Floated Subfloor - Screw density for 2 layers of 3/4" M

Started by korgman on 6 April 2006. 5 replies.

Originally posted at johnlsayers.com, topic 5944.

korgman6 April 2006#1

Hey all! I've been lurking for a while--nice site! My family and I recently relocated. I made some pretty nice recordings in a crappy-sounding attic room in my previous home, but would love to get a decent-sounding space for my new studio. Basically, am turning a family room into a control/tracking room. After I get up and running in this room, I'll begin building an iso room onto the back of the house, etc. I have a thick cement slab that isn't shared by other rooms (split level house) so I figure I have enough isolation as far as the floor is concerned. I've seen where cement reflects even low freqs. and therefore tends to make the room muddy. So in an effort to (hopefully) absorb some of that bass, provide material to fasten the hardwood floor to, and yet conserve vertical space, I floated two layers of 3/4" MDF (staggering the joints) over a layer of 1/2" Celotex. I am screwing the MDF layers to eachother with no fasteners of any kind going through to the cement. I read that fewer screws between layers would result in greater surface friction and therefore greater absorbtion. So I guess I'm wondering what you all think about how many screws per sheet I should use. I'm thinking it would be good to use more screws close to the joints to prevent squeaking down the road--like one screw per linear foot. And I was thinking maybe spacing the screws by about two feet for the interior of each sheet. Also, when I put the hardwood in, do you think I should use staples that are short enough not to go into the second layer of MDF to keep from fastening the two layers together even further? Any thoughts would be greatly appreciated!!! Thanks!

AndreasB6 April 2006#2

GLUE! you're in the US, go and buy a bucket of GreenGlue.. andreas

korgman6 April 2006#3

glue between the layers of MDF or glue the hardwood down or both? thanks for the reply!

knightfly6 April 2006#4

http://www.rd.com/content/openContent.d ... ntId=19882 http://www.hardwoodinstaller.com/hardwo ... ncrete.htm http://www.nofma.org/installation.htm http://www.woodweb.com/knowledge_base/I ... loors.html HTH... Steve

AndreasB7 April 2006#5

well, I'm very happy with the results I got after Sandwhich-glueing the two heavy layers (your's MDF, mine is Particle), in the classic South-North/East-West layer.. you know what I mean, no seams between layers. Just poured the glue and spread it to a 1mm thick layer and glued the second layer on that. If you cannot get good pressure on the second layer you should screw down the second layer tightly and then remove the screws when the glue has dried. And well, you can of course glue your hardwood on top of that OR go for a roll of that foamy soft stuff you generally put under the hardwood floor to get rid of the "step sounds". and as the articles Steve posted, make sure you cover the concrete with something that stop moisture from getting into the construction. I used something called Platon, there's probably something similar in the US. best andreas

korgman7 April 2006#6

Thanks guys! I really appreciate your input. Knightfly, thanks for the links even though I haven't provided the list of things you asked for in the info section. I will get that together before asking more questions.