John Sayers' Recording Studio Design Forum Archive

Ok guys, so my first layer on my ceiling uses OSB3 tongue and groove boards 18mm thickness. I was planning on caulking the expansion gaps, but hesitated due to them... being expansion gaps.

I'm not expecting much expansion as the room will be heavily insulated and airconditioned.

If I don't caulk the joints then mass will be less along the joints. I'm doing 2 layers of plasterboard on top so I shouldn't have issues with the airtight seal though.

I'm leaning towards caulking them ( they'll still expand 25%ish of the original amount as the caulk is flexible, and I believe the OSB shouldn't have drastic temperature changes as it is beneath 100mm rockwool and will have 200mm below it.

What are your thoughts?

Looking into it, I've come to the conclusion that I will caulk the t&g expansion joints. It seems that the expansion joints come into play mainly when the OSB takes on moisture, but as the OSB is a middle leaf inside the water-tight building evelope, is OSB3 (water resistant), my room will be humidity controlled, and the caulking is flexible, I don't forsee this becoming a problem.

Yes, caulk it. Always caulk any gaps, anywhere.

If I don't caulk the joints then mass will be less along the joints.

Right. And there won't be a good seal...

I'm doing 2 layers of plasterboard on top so I shouldn't have issues with the airtight seal though.

Ummm..... You have to seal EACH layer INDIVIDUALLY. Each layer by itself must be fully sealed, if you want maximum isolation.

they'll still expand 25%ish of the original amount as the caulk is flexible,

You should be looking for a better caulk, then! Most good caulks can handle a lot more than 25%.

I've come to the conclusion that I will caulk the t&g expansion joints.

- Stuart -

Hi Stuart, thought you'd say that! Obviously sealing every layer is ideal as there is more redundancy incase of sealant failure, Bmbut I also want the sheathing not to buckle , that's why I considered before caulking it.

My caulk is highly rated Everflex AC50