Damp concrete floor

glineli

Hi

I recently put up a metal shed. It was put on a concrete base. I had the concrete floor put down last week. Since then i have noticed the floor is very damp. I am not sure if the membrane was put down, i imagine it was. But i was wondering can this be put down on the finished floor to prevent the dampness

http://www.wickes.co.uk/damp-proof-membrane-liquid-5l/invt/241217/

It doesnt seem to be as a result of condensation as all the items in the shed are dry. Now i only gave the floor 24 hours to dry as it was raining on Wednesday and i needed to put things back into the shed. So maybe i didnt give it enough time to dry out completely.

thanks

whizbang

I would hazard a guess there is no damproof layer. Not a lot of trouble to put one in at the beginning, but takes preparation.
did you just tell somebody to put down some concrete? did they fill a hole with stone and just pour concrete over the stone?

However, a lot of folks who get metal sheds seem to have water seeping in under the walls.
The best solution now is to put in a damp proof layer on top of what you have and pour another couple of inches of concrete, so the inside floor level is above the level of the bottom of the walls.

policarp

I would say that the concrete is still drying out.
One test to see if concrete has dried out is to put a small sheet of plastic on the concrete and check it every few days by lifting it and checking to see if there is moisture on the plastic.As long as there is moisture on the plastic the concrete is still drying.
Concrete takes ages to dry out completely.

glineli

whizbang wrote: »

I would hazard a guess there is no damproof layer. Not a lot of trouble to put one in at the beginning, but takes preparation.
did you just tell somebody to put down some concrete? did they fill a hole with stone and just pour concrete over the stone?

However, a lot of folks who get metal sheds seem to have water seeping in under the walls.
The best solution now is to put in a damp proof layer on top of what you have and pour another couple of inches of concrete, so the inside floor level is above the level of the bottom of the walls.

Thanks. The problem is i have already got him to put down the floor inside, which is about an inch higher than the surrounding concrete. I see paint shops sell water seal, would that do the trick now?

glineli

policarp wrote: »

I would say that the concrete is still drying out.
One test to see if concrete has dried out is to put a small sheet of plastic on the concrete and check it every few days by lifting it and checking to see if there is moisture on the plastic.As long as there is moisture on the plastic the concrete is still drying.
Concrete takes ages to dry out completely.

thanks. I had a look this morning and there is mositure on the floor again. I am hoping it just hasnt dried out. I guess its only over a week so i should give it a little longer before i panic!!!

mikehunts

Hi,
We put up a metal shed a while back put in the dpm and poured another couple of inches of cement on top of this. Months later the shed was still dripping wet with moisture.
I thought well balls to this I will not be able to put anything into it at this rate. But things finally dried out and now it is how a shed should be-- Dry Inside.

glineli

Thanks, thats good to know. From the sounds of it, its just a waiting game. I put a dehumitifier in last night for a few hours and there was easily a pint of water in the drawer. so i reckon a few hours of that everyday will help speed things up. thanks again

wayoutwest

Concrete drying time = 1mm per day....or about 1" per month.

fergiesfolly

Getting a Steeltech shed.. The base is down and hope to have it delivered this weekend.
Was wondering if anyone had put down the concrete floor themselves. Was just going to get Steeltech to do it, but they're charging €500 for a 17x 10 ft floor, which seemed ridiculous.
How much would the materials cost(DPC and concrete) and is it a job an amateur could handle?

wayoutwest

Is readymix lorry able to get to shed?. You will need just over 2 cubic metres of concrete[3m x 5.1m x .14m]. Its been a while since I had any delivered, but i would think that it might cost around 100 euro per metre. The roll of plastic should only cost about 30 euro. I would have thought you could do it yourself for around 250 euro.

fergiesfolly

My maths was never the best, but doesn't 0.14m = 14cm
According to steeltechs site, you need to fill to depth of 40mm(4cm).

wayoutwest

According to the Steeltech website, you have to pour the concrete floor to a level which is 40 mm above bottom of shed base.....which is sitting on a concrete footing that is 100mm high - therefore, the total depth of poured floor is 140mm or .14 M.

fergiesfolly

Ah. My mistake.
Our base isn't the same as the one on their site.It only needs the 40mm to make it to the top of the frame.Will that make a difference to the DPCs effectiveness?

policarp

fergiesfolly wrote: »

Ah. My mistake.
Our base isn't the same as the one on their site.It only needs the 40mm to make it to the top of the frame.Will that make a difference to the DPCs effectiveness?

If it's an outside shed, just for storage DPM would be beneficial.
Concrete, unless it is porous(badly done) or cracked should be water proof.
100 mm at least for a shed floor.

wayoutwest

Fergiesfolly - So your shed has been fixed to a slab, rather than a 'footing',and you want to raise the floor level so it is higher than the outside ground level. This type of layer is called a 'screed', which is made of sand & cement 3:1 [rather than aggregate, sand & cement 5:1, which is used to make concrete].
You can just about lay a screed [that is that thin] - as long as it is bonded to the slab. Because you want to introduce a damproof membrane at this stage, the screed won't be bonded. The minimum depth of an un-bonded traditional screed should be 60mm or more, in order to prevent cracking. I believe that a 'pumped'creed[rather than traditional] can be layed in a thinner layer[posssibly 40mm] onto an unbonded slab [ie; onto your plastic membrane] because it contains added chemicals that make it stronger.
I would definately be wanting a DPM. to prevent rising damp AND damp caused by water ingress due to the relatively small hieght of floor level above ouside ground level.
You only need .6 Cubic metre of material - get a quote from local pumped screed people - it's got to cost a lot less than 500 euro!

fergiesfolly

Thanks for the replies.
We were originally going to build a block built shed, but changed our minds after the foundation was done.
There was DPC laid before the foundation went down, but I'd presume we'd need to lay more DPC before we put down the screed


edit;
Spoke to a local that does both the normal and liquid screeding and he doesn't see a problem with 40mm, once the DPC is down. Going to call out to have a look before he makes a final decision.