Damp concrete floor

19 Jan 2007
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United Kingdom

My concrete kitchen floor is damp. I have taken up a small section to have a look under the concrete, and it is a 1" screed, with a 3" concrete base, layed directly on compacted earth and clay. No DPM ! Its a 1930's red brick ex-council house.

Do I need to rip the floor out and lay a dpm, then concrete then screed/latex?

Whats my options on this - concrete again or floor boards or plywood maybe??

The floor will be tiled when done. Its currently very uneven, across the room, there is about a 3" drop.

The damp is mostly where the concrete touches the outside walls, upto 7ft into the room. Room is 17' x 13'
Any ideas?
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Depends How much work you want to do. One option you have would be to apply a good surface dpm then screed over that to get a level.
I thought of that. Hitting off the 1" top screed, applying a liquid DPM paint sealer to the 3" concrete underneath, then a 1" layer of latex over the whole floor to level it off.

Would that be ok or would it sink?

What sealer should i use?

Most of the damp is where the floor touches the outside wall, it is above the DPM so thats not bridged and the damp is not rising up the brickwork.
I've never had any comeback using Laybond 1 coat dpm, if youre going to use a latex screed to 1" you'll need to bulk it up with aggregate chippings.
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Sounds like a resonable solution. Will it prevent the concrete arching up in the future and who sells it? I tired build center and jewsons and they both dont sell it!

I need to dig out the bits that have bubbled up with the damp and relay the concrete, then screed.

Any tips on how to screed the floor and get it level? Can i apply latex in layers to get up to my required 1" depth?
Suggest as follows:

1. remove enough of the old screed to allow you to re-lay 6mm of new screed and end up with correct levels
2. prepare surface
3. leave clean and dry
4. apply 1 coat Ronacrete Monoprufe
5. allow to dry (12-24 hours)
6. mix and apply 1 coat Ronafix:cement bonding primer, mix proportions 1:1
7. while wet or sticky mix and apply screed, mix as follows:
1 volume cement
2.5 volumes medium sharp sand
1:1 mix of Ronafix and water, added to cement and sand to give semi-dry screed consistency

Trowel this on to wet or tacky primer, compact and finish smooth with a trowel

Protect with polythene. Allow to cure for 24 - 48 hours.

Use the screed.

You now hav DPM and a thin bonded hard screed.

For more information call Donna or Daniel, 01279 638 700, or see www.ronacrete.co.uk, products, documents, cementitious.
Whaere can i buy it? Im in bristol.

only one coat? The floor area is 20sq m (17x13ft)
Yes only 1 coat because the primer for the screed acts as both a bonding primer and a second layer of DPM.

So yes, you are correct in thinking that you need 2 coats of DPM, but this is achieved with 1 coat of Monoprufe DPM and 1 coat of Ronafix:cement primer.

Bristol; contact
Burdens Limited
Earl Russell Way
Lawrence Hill

Tel: 0117 941 4422
Fax: 0117 955 4748
If you can lay a smooth, flat screed you shouldn't need a latex.

But, if you want to/need to lay a latex, yes.
Thanks. How far does a 10kg bag of monoprufe stretch?

Also if i mix ronafix with cement, 1:1, how far does a 5L container of Ronafix stretch?

Im trying to work out how much of each im going to need to buy.

Also, do i mix the ronafix into a sludge, apply thinly, leave to dry a little then screed over the top?
10kg pack
is enough to apply:
1 coat over 5m2
or 2 coats over 2.5m2

as a bonding primer (1:1 with cement)
1 litre covers 3.5m2

as a screed admixture
at 6mm thick (the min. for a Ronafix screed) you will need 0.54 litres per m2

When you mix Ronafix with cement for the primer, it's a single cream consistency, brushed with a paint brush. DO NOT allow to dry before putting screed on top. YOu have 15-30 minutes before it dries depending on how porous the surface is, how wet it is, any drying breezes, any sunshine on the surface, how warm or cold it is.
Hummmm, just adding up the costs involved, and excluding labour, its working out slightly cheeper to rip out the whole floor, dig down a foot, and fit joists and joist hangers, floor boards.

Any pros / cons to this?
Back ache

Sorry, you appeared to need a technical solution, which I believe I have provided. Of course if ripping up and starting again is easier/quicker/cheaper, it's hard for me to challenge you.
Im not too good at concreting, but really good at wood work, i feel more confident in replacing for wood, but worried about the time, cost etc...

At this stage, im still working out my options. Thanks for the advice you've been most helpful!

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