John Sayers' Recording Studio Design Forum Archive

Thank you for such a valuable resource! I'm still in the planning stages of my home studio but I'm trying to get my ducks in a row before construction time. I have been studying Rod Gervais' book: "Home Recording Studio: Build it Like the Pros" but I can't find a good explanation/tutorial on how to properly caulk the edges of my drywall. The subject of backer rods is introduced without a good explanation to why they are so important. Also, the issue of installing recess electrical boxes seems to be very divided on the web, and very opinionated.

Yesterday, I spent several hours trying to research the issue of caulking, all without very clear answers. Can someone post a good tutorial on how to properly caulk a studio room? Are there varying techniques for: Floor, Wall, Ceiling? etc

Thanks,
Richard

rblythe wrote:The subject of backer rods is introduced without a good explanation to why they are so important

My understanding of backer rod is that it provides a backing for your caulk to sit against, instead of a cavity. It means you aren't trying to fill an entire void with expensive caulk (which would also take a long time to cure as well as possibly 'slumping' due to the excess volume of caulk) but rather, filling the front half of the gap and still getting your seal.

eg: You've constructed your wall with one layer of 16mm plaster board and it's sitting on your concrete slab. The timber bottem plate is sitting on the slab and the plaster board that is attached to it has 8mm clearance above the concrete. You run a bead of sealant on your timber-to-concrete gap (which will be quite a small gap if you have a level slab). Which leaves you with a void of 16 x 8mm. insert an 8mm backer rod in that gap and you have an 8 x 8mm gap which halves the amount of caulk you are using, which in turn halves the cost of your acoustic caulk for the same result. expensive stuff

rblythe wrote:Are there varying techniques for: Floor, Wall, Ceiling?

No, the basic idea is the same. Use backer rod anywhere there is a void that is deep enough to allow backer rod and a caulk seal. In the above example you wouldn't be using backer rod in the first seal between the bottem plate and the concrete as there is physically no room for it.


hope that helps

steve

if I may add ...

The 'backing rod' also provides a contact point to help keep a better seal.

A few caulking pointers.

1. Don't buy single tubes ..... the case price can be cheaper in the long run ... and you'll need it !

2. Don't be in a hurry to cover over the caulking. Give it a day to set, and THEN,

TRIPLE CHECK your seals.

Gravity has an interesting affect

2a. For areas like the seal at the bottom of the wall/floor ... I used a small hand mirror and a flashlight that allowed me to see the 'top' of the seal [difficult trying to lay on the floor and peer in]. Re-caulk any suspects.

This was done for EACH layer of drywall. Backer rod the space, caulk, let set ... triple check, and re-caulk where needed.

It is only at these base construction levels that you'll have the opportunity to achieve an 'Air Tight' seal.

3. A special caulk spreader ... kinda like a rubber edged triangle putty knife can really be useful ... helps push the caulk in place, clear any possible air bubbles ...plus it makes for a nice finish. Well worth the $2

4. did I mention buying by the case My room was nothing huge ... but I still was surprised how much we went through. Of course, being a room within a room doubles things.

OH ... when we did the 'BEEF-UP' prior to any building ... talk about caulking ! Double 5/8" drywall between the joist bins, sealing each layer ... then sealing the furring cleats.

Yeah ... you WILL be an expert after taking on a studio build .... IF you do it correctly.

Only one shot to get it done right.

hope this helps

Right on both counts! The backer rod provides an extra seal, and also reduces the amount of caulk you'll need by 50%, which is great because colored caulk is about twice as dense as drywall, so you only really need half the thickness to get the same surface density.

One of the key points of good isolation is that the surface density of the entire leaf must be consistent at all points, on all sides. So if you were to cut out one square meter of "leaf" from any part of the room, it would weight the same as another square meter cut out from any other part, including doors, windows, HVAC etc. The surface density must be the same all over.

So, since a layer of 16mm (5/8") drywall weighs about 800 kg/m3, and colored caulk weighs about 1600 kg/m3, you can use a bead 8mm thick (half the thickness of the drywall) to get the correct surface density that matches the drywall. But that would leave an 8mm air gap at the back, and one of the big "no-no's" about studio building, is having small air gaps inside the walls. Avoid at all costs! So either you fill the entire gap with caulk (which means you need twice as much, = twice the cost = very expensive!), or you put in backer rod to fill half the void, and backer rod is much cheaper than caulk. Plus backer rod also gives you that extra seal, just in case there's a break in the caulk seal that you didn't notice. Absolutely air-tight seals all around is a critical key requirement.

So the procedure is to leave just enough space at he edge of the drywall so you can push the the backer rod in snugly, all the way to the back, such that it creates a good seal and covers about half the depth of the gap, then seal the rest of the gap with a continuous unbroken bead of colored caulk.

Yes, it does have to be colored caulk: if you use transparent or uncolored caulk, the density is much lower: about 1,000 to 1,200 kg/m3, so you'd need thinner backer rod a,d a thicker layer of caulk, which is hard to do... and expensive! The coloring agent in the caulk adds a lot of mass. It doesn't matter what the color is: white, black, grey, silver, whatever. As long as it is not colorless, you are fine.

- Stuart -

Thanks for all of these helpful replies! The penny saver in me still has a hard time swallowing the fact that each layer of drywall will need to be completely caulked!

I found something related to Rod Gervais here: http://recording.org/index.php?threads/ ... aulk.45289. What are your opinions about the comments from MadMax regarding caulking? For example, he says to

(a) leave a 1/2 gap between all edges
(b) run a bead of caulk before inserting the backer rod
(c) stuff the backer rod over the wet caulk
(d) then apply another layer of caulk to make it flush with the drywall

I see a lot of dollars signs if I need to do that for every layer of drywall!!

Also Stuart: You refer to "colored caulk." Are you meaning that I can use non-acoustic caulk if I buy caulking that has a color component in it? I was planning on using the (gulp) expensive Green Glue Sealant

Can someone please comment on the caulking techniques by MadMax? Is this overkill or is this necessary?

rblythe wrote:Can someone please comment on the caulking techniques by MadMax? Is this overkill or is this necessary?

Yes ... both layers. or better put .... each layer.

You can use DAP Alex PLUS caulking. It is an acrylic with silicon.

rblythe wrote:Can someone please comment on the caulking techniques by MadMax? Is this overkill or is this necessary?

Yes, Max was on a mission and this was overkill.

You will be fine if just install backer rod, assuming you actually need it, and then use acoustic caulking at the edges of the sheetgoods.