Insulation upstand when not having skirting board?

[flanagaj]

With a conventional build, the thickness of the 'dot & dab' / float and set and skirting board will hide the 25mm thickness of the PIR upstand of a screed floor.  If you are not planning on having skirting board, then a conventional build up risks the PIR showing.  In such a scenario, is the only option to use insulation backed plasterboard or bring the plasterboard off the wall using battens?

 

This obviously only applies to a polished slab finish or an insulated garage floor.

Edited Friday at 06:17 by flanagaj

[Nickfromwales]

35 minutes ago, flanagaj said:

With a conventional build, the thickness of the 'dot & dab' / float and set and skirting board will hide the 25mm thickness of the PIR upstand of a screed floor.  If you are not planning on having skirting board, then a conventional build up risks the PIR showing.  In such a scenario, is the only option to use insulation backed plasterboard or bring the plasterboard off the wall using battens?

 

This obviously only applies to a polished slab finish or an insulated garage floor.

Mildly confusing, so which one is it?

 

Are you having a floor covering?

 

More info and less ambiguity please!

[Spinny]

Dot & Dab brings the plasterboard off the blockwork anyway. 12.5mm plasterboard with 2.5mm skim = 15mm. Dabbed off the wall by 10mm and the front of your finished wall is circa 25mm off the block work.

 

Why no skirting board ?

People do use flush skirting with shadow gaps and stuff - is that what you mean ?

 

We have a 25mm upstand but levelling compound and flooring will cover it. 

 

Laying the top part of the screed to cover the top of the upstand could be one answer. Yes creates a small thermal bridge between floor and wall but does this matter much ?

[flanagaj]

7 hours ago, Nickfromwales said:

Mildly confusing, so which one is it?

 

Are you having a floor covering?

 

More info and less ambiguity please!

No floor covering

[flanagaj]

2 hours ago, Spinny said:

Dot & Dab brings the plasterboard off the blockwork anyway. 12.5mm plasterboard with 2.5mm skim = 15mm. Dabbed off the wall by 10mm and the front of your finished wall is circa 25mm off the block work.

 

Why no skirting board ?

People do use flush skirting with shadow gaps and stuff - is that what you mean ?

 

We have a 25mm upstand but levelling compound and flooring will cover it. 

 

Laying the top part of the screed to cover the top of the upstand could be one answer. Yes creates a small thermal bridge between floor and wall but does this matter much ?

My post was confusing.  I have an insulated garage floor slab, but I wasn’t planning on plaster-boarding or fixing skirting board.  Rather than having a 25mm slice of PIR showing, I could either omit the upstand, but that sort of defeats the point of insulating the slab.  
 

[Spinny]

Why insulate the slab, are you heating the garage ?

[Nickfromwales]

If bare walls, who gives a hoot about seeing a bit of PIR around the perimiter?

[flanagaj]

On 19/06/2026 at 20:27, Nickfromwales said:

If bare walls, who gives a hoot about seeing a bit of PIR around the perimiter?

I've subsequently discovered that you can cut a 45 degree angle on the PIR to hide the edge.

 

One final question.  How do you get a smooth enough finish on the slab for PIR.  Do you simply use a piece of timber with a side to side motion and then use a bull float at 90 degrees.  I really need to be able to do the slabs myself with my brother as I struggle to find anyone to do it without changing lots of £££

[Mr Punter]

1 hour ago, flanagaj said:

do the slabs myself with my brother

 

Well that is great news for your project.  Although you may find siblings tricky, at least they know your foibles and are not such a PITA as contractors can be.

[Nickfromwales]

11 hours ago, flanagaj said:

I've subsequently discovered that you can cut a 45 degree angle on the PIR to hide the edge.

 

One final question.  How do you get a smooth enough finish on the slab for PIR.  Do you simply use a piece of timber with a side to side motion and then use a bull float at 90 degrees.  I really need to be able to do the slabs myself with my brother as I struggle to find anyone to do it without changing lots of £££

YouTube vids should help, as seeing pictures and methods will be much more benefit to you.

 

Self Compacting Concrete may help massively as this will want to find it’s own level without much coercion, but I would still recommend getting one chap in to help you finish the slab; you only need them for 1 day max and that can’t be too much £££  vs the risks. 
 

You also need to be able to adapt to the mixes being inconsistent, unless one wagonload will do you?

 

You can also blind the finished concrete with sharp sand, before laying, but if you’re laying a screed on top then this doesn’t need to be that ‘spot-on’ anyways. 

[flanagaj]

12 hours ago, Nickfromwales said:

YouTube vids should help, as seeing pictures and methods will be much more benefit to you.

 

Self Compacting Concrete may help massively as this will want to find it’s own level without much coercion, but I would still recommend getting one chap in to help you finish the slab; you only need them for 1 day max and that can’t be too much £££  vs the risks. 
 

You also need to be able to adapt to the mixes being inconsistent, unless one wagonload will do you?

 

You can also blind the finished concrete with sharp sand, before laying, but if you’re laying a screed on top then this doesn’t need to be that ‘spot-on’ anyways. 

I will have a look at self compacting concrete.  When you say someone to help finish the slab, will a bull float suffice?

[Nickfromwales]

13 hours ago, flanagaj said:

I will have a look at self compacting concrete.  When you say someone to help finish the slab, will a bull float suffice?

It’s knowing how / when to use it. You would also need to seal it as you lay to stop the moisture evaporating too quickly.

 

Not a job you can just ‘do’, if you’re not used to doing it.
 

I know some very good lads who would work a weekend, if you need (want) some help, (and if you can get concrete there on a Saturday). Let me know. 

[Tony L]

Thanks for bringing my attention to SCC, @Nickfromwales.  @flanagaj, according to a conversation I had with Gemini AI, you'd use a dapple bar, rather than a bull float with this.  Based on watching one YouTube video, it looks like an easy enough DIY job for my small garage, although I think I'd be inclined to to pay some experts to do this for me if this was my house.  The sealant, which goes on soon after the pouring & dappling, is super important.