Hi all

I'd love any ideas you may have (& corrections to my thinking?!) for how to fix ufh pipes to my hemplime subfloor so they lay flat while I install an earth floor above.

Floor build-up so far & {proposed} is:

{earth floor}
{ufh pipes - how to hold in place?}
hemplime slab 100mm
breather membrane
foamglass 170mm
gravel
ground

Hemplime isn't like limecrete, in that it's more like a kind of set weetabix you soaked in milk and then left to really dry out - it isn't solid as such, more shredded wheat that can pull apart (if you make it - otherwise it's fine).

My feelings are that the barbed pegs I've come across will simply pull out, and pull big lumps of the floor with them.

I am pondering my options and so far have thought of these possibilities:

- install some kind of metal grid, that can be fixed to the wall at the perimeters (although in places this would be tricky), but in a room 3m x 4m I'm not sure perimeter fixings will be enough to stop this all lifting in the middle of the room with the bending & curling up of the pipes

- install a slim timber grid, fixed at the perimeter, to sit over the pipes, and pour the earth floor between the grid sections, then pour final earth floor above the grid to finished floor level

- hold them down temporarily somehow (?!) and pour a lime screed to cover the pipes, and do the earth floor on top of that

- hold them down temporarily somehow (?!) and pour a wetter-than-normal earth screed to cover the pipes, then do remaining earth floor above that

My motivations for doing an earth floor are: the performance, look & feel; the low embodied energy & costs; maintaining a fully breathable floor build-up.

Thanks for any input, and suggestions for fixing methods / fixings / alternative approaches

Hi Tony - it would be good of those wete options, but unfortunately the issue is the hemplime won't take a fixing like that, they just pull out bringing the floor mix with it. It's kind of like a short-fibre soft shredded wheat, which breaks down into a wider hole when you screw into it, rather than catching. I'm still thinking I'm going to need to create some kind of battening frame, or pour a lime screed (but no convinced that will adhere to the dusty hemplime surface well).

Is there a way to 'tag' someone? I wonder if 'Bot de Paille' might have done ufh on a hemplime slab.

Above the breather membrane you can use a plastic mesh grid to tie the pipes to. This is what we were supplied with via limecrete slab supplier.
Usually i use a142 mesh for sand/screed not sure if theres issue with mesh and lime though??
Perhaps just easier for supplier to deliver roll of plastic mesh ? :-)

Why the gravel in the build up? I thought that the foamglass was usually load bearing and insulating so any other hardcore wasn't required.

With similar floor build ups the the pipes would be fixed onto a clip rail system with self adhesive backing sticking to the breather membrane, pipes then bedded into the slab. So, not being familiar with the hemplime slab, if it won't allow pipes to be bedded/screeded into it, maybe a second breather membrane for the clip rails to adhere to.

Fine

The weight of an A142 mesh will hold the pipes down, if worried fill them with water especially if liquid screed.

A142 mesh is steel fabric anti cracking reinforcement, I have used it lots of times.