Plasterboard or render straight to walls?

[patp]

This is for a new bungalow brick and block construction. We have been told, while on a self build course, that brick and block construction should be wet plastered straight to the wall because other wise the insulation will be compromised in the finished build.

 

Now at the stage of getting quotes for plastering and experienced plasterer is telling us that plasterboard is best as blockwork will move over time and cause cracking to the plaster.

 

We were also keen on rendered plastering to get a good firm wall for hanging pictures etc though this is a lower priority than insulation issues.

 

Opinions?

[Mr Punter]

Wet plastered onto the blockwork is much nicer than plasterboard on dabs.  You will know the blockwork is properly sealed.  If you have plasterboard on dabs the blockwork can let in a fair amount of air.  Any small holes will can let external air in and it just circulates behind the plasterboard.

[CC45]

I'd personally wet plaster - feels solid. PB just feels cheap tbh.

[nod]

As a business I do both options 

Both can easily be sealed 

It’s down to individual preference 

The main areas for air leakage are around windows and exterior doors 

The heads and reveals around these will need to be dot and dabbed But the rest can be wet plastered 

I chose to dot and dab ours

As it gives a warmer feel 

Though I could have rendered it far half the price 

[Mr Punter]

  On 03/06/2021 at 21:11, nod said:

The main areas for air leakage are around windows and exterior doors 

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But if you have dot and dab air leakage can be anywhere / everywhere because often there are gaps in the blockwork, holes smashed through for services and you have a plasterboard tent.

 

I have often felt cold air coming through sockets etc. on dot dab walls.

[Nickfromwales]

It's all down to quality of work, whichever you chose, and attention to detail. I would parge the blockwork, fill and smooth any chases / back boxes etc, foam and seal joist pockets / other penetrations to atmosphere if you have them, and then dot n dab.

You won't get a plasterboard / thermal 'tent' if you mitigate against it. Knowing how / where to successfully mitigate is the key to success. 

[ProDave]

I would do neither.

 

Electrics chased into walls and back boxes sunk into walls is so yesterday, and as an electrician I hate it.

 

I would parge coat the walls to seal them, and then fix vertical 25 by 50mm battens to the wall. That creates a service void to run pipes and cables and the plasterboard screws to those.  A 35mm back box fits nicely in the 25mm cavity and the 12mm of the plasterboard.

 

Then it is SO much easier to do your wiring and plumbing and so much easier if you want to make alterations at a later date.  It's even possible to run the wiring so you can literally add an extra socket just by cutting a hole in the plasterboard and picking up the cable.

 

This is normal practice for an air tight timber frame, no reason not to do it on a block built house.

[nod]

  On 03/06/2021 at 22:06, Mr Punter said:

 

But if you have dot and dab air leakage can be anywhere / everywhere because often there are gaps in the blockwork, holes smashed through for services and you have a plasterboard tent.

 

I have often felt cold air coming through sockets etc. on dot dab walls.

you simply seal around all sockets and Pb edges You can still have air leakage with wet plaster Around the ceiling perimeter is still Pb 

As I’ve already stated Window and external frames have to be sealed properly 

As Nick says Workmanship is crucial

 

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Edited June 4, 2021 by nod

[Nickfromwales]

  On 04/06/2021 at 07:59, ProDave said:

 

I would parge coat the walls to seal them, and then fix vertical 25 by 50mm battens to the wall. That creates a service void to run pipes and cables and the plasterboard screws to thos

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And then you're at the mercy of the shape / state of the walls. No thanks!

No blockwork walls go up precise enough to do that, none that I've ever seen anyhow, so all of the kickers in the blockwork and the out-of-plumb bits transfer unhindered to the plaster-boarded face unless you go about spending an age packing and levelling each batten. Even then you only get a vertical batten but you don't get a straight wall as each batten is not flush with the previous / next batten unless you really turn into the batten fitter of the year. Pointless ball-ache.

Chase the boxes in 15-20mm, clip the cables to the blockwork, parge the boxes in, and dot n dab to an immaculate flat, straight wall. Plasterer only has to finish then as opposed to dub and finish.  

[Nickfromwales]

 

I wish you were around to show a few guys I've met exactly how to D'N'D properly mate. Some are still out there working with 12 miserable dabs to a full board  

[patp]

Interesting debate. I have had a very long telephone chat with a plasterer who is coming out to quote. He was trying to persuade us down the route of dot and dab with the same argument as above i.e. if it is done properly it should be fine. The lecturer who advised block and brick builders to render their walls was an ex site foreman on huge sites so perhaps he saw the dark side of plasterboard?

 

I have read the website of a gypsum supplier who also say that the insulation is better if plaster is applied direct to the block/brickwork.

 

Anyone used lime render?

[joe90]

Personally I don’t like the “feel” of dot and dab (hollow sounding walls). Yes I know if it’s done properly it performs well but I had my build cement rendered then plaster top coated. I can hang anything I want from any wall (apart from the odd stud wall in bedrooms/bathroom upstairs). 

[Nickfromwales]

  On 05/06/2021 at 06:50, joe90 said:

Personally I don’t like the “feel” of dot and dab (hollow sounding walls). Yes I know if it’s done properly it performs well but I had my build cement rendered then plaster top coated. I can hang anything I want from any wall (apart from the odd stud wall in bedrooms/bathroom upstairs). 

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Preferable yes, but you need a good spread to get things dragged and floated on the first sets so the end result is flat / plumb etc. 
For D’N’D I now stipulate a minimum of 70% adhesion, plus a continuous bead around perimeters / sockets etc.

All methods can be done badly so it always falls back to the tradesperson undertaking the work, every time. 

[Oz07]

Obvious benefit of boards is easier first fix for electrical and less damage to blockwork. How do you parge a chase?

[Declan52]

  On 05/06/2021 at 19:12, Oz07 said:

Obvious benefit of boards is easier first fix for electrical and less damage to blockwork. How do you parge a chase?

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It gets fully filled when the scratch coat goes on. 

[patp]

Does anyone know anything about a spray on plaster finish? The, experienced, plasterer has just been to measure up for a quote. He says it is now possible to plaster board the ceiling and spray a special bagged plaster mix over the walls followed by trowelling.

[Oz07]

  On 05/06/2021 at 20:05, Declan52 said:

It gets fully filled when the scratch coat goes on. 

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Metal capping and back boxes?

[Oz07]

  On 06/06/2021 at 15:35, patp said:

Does anyone know anything about a spray on plaster finish? The, experienced, plasterer has just been to measure up for a quote. He says it is now possible to plaster board the ceiling and spray a special bagged plaster mix over the walls followed by trowelling.

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Seems to be all the rage on commercial jobs but still on boards 

[patp]

  On 06/06/2021 at 15:55, Oz07 said:

Seems to be all the rage on commercial jobs but still on boards 

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We have had a plasterer come to quote who wants to use plasterboard. He has a colleague who uses the spray on method and they say it can be done on our walls. Just don't want to be a failed experiment  Looking at the plaster manufacturer's website it does seem to be suitable for use on solid walls.

[Oz07]

If suitable then give it a go. 

@nod?