Hi All,

On the last part of "preparing the ground" from this page:
http://tinyurl.com/homebase-decking
....it says "Place squares of bitumen DPC membrane over the top of the
concrete...".

I forgot to actually look up what this was (I now know "DPC" is damp-
proof-course) so was then wondering round B&Q looking for something
which looked plausible containing bitumen, and ended up with a roll of
bitumen shed felt. Is this a reasonable alternative? I notice on the
B&Q website the roof felt comes under the "damp proof" category.

Thanks a lot,
Adam

Adam wrote:
Hi All,

On the last part of "preparing the ground" from this page:
http://tinyurl.com/homebase-decking
...it says "Place squares of bitumen DPC membrane over the top of the
concrete...".

I forgot to actually look up what this was (I now know "DPC" is damp-
proof-course) so was then wondering round B&Q looking for something
which looked plausible containing bitumen, and ended up with a roll of
bitumen shed felt. Is this a reasonable alternative? I notice on the
B&Q website the roof felt comes under the "damp proof" category.

I use this when building decks
http://www.screwfix.com/prods/49590/...f-Course-100mm

Take the felt back to B&Q & swap it for http://tinyurl.com/3rcygm



--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

On Sun, 21 Sep 2008 02:19:39 -0700 (PDT), Adam wrote:

ended up with a roll of bitumen shed felt. Is this a reasonable
alternative?

The important bit is "damp proof" it's to stop moisture wicking up from
the ground via the support structure into the timber causing it to rot.
Traditionally slate would have been used, latterly bitumen based felts or
plastc DPM as used in walls.

Shed felt has stones on the surface and is a bit thin. The stones will
tend to push through the soft bitumen possibly making holes, so it's
probably wise to remove as many as you can (stiff brush should do it).
Then make a pad from a folded strip say 4 or 5 layers thick that is big
enough to fully support the timber over the concrete/brick/slab support.
Make all your pads the same number of layers thick or the levels will go
out as the structure settles. They still might, thats the advantage of
slate it doesn't compress.

--
Cheers
Dave.

On 21 Sep, 11:14, "The Medway Handyman"
wrote:
Adam wrote:
Hi All,

On the last part of "preparing the ground" from this page:
http://tinyurl.com/homebase-decking
...it says "Place squares of bitumen DPC membrane over the top of the
concrete...".

I forgot to actually look up what this was (I now know "DPC" is damp-
proof-course) so was then wondering round B&Q looking for something
which looked plausible containing bitumen, and ended up with a roll of
bitumen shed felt. Is this a reasonable alternative? I notice on the
B&Q website the roof felt comes under the "damp proof" category.

I use this when building deckshttp://www.screwfix.com/prods/49590/Building/Damp-Proof/Damp-Proof-Co...

Take the felt back to B&Q & swap it for http://tinyurl.com/3rcygm

Thanks, that's only 30cm wide, but my concrete slabs are 40cm across.
Presumably it's a problem if there's a gap in the DPC?

Adam

On Sun, 21 Sep 2008 13:54:03 -0700 (PDT), Adam wrote:

Thanks, that's only 30cm wide, but my concrete slabs are 40cm across.
Presumably it's a problem if there's a gap in the DPC?

You only need the DPC between the timbers and the slabs not over the
entire surface of the slab.

--
Cheers
Dave.

Adam wrote:
Hi All,

On the last part of "preparing the ground" from this page:
http://tinyurl.com/homebase-decking
...it says "Place squares of bitumen DPC membrane over the top of the
concrete...".

I forgot to actually look up what this was (I now know "DPC" is damp-
proof-course) so was then wondering round B&Q looking for something
which looked plausible containing bitumen, and ended up with a roll of
bitumen shed felt. Is this a reasonable alternative? I notice on the
B&Q website the roof felt comes under the "damp proof" category.

Thanks a lot,
Adam

Personally, I wouldn't use anything underneath timbers in a situation like
this - it merely holds any water in place, right where you don't want it -
on the end grain...far better to make a gap somehow between end grain and
concrete, so that air can pass underneath - how this is acheivable is
another matter, probably involving metal bolts or suchlike

--
Phil L
RSRL Tipster Of The Year 2008

On 21 Sep, 22:37, "Dave Liquorice"
wrote:
On Sun, 21 Sep 2008 13:54:03 -0700 (PDT), Adam wrote:
Thanks, that's only 30cm wide, but my concrete slabs are 40cm across.
Presumably it's a problem if there's a gap in the DPC?

You only need the DPC between the timbers and the slabs not over the
entire surface of the slab.

Sure, but there'll still be a gap, unless I'm missing something
obvious. See my piccy:
http://www.snowstone.org.uk/temp/plan.png


Later, Phil P wrote:
Personally, I wouldn't use anything underneath timbers in a situation like
this - it merely holds any water in place, right where you don't want it -

This seems like a good point. There will be rainwater above the DPC
and damp below the DPC, so what's the point in it? Why not just lay
the joists directly on the concrete?

Thanks a lot for the helpful replies so far
Adam

On Mon, 22 Sep 2008 10:51:45 -0700 (PDT), Adam wrote:

Sure, but there'll still be a gap, unless I'm missing something
obvious. See my piccy:
http://www.snowstone.org.uk/temp/plan.png

Overlap the two bits of DPC. One bit under each joist for the entire
length that they are (or would be...) in contact with the concrete
support.

Later, Phil P wrote:
Personally, I wouldn't use anything underneath timbers in a situation
like this - it merely holds any water in place, right where you don't
want it -

This seems like a good point. There will be rainwater above the DPC
and damp below the DPC, so what's the point in it? Why not just lay
the joists directly on the concrete?

Any rain water will soon evaporate and dry in the well ventilated void.
The damp from the ground will rise up due to capillary action and be there
all the time...

--
Cheers
Dave.