Improving acoustics of rooms that have dot and dab plasterboard

PaulDavidThomas

Active Member
I refurbish property. I ended up renovating two properties on the same street in Winchester about 5 years ago. However, I used two very different techniques for various reasons I won't go into. Both houses were stripped back to brick.

The first house, I used acoustic plasterboard ( the blue stuff ) and dot and dab'ed that onto the brick the other was old-school sand and cement onto the brickwork with a skim of plaster over the top.

All I can say is night and day result. The solid walls were just soooo much better - and all of the studies into acoustics I think prove nice dense thick walls are better than 12.5mm of plasterboard with an air gap behind.

If you have this too... You can solve it, in a day without too much mess.

The actual way you do this is mainly controlled by the interface between your plasterboard on your wall and the floor junction. I would always work on the theory, you don't know and follow this technique - you can change if you can think of better solutions.

1. Above the skirting go along and tap. You should easily hear where there is a hollow gap, which is where there is no adhesive.
2. Make each of these points with pencil. Because I have OCD do it in a straight line, perhaps 20mm above the top of the skirting board.
3. If you find areas that are solid, that is fine. Just mark these areas a little differently. This is where the plasterboard adhesive is.
4. Buy a tube of builders foam (Hand Held Expanding Foam 750ml)
5. Go along and drill holes along this line where you have marked just above the skirting board. Make sure the hole is large enough to get the nozzle from the foam gun into. These holes should be about 100mm to 150mm apart. Don't drill where the wall is solid.
6. Hoover out each hole of debris and ensure the nosal of the foam gun goes into the hole
7. Get a little spray gun and fill with water - just empty out a kitchen surface cleaning bottle or similar
8. Go along and use the foam gun to spray into each hole. You might want to put something down to protect your flooring / skirting
9. Let this go off over night - or until hard. Now, just scrape off anything that has come through the hole... This should be on EVERY hole
10. Go up the wall, perhaps a meter and go left to right and tap. This time trying to find where 'air gaps' are. Mark these. Perhaps at intervals of 300mm
11. Now, get a plastic funnel - you know, the one you ( or wife ) use in the kitchen ( Funnel Set )
12. Measure the small end and get an old drill bit - probably a wood drill bit that is twice this size.
13. For each of the holes you have marked at 1m height about 300mm apart, drill a hole at a 45 degree angle down. Then use you finger to clear the hole and leave essentially an 'air gap'
14. Repeat for all holes
15. Go and buy some bags of kiln dried sand.
16. Then use a small paint scuttle to pour the sand into the funnel, whilst the funnel is stuck into each hole. Keep the funnel about 10mm off the brick wall otherwise the sand will not flow.
17. Go ahead and fill the wall.... You might find that tapping the wall will help. But if you put year ear to the plasterboard you will hear the sand trickling down the wall.
18. THIS IS WHY YOU DRILL THE HOLES AT THE BOTTOM, JUST ABOVE THE SKIRTING AND ENSURE THIS IS A SOLID, FILLED SECTION.
19. Once you have gone along and filled all of the holes - you might need a lot of sand. Push some paper into these holes and then use something like a silk filler ( All Purpose Ready Mixed Filler 1kg Tub ) to plug this hole. Equally, you could use some of the foam. If you are using foam make sure you have two nosals - some don't provide two.
20. Now, go another meter up the wall and repeat.
21. Sand and fill, then paint wall.

As you do this you should be able to tap the wall and you will notice the resonance of the wall has gone... This is because it now has a solid mass behind it.

Only do this on walls that are dot and dab onto brick. Do not do it onto stud walls.
 
Last edited:

PaulDavidThomas

Active Member
I did this today on a wall behind a log fire as I wanted it to act as a ‘heat store’. Worked a treat. The entire wall now stays warm as opposed to just the areas where the plasterboard adhesive is.
 

inda1298

Active Member
Thank you for sharing this Paul. A few noob questions if you would not mind as I think this solution may be helpful to me.

Why the expanding foam at all? Wouldn't it be better to attempt to fill with sand completely as there would be more mass added? Or is it to reduce the weight on the drywall, as filling completely with sand would make the load on the wall too much?

Adding foam/sand would not affect the electrical and plumbing in the wall.

Thanks!
 

PaulDavidThomas

Active Member
No question is a silly question and noob questions are perfectly fine.

What you need to do at the bottom of the wall is to stop the kiln dried sand just keep going down. I don't know if you have a solid floor finish or if it's a suspended floor. Thus, if you are in a victorian house, the sand will run down to where the floor boards are and the gaps between the end of the floor boards and the bricks will allow the sand to keep falling into the void under the floor boards.

So, the expanding foam forms a stop point for the sand.

Adding the sand or foam would neither effect the plumbing or electrics. For example it's normal with a sand/cement finish to encase electric wire and plumbing into the wall. Ok, not ideal with plumbing as it will potentially cause slight fractures where the pipe runs due to the differential in heat. However, with plasterboard, this will not happen.
 

raoulx

Active Member
Any tip's for lath and plaster walls?
 

PaulDavidThomas

Active Member
Any tip's for lath and plaster walls?

Now, that's a bitch.

So. If we are talking lath and plaster walls, I am assuming partition walls, so walls between two rooms. Whilst I have see lathe and plaster over brick walls before - slight gap. Was done in older houses with solid 9" external walls.

The problem here is it's down to the condition of the wall. Sometimes it can be blown and others quite stable and really you would take different approaches.

Equally, it depends upon the listing of the building ( if any ).

What I normally do is just rip them out, especially if they are starting to fail. Usually the supporting timber is perfectly stable and prob stronger than putting new timbers in.

Ripping them out is nasty and messy. But it can be done in a day and quite easy to do. Keep the lathes to one side, great if you have a log burner of fire. At bare min - gumtree them, someone will pay for it. Sometimes plasterers will !!

That is perhaps not what you want to hear.

You do have another option. Remove the skirting and overboard with two layers of plasterboard. Because the vertical studs won't quite line up with the size of modern board, you will have to trim the board. Do this both sides. By default you should have an air gap within you L&P wall. As long as you double board both sides, that's ok.

I would not do the kiln dried sand thing, as it will leak. Equally, the studs behind are usually intersected with another stud going at 45 degs.
 

raoulx

Active Member
Wow thanks for the detailed reply and knowledge. I wish I could do that it just means a lot of work being unskilled in any 'trade' field. My room's under construction but I don't think I have the budget if I'm honest. I'd love to do things properly but it will add a fortune and it would end up being doubtful I'd be allowed equiptment by the ends of things if I didn't do things on a budget.

Let's hope I don't regret following what you mentioned!
 

outoftheknow

Moderator
Adding the sand or foam would neither effect the plumbing or electrics.
Genuine question - for electrics in particular is that backed up by a sparky or regulations? When adding insulation around cables it is often/sometimes a requirement to derate the circuits. Maybe not a thing over there but it certainly is over here (Australia)
 

xxGBHxx

Well-known Member
Piping in loose sand into a void behind plasterboard when you know nothing about what's in there?

Ignoring the faff of doing it the weight of that sand behind the plasterboard could be more than enough to pop the plasterboard right off the wall. Unless you did it yourself, you have
  • No idea of the cavity size/depth
  • No idea of how well the plasterboard has been attached
  • No idea if there's an old fireplace or a void someone might have just boarded over that will fill with sand
  • No idea of the structural configuration or loading of the wall you're filling
You also need to make 100% completely sure that the sand has zero moisture in it or you're possibly going to get mold growing in the void.

Another reason not to do this is if you also don't treat the floor/ceiling voids then sound transmission will happen anyway (enough to still be annoying at least). Not to mention as someone else has already said, it will definitely de-rate your electrical wiring which, depending on what wiring it is and how it was originally rated could well be out and out dangerous.

I don't want to be rude as I appreciate you're only trying to give helpful advice but it just sounds like a bodge to me. My opinion is, for what its worth, if you need to do it in a home you intend to stay in then just do it properly as too many times I've been left sorting out the mess cost cutting property developers cause. Not suggesting that's you I hasten to add but worrying about what happens 5 or 10 years down the line isn't generally high on most property developers considerations when they come up with these cost cutting measures...

G
 
D

Deleted member 24354

Guest
There is a building regulation for this subject:

Approved Document E - Building regulation in England for the resistance to the passage of sound and sound insulation.

Resistance to sound: Approved Document E

A huge volume of work went into the writing of this document, including years of trials at the BRE. This document should ALWAYS be your starting point for any acoustic insulation of buildings. Nowhere in the document does it recommend filling plasterboard cavities with sand as a viable means of acoustic insulation.

As @xxGBHxx says, the edge detailing for interfaces is as, if not more, important for flanking noise transmission than looking at a single wall in isolation.

If party wall noise is a problem, there are much better solutions available, that will meet building regulations.
 

xxGBHxx

Well-known Member
There is a building regulation for this subject:

Approved Document E - Building regulation in England for the resistance to the passage of sound and sound insulation.

Resistance to sound: Approved Document E

A huge volume of work went into the writing of this document, including years of trials at the BRE. This document should ALWAYS be your starting point for any acoustic insulation of buildings. Nowhere in the document does it recommend filling plasterboard cavities with sand as a viable means of acoustic insulation.

As @xxGBHxx says, the edge detailing for interfaces is as, if not more, important for flanking noise transmission than looking at a single wall in isolation.

If party wall noise is a problem, there are much better solutions available, that will meet building regulations.

I didn't even want to go into Part E as I'd assumed it would fall on deaf ears as they were ignoring building regs as it was though you are absolutely correct. I was also trying to be kind as I'm sure the advice was well meaning but ultimately I should have really called it for what it is a dangerous bodge that doesn't really fix the problem or meet building regs.

Having read through Part E a while ago it is a very interesting read (as are all the regs to be fair if you're a sad pedantic git like me!) and while the mandatory nature really can be a royal PITA at times theres a lot of very good info and guidance in them. When you go through them you often realise just how terrible many builders, developers and tradespeople are as you get to identify just how much bodging and corner cutting some of them do.

G
 
D

Deleted member 24354

Guest
As part of the Architectural Acoustics module in my Acoustics Post grad we spent a long time on Part E and actually had some of its contributors as guest lecturers and had a visit to the BRE where much of the research took place. It is not the easiest of documents to read, I agree, but it is based on some very sound (pun) Acoustics / Physics.

I was not wanting to be unkind to the OP but neither do I want any AVF members to fall foul of either building regs or trying to explain to their wife why all of the plasterboard is now on the floor and why the cat is squashed beneath it. - a 3 x 3m wall with a 2cm gap would have 288kg of sand exerting pressure on it.

Increasing the density alone is not always the best way to prevent noise transmission. Using dual density materials can often have better results as different frequencies are attenuated as they pass from one density to another. This does not even take into consideration transmission through other voids, air gaps, floor and ceiling structures, shared chimneys, suspended floor voids, structural timbers, raft foundations, attic spaces etc.
 
D

Deleted member 24354

Guest
As a side note, acoustic plasterboard generally is not recommended to use dab n dot for installation. It is normally recommended to be battened with a layer of mineral based insulation between it and the wall / or should be screwed / or should be glued (green glue) / or should use acoustic isolation fixings
 

PaulDavidThomas

Active Member
The fact it isn't written in Part E does not detract from the fact it works.

I applied simple logic. Dense material is better in reducing noise transfer. Plasterboard echo's due to the air gaps. Fill the air gaps.

Now, you are onto a thing in relation to the increase in loading behind the plaster board and that was taken into consideration. This comes from a man who investigated sheering loads on specific screws when insulating the outside of a building and then cladding the wall with douglas fur :)

These are things I do to my own houses... Nothings fallen down yet !!
 

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xxGBHxx

Well-known Member
The fact it isn't written in Part E does not detract from the fact it works.

I applied simple logic. Dense material is better in reducing noise transfer. Plasterboard echo's due to the air gaps. Fill the air gaps.

Now, you are onto a thing in relation to the increase in loading behind the plaster board and that was taken into consideration. This comes from a man who investigated sheering loads on specific screws when insulating the outside of a building and then cladding the wall with douglas fur :)

These are things I do to my own houses... Nothings fallen down yet !!

I went easy on you in my first post as I gave you the benefit of the doubt. After this reply I can see @mushii was nearer to the mark with his, more pointed, response.

So lets get this right. Your "defence" for using a borderline dangerous method when better, proven (and approved), methods exist is "well it works"? How did you take the weight of the board into consideration? What do you know about the load weighting on dot/dab plasterboard? Did you monitor and control the mix the plasterers used to ensure optimum strength and adhesion? Did you control and measure exactly how much plaster was used and its spacing? Did you calculate the adhesive qualities and holding power of the substrate? Your statement is frankly ridiculous.

There are lots of different things that "work" but there's a reason the building regs are what they are and it's the same reason I follow them religiously even when I know of cheaper/faster methods that "just work". I know by following them I am benefiting from 1000's of hours of testing by experts in that specific field and I'm not so arrogant or ignorant that I think I know better than them. It's often expensive and tedious but it pretty much guarantees it's going to be safe and have longevity and not royally f*** over the people who inherit/buy it after me. My house is a testament to people like you (funnily enough it was also owned by a property developer) who like you just did "what worked". 20 years later and I'm picking up the tab as that work almost destroyed the house to its foundation. Like you claim, it did work but the damage it's caused because it wasn't done right the first time is a stark example to me why your attitude is so wrong.

I can just imagine the joy anyone who's bought your houses feels when they go to have a new electric point installed in a few years time and the sparks opens the wall to find kilos of sand spilling out all over the floor. Or the fact that even a 1% gap in your sand filling will make your "soundproofing" almost completely pointless. Or when the new owners decide to tile an area that wasn't tiled and the entire wall falls off the substrate etc. etc.

Things "work" until they don't and it's at that point you understand the reason to do it once and do it right instead of bodging it because it's cheap. That said, being a property developer your attitude fits in perfectly...

G
 

outoftheknow

Moderator
I applied simple logic.
As an engineer (marine so mechanical, electrical, plumbing, fitting and turning, fabrication and general handyman) I’ve always found simple logic by itself doesn’t work. If I’m going off piste from standards (like building standards) that’s when I ramp up my technical part of my brain to research and calculate things like @xxGBHxx mentioned. Then I check a few other things I think of. If after all that I decide it is better than the standards, and I am able to ignore those , I would do my thing.

Leaving aside novel designs and solutions, I doubt I veered from standards and calculations of all known variables more than three times in 2 decades. Even then I reckon those were in the novel solution and “temporary” fixes to be done properly in a few months or so.

Offer your solution pointing out it isn’t recommended but is interesting in an experimental way by all means. I personally wouldn’t offer it as a way to do it because it is cheap and your plasterboard hasn’t fallen off.
 

PaulDavidThomas

Active Member
All perfectly fair points, thank you.

In hindsight, perhaps I should have not recommend it to people who might not know any better. I see the error of my ways.

The reason I used technique wasn't actually for sound proofing, but was actually for heat transfer and as I knew the wall was not going to be disturbed I went with the sand fill option. As it was also removing the void behind the plasterboard this would have also reduced sound transfer. It was in a small area of 2m2. It was also in an area where it would be very unlikely to run cables - however, never say never. The plasterboard is fully supported by physical means so would not pop off, even if I ripped a hole and pulled it.

Now, to answer, in my defence some of the points made.

The substrate the plasterboard was affixed too was brick. The brick was "blue gritted" prior to a normal knauff mix of adhesive was applied. We always over fill on our adhesive in comparison to what knauff recommend as I hate the hollow sound of plasterboard. You'd need a hammer and chisel to get the adhesive off the wall. So, the weak point then is the paper lining on the plasterboard.

I would dispute the fact having a 1% gap makes no difference to the acoustic attributes. But we can agree to differ on that :)

I do take slight offence for the disparaging remarks made in relation to my work, however I can see why you would make a sweeping assumption based upon this kiln dried sand episode :)

If anything I'm wary and conservative when it comes to construction. I never start anything unless I know exactly how to do it and usually over specify as belt and braces means I sleep at night.

From a structural point of view I've been mentored by the director of a large structural engineering company (Multi Million pound) for the past 15 years which has been really interesting !!

If anything I'm more concerned about what is hidden in a build than the superficial finish that is observed as I know that is what is important. When I've renovated property I have seen some awful things. However, I also worry about the superficial.

Perhaps you should see something nicer that I do...

This was my last project.

Well this is me and my mate Rob. We do all the roofing, cladding, brick work, landscaping as well as all the internal works. I built, painted and fitted the kitchen (not the stone worktop). I laid the stone flooring on the anti-fracture matting (.5mm) I fitted the windows & doors all electrics and plumbing. The only thing we didn't do on this project was the plastering. I hate plastering and I don't have that skill.

And before someone shoots me, my Scottish friend who's Part-P advises and signs off on the electrics. I made one mistake on one connection to the heat source pump, but as I always leave additional 'just in case' ducting in builds, the problem was easy to solve.

I do this because I enjoy it. And I do it well.
 

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PaulDavidThomas

Active Member
outoftheknow, oddly enough my friend who does my Part-P was on the Oil rigs doing Marine Engineering !! He got out about 15 years ago - which is where we met as I went and did a flat roof for him as he was struggling. We've been mates ever since.

He was super useful when I had to do some sprinkler systems in domestic properties to over come some open plan issues. The thinks he knew about flow restrictions from bends !!
 

ufo550

Well-known Member
Thats a nice refurb @PaulDavidThomas.

Just another negative, but keen people aren’t confused. When following Part P in England & Wales, there is a very specific process that is outlined, for third party certification. An electrician can’t simply ‘sign off’ someone else’s work. Third Party Certification is only sanctioned by one of the government approved schemes. I know a lot of electrical companies ‘sign off’ other people’s work, but this is not what the statutory regs stipulate; so follow that route at your peril.

Merry Xmas, by the way. :)
 

xVitx

Novice Member
I went easy on you in my first post as I gave you the benefit of the doubt. After this reply I can see @mushii was nearer to the mark with his, more pointed, response.

So lets get this right. Your "defence" for using a borderline dangerous method when better, proven (and approved), methods exist is "well it works"? How did you take the weight of the board into consideration? What do you know about the load weighting on dot/dab plasterboard? Did you monitor and control the mix the plasterers used to ensure optimum strength and adhesion? Did you control and measure exactly how much plaster was used and its spacing? Did you calculate the adhesive qualities and holding power of the substrate? Your statement is frankly ridiculous.

There are lots of different things that "work" but there's a reason the building regs are what they are and it's the same reason I follow them religiously even when I know of cheaper/faster methods that "just work". I know by following them I am benefiting from 1000's of hours of testing by experts in that specific field and I'm not so arrogant or ignorant that I think I know better than them. It's often expensive and tedious but it pretty much guarantees it's going to be safe and have longevity and not royally f*** over the people who inherit/buy it after me. My house is a testament to people like you (funnily enough it was also owned by a property developer) who like you just did "what worked". 20 years later and I'm picking up the tab as that work almost destroyed the house to its foundation. Like you claim, it did work but the damage it's caused because it wasn't done right the first time is a stark example to me why your attitude is so wrong.

I can just imagine the joy anyone who's bought your houses feels when they go to have a new electric point installed in a few years time and the sparks opens the wall to find kilos of sand spilling out all over the floor. Or the fact that even a 1% gap in your sand filling will make your "soundproofing" almost completely pointless. Or when the new owners decide to tile an area that wasn't tiled and the entire wall falls off the substrate etc. etc.

Things "work" until they don't and it's at that point you understand the reason to do it once and do it right instead of bodging it because it's cheap. That said, being a property developer your attitude fits in perfectly...

G
Hi, what’s your solution to increase soundproof on dot and dab walls Without making too much mess and spending lots of money? Thanks.
 

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