Historic Brick Durability 6

[dik]

I've been tasked with part of a project constructed using historic brickwork. The client has stipulated that the bricks, salvaged from the original building, be 'certified' for durability. In past I've relied on a skilled mason to select the salvaged bricks for durability; this is based on the mason's visual observation and developed skills. A 'bad looking brick' is just a 'bad brick'.

Is anyone aware of some simple tests that be made that can quantify the durability of a historic brick. I know it is possible to chemically analyse a brick to obtain the composition with some elements indicating a more durable unit. It is also possible to microscopically examine a thin section for porosity and also run adsorption/absorption tests. I've also seen 'hardness' testing using various materials for 'scratching the surface.

Has anyone encountered a simple test for historic brickwork that is a measure of durability? Is it a matter of testing a few samples from a collection of visually similar objects?

Thanks in advance

Dik

 

[concretemasonry]

The most common test for the durability of masonry products is an actual set of freeze/thaw cycles. The number of cycles survived is a measure of the relative durability. Very often, the results are sometimes surprising with some weaker bricks with high absorption surviving more cycles. This is not a cheap, quick and simple test.

Keep in mind that the salvaged brick have already gone though many years of weathering already.

I have run samples of both new clay and concrete brick and pavers for comparative results. The test is not quick and there is no specific number of cycles required and there is no such thing as a "certification". I have seen some manufacturers that claim a certain number of cycles for new brick, but only time will tell.

It seems the owner wants a guarantee that his salvaged brick would be durable for a non-specific time period. - Pretty hard to stake your reputation on a vague owners requirement.

Dick

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

 

[SlideRuleEra]

IBC 2003 offers this:

2103.6 Second-hand units. Second-hand masonry units shall not be reused unless they conform to the requirements of new units. The units shall be of whole, sound materials and free from cracks and other defects that will interfere with proper laying or use. Old mortar shall be cleaned from the unit before reuse.


This section allows for the use of salvaged brick and other second-hand masonry units, provided that their quality and condition meet the requirements for new masonry units. Second-hand units must be whole, of sound material, clean and free from defects that would interfere with proper laying or use. Most second-hand masonry units come from the demolition of old buildings. Masonry units manufactured in the past do not generally compare with the quality of masonry made by modern manufacturing methods under controlled conditions. Therefore, designers should expect salvaged masonry units to have lower strength and durability than new units.


The (USA) "Brick Industry Association" gives reasons why salvaged brick are not recommended:
Technical Notes 15 - Salvaged Brick

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[dik]

The brick units have to be re-used for historic reasons.

Don't you just hate it when codes take over from reason...

Dik

 

[dhengr]

Dik:
Well.... It wouldn’t be historic brick if it weren’t fairly durable. Enough said.

The biggest thing might be matching the mortar in old masonry construction. Older bricks were not as hard as some of the bricks made and fired today. So, you don’t want too strong a mortar when working with old brick masonry or the mortar tends to abuse or overpower the brick in the finished wall. The mortar should be softer so it yields or gives/flexes/compresses a bit rather than breaking the brick in daily wall action, over time. You may want a sand/lime mortar rather than today’s sand/cement mortars. You should be able to tell which was the old exposed surface of the used brick, and maybe as good a visual inspection as any, is to observe how much ware and erosion exists on that surface and edges, as compared to a surface which was better protected, within the old wall. Then also, detail the wall (no raked joints) so that it drains and dries in both directions. I agree with Dick, I wouldn’t want to stake my reputation on some used brick that the client picked, and its durability, without many tests and caveats.

 

[SlideRuleEra]

Dik - For historic structures, the (USA) General Services Administration uses the following guidelines (as performed by an experienced mason) for evaluation of used bricks:

***ASSESSMENT OF BRICK***

A rating of '4' or below indicates brick in an unsalvageable condition. A rating between '5' and '7' indicates that some remedial measures may need to be taken. A rating of '10' indicates that the brick units are in good, sound condition.

RATING DESCRIPTION

0 - Bricks are totally disintegrated.

1 - Evidence of spalling at least 1/4" to 3" deep.

2 - Slight erosion at corners of brick; slight powdering of surface when rubbed with hand or scraped with fingernail.

3 - Spalling brick in layers when rubbed with hand; fragments do not powder.

4 - Bricks can be broken by poking and jabbing with screwdriver; fragments are semi-hard and resemble compacted clay.

5 - FIRST CLASS OF STABLE, STRUCTURALLY SOUND BRICK: Screwdriver can penetrate the brick by hand roughly 1/4" but brick does not crumble.

6 - Screwdriver can penetrate the brick roughly 1/4", but ONLY with the assistance of a hammer; this may cause coarse jagged pieces to become dislodged.

7 - Screwdriver is unable to penetrate the brick even with assistance from hammer but may make a slight impression in the surface. There may be a slight ring or bounce as the screwdriver hits the surface.

8 - Chisel is necessary to crack the brick.

9 - Chisel is unable to make an indentation or impression in the brick; brick shears cleanly; brick is strong with crisp edges and corners.

10 - A NEW BRICK: Brick with crisp corners; chisel striking the surface produces a clear ringing sound.


IMHO, A simple screening test could be probing each brick with a hammer and screwdriver... if nothing happens this indicates a Class 7, or better brick. A mason could check each screened brick at time of use.


See this link: Guidelines For Evaluating The Condition Of Brick Masonry & Mortar

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[dik]

dhenger: Agreed that the mortar is the tricky part, and one of the main reasons that historic brick restoration fails. A high lime mortar with a little medusa Portland cement, and lots of sand for colour...

I have no problem with the longevity... it's the client that is insisting and I'm looking for a 'quick and dirty' test for diligence.

SRE: Thanks for the source; I've always used a skilled mason and he's looked after the masonry unit selection. I'll take a look at the link.

SRE: tried giving you a star, but, dhenger was the only one that made it.

Dik

 

[dhengr]

Dik:
Take a look at The Brick Industry Association,

http://www.gobrick.com,

their Tech Notes. They used to be called The Structural Clay Products Institute (SCPI). They are in Reston, Virgina, USA. They have some great stuff in their technical notes files. And, I suspect you might find something on the subjects you are interested in their Tech Notes. “Used Brick” used to be Tech Note #15, am not sure of today’s numbering. I don’t know that you are going to find a definitive and economical/practical test which gives you a very specific durability number/answer. This primarily ends up being an educated engineering experience and judgement thing, with the help of your experienced mason as a good assist in making that judgement. Then, your report language and caveats better give you plenty of latitude, because you have no recourse against the brick supplier and his credibility and reputation.

 

[dik]

thanks dhengr... I have a complete copy of the BIA Tech Notes; I'll take a gander at the listing and see if my copy is current. Report has already been completed... the project is moving into the construction phase.

Supplier long gone... brick over 100 years old.

Part of the problem is the client wants an engineer to make the decision on the existing brick, not a skilled mason. I've usually used a skilled mason for past work. Part of the restoration has used mortar that is Portland cement... and not proper mortar.

Dik

 

[Ron]

dik....I have cross-sectioned and examined historic brick on several structures. What I have found is that they are often "hard fired" on the outside, creating a "crust" while the inside remains relatively friable. For the bad ones, the "crust" will often separate and delaminate, particularly when exposed to wetting and drying. For the good ones, a probe such as an ice pick or screwdriver will show the bad brick readily as noted in the GSA notes that SRE gave.

 

[OldBldgGuy]

The mortar for any masonry, but especially restoration of historic masonry and reuse of old units, must always be weaker than the masonry units. A high proportion of lime is necessary. A simple test that is not a guarantee but is reasonable assurance that the bricks are acceptable is to specify that the mason must check each brick with a simple tap of his hammer. If the brick doesn't ring, don't use it. Even soft old bricks will ring if they are hard enough to use and don't have any invisible cracks.

 

[dik]

Thanks Ron, the 'fireskin' can vary appreciably within the same firing. I've seen masons 'chip' a corner off and place this on the inside of the wall so it's not visible.

OBG: I've not seen the 'ring' test used; I wouldn't have expected it, but will try it. The mortar is the biggest issue to allow the joint to 'wick' moisture from the inside. Seen too many failures from remediation using too strong and impermeable a mortar. Another major problem is 'sandblasting' off the fireskin to clean the brick. Seen a lot of that, only to have the brick deteriorate quickly due to moisture and freeze thaw.