Dot and dab versus 2 coat plaster on block walls

[Caroline]

Hi

We have new internal block walls. Was thinking of 2 coat plaster over them but some say dot and dab. Any advice appreciated.

 

Thank you

[JohnMo]

Two coats gives you airtight out the box. Dot and dab, same if you apply the adhesive correctly and form a full perimeter of adhesive. Otherwise you get air leaky walls

[nod]

Dot and dab will give you the same airtightness as Wet plaster base coat But a much warmer feel to it 

[Nickfromwales]

2 hours ago, Caroline said:

Hi

We have new internal block walls. Was thinking of 2 coat plaster over them but some say dot and dab. Any advice appreciated.

 

Thank you

2 coat will also mean your electrician has to chase everything in.

 

D&D means you can save time and still get a great job, as long as you go for dry liners who do this every day and who can listen to instruction; instruction such as all back boxes benched, continuous dabs all round the perimeter of the wall and boards, and no dab oozing out of joints and corners.

 

Defo ‘warmer’ feel to these as above. 

[Mattg4321]

43 minutes ago, Nickfromwales said:

2 coat will also mean your electrician has to chase everything in.

 

D&D means you can save time and still get a great job, as long as you go for dry liners who do this every day and who can listen to instruction; instruction such as all back boxes benched, continuous dabs all round the perimeter of the wall and boards, and no dab oozing out of joints and corners.

 

Defo ‘warmer’ feel to these as above. 

Doesn’t make a huge difference to electrician if you’re doing it properly imo. 
 

35mm boxes still need chopping in a bit for D&D. You don’t want 25mm boxes - that’s for new build estate s@&£boxes. 
 

Same with capping. I always like to fit it even if D&D. Clipping only runs a higher risk of damage from other trades chucking materials around etc. 

[nod]

1 hour ago, Mattg4321 said:

Doesn’t make a huge difference to electrician if you’re doing it properly imo. 
 

35mm boxes still need chopping in a bit for D&D. You don’t want 25mm boxes - that’s for new build estate s@&£boxes. 
 

Same with capping. I always like to fit it even if D&D. Clipping only runs a higher risk of damage from other trades chucking materials around etc. 

I run a plastering company and do both float and set and dot and dab 

But have chosen to use dot and dab on both builds for a reason 

No difference in cost 

[G and J]

11 hours ago, Nickfromwales said:

Defo ‘warmer’ feel to these as above. 

So dot and dab helps an old fashioned masonry build feel like a proper modern timber frame build.   😉 

[Nickfromwales]

3 hours ago, G and J said:

So dot and dab helps an old fashioned masonry build feel like a proper modern timber frame build.   😉 

Not quite……lol.

[Spinny]

What exactly are people meaning by 'warmer feel' ?

I cannot really fathom why 12mm of 2 coat plaster should 'feel' different to a board with 3mm skim.

 

IMO only, dot and dab is a modern convenience and short cut in a world of high labour costs and sometimes questionable quality of blockwork. I think many builders love it because it is relatively quick and easy and it hides a multitude of sins - walls not built plumb - walls lumpy and bumpy - can't be bothered to pay the sparky to chase out ? Why would a builder care if your rooms all get smaller by 30mm in each dimension ? Why would a builder care if you have to mess about with special wall fixings because you have a void behind the p/board. Why would a builder want to pay for and wait for availability from an experienced and skilled 2 coat plasterer when he can call in someone cheap to skim the board ? Also less drying out I guess.

 

More homes these days are built to use plasterboard on the stud walls - I guess internal masonry walls almost unheard of now. So no doubt most plasterers spend most of their time skimming board.

 

IMO if you can find a good plasterer then go 2 coat on masonry walls (provided you had a good brickie doing reasonable plumb work) and provided you can afford to pay for the good brickie and the good plasterer.

 

[JohnMo]

3 hours ago, Spinny said:

lWhat exactly are people meaning by 'warmer feel' ?

I cannot really fathom why 12mm of 2 coat plaster should 'feel' different to a board with 3mm skim.

 

IMO only, dot and dab is a modern convenience and short cut in a world of high labour costs and sometimes questionable quality of blockwork. I think many builders love it because it is relatively quick and easy and it hides a multitude of sins - walls not built plumb - walls lumpy and bumpy - can't be bothered to pay the sparky to chase out ? Why would a builder care if your rooms all get smaller by 30mm in each dimension ? Why would a builder care if you have to mess about with special wall fixings because you have a void behind the p/board. Why would a builder want to pay for and wait for availability from an experienced and skilled 2 coat plasterer when he can call in someone cheap to skim the board ? Also less drying out I guess.

 

More homes these days are built to use plasterboard on the stud walls - I guess internal masonry walls almost unheard of now. So no doubt most plasterers spend most of their time skimming board.

 

IMO if you can find a good plasterer then go 2 coat on masonry walls (provided you had a good brickie doing reasonable plumb work) and provided you can afford to pay for the good brickie and the good plasterer.

 

I would expect, because block work is made from concrete and when covered with plaster suck the heat from your hand. Plasterboard on the other hand with an air gap doesn't feel so cold.  The difference will be also seen in room temperature stability the concrete blocks absorbing and releasing heat energy as room temps fluctuate to give stable room temps. The plasterboard version is somewhat isolated with an air gap will not function in the way. More akin to stud walls.

 

I have always thought dot and dab is a bodge get out jail quick for builders, much like you describe, hide all the rubbish quickly and easily.

[Nickfromwales]

4 hours ago, Spinny said:

I cannot really fathom why 12mm of 2 coat plaster should 'feel' different to a board with 3mm skim.

Ye' cannea change the laws of physics, Jim.

 

4 hours ago, Spinny said:

IMO only, dot and dab is a modern convenience and short cut in a world of high labour costs and sometimes questionable quality of blockwork. I think many builders love it because it is relatively quick and easy and it hides a multitude of sins - walls not built plumb - walls lumpy and bumpy - can't be bothered to pay the sparky to chase out ? Why would a builder care if your rooms all get smaller by 30mm in each dimension ? Why would a builder care if you have to mess about with special wall fixings because you have a void behind the p/board. Why would a builder want to pay for and wait for availability from an experienced and skilled 2 coat plasterer when he can call in someone cheap to skim the board ? Also less drying out I guess.

 

More homes these days are built to use plasterboard on the stud walls - I guess internal masonry walls almost unheard of now. So no doubt most plasterers spend most of their time skimming board.

 

IMO if you can find a good plasterer then go 2 coat on masonry walls (provided you had a good brickie doing reasonable plumb work) and provided you can afford to pay for the good brickie and the good plasterer.

You clearly have near zero real-life experience on sites / projects that have had either / or.

 

It is my own, isolated, opinion, that you have no clue what you are talking about.

 

Myself and @nod have done many homes where quality, integrity, and "best effort" are at the forefront of everything we do.

 

It's a bit of a piss-you-off to hear you dismiss this in a few sentences, to be honest.

 

30mm smaller? How thick do you think scratch-coat and skim is?? 5mm?

[Nickfromwales]

1 hour ago, JohnMo said:

I have always thought dot and dab is a bodge get out jail quick for builders, much like you describe, hide all the rubbish quickly and easily.

Utter, indiscriminate, tosh.

[Caroline]

Thanks everyone for all your thoughts.

Been really helpful and will go down the 2 coat plaster route.

[Nickfromwales]

4 minutes ago, Caroline said:

Thanks everyone for all your thoughts.

Been really helpful and will go down the 2 coat plaster route.

I grew up around this, and would recommend this in a heartbeat.

 

Just........get someone good.

 

........Very good

[Iceverge]

On 24/08/2025 at 18:19, nod said:

Dot and dab will give you the same airtightness as Wet plaster base coat But a much warmer feel to it 

 

What kind of airtightness numbers do you normally see? 

[nod]

5 hours ago, Iceverge said:

 

What kind of airtightness numbers do you normally see? 

Ours was a genuine 2 

But as I’ve previously stated Virtually all the large sites are done as a desktop So not actually done 

They tend to be 2 But with airtightness changes That will have been downgraded to 3 

 

If the DD is done correctly It’s quite easy to get good airtightness 

[Iceverge]

That's actually respectable. 

 

Is there an advantage to downgraded to 3? 

 

 

 

 

[torre]

2 hours ago, Iceverge said:

advantage to downgraded to 3

 

I think the only advantage is for the developers, who can get away without the cost of installing MVHR

[Spinny]

13 hours ago, Nickfromwales said:

It's a bit of a piss-you-off to hear you dismiss this in a few sentences, to be honest.

 

30mm smaller? How thick do you think scratch-coat and skim is?? 5mm?

OK I was being deliberately opinionated. And yes I only have my one experience to draw on - which has been troubled. TBH you could argue my experience both ways. The builder sent a plasterer and (1) He could skim a stud wall no problem but (2) He took a plumb wall and wet plastered it and it was over 10mm out over 2.4m height by the time he had finished with it - thick at the bottom, thin at the top. So you could argue that as a good case for dot and dab where that then wouldn't have happened. I hired another plasterer of my choice who has worked diligently to correct previous problems and wet plaster other walls and ceilings to excellent effect though.

 

In my case where dot & dab has been used it is a minimum of 10mm, and often 15mm of dab. So 15mm dab + 12.5mm board + 3mm skim = 30.5mm and on both sides of a room would be 61mm. Whereas wet plaster can be say 8-9mm plus 3-4mm = 12-15mm and on both sides of a room would be 24-30mm. So dot and dab can lose 30mm from the width of a room or alcove etc.

 

In my case space is tight (don't we all want a bigger building/plot) and some dimensions were planned at the architect stage to fit kitchen/appliances/shelving etc. The architects chosen plaster allowance was 15mm to each wall at that stage which was way before any discussion of dot and dab or not. 

 

I guess you can say it is horses for courses. Large roomy build or refurb with rather wonky existing walls and/or a desire to tightly control cost and minimise delays - maybe you want dot & dab. Tight spaces with a good brickie and plasterer - wet plaster.

 

What I don't like about dot & dab: losing space to blobs of mortar, wall fixing implications, possibly cold (or damp) air gaps

Things to like about dot & dab: quick, easy, and economical, useful for wonky walls.

 

It is all trade-offs and individual perspectives in the end.

 

 

 

 

 

[Nickfromwales]

10 minutes ago, Spinny said:

OK I was being deliberately opinionated.

Myself, probably over-opinionated.

 

Just seen D&D done excellently with great results enough times to be willing to defend it. And if @nod will use this in his own house and his clients 7 figure builds, then it defo isn't any form of compromise; other than, as you say, losing 15mm of GIA per wall.

[Iceverge]

I'm a wet plaster fan, primarily for airtightness but also it gives shoddy workmanship less places to hide. You can see and patch settlement cracks easily too. 

 

I'd be interested to hear had anyone gotten to passive levels with boarding out. I suppose there's no reason it couldn't be done but any dry lined houses I've been in have had a breeze out of the sockets on a windy day. 

 

 

 

 

 

 

[Nickfromwales]

5 minutes ago, Iceverge said:

I'd be interested to hear had anyone gotten to passive levels with boarding out

Did this over Velox ICF and got 0.66 ACH (as-built). Would have been more like 0.4-something if the doors and windows didn't leak so much.....

[Iceverge]

ICF is pretty excellent on its own though. Out of interest why not just screw it to the webs rather than dot and dab? 

 

Speed?