Blown Bricks : Advice please !

[Michael GilliganParticipant @michaelgilligan61133]

[Michael GilliganParticipant @michaelgilligan61133]

Several years ago we had a high garden wall built

Foolishly, I took the builder’s advice and purchased “Scotch Common” bricks.

We are now in the situation where perhaps one in thirty of them are ‘blown’

I want to fill at least some of them, before this turns into an expensive rebuilding exercise. Can anyone advise, please, what material would be most appropriate.

Kindly resist the temptation to suggest JB Weld, or Milliput !!

Thanks

MichaelG.

[JasonBModerator @jasonb]

"Spalled" is the word

Short of cutting them out and replacing I can't think of anything that will look like brick, all the epoxy repair mortars are not designed to look nice. Even then the frost can still get at the moisture in the brick and just spall off another layer complete with the epoxy.

[BufferParticipant @buffer]

In my experience this happens because the mortar is harder than the brick. I have scraped out bricks and turned then around. This normally happens on stone houses and churches that were built with lime and then repointed in cement.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 11/07/2021 19:09:45:

"Spalled" is the word

Short of cutting them out and replacing I can't think of anything that will look like brick, all the epoxy repair mortars are not designed to look nice. Even then the frost can still get at the moisture in the brick and just spall off another layer complete with the epoxy.

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Just what I didn’t want to hear, Jason … but thanks !

MichaelG.

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So … my new word for the day: https://www.heritage-house.org/stuff-about-old-buildings/brick-and-stone/brickwork-spalling.html

’though actually I think the cause of my problem is simpler than described there … We bought a rubbish batch of bricks.

Edited By Michael Gilligan on 11/07/2021 19:29:51

[garyParticipant @gary44937]

render or roughcast the wall is an option if you have a good coping on the wall to prevent water getting in.

[BufferParticipant @buffer]

No it's just a rubbish choice of mortar.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Buffer on 11/07/2021 19:28:41:

No it's just a rubbish choice of mortar.

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Sorry, Buffer … I have to disagree

I have a pile of left-overs, and many of them are just breaking up [no mortar involved]
They appear to have been over-baked, and I’m very suspicious of that black interior.

MichaelG.

[Bob WorsleyParticipant @bobworsley31976]

There is a 20 year old estate in the village, and lots of the bricks are spalling. But only on the walls, none on the houses. These are engineering bricks so unlikely to be softer than the mortar.

Having watched the problem develop over the years, something useful from a dog walk, I think it is the damp getting in the wall. But, we have had hardly any frosty days for years, not this winter, and the bricks still spall so not certain of the reason. The worst affected bricks are the ones on their sides at the top of the wall.

Provided the wall is a brick thick then unlikely to be a safety issue? Just leave them.

[BufferParticipant @buffer]

It even says it in your link the mortar has to be softer than the brick.

[HOWARDTParticipant @howardt]

Time consuming probably but could you cut out the face of the brick and insert a new facing.

[EmgeeParticipant @emgee]

Michael

If it were my garden wall I wouldn't be too concerned, that wall may continue to have spalling bricks showing the black interior, just look on it as decorative features.
It's not weakening the structure, the wall will remain for many more years.

Emgee

[Michael GilliganParticipant @michaelgilligan61133]

Here is the end of the wall … with good bricks and bad bricks:

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Now one from the stock of spares [which has never seen mortar] :

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and that same brick after dropping it from waist height, onto the tarmac :

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and rearranged, for artistic effect :

MichaelG.

Edited By Michael Gilligan on 11/07/2021 20:17:45

[Phil WhitleyParticipant @philwhitley94135]

Bad bricks, easiest and best is to cut the whole brick out and replace them, nowhere near as difficult as it sounds, then clean out the hole, put a mortar bed in, butter one end, pop the brick in, and point up. Did a lot of this on my workshop refurb. The only problem will be getting good bricks that are a reasonable match!

Phil

[GeorgineerParticipant @georgineer]

I'm not a brickologist, but wonder if these are clamp-fired bricks. The clay is mixed with coke or other combustible material, the bricks are assembled into a 'clamp' and fired, and the combustible stuff burns away, leaving a finished brick. One of Dad's friends, Noel Pycroft, used to make bricks this way on Hayling Island. This is different from kiln-firing where the clay bricks are heated in an oven.

Looking at your bricks, the light colour of the outside and the black interior make me suspect that they are clamp bricks which have been fired too quickly and at too high a temperature, leaving the middle unburned and soft. That's much the same effect as barbecuing chicken legs too quickly, where you get burned skin on the outside and raw meat in the middle.

It wouldn't solve anything, but my sense of curiosity would lead me to heat up a sample of the black part and see if it can be made more brick-like.

Is there any prospect of taking this up with the supplier or maker of the bricks?

George B.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Georgineer on 11/07/2021 21:48:40:

I'm not a brickologist, but wonder if these are clamp-fired bricks. The clay is mixed with coke or other combustible material, the bricks are assembled into a 'clamp' and fired, and the combustible stuff burns away, leaving a finished brick. One of Dad's friends, Noel Pycroft, used to make bricks this way on Hayling Island. This is different from kiln-firing where the clay bricks are heated in an oven.

Looking at your bricks, the light colour of the outside and the black interior make me suspect that they are clamp bricks which have been fired too quickly and at too high a temperature, leaving the middle unburned and soft. That's much the same effect as barbecuing chicken legs too quickly, where you get burned skin on the outside and raw meat in the middle.

It wouldn't solve anything, but my sense of curiosity would lead me to heat up a sample of the black part and see if it can be made more brick-like.

Is there any prospect of taking this up with the supplier or maker of the bricks?

George B.

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I will get a gas torch on the black stuff, George, and see what happens

… but it actually appears to be brittle.

Unlikely to get much joy from the supplier after all this time, but I may pop over to see them.

MichaelG.

[pgk pgkParticipant @pgkpgk17461]

I'd wonder if that was claimable on insurance.
If not then I would have a go at cutting out the detects and replacing with something reliable even i it didn't match.

pgk

[duncan webster 1Participant @duncanwebster1]

There are various grades of brick, classified by frost proof ness. see bricks (despite the same name, I have nothing to do with the brick company!) Not that this helps now. Your only answer is to dig the blown ones out and replace with better bricks. This might look a right mess unless you can get something that matches, but as others have said it's not technically that difficult. Not getting mortar all over the face of the brick is the skilled bit

I think the strength of the mortar is more to do with accommodating slight movement of the foundations, if the mortar is weaker than the bricks the mortar cracks and you can remedy it by pointing, if the other way round the bricks crack. as you have said some bricks have blown without seeing any mortar

[JasonBModerator @jasonb]

I'd say they are "overburns" which are often sold off cheaply and used in less critical situations such as garden walls.

Commons are not that good in exposed situations to start with and the overburning will make things worse, water gets in, freezes and spalls the face off.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 12/07/2021 06:51:34:

I'd say they are "overburns" which are often sold off cheaply and used in less critical situations such as garden walls.

Commons are not that good in exposed situations to start with and the overburning will make things worse, water gets in, freezes and spalls the face off.

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Which is, I regret, pretty much where we started … except that I wrote ‘blown’

Thanks everyone … The only relief is that my workshop [which is cavity-walled, with blocks inside and these outside], seems to be surviving O.K. … it’s “only” the solid walls that have suffered.

Presumably the workshop roof keeps them from getting soaked, and the cavity is letting them ‘breathe’

Many expensive and distressing lessons have been learned on this project

MichaelG.

[Chris Evans 6Participant @chrisevans6]

Lots of spalled bricks on my house built in 1860. Builder suggested I treat them with "Thompsons water seal" to prevent damp getting in and making them worse. I haven't bothered, the house will see me out.

[Dave HalfordParticipant @davehalford22513]

Michael,

I used to live in a 30's house which had that issue beneath the damp proof course. The front garden wall was similarly affected with some good bricks.

I used the surviving 20% good bricks from garden wall to replace the house ones, you can chisel the old ones out if bad enough. Otherwise it's a filthy angle grinder job.

If your spares pile has any undamaged ones they should be good, but you need either semi engineering bricks for the top of a wall or shaped capping of some kind.

It might pay to leave it another winter to expose the full extent of the damage and buy any replacements after they a have stood in the yard and had a good frost.

[PeroParticipant @pero]

Hi Michael

I am not sure how many bricks you have to deal with but if there are a lot can I suggest the Arbortech Allsaw for the removal process. I say a lot as the tool is rather expensive. It is however specifically designed for the job ( removal of mortar from between bricks ) and is a lot safer and cleaner than the use of an angle grinder. I have had one for some years, it is not used often but does the job when called on. The company ( Arbortech ) is Australian. They have quite a good website and I believe they have UK distributors for all of their products.

Best of luck with the project.

Pero

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Pero … BUT

Having inspected the free-standing wall that separates our drive from the neighbour, I am almost certain that several courses will need to come off completely, and it may even be better to have the whole thing rebuilt

I originally intended to put a roof between this and the House, to become a CarPort, and am currently somewhat relieved that I have’t yet done that. [grateful for small mercies]

Roughly … in the upper half of the wall [which is, of course, exposed to the wind and weather] there are perhaps only 10% of the Scotch Commons which do not have some visible cracking ! … it can only get worse.

MichaelG.

[PeroParticipant @pero]

Hi Michael

Sounds like full replacement would be the best option, especially if you are planning to use it to support a roof.

On the plus side, it sounds as though demolition should not pose too much of a problem!

Best of luck.

Pero

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