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Floor Screeds And Dpc


DerekJ

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Hi All,

I know there have been threads on floor screeds etc. but they don't quite answer this question.

My concrete garage floor is sound but has no DPC so water seeps up through it on wet days and even ponds in places. So I was thinking of laying a DPC membrane down and putting a 30mm fibre screed on top of that. Put a nice gentle fall to the front door and taper it down to 0.

Anyone have experience of this? The floor is 3.3m x 6m. Is 30mm thick enough or will it crack and lift?

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Yes, it will crack and lift without doubt, and it will do it quickly.

The best bet may be to tank the floor slab, various systems are available, but you won't get away with a 30mm scred, you probably need a minimum 50mm screed and that will need reinforcement.

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Thanks Paul.

Will fibre reinforcement do or should it be something like chicken wire?

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Fibre reinforcement is suitable for use as an anti-crack measure in lieu of a light fabric mesh such as A142.

Be mindful that even if laying a new DPM or tanking system you are note really solving your problem of water ingress just simply holding it behind a.n. other system - whilst undertaking your proposed measures is fine (albeit not thick enough as per Pauls comments) Your issue is that of water ingress which you should also look at - is the water table high ? would installing a land drain / gravel trench divert the water ?

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No one used DPC membranes under concrete floors until recently,I presume the garage wall is single brick, with DPC showing both sides of the wall the concrete floor should be just below this and on the outside the wall DPC should be 2 bricks above ground level or you will have a wet floor. If the ouside ground level is too high dig it out you can back fill with 3/4 stone if it looks unsightly, Look for damaged gutters and down pipes, the old cast iron type can crack from frost, look ok but wreck your walls. Tanking sysems are for cellar and below ground rooms, like your car look at all the simple low cost things before spending money. if you do get it dry and wish to screed over, flood the floor with diulted PVA a couple of days before, use sharp sand with PVA in the mix it will give you a brilliant finish. :love: :love: :love:

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As above. I'd start by checking that all the surface water (rain water) discarges to somewhere away from the garage, ideally either to a soakaway or a surface water sewer. If the water from the roof or any adjacent paving just drains to the base of the walls then eventually it will find it's way back into the building particularly when it rains.

What's the construction of the garage? Is it a section prefab or something more substantial. and what are the subsoils that the garage is built on (sand, clay, chalk, rock etc)?

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Thanks Guys,

Hi Ian,

It's a sectional pre-cast section job plonked on a concrete slab so some water comes in between the wall and base too. Putting a membrane down and building the floor up by 50mm should stop that too (I hope).

Hi Mark,

I live in South Wales, and just about the only place that's not under the water table is the top of Snowdon this year :-)

The drainage is not great and some water does flood onto the floor slab outside and leak under the wall but, because of the way that the garage was installed (before my time) drainage is almost imposible to improve. I did look at this first and try and keep the drainage clear but it's not easy and would be a major job to improve so raising the floor is cheeper and easier.

Thanks again for the advice

DerekJ

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If it's a free standing concrete garage silicone all the external vertical and base gaps of the panels. Black jack a 4 ins strip on the base and outside walls, get some sharp sand with plenty of pva and lay a triangular mortar strip around the complete garage, if the concrete panels look suspect brush Thompsons into the complete garage outside, dont try to seal the water out it wont work you have to stop it coming in. If you do decide to raise the floor level check the building is square and stays that way. My son had a similar problem, in the end we took it down and rebuilt it on a single brick pad with a dpc and sealed all the panels in silicone. possibly a lot of the water is the concrete roof and walls sweating,

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