Polished concrete floor detail

Moggaman

Hi.

in my self build, I am now looking at wall floor junction details. We have just selected polished concrete as our finish floor for downstairs.

I have a cavity wall. I have a sub floor built. My intention was to get plasterers in and get them to plaster walls from ceiling down to sub floor . Then , do floors after. However, it strikes me that if I put I a polyiso strip against wall prior to pouring floor, this will be visible on the edge all around after.My wife would like no skirting, just a clean wall floor , junction.

how do I achieve this?

thanks

Moggaman

I should say , the house is roofed , first fixed etc and ready for slabbing .

thanks

BryanF

Suggest you should bring in a contractor who is going to polish the floor to, spec mix and supervise concrete install. With regards to edge detail, normally a ‘wedge’ of insulation is cut to form separating strip at screed level, so the floor angles to a point at top of floor meeting wall. Best to get the contractor who is polishing this floor to sort these details, ie one person responsible ..

Moggaman

Thanks Bryan.Yes I will have a contractor doing the whole lot. Best to talk to him so.

i presume u mean that the 25mm strip of insulation will be 25mm wide for the most part , tapering into zero at ffl?

Dudda

I wouldn't do the 'wedge' as it can crack. Is the plaster the airtightness layer? That could be an issue. Apply a parge coat first from ceiling to the sub slab to make everything airtight first.

You want to pour the concrete floor first if possible and then plaster the walls. This will hide the perimeter insulation and allow you create a shadow gap using the floor as the straight edge. I'd also polish the floor before plastering. If it's polished and sealed you can put down a layer of plastic and then hardboard, thin ply, mdf or if not a busy site even large sheets of carboard (like you'd get from a furniture shop). Don't tape anything to the finished floor. The adhesive in the tape will stick to and stain the floor as it could be there a while. This is particularly a problem if you start heating up the slab and the adhesive in the tape starts to melt. Although it has faded a lot I'm still looking at a tiny bit here four years later.

What I did is add a service cavity with battens so this hid even more of the perimeter edge and allowed me create shadow gaps that way.

Check out this post I made a few years ago for another Boards member

https://www.boards.ie/discussion/comment/105768995/#Comment_105768995

Dudda

Forgot to mention you have to use flexible insulation for a polished concrete floor to allow it expand and contract so can't use any rigid insulation cut to a wedge. If you don't it will crack and look shlt

BryanF

https://www.boards.ie/discussion/comment/118280965#Comment_118280965

When I mean ‘a contractor’ I mean a specialist that will ultimately grind and seals the final result - they should be brought in to pour the floor, ie not your main builder. Listen to dudda, he does more of this work than I do. I’d concur with the protection requirements, as builders will make sh1t of any concrete floor that’s unprotected - it’s important it’s protected from the day the floor is poured..

Moggaman

would an 8mm insulation roll, between the floor pour and walls, both internal and external walls, have adequate expansion. No 25mm insulation .

thanks

Dudda

If that's the flexible stuff then yes that's what you want

Mellor

My intention was to get plasterers in and get them to plaster walls from ceiling down to sub floor

I wouldn’t install the plaster finish below the finished floor. As the edge strip will be visible as you guessed, and also because the polishing process isn’t gentle. It’s aggressive and messy (depending on level of grind, some slop is com off) - you don’t want that soaking into a finished wall.

Polished concrete is a common finish in my commercial fitouts I’ve done. Although not with out a skirting. Skirting serve a purpose tbh. If you really want that detail you could set to a stop bead close to the floor. Personally I’d go for a flush skirting, colour matched to the wall.

wibago

To achieve a clean wall-floor junction with polished concrete flooring and without skirting, there are a few options you can consider:

1. Use a backer rod: Before pouring the concrete, you can install a backer rod against the cavity wall, leaving a gap between the backer rod and the subfloor. This gap can then be filled with a flexible sealant after the concrete is poured, which will hide the polyiso strip and provide a clean finish at the wall-floor junction.
2. Install a metal trim: You can install a metal trim along the wall-floor junction, which will provide a clean edge and cover up the polyiso strip. The metal trim can be chosen to match the aesthetic of the polished concrete and can be installed using adhesive or screws.
3. Use a recessed baseboard: A recessed baseboard can be installed along the wall-floor junction, creating a groove that can be filled with a flexible sealant or caulk to hide the polyiso strip. The baseboard can be made of a material that complements the polished concrete and can be flush with the subfloor, providing a clean and minimalist look.

It's important to consult with your concrete flooring installer and contractor to ensure that the chosen solution will work well with your specific situation and desired aesthetic.

Mellor

https://www.boards.ie/discussion/comment/120483119#Comment_120483119

Backer rods are installed into gaps before sealant is installed. If you install before the concrete is poured, it will be filled in with concrete, making it pretty useless. You'd need to install something to form the gap prior to the backer being installed.

A metal trim is a pretty poor way to achieve a clean wall to floor junction.

Both of these issues also leave to bottom of the wall exposed to damage. As I pointed out above, a skirting has a purpose (other than covering a gap at the floor). A flush skirting is the only solution that I'd consider suitable.