Damp remedial advice please

[Skaboy607]

Hi,

First time posting here, so hello and thank you for reading my post and any comments.

• I have lived in this current property for the last 8 years and have always struggled with damp / mould issues in various ways.
• Recently, we decided to repaint our bedroom (bedroom1) and discovered some ruin carpet in a carpet plus a mouldy smell.
• Carpet is ripped out now and bare slab exposed but before we put an engineered wooden floor down I would like to solve the issue as best as I can
• IMPORTANT FACTOR NO.1: I am on a timeline, property is 2 bed, and youngest daughter sleeps in one room, my pregnant wife and I currently sleeping on blow up bed in living room
• IMPORTANT FACTOR NO.2: We will most likely only stay in this property for another 12-18 months

I have drawn up a sketch which hopefully is a good aid with the narrative below.

• Floor is ground floor
• Year of the property is 1880, London location
• I am not sure if bedroom1 is an addition or was always there, would the chimney breast have been on the outside of the building
• Since the carpet has been up, the damp smell has gone and the concrete slab seems dry, weather has been dry since carpet ripped up,
• There would be moisture forming next to the air brick and water pooling - from everything i read i think this air brick is redundant given there is no suspended floor and i think the water pooling is condensation a cold spot
• Have always noticed lots of bugs, googled and determined these to be silverfish which thrive in high RH environments
• Is a concrete floor typical in buildings this age?
• Internal wall looks like a gypsum / cement plaster and i am not sure i see a lime behind, could someone confirm?
• I am thinking to remove internal plaster back to brick up to 1.5m and treat in a way that is breathable. My theory, which i think i read on another post here, is that even if the cause is the subfloor and it is coming through the walls because it can't come through the floor then allowing it to come through the walls (Which it can't currently do) will help.
• From what i have read, the walls need to breath and I could achieve this using a lime plaster but this isn't an option for me because i understand it take 2-3 months to properly dry
  • What alternatives are there?
• Kenwood carried out damp proof injection treatment for the previous owner
  • Because the damp proof injections have already been carried out does this change what the best methods are for a beathable wall?

Thank you,

 

[Toby Newell]

Contrary to romantic notions breathable walls do not always reduce damp problems, in your case they would increase them.

Render was only breathable before the 19th century because lime was the only option, likewise breathable paints were the only option.

Poor people, like my Mum, only washed once a week, in a tin bath infront of an open fire, washing was hung outside and windows were left ajar and doors often left open in summer. Multiple open fires not only heated, their chimneys were also powerful extractor fans, nevertheless she still suffered from pleurisy as a child. Breathability is a middle class ideal for period home owners and makes them feel fuzzy and warm inside. In reality modern living creates a lot more water vapour that condenses on cold surfaces. You should aim to live in a way that the house was designed for. Rural properties and most buildings before 1850 did not have any DPC and thus having breathable walls makes more sense, in your case it's that you have rising damp from a bridged DPC that is trapped by the external render and large sponges of concrete slabs that possibly don't have an effective DPM, if at all.

Portland cement concrete was only widely adopted from the early 20th century so your concrete floors are possibly a later addition.

The issue appears, in part, to be that some dipstick has coated the outside wall with cement render thus bridging your probable original slate DPC.

The long term solution would be to remove the external render and repoint ( it was probably rendered in opposition to a more expensive repointing) thisis irrelevant to you.

First rule of damp club is to heat and ventilate, heat, crack windows and run dehumidifiers.

Avoid hanging washing inside, if you have a dryer, run the exhaust outside, fit extractor fans to kitchen and bathroom, run cooker extractor outside if recirculating.

Your concrete slabs are large sponges, the fact they have a bitumen coating possibly means they have no DPM underneath, remove as much of the old bitumen as you can, apply a levelling screed then apply a liquid DPM.

You should be fine.

The damp treatment may help but can take 6 months to work.

I am assuming the black stuff is bitumen, if it is black mold then remove immediately with a mold cleaner, simple chlorine bleach works but the smell may pervade for weeks afterwards.

 

[Lacan07]

As Toby has indicated at a glance i would say the concrete floors are your main problem.

Looking at your photos there doesn't seem to be any lime plaster on the walls.

My take is if you plan to leave in 12 months then I would do nothing. The damp doesn't look very obvious to me, put the old carpet back and when you come to sell install a cheap new one. The work your considering probably isn't worth the gain.

 

[malcolm]

Chances are the floor has no waterproof sheet underneath. If you use waterproof carpet or underlay then water coming through the floor will be trapped by the carpet and it'll smell musty.

A breathable floor finish would be best. I would have thought laminate floor will trap water underneath, though others would know more about what problems that might cause other than pushing more water towards the walls.

 

[Skaboy607]

Thank you for all the replies, this helps narrow down the remaining questions & solutions. I also noticed that not all the pictures had uploaded from before so I have added these also which show some of problems once realised.

Air brick - remove and block up to remove local cold spot?
Remove bitumen and lay a DPM
Engineered wood floor with thermal insulation - this appears to be breathable so sounds positive
Internal walls - is it necessary to remove the plaster up to height of 1.5m? Plaster seems ok......
External walls - @Toby Newell the external walls have been re-rendered, I can see an additional lip has been put on, see below. current proposal from builder is to remove this and replaster with a breathable material, he mentioned lime, and leave a small gap between floor and plaster (i didn't really understand this bit i'll be honest).

It's London, it's Winter. We open the windows and turn heating on as much as we can and we have a dehumidifier already so I hopefully anything we do before putting the room back together can make small improvements.

Thank you all again

 

[Toby Newell]

Thank you for all the replies, this helps narrow down the remaining questions & solutions. I also noticed that not all the pictures had uploaded from before so I have added these also which show some of problems once realised.

Air brick - remove and block up to remove local cold spot?
Remove bitumen and lay a DPM
Engineered wood floor with thermal insulation - this appears to be breathable so sounds positive
Internal walls - is it necessary to remove the plaster up to height of 1.5m? Plaster seems ok......
External walls - @Toby Newell the external walls have been re-rendered, I can see an additional lip has been put on, see below. current proposal from builder is to remove this and replaster with a breathable material, he mentioned lime, and leave a small gap between floor and plaster (i didn't really understand this bit i'll be honest).

It's London, it's Winter. We open the windows and turn heating on as much as we can and we have a dehumidifier already so I hopefully anything we do before putting the room back together can make small improvements.

Thank you all again

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I'm sorry to learn of your situation, I have lived in several properties with damp, it's not nice.

It looks like a lot of condensation. Try and keep it warm, clean regularly with a mold cleaner, do not block ventilation, you want more not less.

Your cheapest option is to install extractor fans if you don't have them. Not sure it is a good investment to re render the outside. I wouldn't bother with the inside either.

For such a small period of time ventillation, heating and fitting DPMs to the floor would be the smartest bet and give the fastest ROI.

You don't need to remove the bitumin, if the floor is flat and clean you can just put a plastic sheet dpm under your engineered floor, most foam underlays also serve as a dpm. You might as well use both as the plastic sheet if very cheap. I have used Duralay timbermate excell on several jobs, you would need a good foam underlay if not removing bitumin and screeding as the slab appears slightly damaged, this would appear to be your best bet.

If you can remove the skirtings and run the floor under to hide the expansion gap, at the same time you can run the plastic dpm behind the skirting.

The most breathable render is no render, most houses were brick or stone built and rendered afterwards as a cheaper option to repointing. The idea of stopping before the ground is to reduce rising damp. This all seems a bit excessive for one year, your home seems cold with a lot of condensation. More heating can be very expensive but the bill will be cheaper than lime plaster rendering and you will have a higher thermal comfort to boot. If you have to hang washing inside then hang over a radiator, open two windows and place a heater fan ( on low or cold ) near the washing. You need two windows on opposite sides to create a draught, turn up the thermostat when drying clothes.

Spend your money on heating, ventilating and running dehumidifiers, this will be cheaper than any remedial works and be more comforting and healthy for you and your young family. Let the new prospective tennants worry about longer term solutions.

 

[Toby Newell]

Also, I don't want to worry you, and your mold problems don't seem excessive, but compared to a lot of things young parents worry needlessly about, like lead paint for example, mold is reasonably unhealthy, especially for very young or very old people and people with breathing issues, I would clean every week with a mold cleaner, and mop up any visible condensation with a cloth spritzed with mold cleaner. Molds generally don't like bright light, so keeping curtains open in the day time can be helpful.

 

[Skaboy607]

Hi @Toby Newell

Thank you for the posts, though the last one has failed in not worrying me!

The post before was really useful and pretty much where I had got to (with the exception of the air brick); the problem isn't so bad that it is worth the expense if we are going to sell in 12-18 months. I will do exactly as you suggest and lay a DPM plus a thermal underlay.

I was going to pull off the skirting anyways so i did that this morning and found some moisture where the wall meets the ground - just to give you an of the full picture - it was a little moist to the touch and the dust (i think it's dust1) on the back of the skirting board wouldn't do that if it wasnt moist.







Meanwhile in another room, front room with a bay window where i have been too lazy to fix the skirting boards and we also experience some mold, i found the below - water droplets that you can touch.



Thank you

 

[Toby Newell]

Hi @Toby Newell

Thank you for the posts, though the last one has failed in not worrying me!

The post before was really useful and pretty much where I had got to (with the exception of the air brick); the problem isn't so bad that it is worth the expense if we are going to sell in 12-18 months. I will do exactly as you suggest and lay a DPM plus a thermal underlay.

I was going to pull off the skirting anyways so i did that this morning and found some moisture where the wall meets the ground - just to give you an of the full picture - it was a little moist to the touch and the dust (i think it's dust1) on the back of the skirting board wouldn't do that if it wasnt moist.

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Meanwhile in another room, front room with a bay window where i have been too lazy to fix the skirting boards and we also experience some mold, i found the below - water droplets that you can touch.

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Thank you

You are welcome, and if you are a little worried then that is good. Looks like black mold and not good especially for very young children or babies as it can sensitise them and cause asthma.

I would paint those areas with a liquid dpm, or to do it properly, strip the first foot and apply a waterproof plaster, its breathable but keeps the worst of the moisture out. You could literally strip the paint and apply a brushed on tanking medium, they are v similar, they contain silicates and form semi breathable waterproof barriers.

Fitting a dpm to the floors up and behind the skirting and then then the thermal / acoustic underlay should be a priority, its quite comfy, if you are careful you can use it whilst you save up for the engineered floor. If you can feel condensation on the foil of the underlay you know you are not heating or ventilating enough.

 

[Skaboy607]

d paint those areas with a liquid dpm, or to do it properly, strip the first foot and apply a waterproof plaster, its breathable but keeps the worst of the moisture out. You could literally strip the paint and apply a brushed on tanking medium, they are v similar, they contain silicates and form semi breathable waterproof barriers

Can you recommend a breathable waterproof plaster please?

I am going to strip the skirting today and get ready for the new underlay and floor.

I had another idea which i think will help.....

I need to temporarily remove the built in wardrobe in order to remove the skirting and and lay the DPM up to those walls to. Otherwise an moisture will be forced to where the wardrobe is which is not what I need! So as I am doing this, i figured around the chimney and any external solid walls which are then closed off by the wardrove i will line with leftover insulation from the floor or some new insulation. That should help reduce the cold on those surfaces?


Thank you

 

[Toby Newell]

Can you recommend a breathable waterproof plaster please?

I am going to strip the skirting today and get ready for the new underlay and floor.

I had another idea which i think will help.....

I need to temporarily remove the built in wardrobe in order to remove the skirting and and lay the DPM up to those walls to. Otherwise an moisture will be forced to where the wardrobe is which is not what I need! So as I am doing this, i figured around the chimney and any external solid walls which are then closed off by the wardrove i will line with leftover insulation from the floor or some new insulation. That should help reduce the cold on those surfaces?
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Thank you

Not necessarily. Any foil backed insulation may condense water on the foil surface. It seems like you have damp at low level.

I would stick to the dpm, heat and ventilation.

I'm not a masonry expert, I deal with wood. There are many similar damp proofing plasters and coatings, they are mostly based on silicate technology.

Sika (British company, also own Everbuild) make a very popular waterproofing additive called Sika 1. The plaster, or slurry is best applied by a professional as it is quite technical, shame we don't have a resident spread or brickie on here.

Seems like a lot of work for a year. You might only need to do 600mm or so, although I think in general people advocate for 1000 or 1200mm unless very damp or below ground .

 

[Skaboy607]

Hi!

Update from me: old plaster removed all the way around and builder has been in with sand/cement/waterproofer on the bare brick and now re-plastered all the walls.

Next step is the floor: builder advises that laying a plastic DPM is going to cause sweating which from some research looks correct.

However, i can't lay any coating whether epoxy or not on top of the bitumen so i am a bit stuck. I did find one Remmers product which can be applied to the concrete slab that has bitumen residue but it is eye wateringly expensive in comparison.

Whilst reading about sweating, and considering the other work that has been completed i wonder whether it could now be considered to install the underlay which has a vapour barrier direct to the slab with wood floor on top?

Thanks

 

[Toby Newell]

Sweating? Please explain. I don't understand. A dpm is (virtually) impervious to water, where is this sweat coming from? You mean condensation on the underside of the dpm, errr, that is the point. And what is the difference between a plastic dmp and a vapour rated underlay? Again, errr,nothing! They are exactly the same except the underlay has some cushioning effect.

You can apply a liquid dpm that is bitumen compatible and then what? At the interface between the concrete and coating, trapped moisture! How is this materially different to a plastic dpm or underlay? Your builder makes no sense.

You mean condensation on the top side of the dpm? There shouldn't be enough space for that! Air movement should be minimal as most of the floor should be touching the underlay / dpm. The more uneven your slab and the cheaper and lighter your top floor the more movement there will be and more tenting and possible gaps. Which is why levelling your slab / applying a thicker liquid dpm and a thicker underlay will reduce this movement and any subsequent gaps.

In your case your concrete slab looks in bad condition, I would advise a thicker underlay or a thicker liquid dpm coating. When I lay floating floors onto concrete slabs I do both, apply a liquid dpm plus a generous thick underlay.

 

[Skaboy607]

Hi!

I think builders making no sense is the main reason I ended up on this forum!

But yes, I believe he means a tenting effect that could happen when moisture is trapped between a plastic DPM sheet and the concrete slab.

I have the underlay you recommended ready to install, just need to wait for the plaster to dry.

Just really not sure which way to go on the floor. No manufacturer will provide a product that can go on the bitumen stained floor except the remmers one (that I have found) and that is £600 in materials.

What I need to establish is whether the £600 remmers solution is warranted or a plastic sheet will suffice. I could put the £600 saved towards a new PVC window (sorry heritage) with trickle vents and a PIV fan.

Thank you