Spalling

[Jonathan]

I've got a terraced house build about 1915 and the brickwork on the outside of the bay window of the bedroom on the second floor is rather badly spalled (either side of the windows towards the bottom). Some bricks have blown their faces off about a centimeter thick.

The previous owner applied some terracotta render of some kind that looks like it's been keeping the water in or something, but I'm not sure. What else causes spalling? Is the fact that it seems to be mostly at the bottom by the windows significant? I wonder if I need to mend my guttering or something?

As to mending them - do I have to do an Arnie and hack out the spalled bricks and replace them? I assume that's the only way. I'd like to get rid of this render while I'm at it, but will that damage the brickwork?

Any tips much appreciated.

Jonathan

[Mike]

One solution would be to remove the render, then re-render with a lime mortar render so the brick damage won't matter too much. But you won't be able to do this now until April at the earliest - lime hates frost.

[bigcat]

"The previous owner applied some terracotta render of some kind that looks like it's been keeping the water in or something, but I'm not sure."

that does tend to damage bricks, but its more often applied after brick damage as a cheap patchup.

"What else causes spalling?"

Water ingress, freezing, render, and inappropriate cleaning methods that strip the brick face off.

"Is the fact that it seems to be mostly at the bottom by the windows significant? I wonder if I need to mend my

guttering or something?"

Probably gutter or the window channeling water there. Lot more common at ground level.

I'd check your drip grooves on the underside of the window sill, mak sure waters not running onto the wall. If theres no groove that might be why.

"As to mending them - do I have to do an Arnie and hack out the spalled

bricks and replace them? I assume that's the only way."

the only decent way, yes. Not difficult if youve got soft bricks, but do take real care not to break other bricks in the process. soft bricks are remarkably weak.

Always take a piece of brick with you to get an exact match, failure to do that is a recipe for a cockup. Patching with bricks that you thought matched but turn out not to will look real bad.

You could also cement the face of the damaged bricks as a patchup, but a) it looks crap b) keep the cement off neighbouring bricks. Lime would be much better for that, and it doesnt matter if it gets onto the sides of the other bricks.

"I'd like to get rid of this render while I'm at it, but will that damage the brickwork?"

Probably. Best move is to ascertain if your bricks are soft or not. If they are, proceeed only with the greatest of care, or youll end up trashing half of them. If you cut the remaining half of a damaged brick with a stanley knife, theyre softies.

Another approach is just to leave the render to fall off in its own time. Very slow though, and its going to look a mess for quite some time.

Dont paint the bricks.

NT

[Jonathan]

Thanks for the good advice. I'll have a look at any water problems first I think, then maybe removing the damaged bricks if soft. I think you're right about the previous owner applying the render to hide something as well - I can see concrete underneath in places. Hmm.

Jonathan

[Mary Fisher]

We have a few bricks on the front of the round bay window near the ground and below the dpc. We haven't worried about it and we don't notice it. Few others could see it because of the planting (not touching the wall).

But in the light of what you said I wonder if it would be useful to re-face the bricks with (exactly matching) resin-based mastic?

Mary

[John Rumm]

Add to that one of the most common ones, repointing of soft bricks with cement based mortar.

[N. Thornton]

From: Mary Fisher ( [e-mail])

Thats where it usually happens, due to damp freezing in the bricks. Resin makes that dampness worse by preventing evaporation from the bricks.

I've never tried refacing bricks, but have only ever heard one thing: it doesnt last.

I'd check the ground levels relative to the dpc, ground should be 6" below it, and if the damage isnt bad enough to affect structural strength, leave it. Or if theyre bad, or an eyesore, replace em.

Cement pointing on old properties is a cause of this: lime pointing allows more water movement and evaporation, cement prevents it somewhat. Also old houses tend to move a bit, cement wont move at all, and is stronger than the brick, so the bricks get damaged. Lime is soft enough not not cause damage, and the lime will crack rather than the brick, which is much preferable. Lime cracks are self healing, it slowly grows hard crystals across the crack by reacting with CO2.

NT

[Mary Fisher]

But it's happening anyway, with nothing preventing evaporation :-)

Nothing lasts :-(

The affected bricks aren't lasting as well as the unaffected ones although neither has had any treatment.

It is. It's only the odd brick, not all of them.

It won't be affecting the structure.

They don't bother us. We're the ones who matter.

Well, what do you mean by 'old'?

I don't think of our house as old because I've known it all my life, it was built in 1937.

Most of the houses here have the spalling, none has been rendered, some have been cement pointed, we mastic pointed ours when we moved in 40 years ago. Others' cement pointing hasn't lasted as long. Lime mortar isn't suitable for our houses, in my opinion - but I'm not an expert. I've only ever seen it used on stone building though. Believe me, if we had a stone built house we'd only have used lime based mortar and pointing.

Thanks for your observations.

Mary

[[news]]

physical errosion (freeze thaw) of imperfectly fired soft bricks is the usual cause of spalling and the best remedy is to chop them out and replace them with sound bricks. the other short term remedy if you are selling the house, is to chop the bricks out and turn them round.

I've done a hundred or so and I've another 50 to do and the best way I've found of getting the bricks out is to drill the mortar with a 6mm x 160mm drill bit right round the brick, as close together as you can get the holes. then do it again on a 45 degree angle to further break apart the mortar and then use a plugging chisel to remove the last bits of the mortar and /then/ use a 4" bolster chisel to joggle the brick loose.

clean out the hole, replace / install new brick and re mortar. leave the pointing 'til you're going to do the whiole wall to ensure uniformity, my rendering bloke said to leave the pointing alltogether if you are rendering to provide a better key.

obviously, if the brick is too far gone you could just drill that into small bits and be done with all the aggro. be warned, it's a drirt, labourios job made all the harder to stomach by the stupid cost of 100 year old red commons.

rendering in this weather is ok if you use the right retardent additives and do it whilst the weather is going to be above 5 degrees for a week. obviously, if you are selling the house and the render starts to degrade in 5 to 10 years, so what :)

RT

[N. Thornton]

From: Mary Fisher ( [e-mail]) message

41b85f3a$0$2656$ [e-mail] Subject: Re: Spalling

Excessive retained damp within bricks is the usual cause of spalling.

Cement pointing, gypsum plaster, cement based renders, and non-porous paint all prevent evaporation. I dont know what kind of mastic youre using but that probably will as well. DPCs prevent evaporation from below the DPC.

High ground levels and blocked underfloor ventilation also cause real problems, in the case of suspended wood floors, which most Victorian houses have.

Leaks from guttering and downpipes, overflowing partially blocked drains, and many forms of damp treatment also make matters worse. So does lack of sufficient heating, and lack of ventilation, often caused by draughtproofiing, installing plastic windows, and blocking chimneys.

Ditto roofing problems such as missing slates or broken gully lead linings, and also sometimes pinholed lead. Also missing flashing or broken fillets can let water in.

Nearly all these problems are routine issues in Victorian houses, and the reasons why damp is a routine problem in such houses. It is nothing to do with bad design or technology, contrary to popular myth, but is simply the result of failure to maintain, plus the fashion for modern works of a nature inappropriate to the type of building.

[Mary Fisher]

We mixed our own compo for pointing, from linseed oil and mastic sand.

But it was only used to re-point, that is to replace the crumbling mortar from between the bricks, it wasn't used on the surface of the bricks so evaporation wasn't prevented from the external and internal faces any more than the original pointing did.

Our house is not Victorian ...

I agree. WE take steps to ensure that those things don't happen.

The fact that spalling occurs in some bricks (just a few) and not all seems to indicate that there's a property of the individual bricks which is different from the rest and has nothing to do with the pointing.

Those are obvious.

Yes, but you were replying to me and I've stated that our house was built in

1937. That makes it VIth Georgian.

Mary

[Andrew Gabriel]

You shouldn't have gypsum plaster in that list. Moisture passes through it very easily. Prolonged contact with moisture will eventually wreck gypsum plaster though.