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Old 01-20-2020, 02:38 PM   #1
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Insulating Basement Block


Hello community, i have a concrete block, unfinished basement and i want to start working on insulating and framing the walls. My question is before i start do i need to scrub my concrete walls and clean them? Or can i just leave them as they are and insulate right on top of them? I will be applying foam board against the wall then framing up against that. I don't see a lot of discoloration on the concrete but I mean it's an unfinished basement so the walls are certainly dirty. Just don't want to spend time scrubbing my walls if there won't be a real benefit to it. Thank you!
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Old 01-20-2020, 03:22 PM   #2
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Re: Insulating Basement Block


Dust is often organic and can support mold growth, so the more you can remove the better. A good sweep and vacuum would not hurt.
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Old 01-20-2020, 06:16 PM   #3
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Re: Insulating Basement Block


I wish you luck. There seems to be zero consensus on how to do this project on this board. Go to a neighbor's house and ask to see how theirs is done.
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Old 01-20-2020, 06:27 PM   #4
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Re: Insulating Basement Block


Which ever system is used, understanding it and doing it properly is the key.

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Old 01-21-2020, 07:38 AM   #5
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Re: Insulating Basement Block


I suppose better safe than sorry. finishing a basement is a big project might as well take the extra time.
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Old 01-21-2020, 07:41 AM   #6
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Re: Insulating Basement Block


that is for sure! always more than one way to skin a cat. researching unfinished basements online is like gazing into a black hole.
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Old 01-21-2020, 08:05 AM   #7
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Re: Insulating Basement Block


Much of the varied information comes from people saying "look this has worked for years" Unfortunately that doesn't mean it will work on your house. Moisture is the biggest enemy and the moisture down at the bottom of your basement can vary house to house and contractor to contractor.

Following the best practices, like building science corp, simply raises your probability of success. They base their advice on MANY homes and many methods. https://www.buildingscience.com/docu...ts?full_view=1

I assume you are in a cold climate so moisture issues can come from outside or inside. Covering the foundation walls with a good layer of rigid insulation ensures that any inside air that reaches that wall will find a surface above the dew poing, no condensation. Add some caulking and detailing of more rigid up in the joist cavities will eliminate cold air infiltrating.

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Old 01-21-2020, 08:13 AM   #8
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Re: Insulating Basement Block


Yes, North Dakota. We've been below zero for almost two weeks so i suppose some people call that cold so to my original question do you think there would be a benefit to washing my walls first? Like hot water/soap? Or just brushing them with a firm brush to get any junk off? BTW I like your signature. That gave me a chuckle.
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Old 01-21-2020, 08:31 AM   #9
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Re: Insulating Basement Block


Long distance advice is difficult and only you have the eyes on the project. Also, only you know what is in your budget so the final choice has to be yours.

I'm old and slow but nearing completion of a deep energy retrofit of my 79 cape and it already feels fantastic. In my basement the poured concrete had those seams that made it difficult to get the rigid foam tight against the foundation, so I used a grinder and custom vac hood. Worked great on the first wall but convinced me to just knock off the major bumps, brush and vac the walls and apply the rigid insulation. I will be sure to seal the bottom to limit any air finding its way behind the foam panels.

So my suggestion would be to brush and vac. Even scrubbing the foundation would never remove everything.

Then build your wall up against the rigid allowing space if needed to keep the wall vertical.

I tend to write a book so will stop here.

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Old 01-21-2020, 10:12 AM   #10
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Re: Insulating Basement Block


Quote:
Originally Posted by Wolves14 View Post
do you think there would be a benefit to washing my walls first?
I powerwashed all my poured concrete basement walls. Wanted to get rid of the 50 years of stuff in all the fissures and potmarks causing that smell like grandma's dirty underwear. Your call, with CMU the surface is a bit smoother so just depends on how bad and how anal you are.
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Old 01-21-2020, 10:19 AM   #11
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Re: Insulating Basement Block


I recently insulated a 10 x 11 corner room in our basement that is to be my Man Cave.

I washed the walls with soap, water and a stiff scrub brush, then followed-up with a 50/50 white vinegar and water solution and stiff scrub brush. A wet/dry shop vac came in handy, because a lot of cleaning solution ran down and pooled on the floor.

Then I let it let it dry thoroughly. I supplied supplemental heat and fans. I put a humidistat in the basement to get an idea of RH beforehand, then let everything dry until the RH got back down to normal at the basement's normal temperature.

I used this method to insulate and frame the outside walls:



But we have concrete walls. I don't know if the sides of concrete block are thick enough for those spring spikes to work. (And they do work! I had one partially-driven, didn't like the way the piece would end up, and tried to pull it back out. Wasn't happening.)

I couldn't get tongue-and-groove insulation, so I sealed the seams with Tyvek® tape. I left a small gap along the bottom and sealed with Great Stuff.

The rim joist I sealed with the same 2" rigid foam, with a layer of 1" foil-backed rigid foam over that on the inside to meet fire code. The rim joists were first seam-sealed with Great Stuff. The excess trimmed-off. The 2" unfaced insulation was left with a ±1/4" gap all around, which was filled with Great Stuff. Again the excess was trimmed-off, then the foil-backed insulation fitted precisely to all edges. I offset any seams in that from those in the 2" unfaced foam and seam-sealed butted pieces of the aluminum-faced foam with aluminum duct tape.

I dare say I created about as close to a 100% moisture barrier as is possible to achieve

The recommended adhesive for rigid foam insulation has all the initial tack of pancake batter, so I had to resort to this kind of thing to get the rigid insulation to stay put as the adhesive cured:



When I attached the vertical pieces of 1x3 I carefully shimmed them as I went along, using a long piece of aluminum angle "iron" for a straight edge, to make everything as flat as possible, so I'd have less trouble when I put up the wallboard.

Here's the almost-finished results (I wasn't quite done around the windows at that time):



The windows were framed-out come level with the vertical wall studs. A 3/4 in. gap was left in the insulation around the windows so the final window framing would come right up to the window wells. (I will tape the lumber that kisses the walls around the windows to prevent it picking up moisture from the contact.)

That corner piece was first glued and screwed to create a single L-shaped piece, then carefully shimmed to create a corner that was plumb and square to both walls.

(N.B.: That photo makes the wall look a little wonky in a couple spots because I didn't get the panning motion quite right when I took the photo.)

Last edited by More Power!; 01-21-2020 at 10:24 AM.
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Old 01-21-2020, 10:46 AM   #12
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Re: Insulating Basement Block


That looks like an awesome job. Once close in it should heat very easily. Not sure what you are planning for air circulation with the rest of the house or outside but that size and tight will need some air.

Do you plan to eventually do the same for the rest of the basement?

Bud
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Old 01-21-2020, 10:56 AM   #13
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Re: Insulating Basement Block


@More Power!
That looks good, you should have a fire stop between the wall and the ceiling, will you have room to push the ceiling drywall right in to the sill plate.
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Last edited by Nealtw; 01-21-2020 at 11:07 AM.
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Old 01-21-2020, 11:03 AM   #14
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Re: Insulating Basement Block


Quote:
Originally Posted by Bud9051 View Post
That looks like an awesome job. Once close in it should heat very easily.
Thank you

It already heats easily. In fact: Those two walls are the master bedroom walls in the house, above. The floor on the perimeter used to get very cold in the wintertime. It doesn't any more. Once I put in the dropped ceiling and carpeting it should be real cozy.

Quote:
Originally Posted by Bud9051 View Post
Not sure what you are planning for air circulation with the rest of the house or outside but that size and tight will need some air.
If you examine the top-center of that photo you'll see a heat register. It's currently maybe 25% open. That seems to be enough.

I will be placing return duct type grills on the inside and outside walls, next to the doorway to the rest of the basement. I'll box those on the inside of that inside wall.

Quote:
Originally Posted by Bud9051 View Post
Do you plan to eventually do the same for the rest of the basement?
I've thought about it. Thing is: The rest of the basement, save the laundry room, is already finished. It has only wood paneling over plastic sheeting. (Original owner did that.) But it'd be a real PITA to tear all that down. And I can't get to the rim joists, in there, anyway, because they put in a plasterboard ceiling. So probably not.

Quote:
Originally Posted by Nealtw View Post
That looks good, you should have a fire stop between the wall and the ceiling, will you have room to push the ceiling drywall right in to the sill plate.
Thank you

I won't be putting plasterboard on the ceiling. It'll be a dropped ceiling that will meet the plasterboard walls. There is no sill plate. The rim joist sits right atop the top of the basement wall. The aluminum-faced insulation goes all the way from the bottom of the floor, above, to the top of the basement wall.
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Last edited by More Power!; 01-21-2020 at 11:08 AM.
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