air brick and damp question

18 May 2017
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United Kingdom
Hi everyone

Little bit of background information.

I live in an ex council house, built 1935.

Recently taken the carpet up to find one corner of the floor was slightly damp. Walls showing no sign of damp.

The floor is concrete construction with asphalt covering. I believe the asphalt was used as a dpm back in the day. The only area where isn't covered with asphalt is where the old stone fire hearth used to be which seems to be concrete. This too has shown slight dampness.

Because the corner of the house was showing signs of damp I went outside to investigate. I found two air vents which were almost buried and blocked up with mud and stones. These don't go all the way through to the house so not really sure what they are for? I also had cavity wall insulation attempted a few years back and was told that they could barely get any insulation in the cavity and they blocked other air vents up.. is this ok, should they be unblocked... I don't have any vents at all on the inside of my property so not sure what these vents are for.

Any help would be greatly appreciated.oxy acetylene


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leaddriver, good evening.

Must admit mixed messages here??
A Concrete floor will not need air bricks, there being nothing to ventilate, that is there is no void under the floor as can be found in say a timber suspended joist and timber flooring situation.
Yes you are correct, Asphalt was used as a DPM over Concrete floors It is well known to fracture with age and can in some cases allow ground water to get to the surface of the Concrete.
Your situation, given the two air bricks located may, I stress MAY? indicate that Historically the Property had Suspended Timber floors fitted which over time may have deteriorated and severe rot in the timber flooring and Joists occurred, at this Juncture Concrete was used as the option to remedy the problem.
As for the Cavity Fill scenario?? if the Installer had Installation problems this could??? indicate that the cavity was narrower than normal, or that the Cavity was obstructed, this in turn could??? induce damp penetration and the resultant water ingress could manifest itself as dampness on the floor slab.
Bottom line a wee bit of a confused situation, as stated mixed messages [not overtly by you, but air bricks and a concrete floor is not unheard of, I have see a few, but it is giving of the wrong message]
Have you found any more air bricks?
Is the positioning of the air bricks in proximity to the fire place? rational is that some fires had an under floor air inlet??

Sorry, no real answers, but some food for consideration?

Hi Ken, thanks for taking the time to reply. Ive only owned the house for 7 years so have no idea if they used to have wooden floors. I know my neighbour (who is council) has been there for years so will ask next time i see them.

With regards to the area where the asphalt has broken down or in the case around the fire where the hearth used to be (where its just concrete) is there anything i can seal the floor with? I was thinking about sealing the whole floor with a bitumen paint?

I do remember the cavity wall insulators saying that the cavity must be narrow and they cant fill it.

My concern is, are the air bricks that i have uncovered are causing the dampness i am experiencing?. After all any rain or dampness can in theory run freely in to them? I cant say that ive noticed any air bricks on my neighbours houses at the same level i am talking about. In fact to be honest the neighbours have a solid concrete path running all around their house which would possibly be above these air bricks (if their houses have them).
The external ground level might be too high & bridging the outside wall DPC, and the shallow cavity might be blocked thus allowing moisture to penetrate across the cavity and affect the inside floor.
If the floor is damp then its almost certain that damp has affected any nearby skirting and plaster.

Pics of the damp areas might help.

Hearth and fireplace areas are always vulnerable to rising damp - and your posted pics show damp soil.
They also show bubbled paint - which usually means moisture vapour behind the plastic paint. Masonry paint should have been used.
Spalled masonry also indicates previous moisture connected damage.

If you only have two air bricks then they would have had no part in ventilating below any possible suspended floor. The air bricks are original BTW.

FWIW: CWI "surveyors" should have examined the cavity & wall construction suitability prior to any attempt to install CWI.
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Plaster and skirting is completely fine, Ive just decorated. There was no tide marks on the wall nor was there any flaking paint and the plaster was solid. No soft spots, because i did test it near to the damp area. The skirting board was fine also.

With regards to the damp fireplace, is there anything i can use to seal it?

There are two air bricks on the side of the house also, again these go to no where in the property.

Should i remove these air bricks, block them up or leave them?

Would putting a channel drain directing it to a near by gully help?

I'd start by clearing all that crap out of the gap between your house and drive to at least the bottom level of the airbricks.
With regards to the area where the asphalt has broken down or i around the fire where the hearth used to be (where its just concrete) is there anything i can seal the floor with?
Airbricks are ventilating the narrow cavity. As to the floor, we have a tarmac/asphalt expert here, why not search through some old threads.
I thought cavities shouldn't be ventilated though?

I'm going to dig the channel out below the air bricks as you have mentioned.

Thanks for all the advice
Some cavities were vented, back in the day. The problem of course, is the cold.
Ok thanks, I've been taking s peek at the neighbours and surrounding houses. Neighbours house has no visible air bricks. Or they were burried like mine.

Other houses have them visible. All have concrete floors

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