firstly a bit of background.

I bought a house last December.

It originally had a semi-detached double garage with a supporting wall
in the middle. (one of the bedrooms is above one of the garages.)

A previous owner had the garage that was under the bedroom converted to
an extra room, and knocked through a door way from the hall.

So the double garage became a single garage & extra reception room.
(there were two separate single garage doors, one of which was removed
and replaced with a wall and window)

The garage floor was 6 inches lower than the Hall floor when they
knocked the door opening through from the hall.

Now at the time, there was a steel gas pipe running along the garage-
hall wall (on the garage wall side to the hall) above the then garage
floor but below the hall floor level. (kitchen is to rear of garage)

So the builder built a wood frame around the gas pipe which is 12ft long
and 5 inches wide to protect said gas pipe in the garage being converted.

They then put down a layer of sand, then a blue plastic damp proof
membrane and filled the garage floor it with concrete till it was level
with the hall floor. They then put a piece of 12ft long 5in wide plywood
to cover this trench containing the gas pipe. This meant that the gas
pipe was accessible at all times.

Now for the problem:

The gas pipe has since been decommissioned (it was corroding badly) and
a new copper gas pipe put in that takes a different route to the
original gas pipe.

I have removed the old steel gas pipe and the supporting wood frame and
the plywood cover. I wish to fill this in with concrete to match the
rest of the garage floor and the hall floor.

This has resulted in a trench that is 12ft long by 5 inch wide.

There is damp proof course across the doorway that was knocked through
and this was covered with concrete.

Now whats the best way of dealing with this 12ft long by 5inch wide now
empty trench? There is a surplus amount of blue DPM material which went
under the plywood cover but is perforated with gripper rod nails and
carpet tacks even though it would reach the existing wall.

Can I put a strip of DPM material down this trench and then fill it in
with concrete or will there be insufficient overlap between old and new
DPM's given the fact that the trench is 12ft long by 5inches wide?

Is there a water resistant concrete I can use to fill this trench in
that will not be affected by the nail holes in the exisiing DPM and
prevent any rising damp problems?

Regards,

Stephen.

"Stephen H" wrote in message
...
firstly a bit of background.

I bought a house last December.

It originally had a semi-detached double garage with a supporting wall in
the middle. (one of the bedrooms is above one of the garages.)

A previous owner had the garage that was under the bedroom converted to an
extra room, and knocked through a door way from the hall.

So the double garage became a single garage & extra reception room. (there
were two separate single garage doors, one of which was removed and
replaced with a wall and window)

The garage floor was 6 inches lower than the Hall floor when they knocked
the door opening through from the hall.

Now at the time, there was a steel gas pipe running along the garage- hall
wall (on the garage wall side to the hall) above the then garage floor
but below the hall floor level. (kitchen is to rear of garage)

So the builder built a wood frame around the gas pipe which is 12ft long
and 5 inches wide to protect said gas pipe in the garage being converted.

They then put down a layer of sand, then a blue plastic damp proof
membrane and filled the garage floor it with concrete till it was level
with the hall floor. They then put a piece of 12ft long 5in wide plywood
to cover this trench containing the gas pipe. This meant that the gas pipe
was accessible at all times.

Now for the problem:

The gas pipe has since been decommissioned (it was corroding badly) and a
new copper gas pipe put in that takes a different route to the original
gas pipe.

I have removed the old steel gas pipe and the supporting wood frame and
the plywood cover. I wish to fill this in with concrete to match the rest
of the garage floor and the hall floor.

This has resulted in a trench that is 12ft long by 5 inch wide.

There is damp proof course across the doorway that was knocked through and
this was covered with concrete.

Now whats the best way of dealing with this 12ft long by 5inch wide now
empty trench? There is a surplus amount of blue DPM material which went
under the plywood cover but is perforated with gripper rod nails and
carpet tacks even though it would reach the existing wall.

Can I put a strip of DPM material down this trench and then fill it in
with concrete or will there be insufficient overlap between old and new
DPM's given the fact that the trench is 12ft long by 5inches wide?

Is there a water resistant concrete I can use to fill this trench in that
will not be affected by the nail holes in the exisiing DPM and prevent any
rising damp problems?

Regards,

Stephen.

A lot depends on the subsoil as to how good your DPM has to be, so no-one
can be entirely sure.
I would paint the side of the existing concrete with a few coatsof bitumous
paint . I would put a strip of DPM in the trench turned up the sides, cut
off just below the surface.
You can buy chemical to add to concrete mix makes it water repellent if you
want belt and braces.
You can also buy chemical to paint on to existing concrete the makes it
water repellant.
However it won't stop positive water pressure so make sure your trench
doesn't fill with water in wet weather.

On 17/07/2012 07:10, harryagain wrote:
"Stephen H" wrote in message
...
firstly a bit of background.

I bought a house last December.

It originally had a semi-detached double garage with a supporting wall in
the middle. (one of the bedrooms is above one of the garages.)

A previous owner had the garage that was under the bedroom converted to an
extra room, and knocked through a door way from the hall.

So the double garage became a single garage & extra reception room. (there
were two separate single garage doors, one of which was removed and
replaced with a wall and window)

The garage floor was 6 inches lower than the Hall floor when they knocked
the door opening through from the hall.

Now at the time, there was a steel gas pipe running along the garage- hall
wall (on the garage wall side to the hall) above the then garage floor
but below the hall floor level. (kitchen is to rear of garage)

So the builder built a wood frame around the gas pipe which is 12ft long
and 5 inches wide to protect said gas pipe in the garage being converted.

They then put down a layer of sand, then a blue plastic damp proof
membrane and filled the garage floor it with concrete till it was level
with the hall floor. They then put a piece of 12ft long 5in wide plywood
to cover this trench containing the gas pipe. This meant that the gas pipe
was accessible at all times.

Now for the problem:

The gas pipe has since been decommissioned (it was corroding badly) and a
new copper gas pipe put in that takes a different route to the original
gas pipe.

I have removed the old steel gas pipe and the supporting wood frame and
the plywood cover. I wish to fill this in with concrete to match the rest
of the garage floor and the hall floor.

This has resulted in a trench that is 12ft long by 5 inch wide.

There is damp proof course across the doorway that was knocked through and
this was covered with concrete.

Now whats the best way of dealing with this 12ft long by 5inch wide now
empty trench? There is a surplus amount of blue DPM material which went
under the plywood cover but is perforated with gripper rod nails and
carpet tacks even though it would reach the existing wall.

Can I put a strip of DPM material down this trench and then fill it in
with concrete or will there be insufficient overlap between old and new
DPM's given the fact that the trench is 12ft long by 5inches wide?

Is there a water resistant concrete I can use to fill this trench in that
will not be affected by the nail holes in the exisiing DPM and prevent any
rising damp problems?

Regards,

Stephen.

A lot depends on the subsoil as to how good your DPM has to be, so no-one
can be entirely sure.
I would paint the side of the existing concrete with a few coatsof bitumous
paint . I would put a strip of DPM in the trench turned up the sides, cut
off just below the surface.
You can buy chemical to add to concrete mix makes it water repellent if you
want belt and braces.
You can also buy chemical to paint on to existing concrete the makes it
water repellant.
However it won't stop positive water pressure so make sure your trench
doesn't fill with water in wet weather.



Adding SBR to the concrete mix would probably be your best bet

Stephen H wrote:

Now whats the best way of dealing with this 12ft long by 5inch wide now
empty trench?

Depending perhaps on what you're going to use the ex-garage for, I might
have been inclined to leave the trench alone, or perhaps to reinforce it so
that a decent thickness of floor-plank could be laid into the top of it so
it would bear weight ok. It sounds as if it's one of those potentially
useful cable ducts that can make running cables around houses so much
easier, even if, say, cables from rooms next to to it come through the wall
at one point, run along the trench, then go back through the house wall.

--
Jeremy C B Nicoll - my opinions are my own.

Email sent to my from-address will be deleted. Instead, please reply
to replacing "aaa" by "284".

Stephen H wrote:
firstly a bit of background.

I bought a house last December.
snip

Just cut a piece of DPM to cover the bottom and one side of the channel and
place this over the top of what you already have, then concrete.

Don't worry about nail holes etc, DPM's get damaged every time they have
hairy-arsed blokes running barrows of concrete over them, that is to say
that your DPM is already damaged all over the place as is everyone else's -
it makes no difference whatsoever, concrete won't 'suck' water up through
these - the entire slab would have to be sitting on pooled water for decades
before any made it to the surface

Update:

Now that I have exposed the trench and removed the wood and old gas
pipe, I am now ready to fill the trench in.

There appears to be a blue DPM under the existing floor. Under this blue
DPM, there appears to be a layer of sharp sand. This is whats on top of
the old concrete floor of the garage. (the garage was converted into a
room, and garage floor was lower than the hall floor)

I happen to have some building sand in the garage. Can I use this for
the trench or must it be sharp sand?

I will then place a DPM in the trench on top of this sand, linking up
with the DPM under the hall floor and the DPM under the existing slab of
concrete.

After placing this DPM, I then will fill in with concrete. What should
this concrete be? 1 parts portland cemenet to 6 parts building sand or 1
parts portland cement to 3 parts building sand?

Regards

Stephen

On 21 July, 21:02, Stephen H wrote:
Update:

Now that I have exposed the trench and removed the wood and old gas
pipe, I am now ready to fill the trench in.

There appears to be a blue DPM under the existing floor. Under this blue
DPM, there appears to be a layer of sharp sand. This is whats on top of
the old concrete floor of the garage. (the garage was converted into a
room, and garage floor was lower than the hall floor)

I happen to have some building sand in the garage. Can I use this for
the trench or must it be sharp sand?

You can fil it with anything you want. I'd choose polystyrene for bulk
fill rather than sand, and sand can take up the reamining gaps.


I will then place a DPM in the trench on top of this sand, linking up
with the DPM under the hall floor and the DPM under the existing slab of
concrete.

After placing this DPM, I then will fill in with concrete. What should
this concrete be? 1 parts portland cemenet to 6 parts building sand or 1
parts portland cement to 3 parts building sand?

whatever you want really. I'd put stone in the mix too.

NT

Regards

Stephen

In article id,
Jeremy Nicoll - news posts writes:
Stephen H wrote:

Now whats the best way of dealing with this 12ft long by 5inch wide now
empty trench?

Depending perhaps on what you're going to use the ex-garage for, I might
have been inclined to leave the trench alone, or perhaps to reinforce it so
that a decent thickness of floor-plank could be laid into the top of it so
it would bear weight ok. It sounds as if it's one of those potentially
useful cable ducts that can make running cables around houses so much
easier, even if, say, cables from rooms next to to it come through the wall
at one point, run along the trench, then go back through the house wall.

I found plywood covered trenches under the carpets when I moved in
and ripped up the old carpets. Very useful they were too. Now
filled with ethernet, speaker, telephone, alarm, home automation,
and aerial cables, as there was plenty of spare space around the
radiator pipes in them.

No way would I get rid of such a useful feature.

Mine are actually formed from galvaised steel troughs, with lips
along the top to take the plywood lids.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]