Economy basement finish with DuPont Thermax
So I have been searching site and came across this article https://www.greenbuildingadvisor.com/article/basement-insulation-part-2
Basement walls were insulated with thermax walls rigid foam with a white finish look, no need to build stud walls and no need for drywall. So I was thinking about doing this and was wondering.
1. Can I cut this and fit this around drain pipes leaving pipes exposed for easy access.
2. After installing this could I have an electrician set up electrical right over this board.
3. What is easiest way to install this directly to concrete, can it be glued?
4. Can I paint this stuff or get paint on it if I wanted to.
5. what would be negative of doing this?
Seems very easy to do, not as professional looking as traditional building stud walls, etc but it would be user friendly for a diyer. Plus it’s a basement, I want it to look good enough to have kids play in
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Replies
1- yes, you can do that. You’ll want to keep an air seal though, so you will need some kind of sealant or gasket.
2- yes, you can do that. It’s often easier to install a strip of plywood over the polyiso and then fasten the electrical stuff to that. You need to use some type of conduit too, to provide physical protection to the exposed wiring. EMT is one option, MC cable another.
3- yes, you can glue it up, but I prefer the purpose made plastic anchors that Hilti makes for this purpose.
4- this can be tricky. You need to use a primer that will adhere to the facer of the Thermax. As long as you use a suitable primer, you should be ok.
5- the only real downside to Dow Thermax is that you’ll have a lighter wallet after you buy the stuff. It’s an excellent product in all other respects.
Bill
Thanks Bill, seems like a solution I have been looking for. My wallet will be lighter but it will easier for me, could save on labor and time. I guess my only challenges would be
1. I still need to build framing for doors. There will be some gaps between wood and concrete, I’m assuming I could attach this to studs in some areas.
2. I have an open extension on my hvac system in ceiling. Can I somehow vent this down from ceiling or is that not normally done. I’m up in the air on if I should build a permanent partition wall for my furnace. Not sure if there is an easy inexpensive way to close off this area
Use treated wood where it is going to be in contact with concrete.
I’m not sure what you mean by an “open extension” for your furnace. Maybe some kind of plenum using studs and drywall instead of ductwork?
Bill
Sorry I worded that wrong. I have a flex duct in ceiling that is available to use. It is not going to anything just hanging in basement ceiling. Contractor left it said if you ever need to heat basement you can use this
I think some people have suggested drywall over foam with none to minimal stud wall. I think gives you a better bang for your buck for finish vs just thermax. Will be hard to get it to "look finished" with just foam - plus damage seems inevitable.
Some grades of Thermax Ag Board have very tough facers, designed to be the finish in high-intensity agricultural applications. These come in both smooth and pebbled surfaces and would be more than tough enough for a permanent finish in a basement. Even more spendy than the basic Thermax, though. Also, sealing the seams with white tape works pretty well and is reasonably good looking. Wouldn't want it for my living room, but for a basement playroom, not bad.
I, too prefer the Hilti fasteners, but I've also glued foam to the concrete and that has held up very well. You could also use standard or recycled polyiso, glued to your walls, and glue a sheet of drywall or plywood to that.
Hope you have better luck finding it than I have. I have not been able to source the white faced product (2") in NJ unless I was willing to buy a literal truck load.
If anyone has any pointers as to where I could get it, I'd love to hear. I need about 15 4'x8' sheets.
Now that I looked into, it is pretty hard to find. You can do the same with foam and then drywall attached directly to it? That would a lot easier to get. I didn’t think you could do that. Can you use EPS foam or would you need polyiso? Also someone mentioned plywood? Could I even use osb? Any reason not to do that? With plywood or osb I could literally drill by electrical outlets right to wall.
My basement is a workshop; that's why I have plywood walls, and I use electrical conduit. Since I'm also fastening shelves to it, I used the Hilti fasteners to attach it to the wall. You could probably use OSB instead of plywood, although the plywood will hold screws better. Neither plywood or OSB should be ON the concrete floor due to moisture in the concrete; raise them by at least 1/4" & fill that with caulk.
As far as where to buy - we buy the Thermax at our local lumber yard; and by that I don't mean the BigBox stores, but the locally owned lumber yards who can probably easily order it if they don't stock it. Another place to try are specialized roofing supply stores - because commercial roofers use lots of foam on all those flat roofs.
One of the reasons we use polyiso on basement walls is that the aluminum facing means the moisture in the concrete does not get absorbed into the foam. Meaning the basement becomes less damp. And the R value is higher.
I used the Ramset system it was very fast not had a fastener come louse. But I do not see anything new about it on the web they may have given up. Ramset let me use the gun for free if I bought a box of fasteners
The surface is tender and must be treated with care to avoid damage. Not the best choice for a kids play room.
Walta
Thanks for all the help, I’m going to call my local lumbar yard tomorrow. How does cost compare to using thermax vs foam with stud walls and drywall? Is thermax too soft, is that why it’s hard to do foam with drywall directly over it? What if I used 1 inch foam then attached osb with fasteners and glued drywall over that. Wouldn’t that be technically what that dricore smartwall stuff is? I’m going to look into the harder thermax but don’t know how crazy price may get. So easy to finish thermax though, dealing with taping and muding would be another challenge for me
If you’re going to drywall over the polyiso, don’t waste the money on Thermax — just use “regular” polyiso since the drywall will give you the required fire rating anyway.
Home Depot can special order Thermax.
Bill
> Home Depot can special order Thermax.
I wish they could order a reasonable amount. When I asked, I believe the Pro Desk quoted me a 100 sheet minimum. Admittedly, this was better than the roofing supplier who needed a 172 sheet minimum!
Another option might be “a warehouse full” online, but I don’t know what their shipping charges would be.
Bill
Tried them too! I contacted them because it says to call to order (see here: https://www.awarehousefull.com/thermax-white-finish-sheathing-2-in-4x8-sheet-r-13/). Via chat, they told me they don't carry it and promptly closed the chat session.
This is seemingly the only polyiso made with large amounts of unobtainium.
Patrick I’m going to call my lumbar yard tomorrow to see if they have it, if you would travel to NJ I’m assuming you must be close to my location which means I might have a hard time finding it too. If it isn’t available, can anyone give me an idea of how to assemble this wall? I’m thinking 1 inch polyiso glued to wall, then green board glued to that. I’m confused about how sensitive the wall will be, if my 2 year old runs a toy car into will it just crumble into dust? Do I use thicker drywall or polyiso to make it more rigid? What would be good combination in thickness? I’m hoping I can find this thermax stuff at reasonable cost, was excited about not having to finish drywall.
Call Dow then, tell them you’re trying to buy their product and ask them who can sell it to you in reasonable quantities. They’ll probably try to help you out and put you in touch with one of their distributors that will be willing to sell in smaller quantities. I’ve done this before with other products. The manufactures are usually happy to try to help you find a way to buy their stuff.
Bill
(For some reason can't directly reply to comment #18 now that there are a bunch nested)
> Patrick I’m going to call my lumbar yard tomorrow to see if they have it, if you would travel to NJ I’m assuming you must be close to my location which means I might have a hard time finding it too.
Keep us posted!
> I’m thinking 1 inch polyiso glued to wall, then green board glued to that. I’m confused about how sensitive the wall will be, if my 2 year old runs a toy car into will it just crumble into dust? Do I use thicker drywall or polyiso to make it more rigid? What would be good combination in thickness?
Any amount is fine, structurally speaking, but 1" may not be enough (thermally) for your climate zone. Whatever thickness, it will be the most rigid drywall wall you've ever felt, since it has continuous support.
I have some walls with paperless drywall over foam, some walls with OSB over foam, and some walls with drywall over OSB over foam. From a fire rating perspective, 1/2" drywall is fine. 23/32" "wood structural panel" (i.e. plywood or OSB) is fine as well. The surface(s) I chose were based on the function of the space. Sometimes drywall over plywood/OSB is nice for mounting things to it.
Yeah this stuff is hard to get in northeast. I emailed manufacturer yesterday and waiting for reply.
I don't think there is any reason to use green board since the foam is a moisture barrier.
> I don't think there is any reason to use green board since the foam is a moisture barrier.
In a basement, I think you have to be really confident that there will never be a 'water event' in order to use regular drywall. I do not have that confidence, particularly with drywall that is glued to foam. I never want to have to take it out, and I therefore chose to use paperless drywall, so that if it ever does get wet, it won't be mold food.
> I’m thinking 1 inch polyiso glued to wall, then green board glued to that.
Forgot to mention this... you will likely need something to hold things in place while glueing. The glue lubricates the flat surfaces and they want to slide around a bit.
Any easy suggestions without actually drilling into wall? Would 6x6 pushed against bottom and several 2x4 leaning into top work? How long does it take to set
Put something like some plywood or a 2x4 under the bottom of the polyiso to leave a drainage gap, then lean something heavy against the polyiso to to hold it in place while the glue sets. Something like “fastgrab” in the PL line will minimize curing time so that you can remove the braces in a few hours at most.
Bill
Atlas Energyshield is a good polyiso product, if you're not purchasing reclaimed roofing polyiso. They have a regular line with a thin foil facer and a Pro line with a 12mil thick foil facer (white on one side) which is rated for exposed use. If you don't need the exposed rating, go with the regular line. I reached out to Atlas's regional rep to find out which distributors in my area I could get it from. I'm gluing and fastening with Hilti IDP fasteners, but I am prone to overkill everything. =(
I thought I read someone suggesting DensArmor (coated glass facer gypsum board) as an alternative to greenboard, but I haven't priced it out to compare yet.
Good luck.
Johns manville has their CI product that is similar to dow Thermax. Menards can order in the Johns manville product and possibly also other stores that carry their line.
Bill
Thanks I’m going to check it out. Wish they designed something that works like top layer of thermax, just some tape for seams and done. I have never done full mud and tape on drywall just patch up on plaster walls, looks like a pain to do
Tape and mud takes practice. As you get better at it, you’ll find you need to do less sanding later. There are some videos on YouTube that can help. I use one very wide (14” I think) knife and a smaller 3” knife. I prefer “hot mud”, which is the kind you mix with water. Mix it until it’s like mayonnaise and then spread it. I use mesh tape everywhere except for inside corners where I use paper tape and a combination of a corner knife and a 3-4” knife. I like the sanding sponges for a finish step. I also like to soak the paper tape in 2-3 foot strips in a bucket of water just prior to applying them, and wipe them between my fingers to get off excess water before I press them into the corner.
Practice in an area where the final finish is least critical and then move into other areas as you gain some experience. It’s not difficult, but it takes practice.
Bill
Got email from company, called J and S supply, said I can order in units of 22 sheets at about 72 a sheet. I put info below. Question I’m asking myself now is do I spend the extra money on material or do I get out the hammer and use polyiso with a 2x4 wall and Sheetrock. Cost might end up similiar, but one being more finished looking than other.
Thank you for your inquiry about purchasing DuPont™ Thermax™ White Finish (WF) Foam Insulation. This product is sold through distributors, and below are a couple of distributors in New York for you to contact.
J&S Supply (several locations in NY)
718-786-3044
General Insulation
781-391-2070
For information regarding attaching the foam insulation to the stud walls, I'm including a link to the DuPont Answer Center that provides details that will help you.
Thermax™ Interior Wall Fastening and Adhesive Recommendations (Residential)
As far as a sealant to use around the drain pipe, please look at our Great Stuff™ Insulating Foam Sealant products at http://www.greatstuff.dupont.com. These products can be sanded and painted to match the color of the insulation board and are designed to seal small gaps and cracks.
If you'd like further information, please reply to this email or call us at the below number.
Greetings all
I have used thermax in this application and make the following practical observations, in no particular order
getting thermax delivered without significant damage to the finish surface is very difficult.
any slight impact shows easily. shipping straps cause major damage if no edge protectors are used
the edges are very very sensitive to UV. just a few hours in strong sun and it looks like toast and is flaky/dusty. it is only clear wrapped from dow....
because most distributors/ suppliers are unfamiliar with thermax, they do not treat it as a finish material.... so its lumped around and stored outside.
it is straightforward to "glue" to the wall using Dow Enerfoam and a pro foam gun [all from awarehousefull who I recommend].
the issue is not waiting/holding it in place to set up, but rather getting it in place, before it sets up [rapidly] . there is also a "pushback" from the enerfoam after about 30s or so. enerfoam has been a great way of attaching insulation to CMU and air sealing it. imho, much better than mechanical fixing for multiple reasons
given the cost, delivery headaches and finish surface fragility, I probably would not use thermax again
hope that helps