Filling 5mm cracks to monitor movement

[thanks]

My brick built property has a loft conversion with long 5mm cracks mainly in the corners.

I plan to fill small portions of the cracks at intervals as a way to monitor movement in the medium term while we get on with extensive refurb and extension work, before finishing.

How can I tell if they used Lime plaster?

If they did, I was wondering what to use and seeing that non-hydraulic putty is a lot of fuss and may well shrink while setting, maybe an NHL fuller would be best?

Thoughts and suggestions?

thanks

 

[a twig]

Think you’re slightly back to front - if you want a lime based filler filler, hydraulic lime based products will be more likely to crack due to reduced flexibility.

Various “fat lime” filler products are available - best of lime, Ty Mawr etc all sell them

 

[thanks]

Thanks, but I'm not sure if you understand my purpose. I'm not trying to seal the crack and hide any further movement.

My aim is to detect progressive movement by being able to observe expansion of the existing crack over time. (I could fit gauges to do this but I think this will do the job).

If there's no movement, I don't expect to see the filled sections crack significantly. If there is movement, I want to know how much!

This is not the normal reason for filling a crack obviously (or as I proposed, small lengths spaced along each very long crack).

 

[Cubist]

The root cause of such wide cracks in plaster is shrinkage of the timber frame beneath. Your loft conversion structure, other than the remaining gable triangle, will have been constructed of, typically, 4x2inch structural grade softwoods. When constructed those timbers would still be damp and, with the aid of your heating system, over the years they would have shrunk and in so doing would pull any surface plaster coating apart at the junction with neighbouring timbers to from the observed cracks. This initial movement is unavoidable and close examination of the interior of the cracks may reveal the presence of small broken strands of fibre buried just beneath the skim coat plaster. If found, these are the remnants of the original 'skim tape' used by the plasterer to provide an armature/skeletal structure to from and turn the corner between two walls or wall and ceiling.

It's possible too that earlier attempts to fill these shrinkage gaps have failed as a consequence of the continued and entirely natural movement of the timbers that results from both external and internal factors. The best you may achieve for the future would be to pack the gaps with a wide mesh like material and then force a new filler into the gap and as far as possible through that mesh - but even this may not last forever.

If the loft conversion was installed before say the 1960s theres a good chance the plaster will be lime based but later than that then it's almost certainly gypsum. Regardless, for such gaps as you have there any type of filler will be effective. However, you could perhaps drill a few shallow holes in the plaster and collect the dust from the drill and then add a few drops of white vinegar to the dust to seeif there is any slight fizzing or frothing. If there is then its likely to be a lime plaster but this is not an absolute test.

 

[thanks]

Thanks, so much useful info there. I'm having to learn a lot very fast about all this and will try the vinegar test.

I take your point about causes (useful in themselves) but cracking in the external render under the loft window suggests movement of the brick not just roof timbers.

Hence my priority is to look for any progressive movement, and not yet be exploring cosmetics.

So I must keep returning the thread to that aspect.

Having read how careful you have to be with non hydraulic filler/putty to avoid shrinkage while it dries, (ie spraying several times a day for several days), I am thinking just use a natural hydraulic filler for the time being, and watch what happens over a year. If cracks form but don't grow over time, that's good. Either way, that's what I want to determine.

We have much more to do before worrying about aesthetics (eg asbestos survey, damp, wall insulation, central heating, double glazing, an extension). We're at square one!

Thanks again both of you. I am keeping notes for later.

 

[Cubist]

Whoa, back up a moment. Are the cracks you are referring to 'Outdoors' or internal as Twig and myself assumed by your reference to 'plaster'?

 

[thanks]

The ones in the OP are indoors and I was advised by my surveyor to monitor them, in part because of the crack outside which also needs investigation.

So I've been seeking advice on a suitable filler to provide a simple way to monitor the cracks inside. I'll also be investigating the external cracks at some point.

You may be correct that the timber is responsible for some of the internal cracks - fingers crossed - but I need to establish whether they are progressive in order to home in on the cause.

 

[stuart45]

Do you know the age of the property, when the loft conversion was carried out, and if the work was signed off by Building Control?
Internal and extenal photos would also be useful.

 

[Cubist]

You can improvise a simple gauge to check for movement with two small hooks, a length of strong string and a small weight. Tie the weight to one end of the string, fix one hook into the first wall and tie off the unweighted end of the string, fix the second hook to the other wall and drape the string over it then mark the wall at the lowest point reached by the weight, sit back and watch to see if theres any change over time.

Is any face the exterior of the loft conversion rendered? If not, the problems you have are unrelated and require different treatment. Cracks in exterior render pose the risk of water penetration which the accumulates in the masonry to appear elsewhere as damp problems OR to further weaken/damage the masonry itself. Depending on how extensive the cracks may be and if there is any sign of separation of the render from the masonry, the needed repairs could be minor. As @stuart45 suggests, some photos would be useful was would more detail concerning the age, type and history of the house.

 

[skierhughes]

Why not just measure, take pictures and make notes on the days you do this?
As you aren't worried about cosmetics at this stage you could make the notes on the walls.
Saves worrying about the different movement rates of any filler you use, has the filler shrunk, has the hole grown etc?

 

[thanks]

Thanks everyone. I don't have all the answers or time to go through each reply for the time being but am grateful for all your helpful suggestions and comments.

Today we met a local builder about adding a stone boundary wall and got talking about many things, although not this! He had rebuilt the chimney some years ago and helped his father build the two semis next door.

This has set us thinking about a lot so I'll now make a decision on how to monitor based on all your feedback and begin to focus on other works - there's a lot!

I should correct one thing. I thought the cracking in external render was under the loft window but in fact it's the window on the floor below, so less likely to be related to the loft cracks. Although the builder did point out outward bowing in the gable wall (with those windows) and slight sagging of the pitched roof of the loft. No concern, but some structural movement, as well as any to do with the roof timbers.

Lots of investigating to do!

Thanks again everyone. I feel inexplicably excited, despite his warnings about the cost of the wall, his horrible experience with an architect and the planning department over his own extension (£14k so far and now having to revise and resubmit). I just want to get on and make this house great again. The enthusiasm of the naive!