Gap filler cracking after six months.

[nww1969]

Team.

Moved into a town house 6 months ago and the first thing I did was use either selleys or Bostic gap sealer
on a small say 1mm or less gap on a brick common wall where it joins the cornice.
I did not paint over it as it as it was white same colour as cornice.

So six months later the gap has appeared again where the filler was put.

So have I possibly used to much water in the cloth when I was wiping over it to smooth off and effected
the strength or does this stuff require painting to protect it from moisture in the air or should I now be
looking at a paintable silicon product.

No other cracks through out only were the brick common wall is between the other town house, the other
walls are all gyprock.

Thanks all

Neil.

[Master Splinter]

Your problem is not enough crack to fill.

If your crack was 1mm when filled, and your caulk has 10% elasticity, then if your crack grows by a further 0.2mm it is exceeding the stretching capacity of the caulk by 100%. Even a polyurethane caulk can only cope with about 25% stretch...and 0.25mm is pretty small by most people's measures!

[nww1969]

Your problem is not enough crack to fill.

If your crack was 1mm when filled, and your caulk has 10% elasticity, then if your crack grows by a further 0.2mm it is exceeding the stretching capacity of the caulk by 100%. Even a polyurethane caulk can only cope with about 25% stretch...and 0.25mm is pretty small by most people's measures!

Hmm Makes sense.
So how do I overcome this , increase the crack ??

[Master Splinter]

Essentially, yes. However a 5mm or so line of caulk may be more noticeable than the crack. Can you hide the crack with an overlapping edge detail or something????