Sealing top of a block wall

[philhjobim]

I have a concrete block wall (heavy block laid 8 inch wide) which a builder just built for me to divide a cast concrete basement (Cast walls, floor and ceiling). The wall needs to provide some isolation from one area (pottery/messy activities) to another (Protools mixdown room).

At the top of the wall the builder has had to go round various obstructions because the ceiling has downstands and stuff, and in places the gap between the top of the last row and the ceiling was too narrow (2 inches) for him to get mortar and part blocks in to fill the whole wall width, so he has filled in the edges of the remaining gap with 1 inch thick cutoff strips of block leaving a void above the middle of the wall. In other places he has just pushed some mortar into the gap (1 inch), and there are some cracks (1-2mm) where it doesnt quite reach the ceiling leaving audible gaps across the wall top in a couple of places.

What should I do to seal the remaining gaps?

In the places where there is a void in the top of the wall (between the facing strips of cut block), should it be filled with something, or will the additional loss be insignificant ? If so does it need to be something solid like fire mortar, or is expanding foam sufficient ?

Thanks
Phil

 

[RICK FITZPATRICK]

the ceiling has downstands and stuff,

What do you mean by "downstands and stuff? What is the ceiling made of? Can you take a picture and post it? Without knowing exactly what you are refering to, it would be difficult to suggest a correct solution.

in places the gap between the top of the last row and the ceiling was too narrow (2 inches) for him to get mortar and part blocks in to fill the whole wall width, so he has filled in the edges of the remaining gap with 1 inch thick cutoff strips of block leaving a void above the middle of the wall.

As I understand it, you are saying these block cutoffs are not full block depths, and therefore, there is a gap between these block cutoffs, which in essence is the same as the void in the middle of the blocks, no? I don't see any way of filling these voids with anything at this point. Probably should have built a filler at the cieling with a level point like a studwall upper plate...however hindsight is always 20/20. The best I could suggest at this point is to find some foam rod backer a little larger than the gaps and squeeze it in further than the face of the block(about a 1/4"), and then use a resiliant caulk to seal the gaps. But still, without really knowing what what "obstructions and downstands mean", its hard to say.

 

[philhjobim]

What do you mean by "downstands and stuff? What is the ceiling made of? Can you take a picture and post it? Without knowing exactly what you are refering to, it would be difficult to suggest a correct solution.

Hi Rick,

Thanks for taking a look at this. Sorry I was a bit vague there.

The ceiling is a cast reinforced concrete slab but it also has two cast beams crossing it as well as slab level changes. I have written a bit of a story about it which has some pictures here:
http://www.hickslondon.com/html/studio_project.html

I have also started testing where we have got to in order out to figure out what else needs working on.
http://www.hickslondon.com/html/initial_tests.html

I have no previous experience of testing transmission loss or studio building, but I am an engineer, have experience of PAs, and have a suitable meter and can follow instructions (well most of the time anyway) We dont mind doing work if we have to, but have no intention of doing any that we can get away without !

As I understand it, you are saying these block cutoffs are not full block depths, and therefore, there is a gap between these block cutoffs, which in essence is the same as the void in the middle of the blocks, no? I don't see any way of filling these voids with anything at this point. Probably should have built a filler at the cieling with a level point like a studwall upper plate...however hindsight is always 20/20. The best I could suggest at this point is to find some foam rod backer a little larger than the gaps and squeeze it in further than the face of the block(about a 1/4"), and then use a resiliant caulk to seal the gaps. But still, without really knowing what what "obstructions and downstands mean", its hard to say.

There is no gap along the top of the main section of wall or between the blocks on the surface, only inside the wall. On both sides of the top of the wall there are thin strips of concrete mortared onto the top of the wall. So If I'm looking at the wall in front of me, as in this picture
http://www.hickslondon.com/html/studio_project.html#mainwallsection
the blocks go up and at the top layer I see what looks like a thin (low) block layer filling between the top full block layer and the ceiling. But in fact it is only a one inch thickness of block cut off, behind that is 6 inches of air, then behind that is the one inch thick concrete block piece on the top of the other side of the wall. But there isnt any gap between blocks on the surface to fill. I guess the question is whether it is worthwhile to drill some holes and fill it with something, or to take one face off and pack it out with something ?

I think I probably need to sort out the end section of the wall first since that is only skinned on one side
http://www.hickslondon.com/html/studio_project.html#ductsection

Thanks for your time, any advice is much appreciated so we know where to spend effort most effectively.
Phil

 

[RICK FITZPATRICK]

There is no gap along the top of the main section of wall or between the blocks on the surface, only inside the wall.

INSIDE the wall, between the two filler block slices is what I meant. This is a two leaf system in that area.

I guess the question is whether it is worthwhile to drill some holes and fill it with something, or to take one face off and pack it out with something ?

"Worthwhile" can only be defined by your determination to meet your Transmission Loss goal. In reality, the wall, if the voids are filled with concrete, becomes a ONE LEAF SYSTEM, whereas the top row of 1" thick cuttoffs now become a TWO LEAF SYSTEM, which from my understanding is actually a BETTER system, although when push comes to shove, that may not be totally true because of the MASS of the single leaf vs, the MASS/AIR/MASS of the two leaf system. I'd tend to bet the single leaf mass in this case may actually be better, although at what frequency is the question. The only suggestion I can make at this point is to do a test. Measure the maximum noise floor in the other room, vs a measurement in the room in question for transmission LOSS. If it meets your goals.. If not, the solution would depend on how much MORE transmission loss you need at what frequency. Worst case scenario may require building a second leaf assembly, such as a stud wall with a couple of layers of drywall with a large air gap. However, you are the only one who can determine if the existing wall is successfull, and what you are willing to do to achieve your actuall goal.

Phil,, I'm certainly no expert on this subject although there is a member here who IS. His name is Rod Gervais, and he is also an engineer,and has built MANY world class studios. And he is an Author of a well known studio construction book called Home Recording Studio...build it like the Pros
http://www.amazon.com/Home-Recording-Studio-Build-Like/dp/1598630342
I can email him if you wish and maybe he can chime in here. Let me know.
fitZ

 

[CMunch]

Not trying to be funny bud,I am construction supervisor and thats not the tidiest bit of block work I have seen,he should have measured it out and maybe started with a cut so that he would be finishing with a half to three quarter block,why should you pay to sort out if you have paid the guy to build wall,make him take two courses off lay a cut of block then finish off with cut maintaining neat 20 mm off ceiling which you can fill from both sides with acrylic fire mastic,then have carpenters fix dressed two by one around top of wall to ceiling,seal again and paint,doubt if what you have will comply with fire regs notice they apply as you have had to have door with intumescent strips.

Laying blocks should not be akward for a bricklayer.

Most of that dollops of concrete will crack away from wall heads with natural movement in the building in a very short space of time.The job you gave him should be no more akward than any bricklayer has to do to build to underside of the soffit on a house.If he didnt want to spend all day cutting rips of block he could always have used a stihl saw and done it in an hour or two.
They always have some bloody excuse why job cant be done properly.

 

[philhjobim]

"Worthwhile" can only be defined by your determination to meet your Transmission Loss goal.
//
Phil,, I'm certainly no expert on this subject although there is a member here who IS. His name is Rod Gervais, and he is also an engineer,and has built MANY world class studios. And he is an Author of a well known studio construction book called Home Recording Studio...build it like the Pros
http://www.amazon.com/Home-Recording-Studio-Build-Like/dp/1598630342
I can email him if you wish and maybe he can chime in here. Let me know.
fitZ

My first transmission loss goal is to get a reasonable result from the wall as it is. I posted the results so far, what kind of figures should the wall achieve when it is properly closed off ?

If you could email Rod to take a look if he can, that would be great. I think Paul has a copy of his book to hand as well

In reality, the wall, if the voids are filled with concrete, becomes a ONE LEAF SYSTEM, whereas the top row of 1" thick cuttoffs now become a TWO LEAF SYSTEM, which from my understanding is actually a BETTER system, although when push comes to shove, that may not be totally true because of the MASS of the single leaf vs, the MASS/AIR/MASS of the two leaf system. I'd tend to bet the single leaf mass in this case may actually be better, although at what frequency is the question. The only suggestion I can make at this point is to do a test. Measure the maximum noise floor in the other room, vs a measurement in the room in question for transmission LOSS.

Yes I was trying to get my head around it in a similar way. At what point does the void become significant in terms of making a weak path in the wall. Going from the fact that wall sockets cut into the wall can make a significant weak point, the loss of material must make some contribution to lossiness, and although its a two leaf situation the two leaves are hardly decoupled, so I wondered if that means the loss of material will dominate any two leaf benefits. I will try to measure that when the thin bits of wall top elsewhere are dealt with. Any thoughts on them ? I was thinking that maybe its best to take off the whimsy single skin bit of wall and pack it properly with cut block and mortar, but that is a lot of hassle.

Does expanding foam do anything useful towards attenuation or is it just a filler with no significant effect?

I see there are some acoustic foams advertised such as this:
http://www.wis-ltd.com/products/fire protection/wis/detailFire&AcousticExpandingFoam.htm
Is that any good (spec mentions 58dB ) ?

The other option I thought of is a pourable fire mortar such as http://www.firetherm.com/products/d...roducts/all/&product=intucompound_fire_mortar

Which could be mixed and fed into the void, and into the space behind the single skin area if a backing board is fitted. Behind the vent ducts it has the advantage that I dont have to either cut one of the vent pipes to get access and then reinstate it somehow, or open up the work that has already been done. Also resolves any fire closure concerns, and as it expands after mixing it will get into all the nooks and crannies and close them up, as that what its intended for around for closing service pipe passages. I was thinking of mixing it and feeding from a plastic bag - like an icing bag, or getting an empty sealant cartridge and using that to deliver it. Is that daft or possible ?

Re measuring noise floor from messy room to mix room. Lowering the noise floor is not the main objective. The noise floor in the messy room at present is little different from that in the mix room, since they are both well isolated from the outside and rooms above by the cast ceiling and walls. So now the mix room is NC30 and the messy room is typically NC35 (when the silencers are on the air outlet which is presently open because we turned it to build the wall). Most of the noise reaching both spaces is coming direct through the walls and slab from the 5 floors of steel frame above, and noise does like to travel in the steel. The main source of noise is the community hall 2 floors above, thats only occasional though, and at a low enough level its unlikely to interfere with mix listening. The sound of woodworking next door is the higher priority as well as limiting the mix sound disturbing a ruminating sculptor next door.

Thanks for your input
Phil

 

[philhjobim]

Not trying to be funny bud,I am construction supervisor and thats not the tidiest bit of block work I have seen,he should have measured it out and maybe started with a cut so that he would be finishing with a half to three quarter block,why should you pay to sort out if you have paid the guy to build wall,make him take two courses off lay a cut of block then finish off with cut maintaining neat 20 mm off ceiling which you can fill from both sides with acrylic fire mastic,then have carpenters fix dressed two by one around top of wall to ceiling,seal again and paint,doubt if what you have will comply with fire regs notice they apply as you have had to have door with intumescent strips.

Laying blocks should not be akward for a bricklayer.

Most of that dollops of concrete will crack away from wall heads with natural movement in the building in a very short space of time.The job you gave him should be no more akward than any bricklayer has to do to build to underside of the soffit on a house.If he didnt want to spend all day cutting rips of block he could always have used a stihl saw and done it in an hour or two.
They always have some bloody excuse why job cant be done properly.

Um yes, I didnt book him so I dont know what standard was implied or expected. I had been thinking that it might be a good idea to find out if a rework of the top layer was an option. He did cut a lot of blocks with a Stihl or similar, but I did hear him say that cutting them across the flat plane with a small saw was not an option. Perhaps mainly because he was block cutting on site which in Notting Hill in a shopping district is something to avoid as much as possible. All the Porsches and Aston Martins in the basement car park (flats for city gents above) are now a nice shade of grey

Thanks for your comments.

There are no fire regs on the wall build, its only fire doors because then they are heavy and stop sound nicely. Still it makes sense to fire seal it anyway.

Phil

 

[CMunch]

Um yes, I didnt book him so I dont know what standard was implied or expected. I had been thinking that it might be a good idea to find out if a rework of the top layer was an option. He did cut a lot of blocks with a Stihl or similar, but I did hear him say that cutting them across the flat plane with a small saw was not an option. Perhaps mainly because he was block cutting on site which in Notting Hill in a shopping district is something to avoid as much as possible. All the Porsches and Aston Martins in the basement car park (flats for city gents above) are now a nice shade of grey

Thanks for your comments.

There are no fire regs on the wall build, its only fire doors because then they are heavy and stop sound nicely. Still it makes sense to fire seal it anyway.

Phil

Oh I see ,thought you were overseeing that part of build lol,kinda makes my post irrelevant,fire regs must be lot more lax there than here,cos if build is over two stories here fire regs are a nightmare,often doubling the cost of a build,and that wall wouldnt comply,so if no fire regs to worry about could just pack spaces with rock wool and fix timber faceplate.Bit o sawdust wont hurt the Astons lol.

 

[philhjobim]

Oh I see ,thought you were overseeing that part of build lol,kinda makes my post irrelevant,fire regs must be lot more lax there than here,cos if build is over two stories here fire regs are a nightmare,often doubling the cost of a build,and that wall wouldnt comply,so if no fire regs to worry about could just pack spaces with rock wool and fix timber faceplate.Bit o sawdust wont hurt the Astons lol.

Looking at the blockwork between this room and the basement carpark the original builders (who handed over the building to the church in 2004) did the same at the top, just mortared to the ceiling. I got them to close lots of cable tray pathways around the basement after handover, when building control had already passed the building, which they did by slapping a bit of ordinary mortar around. On the ground and first floors, which are my area of responsibility, the fire separation to the utility risers is definitely vague, as well as separations in the ceiling voids anywhere thats backroom. Ah well, it must be alright 'cos its a brand new building and building control say it is ! Then again the fire signage that directs you out of the basement into a lift lobby from which you must have a residents fob to open the stairwell door to escape to the first floor is a bit dodgy, and despite five years of emails to architect and building managers to this day it remains incorrect, and only corrected by my notice directing fire flee-ers to another exit. But we stray from the original subject.

I found a half block in the left over pile which explains his problem, his saw only cut about 2 inches depth so cutting round all 4 sides to slice the block in the short direction left a 40mm piece to split at the centre. Cutting the block longways with that size saw would be ........ well, difficult anyway.

Phil

 

[Rod Gervais]

What I would recommend would be a 2 step approach to this -

I would clean the top of the wall of any loose debris........ I would then pack some 4pcf rockwool to roughly 40% of density for the full width of the block - finally caulking the edge at each face to create the an air seal.

Rod

 

[RICK FITZPATRICK]

What I would recommend would be a 2 step approach to this -

OMG..I didn't even have time to email Rod...He musta popped in here by accident. Thanks Rod.

 

[philhjobim]

What I would recommend would be a 2 step approach to this -

I would clean the top of the wall of any loose debris........ I would then pack some 4pcf rockwool to roughly 40% of density for the full width of the block - finally caulking the edge at each face to create the an air seal.

Rod

Hi, thanks for that Rod.

That sounds like it was an answer for how to bridge a gap from the top of a block wall to a ceiling above. Thats not how it is at the moment, as there is already a part block seal at each edge along the top of the wall.

So - I could take off the blocks along each edge and do that. The gap is 3 inches high - is this method okay for such a wide gap? What does pack to 40% of density mean - does it mean squash 40% smaller, or to 40% of original volume ?

Since there are already part blocks along both sides of the wall, I wonder if it is easier (and higher transmission loss) to finish the wall by filling in the void. What type of pourable setting compounds, mortars etc would it be possible to use, and is there a recommended way of getting it in there ?

Thanks
Phil

 

[Rod Gervais]

Hi, thanks for that Rod.

That sounds like it was an answer for how to bridge a gap from the top of a block wall to a ceiling above. Thats not how it is at the moment, as there is already a part block seal at each edge along the top of the wall.

That is correct - I (apparently mistakenly) thought that this was the question...... the original post was this:

At the top of the wall the builder has had to go round various obstructions because the ceiling has downstands and stuff, and in places the gap between the top of the last row and the ceiling was too narrow (2 inches) for him to get mortar and part blocks in to fill the whole wall width, so he has filled in the edges of the remaining gap with 1 inch thick cutoff strips of block leaving a void above the middle of the wall. In other places he has just pushed some mortar into the gap (1 inch), and there are some cracks (1-2mm) where it doesnt quite reach the ceiling leaving audible gaps across the wall top in a couple of places.

So - I could take off the blocks along each edge and do that. The gap is 3 inches high - is this method okay for such a wide gap? What does pack to 40% of density mean - does it mean squash 40% smaller, or to 40% of original volume ?

e.

The percentage relates to "from the existing" volume........ thus a 4pcsf material would be installed with a density of roughly 1.6 pcf.........

all in all I would like to see an 1 1/2" max......... but 3" for an 8" block would work - although you would have to use a trowel consistency caulk for the sealer. A caulk gun application is not going to get that done.

Since there are already part blocks along both sides of the wall, I wonder if it is easier (and higher transmission loss) to finish the wall by filling in the void. What type of pourable setting compounds, mortars etc would it be possible to use, and is there a recommended way of getting it in there ?

I can't think of anything that wouldn't crack in the long run Just stuff and seal...........

Rod