Basement theater...concrete sealing and adhesives

[Paul W]

About to start a basement AV room and have a couple of questions regarding the concrete....

The poured foundation is only a few months old but, before sealing the interior surface, I understand the surface should be cleaned using muriatic acid or a purpose specific cleaner to remove any efflorescence. Other than good ventilation, what breathing protection should be worn?

Unless there are better alternatives to consider, a silicate sealer will be applied to the walls and floor. Since I don't want to penetrate the concrete any more than necessary, what is the best adhesive to attach wood to silicate treated concrete? Liquid nails?
Thanks,
Paul

[Nelson]

I would use a quality masonary cleaner. Check your local ready mix suppliers or even one of the big box stores. I would worry about the fumes from the acid in an enclosed space. I would wonder why/ how much if any efflorescence can accumulate in a few months:confused:? Were there any chemicals added by the contractor to the concrete to accelerate the set time of the concrete or chemically reduce the water for easier pumping/ placement?? Some of those chemicals can leave a white colored film on the surface of the concrete that can easily be removed with a masonary cleaner. Or you have a leak:mad:...As far as attaching the wood. I would recommend a polyeurathane construction addhesive and three to four evenly spaced Tapcons or for quicker installation rent a low velocity powder actuated fastener :D (Ram Set). I have good luck with a .27 caliber using red or yellow loads and 2" washered pins. You will need to use treated lumber any place wood is directly contacting the concrete or any masonary. I would personally use a penetrating type of sealer, as there are generally not as many fumes, but your specific desire, location and future use may lend to using a surface type sealer...Hope this helps! Best of luck!

[timkolody]

Paul,

"Paint" the walls with Drylok. It is available at any paint/hardware/home improvement store. The stuff is very thick and your best bet is to use a wallpaper brush to put it on. It will seal out any moisture period!!!!! You can color it if you want, but I have always used the white. it is also available in a grey too I believe. I am not sure if you have poured concrete walls or cinder block walls, but it will work for both. You will not be disappointed!

As far as the floor goes, use a simple concrete sealer. You can do a search on the net for reviews, it's out there somewhere. Just do not use Thompson's, as it is the worst! Make sure you seal the floor in the areas where you will be framing first. Seal the rest afterwards, as your working will remove the top layer of sealer.

A good way to insulate for sound is to use 2x6's or 2x8's for the top and bottom plates of your walls, and 2x4's for the vertical members. Let me explain how this works.... Line up one side of the 2x4's with inside of the top and bottom plate edge, putting the 2x4's at 24" centers. Line up a second set of 2x4's on the outside edge of the top and bottom plates at 24" centers. This will essentially give you 2x4's at 12" centers. Then use 24" wide insulation, snaked in between the 2x4's. Building it this way, decouples the sound/vibration from one side of the wall to the other. There is no direct coupling between the inside and outside pieces of drywall, except at the bottom and the top of the wall, which are solid and dead.

Also, use a drop ceiling with the thickest insulation you can put in your rafters above it. The drop ceiling provides many benefits: better sound insulation, easy acess to run new cables, or more cables; and easy acess to plumbing and electrical lines for repair or improvement.

One other thing to do, if you can get away with it?????? Put some sort of commercial carpeting half way up the walls with chair rail. This also helps with sound. It is not as important as the above, but is nice.

If you can do it, frame the corners out of the room by putting a 45 degree angle across them. This 3'x3' dead space in the corner happens to be perfect for the 15" IB subs sold by PE. One each in the front corners and you are set for low frequency rumbles and booms!

I have more ideas if you want them, but these are some basic ones to help you get started on the right path.

Tim

[JRT]

Other than good ventilation, what breathing protection should be worn?

Find and read the MSDS for each material you are concerned about using.

If the basement is damp, you might consider looking to see if a paint is available that has nano-silver antifungal additives.

http://www.fraunhofer.de/Images/magazine_2-2006_48_tcm6-64691.pdf

[Paul W]

Seems everyone is on the same page regarding the use of a penetrating sealer on the walls. Drylock is a silicate sealer, correct? I also thought fairly new concrete should not have any efflorescence, but I did find a line about an inch wide along the floor/wall intersection. Maybe I should use the acid only in this small area...and turn on all the fans!

Tim, the floor will "float" on sleepers so no problem with wear. Would you still recommend a different sealer on the floor? Reason? Thanks for the hints on overall construction.

I would still appreciate other suggestions for the best wood/concrete adhesive. I have had inconsistent results with polyethylene; with plain old wood glue performing better with wood/wood or MDF joints. Wood to sealed concrete???

[Dennis H]

I also thought fairly new concrete should not have any efflorescence, but I did find a line about an inch wide along the floor/wall intersection. Maybe I should use the acid only in this small area...and turn on all the fans!"Efflorescence" is just a fancy word for salt on the surface. You probably got it at the wall-floor joint because a little air could get in there while it was curing. Before resorting to toxic chemicals and cooking your lungs, I'd try scrubbing it off with a wire brush and rinsing with water.

[edlafontaine]

DennisH has given a sound evaluation. Concrete is placed with moisture in it that evaporates in the months following placement. I wouldn't worry about that. Of greater concern would be if you have proper water proofing in place. You will not know this until your home goes through a wet season.

Are the areas where the efflorescence has occurred still damp? Are they the coolest location in the basement? If so, apparent moisture may be condensation and not intrusive water.

Don't overlook the need for treated wood in contact with the floor, especially bottom plates under framed walls.

How about mechanical fasteners instead of adhesive? There are masonry screws under several different names...tapcon is one.

[timkolody]

Paul,

I screwed the bottom plate right to the concrete, using concrete screws available at Lowe's etc.. It was very easy, drilled a hole with the bit provided or sold separately, and then sent the screw thru. Very quick, easy and efficient. Not sure why you are looking for an adhesive?


Tim

[Paul W]

I'll try Dennis suggestion first...years ago, I cooked enough brain cells with polyester resin to want to keep the lungs etc in better shape.

The reason to stick with an adhesive is that it seems logical not to penetrate a sealed surface. Earlier this year, I helped a friend lay sheathing for hardwoods over a concrete floor and we had a few cases where the Ramset spikes "blew out" small craters in the concrete. Only a few cases in a thousand or so, but I'd still like to avoid penetration if practical.

This is more trying to "get the prevention right" than solving a problem...I hate the thought of ripping things out and repeating the project. So far this year, we've had up to 7" of rain in one day with no leaks (fingers crossed).

[wingnut]

Paul,

"Paint" the walls with Drylok. It is available at any paint/hardware/home improvement store. The stuff is very thick and your best bet is to use a wallpaper brush to put it on. It will seal out any moisture period!!!!! You can color it if you want, but I have always used the white. it is also available in a grey too I believe. I am not sure if you have poured concrete walls or cinder block walls, but it will work for both. You will not be disappointed!

As far as the floor goes, use a simple concrete sealer. You can do a search on the net for reviews, it's out there somewhere. Just do not use Thompson's, as it is the worst! Make sure you seal the floor in the areas where you will be framing first. Seal the rest afterwards, as your working will remove the top layer of sealer.

A good way to insulate for sound is to use 2x6's or 2x8's for the top and bottom plates of your walls, and 2x4's for the vertical members. Let me explain how this works.... Line up one side of the 2x4's with inside of the top and bottom plate edge, putting the 2x4's at 24" centers. Line up a second set of 2x4's on the outside edge of the top and bottom plates at 24" centers. This will essentially give you 2x4's at 12" centers. Then use 24" wide insulation, snaked in between the 2x4's. Building it this way, decouples the sound/vibration from one side of the wall to the other. There is no direct coupling between the inside and outside pieces of drywall, except at the bottom and the top of the wall, which are solid and dead.

Also, use a drop ceiling with the thickest insulation you can put in your rafters above it. The drop ceiling provides many benefits: better sound insulation, easy acess to run new cables, or more cables; and easy acess to plumbing and electrical lines for repair or improvement.

One other thing to do, if you can get away with it?????? Put some sort of commercial carpeting half way up the walls with chair rail. This also helps with sound. It is not as important as the above, but is nice.

If you can do it, frame the corners out of the room by putting a 45 degree angle across them. This 3'x3' dead space in the corner happens to be perfect for the 15" IB subs sold by PE. One each in the front corners and you are set for low frequency rumbles and booms!

I have more ideas if you want them, but these are some basic ones to help you get started on the right path.

Tim

Hey Tim

A better and much easier way is to simply COUPLE the framing to the concrete wall and then to the drywall with polyurethane construction adhesive, or similar. The sheer mass of the finished structure will absorb all vibration. Top and bottom plates don't need any treatment as the massive concrete wall effectively dampens all vibration before any can reach the top or bottom plates. I used this method myself with perfect results. The problem with trying to decouple is that there’s no margin for error. Too tight and you really didn’t decouple. To loose and you have yourself a vibration problem.

Toby

[donradick]

Guys,

Thanks for a great discussion. I'm definitely going to print this out and
archive it for future basement projects!

One tip:
I poured a bunch of concrete walls at one point.
Standard practice is to spray the forms with a light oil so the form comes
off cleanly. Probably not enough oil on the wall to make a difference, but you might want to do a test: wipe a paper towel over the wall and see what you
pick up.

One question:
So is it "safe" to put treated lumber sleepers directly on a sealed concrete
floor under grade? I'd been thinking about using a slate tile floor directly
on the concrete, or a layer of visqueen if I used sleepers.
thoughts?

-Don

[Paul W]

Don,
No trace of oil on the walls, but good tip.

I plan to use "Hardiplank" (fiber-cement) sleepers with a vapor barrier over the sealed floor. Perhaps overkill, but very easy to do. In my case, the sleepers will provide a floor with a little "give" to help in the bass department...plus channels between sleepers are a convenient place to run speaker cables well away from AC lines.
Paul