Chimney breast sealed. How long till damp?

Davewils82

We're part way through having the old fireplace in our victorian terrace house refurbished. As we're not using it as a fireplace anymore we've had it plaster boarded to make a feature space.

The plan was to leave a vent in the top to stop any damp buildup but the builder has gone AWOL half way through the job.

How long can I safely wait before I need to get a vent in there? (the damp in the first photo is just the plaster drying) 

grumbler

Possibly, never - with a good chimney and a good chimney cap.

Nifty_Purse

It's a Victorian property so the chimney has been exposed to decades of coal fire use. The chimney will be lined with a layer of soot even if it has been thoroughly swept. Soot is hygroscopic (it attracts water from the air). This is why chimneys are at risk of damp decades after any use as an open fire. 

You've already got water introduced to the room from the new plasterwork.
You need to make sure you have a good chimney cowl to make sure no rain is able to come down into the chimney from the top.
You do need the permanent ventilation of a vent. 

Impossible to say how long it will be before there is a problem. But the more moisture = the quicker it will be.

However, if gypsum plaster has been used, damp is likely to be a problem since it won't allow moisture inside the chimney to evaporate out through it.
Victorian houses are/should be lime plastered so that moisture is not trapped inside the brickwork causing damp patches and undermining plaster and paintwork.

youth_leader

I agree with Nifty-Purse, sorry to see your person used modern plaster.  

TELLIT01

If the fire is just blocked by plasterboard attached to a timber frame it should be possible to cut an opening into it and cover it with a grille.

Davewils82

TELLIT01 said:

If the fire is just blocked by plasterboard attached to a timber frame it should be possible to cut an opening into it and cover it with a grille.

This is what I'm hoping. Just wondering if I have weeks/months to do this or just days!

Nifty_Purse

Davewils82 said:

TELLIT01 said:

If the fire is just blocked by plasterboard attached to a timber frame it should be possible to cut an opening into it and cover it with a grille.

This is what I'm hoping. Just wondering if I have weeks/months to do this or just days!

You do have weeks/couple of months to do it. Damp builds up gradually over months/years. It won't be dramatic. Just don't forget to do it or it will ruin your decorating.

m0t

I had one of my fireplaces boarded and plastered  6 years ago, it has no cowl or vent and we've never had visible damp. House was built in the 1920s.

I'd expect you to have a fair chunk of time to get it sorted.