Crack on roughcast rendering

[astraman]

I have a timber frame house where the bottom have is brick and the top half is some sort of treated material with a roughcast render finish.I hav noticed a very fine vertical crack just from underneath the window sill travelling down the way.The crack is very thin but was still wondering if anyone could advise on this as i dont know what to do whether i put some sort of filler in or if something else is needed.
All replies are apppreciated as normal
Thank you.

[buildersmate]

Rendered surfaces on MODERN timberframe houses is achived by attaching vertical battens to the outside of the timber inner skin, then nailing a sheet material to the battens and putting the render subsurface onto that (then final finishing). I suspect that a minor movement in the inner frame structurally has caused minor movement in two or more sheets, which has cracked the joints between two sheets. Timberframes always move a bit as the seasons change.

You can fill it with cement/sand mix and repaint if you wish to, but it is likely to come back again, but I doubt that it will get worse. It is not structurally important as the strength of the structure resides in the timberframe, which is the inner skin.

The bottom half of brick is not structurally attached to the timberframe, by the way - it has its own foundations on which it sits, being tied to the inner skin using stainless-steel brick ties.

That is the normal way modern timberframe is built.

[The Builder]

I'm building an extension for someone at the moment. I use the method BM describes all the time. Actually, I must go and do some... instead of sitting here talking to you lot ;o)

Sand & cement render is applied to expanded metal lath attached to the battens. The first coat merely fills the lath and almost covers it. The second coat should be applied next day while the first is still "green".
Also, coats should be progressively weaker mixes (less cement).

So, a couple of things might have happened.......... either the second coat was applied far too late, or it was too strong a mix.
Your crack will likely be in the second coat. The first one is "reinforced".
It is likely to keep returning. Try mixing some fine sand in with the paint on that area............ or use "Sandtex"

[astraman]

Thanks guys for your input. As its a very fine crack i think i may give the sandtex a go.I was just worried incase this was a major defect and would cause damp etc even though its such a fine crack