Jim Prior, The founder of Quietco (@JimPrior7) has joined us today to talk about Dot and Dab.
Team: Jim, welcome, what key topic do you have for us today?
Jim: Hi guys, today, I want to focus on the ‘dot and dab’ plasterboard techniques that is everywhere, it’s in all the new build properties, it’s the number one plastering technique used by builders…..but it increases the noise from your neighbours and give you less privacy in your home….why are they still installing it everywhere!
Site investigations by the NHBC acousticians revealed that removing ‘Dot and Dab’ adhesive and exposing the block work behind improved the sound insulation of the party wall….that’s right removing the finish plasterboard from your wall reduced the noise.
Team: So why is that?
Jim: The single figure performance improvement was 3dB, however at the frequencies where the human ear is most sensitive (1Khz to 5kHz) the sound insulation performance improved by nearly 10dB, just from removing the ‘dot and dab’ plasterboard.
10dB is a doubling of sound intensity or basically twice as loud
Team: So what does this mean for our clients and homeowners?
Jim: If you have a floor and ceiling that is soundproofed in your newly renovated home that meets all the latest building regulations but your walls in that room are then plasterboarded using ‘Dot and dab’ plasterboard adhesive technique then your walls are making the noise from your neighbour worse
Simply removing the plasterboard will improve the sound insulation of your home!
Team: So a room tested without plasterboard dot and dab technique will perform better than one with dot and dab plasterboard. Why is this?
Jim: that’s right, Dot and dab technique is applied using large dollops of plasterboard adhesive strategically trowelled on the wall. Then you position your sheets of plasterboard on those dollops and tap the plasterboard level to meet the existing surface. This then cures and its ready for finishing plaster. The problem is not only that these dot and dab techniques are often done incorrectly because the adhesive does not always cover 20% of the board, it is the dollops of adhesive that create pockets of air and a channel of air behind the plasterboard.
Like with any wind instrument ….generally the noise is louder at the other end.
Noise travels through these channels of air behind the plasterboard causing considerable noise problems in different parts of your home. The same theory is true for standard off the shelf plaster coving which connects the ceiling and walls and channels the noise further. This technique is used in the majority of homes built 2000 to date.
Some argue it is the fixing method in that 20% of the plasterboard should be covered by the dab adhesive, having worked in the trade and seen this technique revolutionise the speed of plastering compared to traditional sand and cement render, this is rarely the case.
Team: So what is the solution?
Jim: Well traditional sand and cement render where you apply a scratch coat of sand and cement to the block work or brick work followed by a float coat or top coat of render then your finishing skim plaster.
In English this means a layer of sand and cement render mix is applied to the internal walls, it is then scratched “hence the name scratch coat” with a wire comb to provide a key for a second layer of render (the top coat).
The top coat is applied to the scratch coat of render and ruled off to give nice flat level surface, this is then “rubbed up” using a wooden or plastic float.
The finishing plaster is then applied the next day which leaves that nice silky smooth finish we all love to paint.
Rendering your internal brick and block walls has been around for many years, it is still commonly used today on the exterior brickwork of houses. It was used by the romans and still found in buildings built before 1900s. Turns out it is better for sound than the plasterboard cheaper dot and dab technique.
Team: So is it just the way the plasterboard is applied?
Jim: not completely, Thermolite or celcon – aerated blocks need to be mentioned here because most new builds are built using aerated blocks and they contribute to sound transmission up and down walls, low frequency seems to absolutely love the aerated blocks.
Aerated blocks are the grey or white light weight blocks that are recognised by the scratches.
Even if you apply render to these blocks, general modern living noise will transmit up and down and through these blocks very easily. TV noise, conversation and particular tones of voice and dog barking go straight through these light weight blocks. Many of our clients we have help used to be able to have conversations through their party wall of their new build. Many of our enquiries are clients with new build properties say “it’s like my neighbours are in my house”
Some clients have built new extensions, lean to extensions out the back or loft conversions using aerated blocks. They did not notice their neighbours before, they did not hear road or traffic noise before their new extension. Those that have had a loft conversion done using the techniques of dot and dab applied to aerated blocks, have found the noise so bad ….they moved after completing a £60K loft extension
It is better to use 7.3 Newton blocks, they are very heavy and the builders are unable to build as quick compared to the aerated or ultra light blocks. But this dense block has great noise reflection and mass which noise finds it difficult to travel through.
Team: So what can you put over their aerated blocks?
Jim: So say you removed the plasterboard on your walls and oh no….i have thermolite or celcon blocks with the scratches.
Well the party wall definitely needs a soundproofing wall system of some kind….the minimum Quietco would put on the party wall is a 50mm thick wall system starting at our TPS50W range.
For the flanking window walls and other walls perpendicular to the party wall we use TPS30W at 30mm thick,… this sound deadening mat, with high performace foam followed by another sound deadening mat and then a dense 15mm 44kg soundbloc board.
What is unique to us is that we glue this to the wall so you get the maximum effectiveness from our product.
The sound deadening matt sound deadens the light weight blocked walls like when you put your hand on a symbol,…. the foam acts as the resilient layer giving isolation from the finished surface, ….the second sound deadening matt sound deadens the dense, highly reflective soundbloc board.
This combination of materials at 30mm thick is what we use on flanking walls or we install it to aerated blocked walls for flat renovations below a separated ceiling or above a separating floor, after removing the dot and dab.
Team: So Jim what is your key message to customers regarding dot and dab?
Jim: In summary
Dot and dab is not good for sound,
Dot and dab and soundproofing should not be used on the same project
It is in every new build house built 2000 to date,
If you have aerated blocks then you need to sound deaden them to prevent the noise transmitting through them into other parts of the property. Quietco has 3 different systems that do this.
Also remember if you have dot and dab in your home, maybe it is not your neighbours being too loud and maybe some of the problem is closer to home!
Team: Thanks Jim for coming to chat with us today!
Jim: my pleasure, see you all soon!
