Cracks all around new extension. what could be causing it

[platforminc]

Hi All.

I have just completed an extension, timber frame at the top and the original house is brick at the ground floor. About a 2 months ago, I started noticing some cracks in the first floor which is all timber frame + Acrylic coloured render on the exterior.

Now with the very hot weather lately, I did not open the windows on the first floor but I have now done so for cross ventilation etc. I thought the fact that the build is timber frame, just some movement on the timber aspect etc. However to my horror, this week the cracks have all gone onto the ground floor all over the place, which is not timber frame, the ground floor is all brick work. I have cracks all around doors, skirting etc.

Please note that this is a newly decorated house, new skimming, filling, painting etc.

Please see attached pictures and advise on what I can do, I have opened all the windows in the ground floor now for cross ventilation. I closed them all before as the house is empty and dont want to have risk of burgaly etc.

Is there an explanation for the cracks or is there anything that I can do to resolve/prevent ?

By the way, this only started in the last 10 weeks when the weather was getting hotter.

 

[^woody^]

All normal shrinkage.

 

[noseall]

Did you mitre the internal skirting corners or scribe?

 

[^woody^]

Looks like he mighta mitred.

 

[platforminc]

Not sure what you mean, but it you mean how the angles were cut, it was using a mitre saw.

Does that make any difference?

 

[platforminc]

All normal shrinkage.

To fix it, can I just put caulk over it in its current state or use a small filling knife to hack out the face then fill it ?

What kind of caulk?
Will it happen again ?
Does opening the window have any effect?

 

[bernardgreen]

Will it happen again ?

That depends on how much moisture remains in the timber.

Timber needs time to dry out before being cut to size, it can be dried naturally ( seasoning ) by being stored in dry conditions for several months or it can be dried in a kiln

the process is called seasoning because in the good old days timber was loosley stacked for at least a year of seasons

 

[^woody^]

To fix it, can I just put caulk over it in its current state or use a small filling knife to hack out the face then fill it ?

What kind of caulk?
Will it happen again ?
Does opening the window have any effect?

You need to give the extension about 12-18 months to settle down

Internal skirtings are scribed not mitred, for the very reason you are seeing there. It will continue to crack and you will be forever hacking it and filling.

Opening windows produces a cooling breezy effect.

 

[noseall]

Does that make any difference?

Massive. Internal corners should be scribed.

An Idiot on this very forum Called Joe-90 used to insist that internal mitres was the done thing. He was the most clueless diy'er I have ever come across. There is a long thread somewhere in the archives about it.

 

[Notch7]

Every junction you have a crack is plaster to wood, or wood to wood.

Wood shrinks.

It akways happens. In 30 plus degrees it might happen faster

 

[John D v2.0]

I did not know that about internal skirting boards! Learnt something new today

 

[noseall]

Wood shrinks.

Across not along the grain. Even ancient timber retains its length. (ooer missus!)

 

[Notch7]

Massive. Internal corners should be scribed

I hadnt realised it reduced paint cracking.

I guess its logical as shrinkage one side only exposes more skirting as it runs on.

 

[bernardgreen]

Across not along the grain.

The amount a piece of wood will shrink along its length ( longitudinal shrinkage ) is typically 0.05% to 0.25% pf the length depending on specie and moisture content before drying

 

[Notch7]

Across not along the grain. Even ancient timber retains its length. (ooer missus!)

Yes, that is a fair point, although there is more to the story......

Timber shrinks most tangentially, about half radially and a small % longitudinally, say 0.2%-0.3% from green.

As timber shrinks the most tangentially, ie around the growth ring if you look at end grain, All timber will cup in a way that flattens the arc. Thats why its best to lay floorboards smiley face up, so you get a slight bump in the middle and the sides stay tight to the joists.

Timber with non straight grain, for example oak may exhibit quite noticable changes lengthwise because the grain is not parallel to the long edge.