Damp concrete floor.

[amfisted]

Afternoon, all.

I live in a detached bungalow, built about 1973. It has concrete floors throughout, all of which are pretty well bone dry. Or so I thought till today.

We've had a persistent problem with mould in one internal corner of our master bedroom. Over the 4 years we've been here it's manifested itself as moisture on the bottom few inches of the wall, along with some visible mould which has till now been easily removed with a proprietary mould killer. I always assumed it was condensation because of its limited nature.

During the last few days the mould has become significantly worse and now appears to have infiltrated beneath the paintwork of the skirting in the area of damp. I lifted the carpet today to have a look. To my dismay the underlay and the floor beneath was pretty wet, with an overpowering smell of mildew. Looks like the previous owners have tried to address the problem because someone has used some form of bitumen paint on the concrete floor, but the moisture appears to be on top of this.

Despite the clue represented by the bitumen, I'm unsure as to whether this is rising damp caused by a failed DPM or condensation. Since having a wood stove fitted I've had problems with condensation in the loft (now dealt with by providing ventilation) and because this bedroom is usually unheated I wonder whether the warm air from the stove output has condensed under the carpet on the cold floor.

I intend to bin the carpet because it stinks of mold, and I'm wondering whether laying insulation over the concrete floor to provide a barrier against damp would be sufficient to protect a new carpet and underlay. Obviously I'd want to avoid digging up the floor and relaying with a new DPM, but if that's the only way forward, well so be it.

Many thanks in advance for any advice, in particular about modern forms of insulation that might be suitable.

 

[amfisted]

Having done a bit more research, it seems that what we need is some sort of permeable membrane which will allow the floor to breathe, rather than covering it with an impermeable membrane such as a polythene sheet. Is this feasible if we intend to lay a carpet on it?

 

[motorbiking]

Do you have any water or central heating pipework buried in the concrete? it may be leaking, particularly given there was a bit of a copper shortage in the early 1970s which meant pipe quality wasn't great.

 

[amfisted]

Thanks for your response.

No pipes that I'm aware of, no. All the CH pipework is surface mounted and routed via the loft space to each rad, and to the best of my knowledge all the water supply pipes are on the other side of the property.

The bottom line, I guess, is that I need to take up the carpet and dispose of it then make a proper inspection of what I'm dealing with. I've read the Wiki entry about laying a liquid DPM, so if that's whats required then we'll just have to put up with a couple of weeks of disruption to get the problem sorted.

Thanks again.

 

[Notch7]

Id be tempted to run a dpm across the floor and up behind the skirting.

I know that involves removing the skirting, butbthen you can chip off a strip of plaster if it goes down to the concrete floor.

I would suggest also laying a new underlay which has a vapour barrier.

 

[amfisted]

Many thanks once more.

When you say to "run a DPM across the floor", do you mean sheet material such as this? https://www.ukflooringdirect.co.uk/...MI_Mzv0tfH3wIV7r3tCh0AjgkNEAQYAiABEgIMPPD_BwE

And would that be carpet underlay with a vapour barrier?

I'll be replacing the skirtings anyhow because although they feel solid, they could well have been compromised by the damp. So they'll be replaced with new wood which I'll treat first. I'll be sure to remove any plaster behind the skirtings.

 

[Notch7]

Id be tempted to apply a liquid dpm.

That way you wont have any issues at the corners.

A decent quality liquid dpm is something like drybase -a damp surveyor recommended it to me

https://www.safeguardeurope.com/products/drybase/drybase-liquid-applied-dpm

A few reviews:
https://www.amazon.co.uk/Drybase-Liquid-Proof-Membrane-Black/dp/B008KMCWNI

 

[amfisted]

Much appreciated again. Hopefully the safeguard will be back in stock with that seller soon, and if not, available elsewhere.

Edit: I've checked and its still in stock and available direct from Safeguard themselves, so once I've taken up the carpet and established that its not condensation which limited to one small area, I'll order. The room area is approx 16 sqm, so I reckon two 5 litre tubs will do for an application of two coats on the accessible floor (there are two fitted wardrobes in the room, but they're well away from the damp area). It also appears to be available from an Ebay seller, though whilst the tub looks exactly the same as the Safeguard product, it isn't advertised as such. I'll ask the seller to confirm that it is the same product.

 

[amfisted]

I've taken the carpet up and as stated above, the floor has been painted with bitumen. I rang Safeguard to check whether its OK to apply Drybase DPM over the bitumen, and not entirely to my surprise they said no, it would either have to be removed or I would have to screed over the top of the bitumen first; and even then there would be no guarantee of a solid base for the DPM.

I've had a go at removing the bitumen with a heat gun and it's obvious that it would take me a month of Sundays to get it off. So I've given up the idea of going to that much trouble and mess, not least because 'er indoors has little tolerance for disruption unless she creates it herself. I reckon my only option is to buy the DPM in sheet form, lay that down over the floor and then carpet over the top. On the positive side, the floor seems dry now that the carpet and underlay have been removed, so I'm starting to think that it is condensation after all.

Any further advice welcome!

 

[amfisted]

This is all new to me, so the following probably sounds like a horrible bodge. But here goes.

Given that the problem appears to be condensation (but I can't be absolutely sure) would there be anything to be gained by laying a damp proof membrane in sheet form over the bitumen painted concrete, followed by insulation boards on top? And underlay/ carpet on top of that?

Standard floor insulation boards appear not to be available in less than 50mm thickness; however, I've found underfloor heating boards at 6mm. Would they be suitable for this task?

Would the above arrangement be likely to do anything to keep both damp and/or condensation at bay?

 

[Notch7]

This is all new to me, so the following probably sounds like a horrible bodge. But here goes.

Given that the problem appears to be condensation (but I can't be absolutely sure) would there be anything to be gained by laying a damp proof membrane in sheet form over the bitumen painted concrete, followed by insulation boards on top? And underlay/ carpet on top of that?

Standard floor insulation boards appear not to be available in less than 50mm thickness; however, I've found underfloor heating boards at 6mm. Would they be suitable for this task?

Would the above arrangement be likely to do anything to keep both damp and/or condensation at bay?

I'm sorry if I've steered in the wrong direction -I hadn't considered the existing bitumen dpm.

I don't about your area, but its been completely dry down here for over a week, so maybe its a bit early to assume it is condensation.

If its condensation, then you need to prevent warm vapour getting to the cold floor -which a dpm sheet will achieve. underfloor heating boards would probably help a bit as well

 

[amfisted]

Thanks again. DPM sheet plus boards seems like a cheaper and less messy option, so I’ll go with that. The damp on the floor appears to be confined to a narrow strip a few inches wide alongside the wall and extending a couple of meters in both directions from the external corner. There are no other areas where moisture is obviously present.