Damp, Floors, Airbricks etc.

Hi, new to the forum!

Apologies this may be a long post!

I've just bought a property built around 1900, and not surprisingly there is some damp in the bottom of the ground floor walls. These are of solid construction (i.e. no cavity).

The original survey didn't highlight this, and it was only when I engaged a structural engineer to have a look at some other issues (post purchase) that I became aware.

The recommendation of S.E. was to remover the rendered plinth around the property and inject a chemical dpc. He also recommended lifting e few floorboards along the wall to see if there was any timber damage.

Actions/Investigations to date:

1) I have removed the rendered plinth from the outside wall revealing a slate DPC and damp brickwork (some spalling of brick). The wall has already had a chemical dpc treatment judging by the holes in the bricks. See image


2) I have taken the plaster and render off the inside of the wall. Interestingly the top half of the wall had old lime backing plaster, whereas the bottom half had a much tougher sand and cement mix (I'm guessing this was done as part of the chemical dpc work).
Gypsum was skimmed over the lot.

3) I have lifted two or three of the floorboards near the wall. It appears the joists have been replaced fairly recently (they run parallel to the damp wall rather than perpendicular). The old joists have been left in place, and appear to have "dropped". From what I can see, the timber that the sits between the sleeper wall and the joists has degraded quite badly, and the new joist are "packed out" to top of these rotten timbers to the required height. The suspended floor appears to have some sort of concrete oversight underneath it (maybe 100mm from bottom of the joists); however it appears to have disintegrated near the wall, and there is a lot of moist soil/aggregate in its place. See image


Action Plan.


Wall
I intend to leave the plinth off as it will give the brickwork a better chance to dry out.
However, to prevent further ingress from splashing (and given some of the spalling on the brick), should I be looking to put some sort of breathable coating on allowing evaporation? If so, what sort of product?

I have a plasterer visiting in a couple of days time to discuss what to do about the inside of the wall. From a brief telephone conversation he was talking about s&c with a waterproofing additive, and then skim over. Is that wise or should something like limelight / renderlight be used as backing coat?


Drainage

There is a patio which butts up against this wall, the falls are all over the place so some rainwater can actually fall towards the house. Ideally I would install a new patio which fell away from the wall, but there's about 50 square yards of it, and I just don't have the time just now.
I was thinking of installing a concrete/mortar channel along the length of the wall just below the slate dpc. I should be able to get enough fall on it to run through to a gully pot and carry any surface water away.
My concern with this however is that I don't have a lot of wall to work with. There is 1 course below the dpc, and then the next course down starts stepping out for the footings. So I need to incorporate the channel with only a couple of inches of fall available.
Does this sound sensible or is it a really dumb thing to do?



Floor

The house has two airbricks at the front and one at the back. The wall which has the most problems is the flank wall between the two.
I intend to make sure these are clear before adding a further two 9 x 3 airbricks at the back.
Should I install any on the flank wall or is that likely to disrupt the airflow too much between front and back?

With regards to the timbers, I need to lift more boards to find out how much other damage there is. But as a a general principle I will:
i) Replace the timbers on top of the sleeper walls (with a plastic dpc underneath)
ii) Check the joists. If the old ones are damaged beyond repair, then replace them. For any that are in good condition (including the new ones that have been added), treat them with a timber preserve.
iii)I'm not sure what to do about the compromised oversight. Just dig it out a bit and blob a bit more concrete down there? Should I stick a bit of DPM under it?

Apologies for long post with various questions dotted throughout - it does help get my mind in order a bit though!

I'm working through a similar issue on a similar property at the moment. I can't comment on everything you have there, but mainly on the damp issues I have so far gleaned the following (from discussion with a few in-the-know types, including an independent damp specialist). I understand the following (as-in this is what I've been told, not what I know) :

Old DPCs such as Slate or Bitumen are very resilient and often get the blame when actually there's nothing up with the original DPC. Far more often Pentrating Damp / Condensation / poor construction can be the cause but the DPC gets the blame. You having a chemical DPC as well probably only helps (although I was also told that sometimes in the case of bitumen DPCs, the chemical DPC 'carrier' is actually a solvent of the bitumen, so must be used with care).

Therefore chances are that you're seeing the effects of the old plinth 'retaining' moisture in the wall, and worse; if it was bridging the DPC, then obviously allowing moisture to get above the DPC. Hence any moisture in the wall / behind the plinth now finds it even harder to escape (as concrete aint that breathable) and the wall gradually gets damper. My own guess is that water simply ran down the wall and permiated behind the plinth quite easily once it'd found a route in.

I also understand that walls take a very long time to dry out, so don't expect the problem to appear sorted for a few months, even though by removing the plinth and un-bridging the DPC you may have removed a lot of the cause.

Rather than fudging a concrete/mortar channel along the wall, get something like an Aco drain designed specially for the job. There's Aco kits available for ~£50 odd that would do the job better.

Hope that helps a little.

Hopefully, some others will add to this. I'll carry on watching this one with interest

you might consider trenching a channel beside the wall and filling it with clean stones.

1. More pics would help: detailed and larger views from inside and outside.

2. If possible, scan a plan diagram of your house floorplan, redline damp suspect areas, and blueline suspect floor areas.
Indicate low level vent positions by a "V"
Indicate any solid floors.
150mm min clear req'd below joists, but, in practice, far more depth (esp in damp conditions) is req'd.
Show how joists are running.

3. Why was a SE involved - do you have a report?

4. Lift boards in opp corners of suspect rooms/floors, and pic. as above.
Can you access any other crawl space below any other suspended floors?
A section drawing of oversite to FFL, esp. at "infill" areas, would help.

5. Locate the DPC all around the house - i presume it's just above the bottom course in pic 1? Scan a section drawing of GL to FFL.

6. Limelite is an excellent material, but expensive. A mix 6:1:1 S:L:C will do fine and much cheaper. Skim with board finish. But no rendering yet, wait.

7. The pointing looks rather shallow - how deep is the rake-out?

8. The patio business can also wait for now.

Ask your question here . Lots of similar problems are encountered there and the people on the forum are excellent. In many cases interfering with the damp course is unnecessary. From what I can see in your picture, some of the problem may be the cement pointing that has been put in. It stops the moisture getting out through the mortar. If it is a cement render on the plinth, that should go too.

Cement (even a small amount) is in appropriate for buildings of that age, and is unnecessary. It causes problems rather than cures them. Rising damp in brickwork or blockwork is a myth, and it cannot happen. For an example of it not happening, go and see old brick and stone river bridges and see how far above the water the damp appears on the bricks/blocks that have been sat in the water for decades (or even centuries).

Hi all,

Thanks for the replies. Unfortunately some scrote tried to break into the property last night so have spent most of the day sorting that out.


Hi Dann09 - hopefully in answer to your questions:

1) Will take more pics tomorrow
2) I've drawn a plan view - hopefully it is self explanatory - all floors are suspended timber
3) I got SE involved as the architrave double doors from front room to back room was sagging. He has recommended replacing 4 x 2 wooden lintel with a steel
4) Cross sectional schematic attached
5) Will do
6) Thanks for the tip. Why the wait? Bricks to dry out?
7) Not sure what you mean by rake out? Do you mean how much old mortar was raked out?
8 ) Wholeheartedly agree!

Plan View

x-section (plinth now removed)

Again many thanks all for the replies and suggestions.

Thanks for the new view.

3. Sounds like much DIY work has taken place.

6. Wait until you have determined the cause (s).

7. Yes. Rake out depth 15mm min. 25mm VG

Annotate the old, and the new pics into the scanned plan indicating point of view.

Do your floors squeak with that square edge boarding?

Thought I would add my thoughts as I have been tackling a similar damp situation in a Victorian house I bought a few months back. It might give you something to think about.

1. That sand and cement plinth was bridging your DPC, rendering it pretty much useless. If you do want to put a plinth back, it should be above the DPC only.

2. Buildings of this age were designed to breathe. You might want to think about using a lime based mix if you do replace the plinth, as it will allow the wall to breathe. Using OPC (cement) will just trap moisture. I have just had my house repointed, and used lime mortar instead of OPC. As suggested a lime based plaster internally would also be beneficial - make sure if you paint it that you use a breathable paint.

3. If you need to lower your external ground level of fit drainage and want to ensure water is drained away quickly and effectively take a look at http://www.pavingexpert.com/dpc01.htm it is an excellent site and shows you exactly what you need to do. A linear drain (Aco) would seem to work well here as someone else suggested. You don't need much of a fall for it to drain away so you should be fine.

4. There is always a big debate about whether rising damp is real or a myth. I sit in the middle - I know I have rising damp in my house and have seen it elsewhere. However, I know damp proof companies throw the term around a lot and use it to sell their products. I would never get a chemical DPC injected in my house. It is better to find a solution to whatever is causing the damp - whether thats reducing the external ground level, ensuring rain water goods are operating correctly, no leaking drains etc.


Good luck!