Concrete slabs and freezing
Dave Winslow
heaving.
I have always put footers below the frost line to avoid seasonal movement
which makes perfect sense. But what about slabs? The basement floor in most
cases is below frost so its not an issue, but what about unheated garages
etc. My Dad had a concrete walk poured in his back yard and as I remember it
was just 4" and floated. There were few if any real cracks after 30 years.
My particular interest now is because I have to pour a slab for placement of
a hot tub. Frost line around here is 4 ft. The area gets very wet, water
table is well above 4 ft most of the year. I plan to put about 8" of gravel
and a 4" reinforced slab. What do you guys think?
Thanks,
Dave
raymondj
<Da...@Winslow.mv.com> wrote:
>I have never understood the principals of concrete footers, slabs, and frost
>heaving.
>
>I have always put footers below the frost line to avoid seasonal movement
>which makes perfect sense. But what about slabs? The basement floor in most
>cases is below frost so its not an issue, but what about unheated garages
>etc. My Dad had a concrete walk poured in his back yard and as I remember it
>was just 4" and floated.
What was the concrete walk supporting? Right, nothing.
Matt Morgan
the water and freezing/thawing, footers will keep the concrete stable and in
one piece.
Bob G.
4 foot frost line...? ok... I assume the slab will be about 8X8 foot
I would dig a 5 foot hole at each corner... plus one dead center ..
and use them for footers...
Those plus the weight of the water in the tub (Ikeep my tub heated
year round) will keep it in one place...
Gravel then a re-enforced 4" slab will work... Your Dad does not
live anywhere close to you does he...? Just wondering how that walk
lasted 30 years floating on soil in a place with a 4 foot freeze line.
Bob Griffiths
Dave Winslow wrote:
>
> I have never understood the principals of concrete footers, slabs, and frost
> heaving.
>
> I have always put footers below the frost line to avoid seasonal movement
> which makes perfect sense. But what about slabs? The basement floor in most
> cases is below frost so its not an issue, but what about unheated garages
> etc. My Dad had a concrete walk poured in his back yard and as I remember it
Dave Winslow
Thanks for responding, but the problem I see is that frost will still get
under the slab, lift it and the tub up, and footers will be meaningless no?
Yes if I keep it hot year round I would have no problem, but I'm not sure I
want to pay for that, the trek from house to tub in Feb might not be real
popular.
My father's place was in mass, frost line is about 3 ft I think there. I am
in central NH.
Thanks again, Dave
Bob G. <rg...@fred.net> wrote in message news:3937E8...@fred.net...
Dave Winslow
Matt Morgan <morga...@earthlink.net> wrote in message
news:t_TZ4.3278$1d5....@newsread2.prod.itd.earthlink.net...
How does this work? If footers are below frost, and slab is not, then I
would expect the slab to be lifted and crack away from footers.
Thanks, Dave
Bob G.
The ground under the slab itself will still freeze
HOWEVER...it will try to push up on the concrete but will instead
compact the Gravel. The footers anchor the slab...I would not be at
all suprised if in 2-3 years you had 1-2- inches of air under the slab
As for the trip out to the tub....(Ya RUN...no not really I use my
Tub on a regular basis and use it until the outside tempature hits
10 degrees...The tub is only about 30 feet off my rear patio..takes
a few seconds to walk (I have a pair of Speedo shoes that I wear right
into the tub with..then take them off)...And I find that when you
get out you have about 30 seconds before you feel the cold...BUT its a
1 minute deal to close up the tub and RUN into the house..oh well
I do feel the cold for 30 seconds...
Kept the tub at 102 all winter...electric (I heat with electric $$$$
24/7 deal...bill went up about 20 bucks a month...75 cents a day I
can deal with that..
Bob
Donut
especially if it's steel reinforced) . Having gravel under the slab drains off
water, and makes even lifting more likely. Soil conditions play an important
part in what happens. Sometimes a little cracking is no big deal. Even the best
slabs often crack. If you want to just pour a 4" slab, consider making the outer
edge 8" thick and use rebar or wire mesh to hold it together if it heaves. YMMV
Dave Winslow wrote:
> I have never understood the principals of concrete footers, slabs, and frost
> heaving.
>
> I have always put footers below the frost line to avoid seasonal movement
> which makes perfect sense. But what about slabs? The basement floor in most
> cases is below frost so its not an issue, but what about unheated garages
> etc. My Dad had a concrete walk poured in his back yard and as I remember it
> was just 4" and floated. There were few if any real cracks after 30 years.
>
> My particular interest now is because I have to pour a slab for placement of
> a hot tub. Frost line around here is 4 ft. The area gets very wet, water
> table is well above 4 ft most of the year. I plan to put about 8" of gravel
> and a 4" reinforced slab. What do you guys think?
>
> Thanks,
>
> Dave
--
Donut
To email remove the 'u' from do...@gilanet.com
ry...@my-deja.com
Look into 'white beadboard' insulation (like 'blue styrofoam - but
cheaper).
Up here our builders place a piece of white beadboard the width of the
grade beam and 8" thick (deep) under grade beams to take up any
compression that frost might deliver.
I would lay 4' X 8' sheets of white beadboard (the thicker the better -
but at least 4" worth) on the surrounding area (8' away if you have the
space) from the structure walls and lay 2" beadboard under the
structure slab as well.
The theory here is that the frost is going to have a hard time
penetrating the white beadboard. Snow does the same trick its an
insulator - but you cannot always count on it snowing. No frost - no
heave. The 2" thick beadboard under the structure keeps **some** of
the heat inside - but allows some to pass into the ground underneath -
thus further preventing frost from getting in. This theory has been
proven in our area with a structure that has not moved in 15
years. .... and we're talking 20 below zero (during the day) for two
months at a time.
The other factor that causes soil movement is the type of soil. Check
out the type of soil you have under the structure. In our area it is
clay - which expands and contracts with moisture content.
One crummy thing with this property of clay is if you have a large tree
near the proposed structure - and you plan to cut the tree down. Once
you do that the tree is no longer sucking water out of the clay - so
when the next rains come - the clay starts to expand. I've seen houses
here where they put the foundation walls on piles - but 'flotated' the
basement floor on the ground. After the trees were cut - the basement
floor buckled BIG TIME.
The owners jackhammered and removed all the floor cement (UGH!!) poured
water into the basement and let it sit (so the water would get the clay
totally soaked) then re-levelled the clay, put in new weeping tiles and
pea gravel and - one fellow re-poured the floor. The other guy went a
step further and, instead of concrete, he built a wood sub-floor one
foot over the clay surface - so he would not have the concrete heave
again.
That was a good choice as the first fellow (who just poured concrete
over the floor ended up with minor cracking and some minor heaving.
If you have clay there - I suggest digging down and backfilling with
gravel / sand.
Sent via Deja.com http://www.deja.com/
Before you buy.
Daniel Hicks
But dry soil doesn't heave when frozen.
Too Much
of that they put a 4 mill. plastic barrier. Then they pour the slab.
I live in a house with this type of a basement, and in the coldest months, I can tell you that the ciment floor is still
warm on bare feet.
Dave Winslow
Daniel Hicks <danh...@ieee.org> wrote in message
news:393861CB...@ieee.org...
> Dave Winslow wrote:
> >
> > Matt Morgan <morga...@earthlink.net> wrote in message
> > news:t_TZ4.3278$1d5....@newsread2.prod.itd.earthlink.net...
> > > The footers are a good idea for the hot tub. With the excessive
weight of
> > > the water and freezing/thawing, footers will keep the concrete stable
and
> > in
> > > one piece.
> > >
> >
> > How does this work? If footers are below frost, and slab is not, then I
> > would expect the slab to be lifted and crack away from footers.
>
> But dry soil doesn't heave when frozen.
Thanks Dan. Why would the area by dry? If the ground next to the slab is
good and wet (which it is often) then would we not expect water to get under
there? It may be down a ways, but if water freezes 2 ft below the slab,
would we not expect heaving? Thanks again, Dave
Daniel Hicks
Not much rain will soak through the concrete, and water can't get in
from the sides due to the footing. Unless the water table is really
high the soil under the slab will stay fairly dry. This can be helped a
bit by filling with sand or pea gravel. If one is really concerned,
fill the area with several inches of cardboard. (Yes, it's done.)