cavity wall full of wet sand

toejumper

please bare with me probably a stupid question. removed some units out of the kitchen to find the wall is damp. dh has removed a few bricks and the rock wool is wet through i put my hand further down to find wet sand and loads of old bits of brick, surely there shouldn't be any wet sand and it must be sat ontop of the dpc membrane.

Wookey

Shouldn't be anything in the cavity other than the insulation, it may just be a few bits of rubble that have fallen down from a hole where a pipe has been taken thru the wall, if your bathroom is above and it has waste pipework going thru the wall then its the most likely culprit. Remove what you can and see if the wall drys up.

27col

There should not be anything in the cavity except insulation. The rubble will not have sat on the dpc but it sounds as if it has bridged the cavity. Do what Wookey says and clear out as much as you can.

toejumper

Thanks tried to get most of it out with the hoover. think we might have to take a brick out further down. lets hope this will stop the damp looks like its been there for some time.

David_Aldred

Hi toejumper,
You might want to check the level of the damp proof course (dpc) in both the inner and outer leaf of the cavity wall as they may be at different heights up the wall and you need to ensure you remove all debris to below the level of the lowest dpc. Also check the dpc does not protrude excessively into the cavity of the wall as it will often act as a ledge if this is the case directing moisture inwards.

If you take bricks out externally to clear the cavity of debris put bricks back afterwards and do not be tempted to put air bricks back instead which some people do, as such air bricks would create a cold spot on the wall prone to condensation.

Make good insulation disturbed but be mindful the rate of drying down is only at best around 25mm wall thickness per calender month so it will be some time before you should expect the masonry to have dried down. Also bear in mind if the cavity has been compromised for some time, then salt could have migrated into the plaster and if this has happened the plaster may not dry down and will need patch replacement to a specification able to hold salts back within the wall. Hope this helps, kindest regards, David Aldred Independent damp and timber surveyor

Mankysteve

my parent ended up with a bad dry rot problem from rubble drooped down between the cavity. Make sure its sorted if you have got a problem but on a new house this shouldn't be a problem

toejumper

David_Aldred wrote: »

Hi toejumper,
You might want to check the level of the damp proof course (dpc) in both the inner and outer leaf of the cavity wall as they may be at different heights up the wall and you need to ensure you remove all debris to below the level of the lowest dpc. Also check the dpc does not protrude excessively into the cavity of the wall as it will often act as a ledge if this is the case directing moisture inwards.

If you take bricks out externally to clear the cavity of debris put bricks back afterwards and do not be tempted to put air bricks back instead which some people do, as such air bricks would create a cold spot on the wall prone to condensation.

Make good insulation disturbed but be mindful the rate of drying down is only at best around 25mm wall thickness per calender month so it will be some time before you should expect the masonry to have dried down. Also bear in mind if the cavity has been compromised for some time, then salt could have migrated into the plaster and if this has happened the plaster may not dry down and will need patch replacement to a specification able to hold salts back within the wall. Hope this helps, kindest regards, David Aldred Independent damp and timber surveyor

Thanks have taken a full bucket of wet sand and rubble out of the cavity. dh has taken the plaster off the wall and there's loads of salt. have put the camera down the cavity to see what else is down there. found a large bottle brush 2 black cups and a carrier bag, seems as if some couldn't find a bin and shuved it down the cavity, theres also a air brick were the damp seems to be, should we block it up and put another one some were else. dont want to block air bricks if its going to cause problems with the floor boarding. have allready removed 1 air brick when the extension was built. Thanks steph

Mankysteve

I would revove the ir brick clean behind it and reinstate.

David_Aldred

Hi toejumper,
It is important that air bricks venting beneath suspended timber floors to remove moisture laden from sub floor voids are not blocked / replaced with bricks but are ducted (think tubed) often with slate or some other type of material to make an effective duct all the way through the depth of the cavity wall from outside to the sub floor void.

Sometimes vent bricks are simply fitted to vent the cavity of the wall in effort to remove moisture laden air from the cavity (you may sometimes see such at high level) but as I said in my ealier post this can be a bit of a two edged sword as it tends to create a cold spot on the internal face of the wall and there should be enough backgroudn ventilation within a cavity without providing specific vent bricks to achieve this function.

Just to complicate matters some vent bricks in older houses meant to vent the sub floor void beneath suspended timber ground floors are not always tubed through the cavity wall but simply rely on bricks being knocked out in the inner leaf of the cavity wall somewhere adjacent to where the vent brick is seen externally. Again where this is found ideally the set up should be changed to having the vents tubed all the way through the cavity wall so it can do its job effectively rather than simply vent the cavity. If the vents externally are higher than the sub floor void then periscope ducts can be bought from builder's merchants. Hope this has not confused you, kindest regards David Aldred Independent damp and timber surveyor

toejumper

Thanks David i really appreciate your advice with this, the builder came yesterday and has had a look he seems to think its condensation problem. the air brick is on a wall that get weather beaten it get all the rain and wind etc. what he suggested is to block the air brick up and put vents on the wall but on the inside under the flooring so it will still get air into the cavity but not cold or damp air from the outside. but i would still like to put another air vent in but on another wall which is more sheltered from the weather. i am a little confused on which venting you mean. the house is about 70 yrs old. this is what we have done so far

cleaned most of the debris from the cavity
removed all the wet rock wool to where we can reach
re pointed the outside with cement to seal any cracks etc
painted the outside wall with weather seal paint
have also ordered some dpc cream this one http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=150405675971&ssPageName=STRK:MEWAX:IT

Thanks Steph

ormus

suspended floors must have air bricks fitted below the DPC.
cavity walls do somtimes have rubble/rubbish inside them. some brickies were not too careful in their workmanship. also others put things down there and no one notices. or cares.
ive seen many problem cases of partially blocked cavities.