to freeze thaw cycling deterioration than the average brick, and this is making the effect of minor water penetration by whatever means, a more significant issue than would be the case with most brick.

5. I am having diffulty justifying in my mind that we can say that we have completed our investigation without having investigated the properties of the brick, particularly with regard to freeze-thaw cycling durability, but you people know more than I about this, and I respect and value your views. My feeling is that a reasonably prudent engineer would test the brick itself when an analysis of the other usual factors causing brick deterioration does not identify any clear cause of the spalling. But if you tell me that an investiagtion of the brick is not an appropriate thing to do, then I will respect your views and drop the idea. One thing that leads me to think that it is a brick problem is that the 16 year old replacement areas of brick in the same wall are performing fine to-date, although perhaps 16 years is not long enough to be sure of anything. Also we had the same problem with the brick facing of an exterior cantilevered retainign wall and replaced all the face brick in 1997 and the replacement brick is performng fine.

 

[dik]

Can you describe the complete wall construction from say inside to outside? drywall/lath and plaster, wood studs, inslulation, air space, two wythe
brick wall? or of that ilk.

Is there a vapour barrier?

Old masonry used to rely on the mortar to 'wick' the moisture out and there was no real vapour barrier. Can it be that moisture is accumulating at the outer skin and freeze thaw is spalling the masonry face?

Is the area damaged, frequently wetted? Many masonry problems are caused by moisture.

Has there been any improvements to the building... air tight doors and windows, HVAC?, etc. Trapping more moisture within can be a problem as well as creating more moisture from heating, cooking, etc.

curious mimes want to know <G>.

Dik

 

[ajk1]

Thanks Dik. You raise good points and I will try to answer them as best as I can. I feel that this really needs an enginer's engineer to solve the problem; it does not seem to be that the usual boiler plate problems/solutions are necessarily applicable here. Please note that my moniker of hope9010 and ajk1 are both me, just depends whether I send from the office or from home.

1. The wall is a crurved east wall of the buildng. The assembly is given on the architectural drawings as follows, and investiagtions to date have tended to confirm this:

Starting from the interior side, the wall above the level of the interior ceiling (i.e. where the majority of the brick spalling is located) is as follows:

- 1.5" of fibreglass insulation with foil backing vapour barrier
- 1/2" parging
- 4" brick interior wythe
- 1/2" vertical collar joint between wythes
- 4" brick exterior wythe


No breaks have been found in the vapour barrier, but a detailed inspection of all of it has not yet been made. I expect that the vapour barrier may not meet current standards. (It should not cost much to provide a vapour barrier meeting current standards).

The wall is curved in plan view, so that is most likely why it is brick and brick rather than brick and block.

The room is the main sanctuary of a synagogue, and is generally used only once a week, plus any weddings etc., but most of the time it is empty. The humidity in winter is low in the room, and in summer is high. Last weekend I measured the humidity in the room when the people were in it, as 27% and the air temperature as 74 deg. F at seat level. I don't know what it would have been in the ceiling space above.

The ceiling space is NOT a plenum. Ducts are used for supply and exhaust.

2. There is another east wall of the building with severe spalling near its top; that is the east wall of the top storey fan room. This wall construction is:

- 4" solid block interior wythe (no insulation, no vapour barrier)
- 1/2" vertical collar joint
- 4" brick

The fan room is not a high humidity area; I expect in the winter that it varies between 15% on a very cold day (minus 15 deg. C outside), to 30% when the outside temperature is near zero deg. C (32F).

3. Yes it is quite possible as you suggest that moisture is accumulating at the outer skin of the brick and freezing. But why should that be more prevalent on this building,than on other buildings?

4. There is no apparent damage to the wall. Near the top of the wall can be seen some mortar joints where there is a gap between the mortar and the brick, that perhaps could let rain penetrate to the vertical collar joint. There is a horizontal steel shelf angle located at about the interior ceiling level, that supports the exterior brick. If water gets into the collar joint, it would be blocked by this shelf angle. This might explain why the spalling predominates above the ceiling level.

5. There have been improvements to the building in terms of a new HVAC system but the spalling issue predates this by many many years. There has been no change to the windows, though an upgrade is scheduled. New roofing and increased insulation were installed about 3 years ago, but this was long after the brick spalling was already very severe and had gone thru one large repair of spalling.

6. One other point- the contractor who built it in 1965, thought that the bricks were very absorbent and applied a sealer, although this was not specified by the architect. I think that this was a bad thing to have done.

My own theory is:

a) the bricks have below average freeze-thaw durability properties (tests would be required to confirm this);

b) any moisture penetration of the wall is most probably mainly due to driving rain from the east;

c) due to poor freeze thaw characteristics, and perhaps exacerbated by the sealer applied to the wall in 1965, moisture penetration of the wall has caused spalling that might not be caused by moisture penetration of a wall built with more durable brick;

d) the spalling predominates above the ceiling line becasue moisture penetration is trapped in the collar joint by the supporting steel shelf angle;

d) the spalling predominates on the east wall because the driving rains come mainly with east winds in this city (as confirmed by the National Research Council);

e) I do not believe that the interior environment of the building is a significant source of moisture penetration to the wall in this building, although I agree that this is often the case in other buildings, particularly if they have hiugher humdity. The evidence to date does not support this theory for this building, in my opinion.

I am very interested in your further thoughts on this. Thanks for your help to-date.






No breaks in the

 

[tony1851]

Hi ajk.
A pic or two would have helped here, but this is a common problem in older brick buildings.
It seems clear that the bricks are basically not frost-resistant. The fact that most of the decay occurs above the level of the ceiling suggests that those bricks are not drying out as well as the bricks lower down; they will also be more exposed to the weather than the bricks lower down the wall. This results in them staying saturated for longer, which obviuosly causes problems when the frost comes. The insulation and parging behind the wall in the roof space will ensure that the brickwork remains cold and damp for longer.
Any sealant put on the wall will also have prevented the brickwork from breathing, and will trap any moisture getting in through perpends or other cracks.

 

[dik]

Is the 1/2" parging on the inside of the insulation? or against the brick and a drywall/plaster surface?

It's a matter of determining where and if moisture is the issue and the source or if the material is deficient.

Do you know the type of brick unit used? Do they have vertical holes? or a 'frog' (depression on the top side of brick unit)? The latter are more likely to have a fireskin, although the building is not likely old enough.

Are there any other buildings in the area (or city) that have what appears to be the same brick? Are they deteriorating, too?

Have you taken any cores of the brick to check for porosity? and moisture content? and cryptoflorescence? Additional testing is likely required.

Is the extent of the damage localised to particular areas or is it at random?

With the double wythe and the void between, is it possible that moisture is entering the interstitial space? It would tend to migrate outwards.

In Canada? What city?

I've put together a small paper on historic brickwork, and it can be found on slideruleera's web site.

Dik

 

[hope9010]

Thanks Tony1851. Your thinking is very much in accordance with mine. I think that some engineers are so enthralled with the elegance of the idea that the moisture comes from the inside of the building (and often it does), that they can't let go of it even when the evidence seems to be to the contrary (i.e. vapour barrier on the wall; low humidity in the room; problem confined almost exclusively to the east wall subject to the wind-driven rains).

Thanks dik; I'll try to respond to your questions:

- the 1/2" parging is on the inside face of the inside wythe of brick; in my prior response I listed the materials in sequence, starting from the inside and moving to the outside;

- the brick has vertical holes, not frogs;

- you make a very good point about determining whether there are any other buildings in the city with the same brick, and whether they are also deteriorating. I can't recall seeing any other buildings with this brick, but I will keep my eyes open, and try to make some inquiries;

- no cores or other testing of the brick has been done to-date, except 3 Rilem tubes, which reportedly showed that the brick has less than average absorption (I was not involved in that test). But the bricks had a sealer applied in 1966 so that may skew the Rilem tests. For reasons not clear to me, the general input from this forum has been to belittle the idea of testing the brick itself.
- the extent of the damage predominates on the top part of east facing walls; I would guestimate the number of spalled bricks at about 2500; there are scattered bricks here and there on other walls but the total would be comparatively few - perhaps 50 as a ball park guess, but even this really should not be happening with a good quality brick in walls that have been built in accordance with the building science and practice of the time (1966).
- As you note (and I noted as well in my previous response in this string of correspondence), it is possible that moisture is entering the collar joint (i.e. the intersticial space between the 2 wythes), but it seems that it would only get there by wind-driven rain on the east wall;
- the city is Toronto;
- I will check the website that you suggest

- we have done no testing of the brick to-date.
o What specific tests would you recommend?
o Any ASTM tests that you would recommend?
o What tests would you perform on the cores?

- As far as I can recall there is no efflorescence on the brick.What is cryptoflorecence?

 

[a2mfk]

Can you post a few pictures of the overall wall and the spalling?

I would think any sealant applied to clay brick is bound to fail due to irreversible moisture expansion of clay brick (property of all clay brick products). It probably failed right away since most of this type of expansion happens within the first few years. It would probably have to be reapplied annually to have any effectiveness. And as someone indicated, this may have made the problem worse in trapping moisture within the brick.

I am wondering if on those days where the temperature alternates above and below freezing, the upper portions of the wall actually got warmer due to more sun exposure, and then at night would freeze? Perhaps the lower levels of the wall stayed at a more constant temperature. Wall faces east, maybe the top portion of the wall gets just enough sun during these times of year to thaw and the bottom portion of the wall stays cold. Especially during those months when the sun does not rise very high in the northern latitudes. And the predominant wind is easterly.

Is there anything with the wall and roof construction that may be contributing to excess moisture, parapet cap, no gutters, bad flashing and drip edge, etc.? But you said these stones have been turned over...