Hairline cracks in roof plaster on new extension

[duchard]

I have recently had a new ground floor kitchen extension completed and I have noticed two hairline cracks in the roof. These are pretty straight and run upwards from then bottom of the roof to the start of the velux windows. The plaster has been on for about 12 weeks now and I painted over this using water down emulsion and then a couple of normal coats.

Could this be just settlement and I can simply repaint over these cracks or does this sound like a cowboy plaster job?

I have heard it could that the plaster board joins haven't been correctly connected.

Any advice appreciated.

 

[Richard C]

I have recently had a new ground floor kitchen extension completed and I have noticed two hairline cracks in the roof.

I’m a little confused; it’s a new ground floor kitchen extension but the cracks are in the roof! Do you mean ceiling?

These are pretty straight and run upwards from then bottom of the roof to the start of the velux windows. The plaster has been on for about 12 weeks now and I painted over this using water down emulsion and then a couple of normal coats.

So is it a vaulted ceiling as you would get in a loft extension? Are the cracks on the same window or on different windows? A picture may help explain things better & a guide to where/how bad they are.

Could this be just settlement and I can simply repaint over these cracks or does this sound like a cowboy plaster job? I have heard it could that the plaster board joins haven't been correctly connected.

Settlement cracks often appear in new buildings & on conventionally plastered block walls can usually be successfully repaired with filler but straight line cracks in skimmed plasterboard ceilings or dry lined stud walls are not a good sign as it usually indicates a failure along the joint line where 2 boards meet. Unfortunately, once board joint fails/cracks, it’s unlikely you’ll permanently repair it with filler & it will most likely crack again without more aggressive remedial work. As for a cowboy plastering job, there is no way of telling without seeing it, assessing how well it’s been done or if something else has caused it; what’s the finish of the plaster like? Board joint cracks are caused by movement which could be for any number of reasons;

• Movement of the new extension structure; are there other cracks?
• Insufficiently sized or badly fixed timber joists, studs or roof trusses (not sure what you have yet)
• Wet timber used in construction
• Incorrect boarding or badly located plasterboard joints (around windows etc.)
• Boards insufficiently supported particularly along joints
• Insufficient board thickness; 12.5mm are commonly used for both walls & ceilings now
• Too wide a gap left between boards (they should be close butted)
• Joints not or insufficiently tapped
• Insufficient board fixing screws
• Drying out too quickly, usually caused by central heating
• Differential expansion between two adjacent, dissimilar materials

& I’m sure there are a few others.

 

[duchard]

Thanks for your reply Richard.

Yes I meant the ceiling rather than the roof.

Both cracks appear at different places but yet they are symmetrical in their appearance and where they begin and end.

I have since had reply from my builder who assures me this quite normal with the rise in temperature but he is coming to take a look.

The build was done over the recent harsh winter we have had and the cracks have only appeared since these least warmer days so that does tie in. Hopefully this is the case and I can then repaint over maybe..

 

[roughcaster]

As a matter of interest, do these cracks run along the length of the boards ( 8ft), or are they across, where two ends of the board meet,,,, shorter cracks (4ft)?

 

[duchard]

shorter yes about 3 ft

 

[roughcaster]

I've found that skimmed plasterboard will often crack where cut/unbound ends meet, even though the joint has been fibre taped.

 

[duchard]

Is this a simple fix of painting over or more complicated?

 

[roughcaster]

It's not a major problem Duchard, but paint wont fix it on it's own. The best way would be to re-tape over the cracks, after making sure, as our RichC advised, that the board/s are firmly fixed/extra screws,, if required. After taping, let it dry then sand it down with sandpaper. I'd use an old, well worn piece of 120 grit paper. You don't want it to be too rough, as it will scratch the wall. I often use a very fine "180 grit" as well, for sanding smaller, taped patches, guaranteed not to scratch.

 

[Richard C]

I have since had reply from my builder who assures me this quite normal with the rise in temperature

Well he would say that wouldn’t he

but he is coming to take a look.

It’s good that he is but don’t let him fob you off with a load of old bullshite; as RC says, it's not a major problem but a bit of filler & paint alone wont permanently fix it.

I think RC’s thinking may be going in the right direction & it could be unsupported cross joints; the worry is they may be inadequately supported which means it could happen again. You can get away without noggins (cross support between the trusses/joists) when using 12.5mm boards up to around 450mm centres but go much more than that & you should really provide noggins to support the cross joints. Strange the cracks are only 3ft, maybe they used small boards which doesn’t help & is unnecessary unless access is a problem. It’s impossible to analyse what's caused it without a lot more info about what’s underneath it all.

 

[SCUDmcCOY]

i think roughcaster should quit wasting his time on this site and release a book. .the man gives good advice every time.

 

[roughcaster]

Thank you Scudy.

Myself,,,, along with all the other plasterers/builders that offer advice here on the plastering/rendering forum, try to give the best we can, to help folk out.

 

[duchard]

Thanks for your replies.

I will wait to see what my builder says and let you know what I do.