Kitchen - DPM / Dab & Board

[Causer93]

Hi all,

First time poster on here, a couple of years general labouring experience, now renovating a house alongside the day job... wondering what I’ve gotten myself into!

Our 1930s dormer bungalow is positioned on a slope, and at the rear of the house where the kitchen /diner is, the internal floor level is ~10cm below ground level and 30 cm below DPC. I believe moisture is entering the building horizontally from the external ground, and the internal plaster is bridging the DPC resulting in evidence of rising damp on the walls.

The plan to remedy this is to firstly hack all the plaster back to brick, and lift floor boards to remove all the old rubble that’s accumulated in the crawl space. Then apply a tanking slurry to the concrete floor and interior walls below ground level.

Following this, I will reinstate the floor boards and install a water resistant subfloor (the finished floor will be LVT).

Subsequently, I’ll fix a 1.2 meters permaguard damp proof membrane to the external walls, and interior adjoining walls. The DPM can be sealed underneath the water resistant subfloor.

I’ll dab and board the walls, skim / mist coat, and anti-condensation paint. I’ll seal the void between the board and subfloor with expanding foam.

I was hoping to get wider feedback from the community on the following:

1) firstly, is the plan sound?

2) is the tanking slurry in the crawl space required, or is it acceptable to have a damp crawl space below ground level?

3) DPM / dab and board is as per manufacturer recommendations, but should I be worried about condensation forming on the inside of DPM / paper side of board?

4) I thought promoting ventilation behind the board would be advantageous, but online advice recommends sealing this area off to prevent the ingress of moisture, hence the expanding foam and anti-condensation paint. Is this correct?

Thanks all!

[dewaltdisney]

If I read you right the damp course is bridged by the ground level? I would focus on lowering the ground level earth to below the DPC and installing a french drain to divert the water run off that is currently soaking the area. This is not as onerous as it sounds as it is basically a trench dug next to the rear wall during the ground level reduction and a drain pipe with holes drilled in laid in a gravel backfill. Clearly, you need to work out where this diverted water will flow but that is the idea. The reduction of moisture in the area may obviate the need for your wall sealing.

DWD

[Causer93]

Hi, thanks for getting back to me.

Sorry for not being clearer. No, the external ground isn’t bridging the DPC.

The external ground is 15-20 cm below the DPC, but the interior floor is a further 10 cm below the external ground (I.e. 25-30 cm below DPC).

Plan is to reduce external ground level this year, and insert a French drain as you say. Unfortunately a leak and rotten floor joist means the kitchen needs to be done before the external work. However, due to the landscape the crawl space will always be below ground level.

[dewaltdisney]

I see, I think that a French drain will solve many of the ongoing issues if you get it down to the corresponding internal crawl space level. This will reduce any moisture leech into the sub-DPC brickwork and in turn hopefully solve many of the issues.

DWD

[Causer93]

Thanks DWD, really appreciate the feedback!

I’ll get digging! Other factors that I don’t think help is the fact the previous owners put a new block work patio over the top of the old crazy paving, and it’s sloped towards the house!

[dewaltdisney]

That would do it, it will channel the runoff water to the wall. If you have not got one this is a great buy https://www.screwfix.com/p/titan-ttb631 ... 240v/4172g The heavier Titan will really break through the patio and ground. My one has been a great help over the years.

DWD