Advice please on filling crack between brickwork and rendering

[Keefiedee]

We have an old timberframed house which was completely renovated 40 years ago.

The side walls are rendered, and the end walls are brick.

I have a problem with the rendering on one corner in that the fillet between the rendering and the brickwork has come away. See:

and

friendly neighbourhood jobbing builder pointed the crack with lime mortar, but it pretty much all fell out over the winter.

The rendering is about an inch thick, and the piece adjacent to the crack does sound hollow on tapping, but in spite of that seems quite stable and unlikely to fall down for a while yet - I can't get any movement when I try and pull it away from the wall. On the other hand, I can't help wondering if it is imperceptible movement that meant the lime mortat fell off, or if it was a bodged up job!

How would you tackle this? I presume lime mortar is the right thing to use - if so, what proportions? I know PVA is used in these situations - does one it paint onto the rendering/brickwork. If so, does one let it dry before applying the mortar, and/or does one mix it in with the mortar? Presumably it is important to wet throughly before applying mortar even if PVA has been applied. Should I try and filll the crack with anything else before applying mortar, and if so, what. Is there any other kind of mortar that is more flexible and more likely to stay put?

Sorry for all the questions, but this is not (yet) an area of expertise I have developed yet!

TIA

Keith

[Bob Minchin]

I reckon you will always get movement there and any form of rigid filler lime or not, will fall out in time with seasonal movement. Maybe you could inject a high modulus silicone in there and rub some sand into the surface before it cures. With this as a key you might just get masonry paint to stick to it and give a reasonable texture.

Bob

[Keefiedee]

"High modulus silicone" - such as? Link please if possible.

It is not just a question of filling though - there is a need to create a smooth rounded end to the rendering where it meets the brickwork - you will see from the photos that the rendering hasn't come away at the edge all the way down - at the top the is just a crack between the rendering and the brickwork, while lower down the whole edge of the rendering has come away.

Keith

[Jim K]

I'd look at trying to make a "movement joint" here so that it can move without cracking and falling out. ISTR polysulphide sealants used in these circumstances?? you'd need to tidy the render edge and leave a gap say 10/15mm into which you squirt the sealant which then (when set etc) stretches to accomodate the (hopefully seasonal) movement that there appears to be going on in the wall..

Cheers Jim K

[Jim K]

go to google.co.uk

put the words in the box, click the search button - simples....

Jim K

[Keefiedee]

Yes - I can see a "movement joint" is exactly what is required.

Any tips on how to create that? My immediate thought is to fix a thin (5 to 10 mm) piece of wood to the brickwork and then build the render up onto that. But how to stop the render sticking to it so it can be removed to leave the required gap?

Is "high modulus sealant" the same as "ISTR polysulphide sealant"? Found the former on google, but not much of a result with the latter!

Keith

[Keefiedee]

Actually, on looking at it again, the gap is not that thick at all.

What I think I might just need to do is to angle grind the render that has come away to a straight line, then put some sort of tape on the brickwork to stop the render sticking to it, replace the render over the tape without getting it on the brickwork, and when all complete fill the edge between render and brickwork with hign modulus sealant. Would gaffer tape do? Would it actually matter if the render actually stuck to the tape - presumably gaffer tape would accommodate a small amount of movement?

Further thoughts please - does this make sense to those with more experience than myself?.

Keith

[Jim K]

the ISTR is "I seem to recall" so just put the other 2 words in and voila....

Jim K

[Dave Liquorice]

Trim back all the fillet, carefully as you say the render is blown. It will fall off at some point, hit it a bit hard and it might fall of now...

Then repoint with a fairly strong cement mix, 4:1 sand:cement. Might be tempeted to use some sharp sand in the mix (1:1 sharp:building or

1:2 sharp:building) to give a bit of texture by brushing the surface with water when almost set.

Lime mortar is "flexable" but not like a silicone is "flexable". Lime mortarstill cracks but then self heals. I wouldn't use a silicone sealant for the job.

[Keefiedee]

Sorry, I meant how do I go about creating a movement joint?

Keith

[Jim K]

(can you see the evolving self-help based pattern here?;>)

Jim K

[Keefiedee]

advice about movement, or expansion, joints in paving etc., i.e in a horizontal surface, which is quite different to the difficulty I have here which is trying to create a vertical rendering edge that cannot be allowed to adhere to the underlying brickwork because of movement, yet needs to be watertight. It was your very helpful suggestion that I need to create a Wmovement jointW - but in my inexperience I do not know how to create an edge to the render in thin air, as it were, and keep it from adhering to the brickwork underneath. I was wondering whether I needed to build up the render edge using ? expanded metal lath ? with gaffer tape on the back to stop the mortar adhering, but I felt that seems a bit Heath-Robinson-ish and assumed there might be a better way which someone might be able to suggest.

I'm not sure I appreciate this rather patronising comment. I, perhaps mistakenly, thought this newsgroup was a place where the experienced were happy to help and guide the inexperienced. It has certainly been very helpful for me in answering questions in the past that I could perhaps have googled, but googling doesn't allow one to find someone who has had a similar problem and found a good way of dealing with it.

Keith

[Keefiedee]

advice about movement, or expansion, joints in paving etc., i.e in a horizontal surface, which is quite different to the difficulty I have here which is trying to create a vertical rendering edge that cannot be allowed to adhere to the underlying brickwork because of movement, yet needs to be watertight. It was your very helpful suggestion that I need to create a Wmovement jointW - but in my inexperience I do not know how to create an edge to the render in thin air, as it were, and keep it from adhering to the brickwork underneath. I was wondering whether I needed to build up the render edge using ? expanded metal lath ? with gaffer tape on the back to stop the mortar adhering, but I felt that seems a bit Heath-Robinson-ish and assumed there might be a better way which someone might be able to suggest.

I'm not sure I appreciate this rather patronising comment. I, perhaps mistakenly, thought this newsgroup was a place where the experienced were happy to help and guide the inexperienced. It has certainly been very helpful for me in answering questions in the past that I could perhaps have googled, but googling doesn't allow one to find someone who has had a similar problem and found a good way of dealing with it.

Keith

[Keefiedee]

advice about movement, or expansion, joints in paving etc., i.e in a horizontal surface, which is quite different to the difficulty I have here which is trying to create a vertical rendering edge that cannot be allowed to adhere to the underlying brickwork because of movement, yet needs to be watertight. It was your very helpful suggestion that I need to create a Wmovement jointW - but in my inexperience I do not know how to create an edge to the render in thin air, as it were, and keep it from adhering to the brickwork underneath. I was wondering whether I needed to build up the render edge using ? expanded metal lath ? with gaffer tape on the back to stop the mortar adhering, but I felt that seems a bit Heath-Robinson-ish and assumed there might be a better way which someone might be able to suggest.

I'm not sure I appreciate this rather patronising comment. I, perhaps mistakenly, thought this newsgroup was a place where the experienced were happy to help and guide the inexperienced. It has certainly been very helpful for me in answering questions in the past that I could perhaps have googled, but googling doesn't allow one to find someone who has had a similar problem and found a good way of dealing with it.

Keith

[Jim K]

first page of results 9th link down....your call

??so??

Speaking for myself I am more than happy to contribute to person(s) quests for information if I beleive I have thoughts/experience that

*may* be of use. However what is rather soul-destroying is occasional posters who appear (as you appear) to be unwilling to actually put *some of their own* time and effort into helping themselves, rather than just sitting back expecting an *instant solution* to drop in their lap - gratis.

You request help and guidance - and that is what I have offered along with a mechanism for gleaning information *yourself*. If after investigating for *yourself* there are still mysteries - posting back here, I am sure, wll bring positive responses along with discussions as necessary.

"You get out what you put in" is an adage that summarises this resource in my mind - YMMV...

Jim K

[stuart noble]

I'd get myself a bag of B&Q gen purpose mortar. Mix that with a 4 water/

1 pva mixture to a stiff cake consistency, and fill the gap. It's probably just the usual live render issue where it didn't stick to the brickwork from day 1. This can result in a chicken and egg situation where it's the water getting in that causes the movement, so you have to think in terms of stopping it rather than accommodating it. FWIW I have done this kind of thing several times. Don't make it more complicated than it needs to be :-)