We've had a new porch & door fitted recently but we noticed the other day
that the varnish on the sill beneath the door develops a white "bloom" when
it gets wet.

https://www.dropbox.com/s/rp2xi7zjb7...2008.jpeg?dl=1

What's causing this? Is it a problem?

Tim

On 19/02/2016 08:25, Chris Hogg wrote:
On Thu, 18 Feb 2016 21:17:31 -0000 (UTC), Tim+
wrote:

We've had a new porch & door fitted recently but we noticed the other day
that the varnish on the sill beneath the door develops a white "bloom" when
it gets wet.

https://www.dropbox.com/s/rp2xi7zjb7...2008.jpeg?dl=1

What's causing this? Is it a problem?

Tim

This is rather speculative, because I don't really know, but IME it
happens on new varnish that hasn't yet fully polymerised and hardened,
and is still a bit 'green', even though superficially 'dry'. It seems
that the varnish is still capable of absorbing water and forming a
sort of emulsion within the varnish layer, resulting in the whitish
spots seen in your photo. It's obviously reversible, as the effect
disappears when the water eventually dries. The effect seems to become
less over time (weeks/months), I presume as the varnish finally
hardens completely. I doubt that it's a problem.

I would tend to concur... I presume it was a water borne finish? It
ought to cure fully, but may have difficulties if it was applied in the
cold and the damp.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:
On 19/02/2016 08:25, Chris Hogg wrote:
On Thu, 18 Feb 2016 21:17:31 -0000 (UTC), Tim+
wrote:

We've had a new porch & door fitted recently but we noticed the other day
that the varnish on the sill beneath the door develops a white "bloom" when
it gets wet.

https://www.dropbox.com/s/rp2xi7zjb7...2008.jpeg?dl=1

What's causing this? Is it a problem?

Tim

This is rather speculative, because I don't really know, but IME it
happens on new varnish that hasn't yet fully polymerised and hardened,
and is still a bit 'green', even though superficially 'dry'. It seems
that the varnish is still capable of absorbing water and forming a
sort of emulsion within the varnish layer, resulting in the whitish
spots seen in your photo. It's obviously reversible, as the effect
disappears when the water eventually dries. The effect seems to become
less over time (weeks/months), I presume as the varnish finally
hardens completely. I doubt that it's a problem.

I would tend to concur... I presume it was a water borne finish? It
ought to cure fully, but may have difficulties if it was applied in the
cold and the damp.



Thanks for the feedback. This concurs with info from the joiners and their
varnish suppliers. I shall stop worrying.

Tim