damp - cavity wall bridged

downshifted

We are hoping to buy a bungalow - the survey has revealed some damp caused by the ground level being too close to the damp course and possibly the cavity wall being bridged by old fallen debris

We have had a quote for sorting this out which seems very reasonable - but how exactly will they check for and remove the debris? We could change the ground level ourselves, but we couldn't go poking around in the cavity walls to remove debris - could we?

Many thanks in advance for any advice

downshifted

Kiran

They will drill a hole through your wall, normally on a mortar line so it can be patched easily afterwards, and use a laborascope (sp?) Think key hole surgery camera. They will then be able to see iside the cavity and identify any debris that may be in the wall

downshifted

I have now discovered that they had megafoam cavity wall insulation many years ago - will this make a difference to the cause of the damp/ability to view the cavity wall?

Gizmosmum_2

downshifted wrote: »

We are hoping to buy a bungalow - the survey has revealed some damp caused by the ground level being too close to the damp course and possibly the cavity wall being bridged by old fallen debris

We have had a quote for sorting this out which seems very reasonable - but how exactly will they check for and remove the debris? We could change the ground level ourselves, but we couldn't go poking around in the cavity walls to remove debris - could we?

Many thanks in advance for any advice

downshifted

Might be worth seeing if the current owners have a CIGA guarantee - usually issued when cavity installed, it might cover the cost if the installation is at fault.

David_Aldred

Hi - I think the original megafoam company may no longer be trading but this is unconfirmed. In my experience cavity wall insulation can in some situations certainly compound dampness problems to a property and some clients have had to have it removed in order to resolve the problem though there are many cases where the installation was without visible problem. Please consider reading my previous posts on this forum regarding problematic cavity wall insulation, cavity wall ties and dampness which may be of assistance with background information upon the matter. Kindest regards, David Aldred Independent damp and timber surveyor

downshifted

Thank you for your comments

They didn't pay for the guarantee anyway (we have found lots of paperwork left in the house now we have completed) so Megafoam would not be interested even if they do still exist

We have had some other builders look at the house now and they agree the path is too high, also there is some run off probably coming from the next door property and they say the run of guttering on that side of the bungalow is very long - there used to be a downpipe half way along which you can see has been removed, probably when they had the extension done.

We move in tomorrow so will be able to keep a close eye on it for a few days - while lowering the path (well, removing the closest run of block paving and replacing it with gravel or similar)

David Aldred - I will certainly look at your past posts and come back with an update in due course

Cheers - downshifted

David_Aldred

When asking the builder to lower the paths they should where possible be 150mm below the level of the damp proof course (dpc) to stop rain bouncing off the surrounding ground and bridging the dpc, plus any debris blowing and accumulating next to house walls will not bridge the dpc if paths are some way below the dpc. However there are seperate dpc's to inner and outer leaves of brickwork to the cavity wall so if you think about it if the cavity is clear the outside brickwork / dpc should be able to do what it wants to some degree without upsetting the dpc to the inner leaf of the cavity wall as this is the principle of the cavity wall construction.

The lowered paths should slope down and away from the property rather than towards it and discharge into rainwater gullies away form the house. Where paths cannot be lowered you may have a builder recommending to you to excavate a trench next to the house and backfill with stone chippings (sometimes called a french drain) as an alternative. This is not something I recommend as it simply acts as a sump collecting rainwater from surrounding ground and allowing it to bear against house walls where it may permeate sub floor voids making dampness worse instead of better. A preferred alternative under such circumstances would be to lay a modular drain trench system such as Aco or similar with sealed joints. If you have never seen this type of drain look on garage forecourts for a long galvanised line of grid beneath which is the modular drain trench system and these should be available from good builders merchants.

When removing the debris from the cavity remove it to well below the level of the lowest dpc which is likely but not always lower in the inner leaf opf brickwork than it is in the outer leaf of brickwork to the cavity wall especially where suspended timber floors are present as the dpc is usually below the level of the floor joist in order to give it some protection from rising dampness.

You can remove the debris by making yourself a little rake that you can drag along the cavity but it is likley you will need to remove bricks about 900mm centres. Ensure you put bricks back to match the existing elevation and do not be tempted to put air bricks back as an alternative which many builders do. The reason for not putting air bricks back is it will tend to create a cold spot on the internal leaf of brickwork prone to condensation.

If solid floors are present then weep joints to the external leaf of the cavity wall at its base at max 900mm centres will help to drain condensate / penetrating dampness from the cavity within the wall outwards before it is tempted to migrate internally. These weep joints should have insect mesh / weather protection sleeves available from builder's merchants.

Remember the rate of drying down is slow and at best 25mm wall thickness per calender month is the best that can be hoped for once moisture sources are resolved.

If the floors are suspended timber check the condition of the floor joist ends which if built into the external walls that are damp may have suffered as a result. Good sub floor ventilation ducted all the way through the depth of the cavity wall will assist with preventing further decay and boron paste to timbers considered at risk during the drying down phase may help too.

If floors are solid check the floor / wall joint to ensure there is not a gap at this point where dampness may be emerging from. If this is the case sealing of the floor / wall joint may be required ensuring timber skirting is isolated from the dampness.

When debris has been compromising the cavity of the wall for some time the dampness resulting and evaporating from the wall internally may have brought with it contaminates such as salts that could build up within the plaster thereby degrading it such that it will not recover. If this is the case the plaster will need replacement to an appropriate specification that will hold salts back within the wall. Remedial treatment product manufacturers can help advise on appropriate plaster specifications. Alternatively there are dry lining systems that can be used such as Oldroyd, Platon, Delta etc which again are available from builder's merchants or through remedial treatment product manufacturer's such as Safeguard, Wykamol, Sovereign etc.

If re-plastering and floors are solid ensure the plaster is kept 25mm from the floor / wall joint.

Checking the condition of the cavity wall insulation during prolonged cold wet weather will give an idea of whether it is becoming wet and whether this will be an issue contributing to the problem. Other factors can be hard dense cement renders, cement mortar re-pointing and painted walls which can restrict evaporation outwards comapred to how the property was originally designed to function as a breathable structure. If the bricks are wetter they are colder and if they are colder they are more prone to condensation such that a downward spiral of dampness can occur that will sustain the problem during more fravourable weather. Indeed the sun shining upon such damp walls can actually drive the moisture inwards. While doing all of this also check the condition of the cavity wall ties which may have suffered accelerated corrosion as a result of the issues discussed. Not a complete list of things to have in mind but hope this helps, kindest regards David Aldred Independent damp and timber surveyor

downshifted

Thank you so much David - what a lot to think about while we unpack the boxes and get used to our new surroundings - I very much appreciate your input and will report back idc

downshifted

An update :-) and 2 more questions please

The path has been lowered. We had the cavity wall raked out during a long dry and sunny period. The insulation was damp - the foam oozed moisture when squeezed hard. There wasn't much else in there. It was particularly wet where a leaky gutter had been left pouring rain down on the side of the house while it was empty all last winter (according to our neighbour)

Inside it doesn't feel or smell damp, and there are no marks on walls and no signs of salts on the walls. We have put bits of vinyl underneath certain pieces of heavy furniture and they do appear to show damp marks where the weight presses down. There has been some kind of growth between floor tiles - sort of yellow and crumbly - we have removed the tiles. We had our surveyor look at it - he didn't recognise it. We have bought a small damp meter and get readings of between .4% and .7% on the affected walls and higher on the floor. We don't really know what that means but plan to measure it over time in the hope it decreases!

Meanwhile - am I right to be worried that the floor may be damper than the walls and can I do anything more at this stage? Also will a dehumidifier help it to dry more quickly?

Many thanks

downshifted

David_Aldred

Hi downshifted,
With regard to your damp meter and areas drying down you are wanting the readings of the suspect areas to reduce in value such that they are similar to the known areas that are without fault if the plaster is of the same type in both areas such that it is not so much the value of the readings but the pattern of them which is of primary interest when used on walls.

If the floors are solid and you are wanting to know if they are acceptably dry you could try the following:

Choose an area of th efloor you wish to sample and that has had the tiles removed / free of floor coverings for at least around 72 hours. Then uUsing a clear sheet of polythene duct tape a square of the polythene to the floor (about 18" / 450mm square will usually do) with a clothes peg stood up inside it in the middle such that it makes a pyramid shape with a void inside. Ensure the polythene is fully sealed to the floor / is without any holes to it so there is no chance of air escaping / leaking. Inside this also put a hygrometer that will measure relative humidty and leave it for at least 72 hours. After this time if the floor itself is chronically damp you may see droplets of moisture to the inside of the polythene sheeting but in any case look at the value of the hygrometer. For moisture sensitive floor finishes you are wanting to see values of less than 75%RH. With regard to floors being the last thing to dry down, yes you are correct in that for example a new solid floor within a new property is often the last thing to dry down. Kindest regards, Dave Aldred Independent damp and timber surveyor

downshifted

David - I am sending you a pm. kind regards downshifted