From Newsgroup: uk.d-i-y

I am just about to completely rebuild our utility room (aside from the
boiler it is gutted back to bare plaster). Currently it has a concrete
solid slab finished in what looks like a quarry tile. The tiles are
pretty even and well fixed. The room is about 2.2 x 3.2m, and the floor
slopes about 20mm downhill across the narrow axis.

I want to raise the level, as currently there is a step down of approx
130mm from the kitchen, and then a step up of about ~150 to the frame of
the door leading outside. So when done it will be on level with the
kitchen, and also eliminate the need to step up and over the back door threshold.

Since I have plenty[1] of spare PIR insulation boards to hand it would
seem daft not to also take advantage of those and make an insulated
floor while I am at it.

Initially I thought about sticking down a DPM (lapped up the walls) then
a layer of 60mm + 25mm PIR, and then screeding over. However that would
mean the screed at the "thin" edge would only be about 40mm deep. Which
would suggest needing to use a fibre reinforced concrete. Also it would
need a fair amount of curing time.

Then I though of using something like Hardiebaker board - a couple of
layers of 12mm laid in opposite directions and bonded with PU adhesive
would make a very strong floating floor on top of the insulation. Finish
it with some fibre reinforced SLC and it would be good to use in a few
hours. Only problem is the slope - it would need a massive depth of SLC
at the "deeper" end of the room.

So further options - build up extra layers of hardibacker (can get 6mm
as well as 12mm) at the deeper end, and let the SLC remove the "steps".

Or possibly, and my current favourite, cut 0 - 20mm firring strips out
of treater timber, pu them in place on top of the DPM at 300mm centres,
then glue some 12mm OSB3 on top. That gets rid of the slope. Add 85mm
PIR layup on that, then 24mm Hardibacker, and SLC to finish.

Any other options you can think of?

(The floor needs to be decently strong, feel solid, and be able to cope
with a washing machine bouncing about on it. Final finish will be glued
down LVT planks)


[1] Probably 8 or more 60mm, and 4 x 25mm
--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk | \=================================================================/

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From Newsgroup: uk.d-i-y

On 03/03/2026 01:10, John Rumm wrote:

Any other options you can think of?

(The floor needs to be decently strong, feel solid, and be able to cope
with a washing machine bouncing about on it. Final finish will be glued
down LVT planks)

The floor on my build is block/beam, DPM, 100mm concrete, DPM, 100mm
celotex, ~50mm concrete screed, with 16mm UFH piping in it. Solid as it
can get, so you'll be fine with ~50mm of concrete.
I did have to chisel out a small section to get access to a drain, it
wasnt easy.
Just order in some poured screed, its quite expensive for what it is,
but sets perfectly flat in a day, and strong with it. Mixing up and
laying semi dry is a long, slow, hard job. Cheaper, but essentially a
real pain to do well. Poured concrete is so much better.
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From Newsgroup: uk.d-i-y

On 03/03/2026 01:10, John Rumm wrote:

I am just about to completely rebuild our utility room (aside from the boiler it is gutted back to bare plaster). Currently it has a concrete
solid slab finished in what looks like a quarry tile. The tiles are pretty even and well fixed. The room is about 2.2 x 3.2m, and the floor slopes about 20mm downhill across the narrow axis.

I want to raise the level, as currently there is a step down of approx
130mm from the kitchen, and then a step up of about ~150 to the frame of
the door leading outside. So when done it will be on level with the
kitchen, and also eliminate the need to step up and over the back door threshold.

Initially I thought about sticking down a DPM (lapped up the walls) then a layer of 60mm + 25mm PIR, and then screeding over. However that would mean the screed at the "thin" edge would only be about 40mm deep. Which would suggest needing to use a fibre reinforced concrete. Also it would need a fair amount of curing time.

Any other options you can think of?

Grit sand to level the base, 60mm PIR, 65mm screed.
You should probably consider where any adjacent DPMs are.

--- Synchronet 3.21d-Linux NewsLink 1.2

From Newsgroup: uk.d-i-y

On 03/03/2026 01:10, John Rumm wrote:

I am just about to completely rebuild our utility room (aside from the boiler it is gutted back to bare plaster). Currently it has a concrete
solid slab finished in what looks like a quarry tile. The tiles are
pretty even and well fixed. The room is about 2.2 x 3.2m, and the floor slopes about 20mm downhill across the narrow axis.

I want to raise the level, as currently there is a step down of approx
130mm from the kitchen, and then a step up of about ~150 to the frame of
the door leading outside. So when done it will be on level with the
kitchen, and also eliminate the need to step up and over the back door threshold.

Since I have plenty[1] of spare PIR insulation boards to hand it would
seem daft not to also take advantage of those and make an insulated
floor while I am at it.

Initially I thought about sticking down a DPM (lapped up the walls) then
a layer of 60mm + 25mm PIR, and then screeding over. However that would
mean the screed at the "thin" edge would only be about 40mm deep. Which would suggest needing to use a fibre reinforced concrete. Also it would
need a fair amount of curing time.

Then I though of using something like Hardiebaker board - a couple of
layers of 12mm laid in opposite directions and bonded with PU adhesive
would make a very strong floating floor on top of the insulation. Finish
it with some fibre reinforced SLC and it would be good to use in a few hours. Only problem is the slope - it would need a massive depth of SLC
at the "deeper" end of the room.

So further options - build up extra layers of hardibacker (can get 6mm
as well as 12mm) at the deeper end, and let the SLC remove the "steps".

Or possibly, and my current favourite, cut 0 - 20mm firring strips out
of treater timber, pu them in place on top of the DPM at 300mm centres,
then glue some 12mm OSB3 on top. That gets rid of the slope. Add 85mm
PIR layup on that, then 24mm Hardibacker, and SLC to finish.

Any other options you can think of?

(The floor needs to be decently strong, feel solid, and be able to cope
with a washing machine bouncing about on it. Final finish will be glued
down LVT planks)

[1] Probably 8 or more 60mm, and 4 x 25mm

Get the floor level first, then increase the depth of PIR and
top it with a floating floor of something like Fermacell which
used to be available as T&G boards about 40mm thick, which can
be glued and screwed along all the joints.

Getting the correct quantity of boards might be an issue, since
it might only come in pallet loads.
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