damp

[ken46]

3 years ago i had a garage built in cavity wall filled with rock wall.
coping stones were laid on top with a dpm cavity tray underneath.
since then i have built above removing the coping stones but left the dpm.
i have since noticed that the inside blockwork BELOW the dpm is very wet even to the point of leaving a tide salt mark.
thinking that it might be cr*p on the ties and bridging i removed a few of the internal blocks to reveal nothing.
the damp blocks run the entire 9 metres of the side elevation, i suspect that the dew point is in the centre of the wall as it should be but is condensing on the underneath of the now redundant dpc and soaking the top of the rockwall under it, therefor bridging to the inside blocks.
am i right? and if so the only course of action i can think of is either remove the dpm in stages ie: remove various blocks cut out and replace or
drill air holes in the outside below, near ground level and also just below the original weep holes of the dpm.
im slightly dubious about holes as this may decrease the internall cavity temp and cause a dew point on the inner block causing a bigger problem.
has anybody else had a similar problem? grateful for any advise
thanks.
ken.

 

[Building Contractor]

OK a few questions:

1/ Why did you use a cavity tray to top off when you built your garage?

2/ Where are the weep holes for the tray and are they still there?

3/ If they are still there, which side of the wall are they venting to?


It does sound like you have a ingress of water coming down the inside of your wall and nowhere for it to go

 

[ken46]

thanks for your reply.
the cavity tray was put in about a foot below what was then a parapit wall to the garage.
on the top of the wall was coping stones so it was there in case any rain got in.
when i decided to build above the stones were removed and the bricking continued but the cavity tray was left in as i didnt feel it would do any harm.
the weep holes are still on the outside above the cavity .
Im not sure what u mean about where they are vented to.
presume the outside.
but the damp is definatly below the inside edge of the cavity tray.
cheers
ken

 

[Building Contractor]

What probably has happened is that when you have built on top of the existing wall, in the process of laying bricks and blocks some cement does fall down into the cavity, usually it goes to the bottom, but in this case it will be sitting on the cavity tray. My bet is that the weep holes have become blocked and so any water that is coming into the cavity is becoming trapped and trying to find its way out, that would account for the salt marks as the water is sitting for a while before been absorbed into the wall eventually. You'll have to see if you can un-block them or if the cement is to hard, you will have to remove some bricks and break the cavity tray.

While on the subject you will need to look at why you are having water coming in to start with, probably it was built in the winter months and so the cement beds will have some capillary action, best bet is to seal it with something like Thompson water seal