# How is vapour barrier of basement wall typically tied in with rim joists?



## Bud9051 (Nov 11, 2015)

The recommendations for basement wall insulation don't exactly match where you are and where you are headed. Run this search "BSD 103 understanding basements" to access a good article. Sorry I can't post the link as they require a sign-up for the second visit but the information is good. But the search will get you in.

Although I don't like using a true vapor barrier some codes still require it, so check you local code department.

Also, all moisture issues need to be corrected before those walls go up. Covering an insulated wood wall with plastic is a sure way to run into mold issues.

Bud


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## 123pugsy (Oct 6, 2012)

Vapour barrier is required here in Ontario.
I refused to use it so I had only one choice and that was to spray foam the walls as well.

Before you insulate, get a quote from them to do your walls as well as the rims. You may be surprised and it may only be a bit over your budget.


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## Red Squirrel (Jun 29, 2009)

Yeah I definitely want to use a vapour barrier and make it as tight as possible weather or not it's required, a leaky insulated wall may as well not be insulated. I originally was going to do full spray foam, I got a quote, I think it was around 3k to do the whole basement, and a bit over 1k to do the rim joists. So it's still an option but I'm leaning towards batts. Weeping tiles were recently redone so moisture won't be an issue. 

Often people shove fibreglass in the rim joists, is that often the only thing that is actually done? I don't think I've ever seen it done properly come to think of it. A leak in vapour barrier pretty much negates the whole idea of having one, too.

My house is old so the existing vapour barrier is pretty poorly done, and not taped anywhere, and I suffer from it in winter, so if I'm going to do the basement I want to at least do that part right.


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## 123pugsy (Oct 6, 2012)

Moisture can come through the foundation and condense on the vapor barrier.

Google "mold on basement insulation", hit images, and you may think the extra cost is worth it.

My spray foam is about 1/2 way down at post 575:

http://www.diychatroom.com/f49/total-house-rebuild-bungalow-two-storey-276978/index39/

No moisture is coming from the outside with this stuff installed.


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## lenaitch (Feb 10, 2014)

My vote would be spray foam as well. I'm not sure I understand your original post. If your wall has been framed, I assume the studs are in front of the foundation wall, along with a base a top plate, and the joist bays leading to the rim joist behind the stud wall. If so, you could stuff batts in the joist bays. If you want to use batts in the stud wall, the vapour barrier (req'd in Ont) would run from the top to the bottom plate and sealed around the perimeter with tube sealant.


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## Red Squirrel (Jun 29, 2009)

Problem if I only stop the vapour barrier at the top plate, then what about the space between the top plate and wall, the air can still leak through there. Also need to seal the rim joists themselves, batts arn't good enough to seal, so either have to cut vapour barrier and tape all around (kinda a pain) or spray foam. So will do spray foam for rim joists for sure. I guess I could ask them to spray it all the way to the top plate of my wall, then it will seal that area. 

I might just go ahead and do spray foam for whole area but want to see what my options are for batts. It's been done many times so I'm sure there's a proper way of tying in vapour barrier for a proper seal.


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## 123pugsy (Oct 6, 2012)

You need to bring the VB over the top of your stud wall and into the rim board area. Staple it in place and the spray foam will spray right over it sealing everything off.


Insulate the walls first.

If you're gonna use insulation, at least use Roxul as it doesn't absorb moisture like fiberglass.


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## Red Squirrel (Jun 29, 2009)

Yeah plan is to use Roxul. Since the joists sit on top of the wall, what is best way to deal with that, I guess I can just kinda shove it all around and staple it. I'd probably use acoustic sealant for the seams, then tape it to the wood too for good measure. The foam would then cover that part. Or if I go that far I may even end up just vapour barriering the rim joists too... But foam is probably best bet.


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## lenaitch (Feb 10, 2014)

Red Squirrel said:


> Problem if I only stop the vapour barrier at the top plate, then what about the space between the top plate and wall, the air can still leak through there.


Ya, sorry, brain gap until I saw your diagram. Another option could be cutting rigid foam for the joist pockets and sealing around the perimeters with canned foam.


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## Red Squirrel (Jun 29, 2009)

Been thinking this over more as I want to try to do it all myself to save money and probably start on that this year. Easy route is to get the rim joists spray foamed and ask them to also extend a layer of foam all the way to the top plate of wall. That will create a continuous seal and then I can just vapour barrier to the top plate. Trying to bring vapour barrier into each individual cavity from the wall would prove to be tricky. 


Another option that's cheaper and more DIY I've thought of is I could do the classic rigid foam, but also add a piece that is horizontal and extends to the top plate like in my attached pic. I could then seal them in with caulking or acoustic sealant. Maybe even fire caulk? As long as it's something that will seal decently and last. Think this would work ok? I'm leaning towards that route. Should probably do that before any electrical that way I can drill through the foam and top plate and pass wires in, vs trying to cut foam around existing wires. I'd then caulk the holes in. Then for the regular wall I just need to bring vapour barrier up to the side of top plate as normal and have continuous tape, but then also small sections to tie it in to the foam between each joist section. 

I understand this is probably above code, I think most people just foam the end part of the joist and call it a day, but may as well try to make sure I get a very air tight seal as best as I can. Rest of house is terrible but at least I can do this right if I'm going to do it. 

As a side note I plan to install a wood stove at some point, for the wall what is the best way to prep for the exit pipe? how is that general area typically vapour barriered/instulated? I imagine you can't have plastic tapped right to the pipe or it will melt.


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## 123pugsy (Oct 6, 2012)

Use acoustic sealant. It doesn't dry up and crack.


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## stick\shift (Mar 23, 2015)

I think you may be missing the difference between air sealing and vapor barrier. You are correct in that you want to stop the movement of air (air sealing) but the vapor barrier is not what does that. Generally speaking, unless required by code, below ground walls should not have a vapor barrier but yes, they should be air sealed.


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## Red Squirrel (Jun 29, 2009)

I thought the whole point of vapour barrier was to air seal? Without one you get air leaks and your insulation is just acting as an air filter. Cinder block is not really air tight so definitely want to vapour barrier the wall too. This is about creating a continuous sealed envelope. 

Though my pic may have been missleading, the light blue line represents the "cold side" that needs to be air sealed, the darker blue is the vapour barrier, and then the pink is the foam. So between the foam and wall vapour barrier it creates a continuous seal. I will want to caulk or foam the bottom plate of the wall too or air can leak through there.


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## stick\shift (Mar 23, 2015)

> I thought the whole point of vapour barrier was to air seal?


Then it would be called an air barrier. Yes, vapor barrier and air barrier are different things. Common on a concrete basement wall is rigid foam glued to the walls and then the seams taped. Done well, this can be an air barrier. It is not, however, a vapor barrier, as the foam is considered a vapor retarder and lets the wall dry to the inside instead of trapping the moisture in the wall.


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## Red Squirrel (Jun 29, 2009)

Well that's new to me, so are you saying that vapour barrier plastic is actually not air tight? I know about using foam too, but that's easier to do for a wall that is not already framed, and I feel the R value is too low, and by adding batts on top after you end up with a vapour barrier not being on the hot side, which can be problematic. Typically people here frame first, then use batts then vapour barrier on top as it keeps it on the warm side which will prevent condensation. Most of the time they use fibreglass though, but I'll be using Roxul. Don't like the idea of fibreglass touching the bare wall.


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## stick\shift (Mar 23, 2015)

Rigid foam is not a vapor barrier, it is a vapor retarder. Generally speaking, vapor barrier is not advised on below ground walls as moisture will move through the soil into the concrete wall and into the living space so you want the wall to be able to dry to the inside. Additionally, the foam creates a thermal break to prevent condensation.


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## Red Squirrel (Jun 29, 2009)

So foam is not air tight? I always thought it was, and made a proper replacement for plastic in situations where you just want to insulate at same time or where plastic would just be harder to install. 

But I'm still confused with the whole vapour barrier/retarder thing, I always figured vapour barrier was just a word for something that will make the space air tight as to not let air in/out so that you can retain heat better. 

As far as moisture, if there is any then you have to fix that problem first. Moisture is something you fix on the outside, but vapour barrier is something that is on the inside. Idealy you want a continuous evelope for the entire building but that is often not achieved due to imperfections in the building process etc.


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## stick\shift (Mar 23, 2015)

If continuous and the seams taped, the foam could be your air barrier. That said, it is still going to let some moisture through - it is a vapor retarder but not a vapor barrier. If the foam is thick enough, it creates a thermal break so you do not get condensation forming on the inside of the foam.

One more thing to define - moisture is not solved on the outside, water is. There are ways to move water away from the foundation but a below ground concrete wall is going to let moisture (vapor) pass through from the soil into the house. This is why you don't want a vapor barrier below ground, as you want to let the wall dry to the inside instead of trapping that vapor and allowing it to condense into water inside the wall.


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## 123pugsy (Oct 6, 2012)

Red Squirrel said:


> So foam is not air tight? I always thought it was, and made a proper replacement for plastic in situations where you just want to insulate at same time or where plastic would just be harder to install.


Inspector in my area would not accept foam board as a VB. He insisted on a sheet of poly in front of the Roxul which would have been in front of 2" Styrofoam.
I told him no way I would do that as I've seen so much moldy insulation every time I've opened a basement wall.

Spray foamed the whole works, no VB, sweet.

Sometimes, saving money is not the only thing. Think about it as an investment in your home.


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## Red Squirrel (Jun 29, 2009)

Yeah spray foam would be the ideal thing, but at ~4k (got an estimate many years ago, would need to get another) I'm just trying to see what is the best method to insulate myself. Most people here just put fibreglass insulation and vapour barrier. I think most don't even bother with vapour barrier for the rim joists and just shove batts in there. But I want to do better than that. Suppose my best option might be to get the rim joists professionally spray foamed and have the foam extend to the top plate of the wall. Then I'll just do batts/VB for the wall itself. 

As a side note some people say you should not insulate all the way to the bottom, but that seems a bit counter productive to me, is there any reason for that? I would want to insulate right to the bottom unless there is actually a reason not to. I suppose once you get to a certain depth the wall won't be as cold but if I don't insulate to the bottom it's basically a break in the thermal envelope. Given the subfloor is not insulated (just drycore) there will be a thermal break no matter what but may as well make it right at the bottom. 

I do have some money coming in soon though. Tax return, company shares etc... so maybe I will just splurge and do full spray foam. But I was kinda thinking of putting that money towards a wood stove. With the carbon tax I really need to start thinking about cheaper ways to heat. Solar is another thing I have on the back of my mind but more expensive to do. Wood stove would see immediate results. Costs of everything keep going up so money is getting tighter every year.


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## 123pugsy (Oct 6, 2012)

Red Squirrel said:


> Yeah spray foam would be the ideal thing, but at ~4k (got an estimate many years ago, would need to get another) I'm just trying to see what is the best method to insulate myself. Most people here just put fibreglass insulation and vapour barrier. I think most don't even bother with vapour barrier for the rim joists and just shove batts in there. But I want to do better than that. Suppose my best option might be to get the rim joists professionally spray foamed and have the foam extend to the top plate of the wall. Then I'll just do batts/VB for the wall itself.
> 
> As a side note some people say you should not insulate all the way to the bottom, but that seems a bit counter productive to me, is there any reason for that? I would want to insulate right to the bottom unless there is actually a reason not to. I suppose once you get to a certain depth the wall won't be as cold but if I don't insulate to the bottom it's basically a break in the thermal envelope. Given the subfloor is not insulated (just drycore) there will be a thermal break no matter what but may as well make it right at the bottom.
> 
> I do have some money coming in soon though. Tax return, company shares etc... so maybe I will just splurge and do full spray foam. But I was kinda thinking of putting that money towards a wood stove. With the carbon tax I really need to start thinking about cheaper ways to heat. Solar is another thing I have on the back of my mind but more expensive to do. Wood stove would see immediate results. Costs of everything keep going up so money is getting tighter every year.


I hope you have a source of free wood.
That sure wouldn't be cheap to buy I imagine.

Insulating halfway down, nonsense!
They may have been referring to the minimum requirements of a new home build.

Remember, Ben Franklin said to not believe everything you read on the net.


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## 123pugsy (Oct 6, 2012)

Remember when you're comparing costs to include the foam boards, the Roxul, the VB , the tuck tape, the acoustic sealant and any cans of great stuff.

As a whole, all those things really add up.


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## Red Squirrel (Jun 29, 2009)

Wood is pretty cheap if you get it yourself. Just need a license and to pay a small fee per cubic meter that you take. Lots of free source too, like sometimes people just want a tree taken away and will let you take the wood. But if I got lazy I'd probably just buy it, still fairly cheap. Natural gas is only going to go up, especially now that the government seems to have a war on it's usage and wants to tax it from every direction and even talks about banning it. 

And yeah kinda figured it was odd to only insulate half way. I'll do all the way to the bottom.


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## Gary in WA (Mar 11, 2009)

I haven't talked to you for awhile... hope you have been well. They leave the bottom with no insulation when they use a plastic vapor barrier- that completely stops the incoming moisture- then it dries and it gets to the bottom. Your code requires a vapor barrier on the concrete- but not necessarily a plastic (Type1) sheet; 

"It is also required where wood members are applied in direct contact with below-grade concrete or unit masonry for the installation of insulation and/or finish."------------------------- AND; In the case of walls, the dampproofing must extend from the basement floor up to ground level. Permissible dampproofing materials include polyethylene film that is 0.05 mm, or thicker; type S roll roofing; or any membrane or coating with similar properties. This implies that a variety of plastic foam and specially faced insulation materials also satisfy requirements for interior dampproofing. However, in general such materials with a permeability of less than 170 ng/(Pa.s.m2) should meet the requirements for low-permeability materials in Section 9.25 of the NBC 2005, if they are applied to the interior surface of the above-grade portions of the foundation wall. from; http://www.nrc-cnrc.gc.ca/ctu-sc/ctu_sc_n70

So, that 170 ng is about *3 perms in US*, far from plastic at *0.6 perms*- Type S roll roofing- (mineral faced asphalt saturated felt at 3+ perms) would work but not let it condense to pool at the bottom if not wanting to leave a bottom strip off. There are other ways than using plastic on the wall- housewrap also comes to mind; https://www.google.com/url?sa=t&rct...sg=AFQjCNFihWruFRtcUxT69Jt2X7jykMDFpA&cad=rja

Plastic vapor barrier problems; http://users.encs.concordia.ca/~raojw/crd/reference/reference001343.html

A very good read by BSC member- check out the *Frame/FG/Latex paint wall *and results, as well as the history leading up to code requirements; https://www.google.com/url?sa=t&rct...sg=AFQjCNEGWatpc0hpVem-yYyVnvgsRZ6Sbg&cad=rja

Gary


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## Red Squirrel (Jun 29, 2009)

Hmm yeah too late to add anything to the walls now, since the studs are already in place. Well it could be done but very tedious and there would be lot of seams. Studs don't touch wall, I made sure of that. But that explains why there was tar paper on there before, I thought that was odd since I had never seen that before. There is a rubber spray on membrane on the foundation outside though. But I guess some moisture can still come in from bottom as mentioned.


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## Gary in WA (Mar 11, 2009)

Summer will drive the outside moisture through the concrete above grade to your insulation. Code requires something on the inside above grade... or the gap-- which give convective loops around the fibrous insulation, degrading the R-value and depositing moisture at the top of wall. Tar paper was a good fix back in '95 and even extruded foamboard as mentioned on pp 2; https://www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/95-207.pdf But tar paper of old is not the same today- so it has to be roll roofing- underlayment- without the granules works as it is much stronger than thin papers of today; http://www.fortifiber.com/pdf/fortifacts/fortifacts_ask_vs_felt.pdf

Someone else; http://www.askthebuilder.com/vapor-barrier-on-foundation-walls/


Gary


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## Red Squirrel (Jun 29, 2009)

Been pondering this and since rigid foam is actually not a vapour barrier I think I will go with a spray foam kit and do the rim joists myself with that. Can do a "L" shape where I spray the very end, then the bottom all the way to the top of the top plate of my wall, covering the gap between that top plate and the foundation top plate, as well as any holes that were done for electrical, and trying to get as close as I can to the edge of the top plate to meet up with the vapour barrier. Doing the plastic would be too tedius, trying to tape it all right in those oddball corners etc. Then I will do batts and plastic for the main wall cavities. I will probably stick some batts in the rim joists too as foam should not be exposed due to fire risk. 

Considering how badly done my upstairs is, I think anything I do in the basement is going to be better than the upstairs, so no sense in trying to go with 100% seal.


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## Red Squirrel (Jun 29, 2009)

Finally got around to foaming today. It was kinda tricky to do that L shape that I wanted as in lot of places I could not get the gun at the right angle or evne see inside the cavity but I did what I could. To ensure the wall is air tight I also foamed between the top plate and the wall from underneat. 

I will fully inspect tomorrow and any areas that may not have gone thick enough I'll just apply canned foam or something. For the actual rim joists itself I'd say even if I did miss some spots it's going to be better than what it was! There was no vapour barrier at all, just paper backed insulation but the paper was not even taped. I'll shove those batts back in for extra R value, and add roxul in the ones that had no insulation. It will also act as a fire block as spray foam should not be exposed. 

Being my first time and in some cases being at an awkward angle, and also racing against the clock to move from one place to the other, I was a little sloppy, but I think it turned out ok. Now breathing in lovely VOCs before bed time. lol. I had to crank the furnace to 11 for a couple hours to acclimate the chemicals and the surfaces so at least it's fairly warm in the house even with the basement windows open. haha. I also don't want to run the furnace until things settle. 









In spots where the top plate was too far from the wall I shoved fibreglass then tried to top spray it as best as I could. Fibreglass is just to have something to hold the foam while it cures, but I'll leave it there for what it's worth. 

As a side note, roxul feels fairly dense, does it actually have somewhat airtight properties to it? It almost feels like even if I may have missed some spots while sealing, the roxul might kind of help too as far as air penetration goes. Obviously it does not replace a vapour barrier butt almost feels like it might make up for any imperfections in the air sealing.

Most importantly, with all this, I managed not to get any in my beard.


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## 123pugsy (Oct 6, 2012)

Roxul has zero air sealing.

Is it my eyes or is your ceiling only 6' high?


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## Red Squirrel (Jun 29, 2009)

Figured. It just feels so dense compared to fibreglass that I thought maybe it has somewhat air blocking properties. Ceiling is 7 feet, but the first 3 pics are crawlspace area so it's like maybe 5 feet. Was easier to get pics there as it's more open, so not much pics of basement part. It's a split level house so about half crawlspace half basement. 

Was inspecting my work after and realized I missed lot of spots where it did not expand as much as I expected so it's not fully sealed, will probably just use canned foam and go fill those in. 

Overall I'd say it is a decent product, I'd probably use it again. Was Touch n Foam 200 from Home Depot. It's not as good as what the pros use though, theirs expands way more. This product is more or less like "great stuff" except it probably expands a tad more, and due to the higher pressure it spreads way better. 

Oh as a side note, to show importance of air sealing, when I pulled out the old batts that were in the rim joists I was getting dust clouds and even sand. That's all dust being brought in by air movement. That indicates lot of heat loss!


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## NotyeruncleBob (Mar 9, 2017)

I know that you can a lot more yield out of the foam if you lightly mist some water on the surface before spraying. I'm guessing that the older wood in your basement could be pretty dry and pulling moisture out of the foam. Did you do any misting before spraying?


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## Red Squirrel (Jun 29, 2009)

I heard that too, but then the instructions say to ensure it is very dry. 

I ended up getting the touch n foam 15 (a smaller version) so I can fix the places I missed or that did not get enough coverage. I'll do that tomorrow as it's suppose to be warm out so don't need to crank the furnace this time.

Also some of the product seems to still be wet, that's from when I was near running out, so I just sprayed it over existing foam for what it's worth, just to see if it will expand a bit more. Will that dry up eventually? Or do I need to even worry about that as it will be covered with roxul anyway.


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## Red Squirrel (Jun 29, 2009)

Well I probably should have just went with the bigger kit, two of the 200 is more expensive than the 600, and looks like I need to get another 200 as there's lot of awkward spots I missed. I was also rushing more than I really should have so missed some areas entirely, kept forgetting I had lot of spare nozzles, so should have taken a break half way to inspect my work to see what else I need to do instead of just going over areas I already did (which is what I did to "use up" the rest).

So think tomorrow I will bite the bullet and just buy another system 200, and to try to force the foam into the awkward spots I'll try to make a custom nozzle or something. I'm thinking some plastic tubing and I can tape/hold it against the nozzle. 


Here's some pics of the work, can't see the spots I missed as they are on top. 






the lines along the joists were kinda useless, they are too far so it was not expanding enough, I will just use cut batts for those sections, I did those lines when I had spare foam left and just wanted to use it up, but didn't do everywhere. 




If anything by doing this job I gained an appreciation for how much the pros charge, it's not as easy as it looks to get every nook and crannie as some areas are just physically awkward to spray into, and being in the hazmat suit with mask and glasses and having to crank the furnace up to acclimate the surfaces you really put on a sweat! That and when you stop to spray it wants to drip so I was making quite a mess, a pro would probably be better at managing that. I had my furnace set to 27C so I can get the rim joists to the required 16C. This time it should not be so bad since I still have a base coat of foam now. 

May as well bite the bullet and get another system 200 to finish the job properly then use the extra to just thicken up the rim joists. Then I can just shove some fibreglass batts for fire block. Roxul for the walls and then vapour barrier from top to bottom. That's why it's important I foam continuously up to the wood as I need to complete that air seal.


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## 123pugsy (Oct 6, 2012)

You're not alone.
The sprayers I used had a bigger gun which could not get into all the spots.
I had to cut a slot in the subfloor on two ends of the house for them.

And they still missed spots which needed touch ups.


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## Red Squirrel (Jun 29, 2009)

Good to know it's not just me. 

Finally have more time off. Going to fix my work tomorrow with a new kit. I'll try something different:



This should hopefully let me direct the spray better downwards so I can get between the top plate and the foundation. Just not sure how fast that's going to get clogged up though, and hopefully it holds. I used a heat gun to soffen it up and shoved it as far as I could, then twisted a piece of wire very tightly.


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## Red Squirrel (Jun 29, 2009)

Well the deed is done, my mod worked! Only issue is while trying to maneuver the step ladder and canisters behind the hot aisle of my server room (very tight to work in there) I took too long and then it clogged. But I had done the worst areas already. Then I just proceeded to thicken the existing work I had done and was able to mostly bring it all the way up to the top plate by building it up. 

I may have wasted more than I needed near the end though. When it started to turn white I figured it was because it was done, but I had quite a lot left. 

Bags of waste are sitting outside now, don't want to throw them in the trash until they cool off internally.


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