Kitchen designer wants to add bituman to the internal walls - advise?

[jennyreading]

Hi there,

I'm looking for advise please.

I'm getting a new kitchen put in and the builders removed the units yesterday. They've discovered dampness on the wall behind the base units. They advised that the damp issue is mainly a result of the concrete floor not being done correctly; the DPM hasn’t been fitted high enough up the wall which means the water is seeping through the bricks into the kitchen. They want to paint the lower section with bitumen behind all units to solve this issue.

However, I'm not keen as the external walls have masonry paint, so painting the inside with bitumen sounds like it'll just trap the existing moisture within the walls causing further issues down the line.

I've gone back to suggest lime plaster instead of bitumen on the inside, and removing the masonry paint on the external walls. However, they're resistant to it.

Any advice on how I should handle this?

Thank you.

 

[Toby Newell]

Hi there,

I'm looking for advise please.

I'm getting a new kitchen put in and the builders removed the units yesterday. They've discovered dampness on the wall behind the base units. They advised that the damp issue is mainly a result of the concrete floor not being done correctly; the DPM hasn’t been fitted high enough up the wall which means the water is seeping through the bricks into the kitchen. They want to paint the lower section with bitumen behind all units to solve this issue.

However, I'm not keen as the external walls have masonry paint, so painting the inside with bitumen sounds like it'll just trap the existing moisture within the walls causing further issues down the line.

I've gone back to suggest lime plaster instead of bitumen on the inside, and removing the masonry paint on the external walls. However, they're resistant to it.

Any advice on how I should handle this?

Thank you.

View attachment 11832

Dpm goes underneath the floor, ie concrete, I assume that you mean damp proof course that is an impermeable layer fitted in the walls, that is nothing to do with the dpc.

The issue could be they have built up the floor bridging the dpc in this case the floor should be removed.

You are correct in your assesment. The moisture will be trapped, they need to let the rising damp from the bridged dpc evaporate, plastering whether lime of gypsum + a breathable paint + renove paint from exterior. Your operatives are either ignorant, lazy or both. And I don't mean that in a derogatory sense, just a literal one.

 

[a twig]

The easiest solution would be to leave the walls bare behind the cabinets to allow moisture to escape, space the cabinets 50-100mm away from the wall to allow ventilation to facilitate that and then have deeper worktops which would bridge the gap (assuming you have space in the kitchen to do so)

 

[William]

Agree with your own reservations and above advice - bitumen will never 'solve' a damp issue and could potentially have negative consequences.

 

[paulc]

The easiest solution would be to leave the walls bare behind the cabinets to allow moisture to escape, space the cabinets 50-100mm away from the wall to allow ventilation to facilitate that and then have deeper worktops which would bridge the gap (assuming you have space in the kitchen to do so)

Most kitchen units have a 70mm service void behind the back panel, so I don't think there is any real need to pull them away from the wall. Getting air to circulate is going to be a problem regardless, especially if kick strips are being fitted. One answer might be to install a plinth heater plumbed in to the central heating system - I have one in my kitchen, and it does pull a bit of air out from under the units as well as injecting a bit of heat under there.

At the end of the day, it is your kitchen, and you are paying for the work. You have final say on what goes on the walls.

 

[a twig]

Agree re: difficulty in circulating hence suggesting pulling them further forward, you can fit ventilation grilles in the kick plates and likewise to the rear of the boards that close off the end of a run of units.

Heat generated from cooking, ovens, toasters etc and use of extractor hoods usually means there is more air movement that one would think, so it’s just a matter of facilitating that movement.

Certainly not say this is the best method but potentially the easiest in my view.

 

[Zebra]

Is it solid wall or cavity? I don't actually think the bitumen is necessarily a terrible idea in all cases. In modern constructions it's used in some cases: my new below-ground-level side extension has it on the internal side of the external leaf of the cavity, above and below the dpc. However, as you've rightly assessed, what's going to happen then to whatever dampness you've got evaporating into the room now? Is it possible to remove the masonry paint externally?
You don't really want all that moisture evaporating into the room, you really want it evaporating to the outside.

 

[jennyreading]

Dpm goes underneath the floor, ie concrete, I assume that you mean damp proof course that is an impermeable layer fitted in the walls, that is nothing to do with the dpc.

The issue could be they have built up the floor bridging the dpc in this case the floor should be removed.

You are correct in your assesment. The moisture will be trapped, they need to let the rising damp from the bridged dpc evaporate, plastering whether lime of gypsum + a breathable paint + renove paint from exterior. Your operatives are either ignorant, lazy or both. And I don't mean that in a derogatory sense, just a literal one.

It’s definitely a DPM. I’ve reattached a photo and I can see a bit of plastic sheet poking out the sides of the floor.

Will definitely look at getting the exterior paint removed.

Thank you.

 

[jennyreading]

Is it solid wall or cavity? I don't actually think the bitumen is necessarily a terrible idea in all cases. In modern constructions it's used in some cases: my new below-ground-level side extension has it on the internal side of the external leaf of the cavity, above and below the dpc. However, as you've rightly assessed, what's going to happen then to whatever dampness you've got evaporating into the room now? Is it possible to remove the masonry paint externally?
You don't really want all that moisture evaporating into the room, you really want it evaporating to the outside.

It’s a solid wall.

We asked the question to our kitchen designer about the existing damp and he’s saying the exterior paint is probably not proper masonry paint so water will just escape from the bricks outside. I’m not sure I believe it as even the cheap exterior paint will likely be polymer-based and therefore not breathable.

So we’ll definitely be looking at getting the exterior paint removed at the very least.

 

[jennyreading]

Agree re: difficulty in circulating hence suggesting pulling them further forward, you can fit ventilation grilles in the kick plates and likewise to the rear of the boards that close off the end of a run of units.

Heat generated from cooking, ovens, toasters etc and use of extractor hoods usually means there is more air movement that one would think, so it’s just a matter of facilitating that movement.

Certainly not say this is the best method but potentially the easiest in my view.

Good idea regarding vents - will suggest that. Thank you.

 

[Toby Newell]

It’s definitely a DPM. I’ve reattached a photo and I can see a bit of plastic sheet poking out the sides of the floor.

Will definitely look at getting the exterior paint removed.

Thank you.

View attachment 11837

Ok. Slightly confused, the usual problem is that the dpm is too high which allows the slab to bridge the dpc, the dpm is normally below the dpc.

The common sense consensus appears to be to let the rising damp expire via the outside by exposing the brick. As has been said, if you have an effective dpm then a waterproof coating on the interior is not always bad if the exterior can breathe.

There are relatively few scenerios where an impermeable exterior coating is desirable, one being when you have a South or South West facing wall that is exposed and / or at elevation which recieves a disproportionate amount of sideways precipitation.

 

[Zebra]

Is there even a DPC?