Damp proofing floor

[SakuraParticipant @sakura]

I'm sure some of you have dealt with this. What's the best surface sealer to stop damp coming through a concrete floor with no damp proof membrane.

[SakuraParticipant @sakura]

[Jim Young 2Participant @jimyoung2]

Not cheap but……

**LINK**

[SteviegtrParticipant @steviegtr]

I just used floor paint when I built the garage , but have a membrane down under it. The paint supplier where I bought the paint had 2 pack paint. Supposed to hold back anything , so maybe the 2 pack is the best. Very expensive though.

Steve.

[Jim Young 2Participant @jimyoung2]

Any DPM will need protection.

you might find this thread elsewhere useful

**LINK**

( saves typing it all again).

[JohnFParticipant @johnf59703]

Another possibility here but again not cheap **LINK** however may be better to look at the long term advantages !

John

[Dave HalfordParticipant @davehalford22513]

Just do a search for tanking paint

[Russ BParticipant @russb]

Once you seal a concrete slab, you introduce hydrostatic pressure under the slab which can lift/twist/crack the slab, as well as trapping the moisture therefor increasing its content and potentially creating heave issues.

Far better to address the cause rather than try to halt the effect, I'd try to consider any changes that could be easily made externally to mitigate the moisture, perhaps a simple french drain nearby, or check gullys and gutters aren't blocked, or leaves have rotted down in inaccessible places creating a higher than ground level sponge slowly releasing water.

Edited By Russ B on 11/06/2020 13:22:02

[John Paton 1Participant @johnpaton1]

And watch out also for moisture coming up at the junction of the slab and the wall. Once you seal the top of the slab the concrete will end up being wetter than before so the moistire will tray and escape around the edges.

At best this will be a narrow band of damp but if the top of the floor slab is above the damp proof course in the wall the moisture can track across and migrate up the wall. Ideally the DPM on the floor should connect to the DPC in the wall. If it is at the same level as the floor surface then consider grinding a bit of a chase between the two , blow out any dust with an airline, prime with special primer and fill the crack with polysulphide mastic or other slightly resilient compound with good adhesive and water resistant properties.

If rising damp in your wall does not concern you (typically a bit of a tide line up the wall often with salt crystals) then don't worry about this detail but if you want paint to hang onto the walls or if there is timber there you will be well advised to look at the interconnection. It is a common problem and as Russ correclty points out there is considerable hydrostatic pressure which builds up one the slab is no longer able to 'breathe' to release the moisture.

The the detail you are adopting the slab will tend to have less thermal insulation value too but that is a minor consideration. Also use chemical (resin) anchors and non ferrous / stainless fixings if bolting down machinery etc as the floor will be relatively wet below the 'paint'.

All 'doable' but not as straightforward or reliable as having the DPM below the slab.

[Adrian 2Participant @adrian2]

Sealing the concrete floor will hold the moisture in it at bay. However in so doing, another problem may raise its ugly head . Condensation!!

The unsealed concrete surface can absorb and hold moisture from the atmosphere, releasing it back when conditions allow.

I painted my garage floor with floor paint, it looked great in British Racing Green. Come the winter I had my own indoor swimming pool. It cost more to strip it all off than the paint cost in the first place.

Adrian.

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