I have just bought a house and a part of it has an earth floor. I
have plans to change it in to a garage or possibly a liveable area. I
am keen to learn a bit of DIY and my first job would be to lay a solid
floor where the earth currently is. I have never done any work with
concrete before and would be grateful of any advice on the best way of
doing things. How deep would I have to dig? What are the best ways to
waterproof the floor? The walls are damp and someone has suggested
laying a ventilated floor, does anyone have any advice about this?
email@example.com (John) wrote in message
This can definitely be DIY'd although I personally wouldn't make it my
first experience of using concrete. For a garage sized area do not
even think of mixing your own concrete, get it from a supplier, just
tell them what amount you need and what it is to be used for and let
them worry about the mix. Make sure you over order and have an area
for them to unload any unused excess onto as they will not keep any in
the mixer. Of course you have to have access for them to pump it into
your 'garage' but unless you are in a particularly peculiar situation
this is unlikely to be a problem. If you need to barrow it get some
help and lots of it. In general have enough help available so that you
and at least one helper do not have to be disturbed at any time from
doing the main job.
If it's a garage you will not need a insulation layer, but if it
becomes part of the 'liveable' part of the house you will by building
regs need to have one. You need to dig down about 300mm below the
required finish level. Lay, level and compact a 125-150mm scalpings
layer with a wacker (plate compacter, can be hired). Then lay a damp
proof membrane on this. This has to be lapped into the damp course of
the existing walls so make sure you leave enough at the edges to do
this. Oh wait, you said your walls are damp so chances are you will
need an injected DPC, something else you can hire and DIY. Now lay
50mm or whatever the building regs require of foam insulation board on
top of this. To get a level finish you can attach some insulation
board to the walls so the top of the board is at the floor finish
level. This is then used as a guide when you tamp down the concrete
for the final finish. You don't have to do this but the foam on the
walls also allows for expansion of the slab. If you don't do this then
attach some straight pieces of wood to the walls at the finish height,
AFTER you have lapped the DP membrane up the wall to achieve the same
effect. Then pump in a minimum of 100mm concrete on top of the board.
If it's going to be a garage 150mm of concrete should be the minimum.
Start putting concrete in at the end furthest away from the exit to
slightly above your finish level references and spread it about with a
rake. You will need a straight piece of wood shorter than the distance
between walls but long enough to sit on the reference foam/wood. Start
tamping from where the concrete first went in. Hold the piece of wood,
or more likely you and a helper hold the wood one at each end and in
short vertical movements compact (tamp) the concrete to the finish
level moving the wood toward you as you tamp and clear the top of the
reference levels of concrete so the tamping wood can sit on them as
After about half an hour to an hour after this is done you can start
troweling the surface smooth. You will need some largish boards to
kneel on so as not to sink into the still wet concrete. Do not over
trowel or the surface will end up dusty. The troweling should just
bring a small film of water to the surface if it's the right time to
start trowelling. When the concrete has had about 2 hours drying
spread sand over the whole surface to about 30mm deep and keep this
wet for at least a couple of days preferably a week to help the
concrete cure properly. If you are not confident at doing this, you
can finish at a level below the required final level, say 30mm and
make up the final level with a screed or sand/cement mix which you can
trowel over the concrete when it has dried. Or you can finish to a few
mm below your required level and when the concrete is dried buy a self
levelling screed which will make a nice final floor.
If you used wood reference levels these can be left in and screeded
over or removed and filled with concrete.
As far as the ventilated floor goes this is normally done using air
bricks placed into the walls under the level of a wooden suspended
floor. So I don't think it is relevant to you. Unless you decide to
make it a livable space in which case wood on joists is definitely the
best DIY way to go, much easier than messy and difficult concrete
Just finished a helping a friend replace his tile on soil floor and am in
the process of doing my own.
1. removed tiles etc and dug down 8" - 2" for sand, 2" polystyrene, 4"
2. did not use hardcore since the floor was old and compacted
3. ordered builders sand, poly and damp proof membrane (DPM, sometimes
called visqueen) of 1200 gauge from a builders merchant. Phone arounf for
the best price.
4. put down sand (it's to stop DPM from being punctured) and then DPM.
Can be tricky if you have chimney breasts etc. Make sure sand is flat
by draging planks around.
5. put down 2" thick poly and also 1" around the edges for an expansion gap.
6. put in 2 x 4"'s with their tops at the final floor level. These will
act as levels.
7. order readymix concrete. I've priced the materials for mixing my own
and it was the same as readymix, and didn't included mixer hire.
8. I've taken the glass out of a double glazed window. For me this involved:
a) remove rubber strips from around edge of glass inside
b) remove plastic bits outside which have a thinner rubber strip
attached - 1 at top and bottom and 2 at the sides - easy.
This will allow the mixer to poke it's shute through the window. These
go up to 8', or perhaps longer with extensions if available.
9. my friend made a shoot out of an old door (nice slippy painted
surface) and some planks for te sides. He needed this since the mix is
quite stiff and had to move it to a back room he was also doing. I'm
going to borrow it for the single room I'm as it worked very well and
saved a lot of raking.
10. get as many helpers as possible., all in rubber boots and wearing
rubber gloves - shorts and tshirts are a good idea as you may "glow" when
spreading the concrete.
11. when it arrives spread it using garden rakes and then tamp it using the
levels and te edge of a plank. You may want to put some extra concrete
into buckets for filling in depressions, rather thhan shovelling it
around (it's heavy).
I think you have 20-30 mins of the drivers time so don't let him rush
you. He'll probably want to dump all of the concrete out so get your
12. trowel it smooth - after 1 hour or a few hours, depending on where the
advice comes from. We waited about 1 hour.
13. to economise we are just using concrete. To get the best result you
may want to add 2" of cement (and dig a further 2"). My friends floor
looks ok and he's only putting tiles down. I'm goging to do te same but
I'm putting laminate floor down so will keep my toes crossed in addition
to my fingers.
14. if it's below te wanted level you can always add a self levelling
compound or some cement.
Good luck, it's not rocket science.
The job is simple enough - maybe hardwork if you are not used to this sort
of thing - but not rocket science.
The finished result you want is: hardcore/blinding/dpm/insulation/concrete.
If the ground is really hard and been down decades you only need dig out
enough to get the top of concrete at the finished floor level required - if
you have a damp course in the walls this should be the finished level - but
with earth floors I doubt that.
If you are using as a garage then no need for insulation,
Simple sequence -
dig out to required depth
compact with wacker plate if required .... and definitely if any hardcore is
blind the finish with sand ... no big deal on thickness - just enough to
ensure DPM can't be punctured by stones
lay DPM (visqueen)
lay 50mm polyurethane insulation (or not if a garage)
lay 100mm concrete ..
DPM should fold up the walls so it covers sides of slab - temporary tack up
Work out volume of concrete needed, if up to a m3 then this is an easy job
with a small cement mixer - greater than that then buy in Readymix .... if
less than 6m3, then a minimix company will be much cheaper - you pay for
airspace if less than 6m3
A good enough gp mix if mixing yourself would be 5:1 of all-in ballast and
cement, don't mix it to wet to prevent water separating out.
If buying in ask supplier for a gen mix, they will supply right mix for the
I'm not saying DONT lay a concrete floor, but you should be aware of
There are two building techniques, the old one which was used in your
house amd which relied on the building materials being breatheable, so
any damp which got in on a wet day could evaporate out on a dry day.
That system worked very well for hundreds of years until carpets
Then was invented the new building technique which has been used for
the last hundred or so years and relies on impermeable surfaces like
damp proof courses to stop water getting into the building structure
at all. That system works very well too.
The problems come when you do a mix and match of the two and if you
have damp walls then I suspect that the old breatheable limewash
finish has been covered with a new impermeable emulsion paint, which
traps moisture until it breaks out in damp and desperation.
A concrete floor will not allow any moisture out, so any water will
move sideways to the nearest place it can escape, which might be your
already damp wall. Hence the infamous rising damp. So before
concreting the floor think about where any water will go when you do.
It would probably be a good idea to damp proof the walls now when they
have had a good drying summer.
Alternatively, you could go the traditional route which has the
advantage of being eco friendly and less graft for you - which is to
leave the floor breatheable. It doesn't have to remain as earth.
Pammet tiles bedded in weak lime mortar (which is breatheable) would
be fine too. Then strip impermeable layers off the wall, limewash them
and relax with damp problems solved. A purist, me. Or lazy.
~~ Anna Kettle, Suffolk, England
|""""| ~ Pargeting, decorative and traditional
/ ^^ \// lime plasterwork
|______| www.kettlenet.co.uk 07976 649862
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