XPS and Epoxy

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Re: XPS and Epoxy

Postby fonsan » Sun Jan 29, 2023 3:10 am

woodie72 wrote:
fonsan wrote:

The thinnest wood i can get a hold of where I am (EU) is 3 mm ply wood for about 9 euro/usd. Presuming having to do both faces of a composite panel it would end up being 2oz cloth with epoxy, 3mm plywood, epoxy, xps foam, epoxy, 3mm plywood, 2oz cloth epoxy

This would more than double the cost and work per sqm and it seems to me that the more elegant solution is just to chose a heavier cloth instead of adding plywood to the mix. I am getting the feeling that 2-4oz cloth might be sufficient in terms of surface resistance as I don't really mind repairing any damage.

I am starting to realise that what I am asking about is the rigidity of the structure and not the surface resistance to damage as it seems that the rigidity will dictate the thickness of the fiberglass cloth


I don't know from which country you are in Europe, but there's birch ply ranging from 0.4mm to 2.5mm. It's In 0.2mm increments up to 1.2mm, 1.5mm, 2mm and 2,5mm is available. Costs a penny, but it's available. Must be available in more countries in Europe.
https://www.intriplex.nl/plaatmateriaal/multiplex/berken/?p=2


Good point! I am not really going for weight but economical which makes me realise that I should take a second look at OSB (sanding and surface treating it ofc
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Re: XPS and Epoxy

Postby tony.latham » Sun Jan 29, 2023 11:29 am

I am not really going for weight but economical which makes me realise that I should take a second look at OSB (sanding and surface treating it ofc


What's OFC?

One of my core beliefs is that OSB has no place in a camper. Glues and screws don't like it. Water does. If water finds a way in, it swells and will always be spongy. It's a corner you don't want to cut.

:thumbdown: :frightened:

Put another $50 or so into your project. It'll be stronger and will last longer.

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Re: XPS and Epoxy

Postby fonsan » Sun Jan 29, 2023 12:02 pm

tony.latham wrote:
I am not really going for weight but economical which makes me realise that I should take a second look at OSB (sanding and surface treating it ofc


What's OFC?

One of my core beliefs is that OSB has no place in a camper. Glues and screws don't like it. Water does. If water finds a way in, it swells and will always be spongy. It's a corner you don't want to cut.

:thumbdown: :frightened:

Put another $50 or so into your project. It'll be stronger and will last longer.

Tony


In texting and internet slang, OFC means “of course.”


Yeah after researching a bit it does not seem worth it at all.
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Re: XPS and Epoxy

Postby jakejakejake » Sun Jan 29, 2023 2:43 pm

tony.latham wrote: OSB has no place



ANYWHERE! It really is a garbage material, propped up by marketing to sell consumers what once was trash as a viable building material.
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Re: XPS and Epoxy

Postby Squigie » Mon Jan 30, 2023 1:31 pm

In texting and internet slang, OFC means “of course.”

You might want to check your sources on that again.
OFC might be taken as "of course" by some people, but the more accepted and common meaning is "of f***ing course". -- As in, absolute agreement (friendly conversation) or a hostile dismissal (unfriendly exchange).
Be careful how you use that internet shorthand.
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Re: XPS and Epoxy

Postby fonsan » Thu Feb 09, 2023 5:33 am

https://www.youtube.com/watch?v=xVh3iC8EGds

163 g / 6oz on 30mm / 1.1 inch foam break test when standing with a 50 cm/ 20 inch gap
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Re: XPS and Epoxy

Postby hidesertrocker » Fri Feb 17, 2023 12:51 am

kstills wrote:I'm not sure I have the best epoxy for this build, I bought sample bottles of 'table top' epoxy off Amazon for this test because they advertised 72 hour cure. I'm going to get some from the countertop guys and give this another try. Primarily because after all was said and done, the adhesion pretty much sucked. Again, it's probably good enough for interior, non structural work, but why accept poor adhesion if I can get better with another brand?


I may have missed it if it was mentioned earlier, but for your application what you're looking for is generally known as laminating epoxy. The brands that others have mentioned are all good choices. However, some have multiple products for different applications. 'Table top' resin is mainly formulated for clarity, and mainly used in a thick layer to encapsulate something, without using a reinforcing fabric. Doesn't mean it can't be used in your application. It would be better as a top coat due to it's self-leveling nature. There are other products/methods for filling in weave that would be better suited to what you're doing, since ultimately you are going to be painting over it. Less important than cure time is working time (aka 'pot life'). Something in the 1to 2 hour range would be your target, depending on how complicated your layup is (like compound curves or if you're covering a large area) and how comfortable you are with the process (including assembling everything you need before you start).

Something I noticed in a different post was use of a 'mat' fabric. I think what follows might have been mentioned earlier, but I might be confusing this with another thread. Mat fabrics typically are coated with a binder that usually requires styrene to dissolve. Make sure the fabric and resin you choose are compatible. I don't know the size of the cabinetry you're contemplating, nor what you're planning to store in them, but mat may be overkill. Typically it's used to build thickness inexpensively (that whole strength being related to the square of thickness thing -- but don't hold me to that, I'm probably remembering that factor wrong).

Depending on the size of what you build, you may be able to use gravity and pressure to your advantage. You don't need to go full vacuum bagging mode, but some techniques/materials might produce the surface finish you're wanting. There are several materials that epoxy won't stick to, like release film, wax, mold release, and some mylar films. Find a flat surface, maybe glass, a countertop or table. I'd suggest using release film, laid on top of the flat surface. After laminating one side of your work piece, turn it upside down on the release film. Apply some pressure to the work piece via weights, clamps, etc. You don't need to crush it, even pressure is more desirable. Unless you are really good at applying the minimum amount of resin, some should squeeze out (which is good, unless it's too much and flows off the film and makes a mess). There will still be pinholes and other minor blemishes, but you should be able to get a pretty uniform surface with less effort than other methods.

Several vendors and manufacturers have good online resources for info that may get glossed over in videos. Apologies if you're aware of these, but others may not be, so I'll list them below. Some of the info may be product/company specific, but most of it is generally applicable to what you're trying to accomplish.

https://www.fibreglast.com/category/Learning_Center
https://www.westsystem.com/instruction-2/
https://fiberglasssupply.com/how-to-and-tools/
https://support.jamestowndistributors.c ... ct-Support
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Re: XPS and Epoxy

Postby RJ Howell » Fri Feb 17, 2023 10:02 am

fonsan wrote:https://www.youtube.com/watch?v=xVh3iC8EGds

163 g / 6oz on 30mm / 1.1 inch foam break test when standing with a 50 cm/ 20 inch gap


Thing I see with his testing: The edges are not supported. I'm about to head into another build of my truck camper and will be doing a major portion as SIP construction. The edge should be either fiberglassed or Splined. I have a spline system I need to test out that I believe will give the structural wants without major weight addition.

I drew this and shared once before for another. I am going to test a few materials for the spline and then fiberglass over. My though is to work with 16" widths, possibly going down to 12" if required. Ends would be done the way.

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Re: XPS and Epoxy

Postby QueticoBill » Fri Feb 17, 2023 7:54 pm

I don't believe a spline is necessary if the seams of the skins are offset 12" or so from foam joints. Honeycomb would work as well structurally and has no stiffness or cohesiveness by itself. Using say 1/4" ply skins, probably a gap between foam of 8" or so would not impact it structurally.
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Re: XPS and Epoxy

Postby fonsan » Sat Mar 04, 2023 12:32 pm

https://www.youtube.com/watch?v=z9iySKmGPeI from the excellent explore composites channel

He is using 1.5lb/cubic foot XPS which is about 20kg per m3. He does not state but looking at the poor surface adhesion he is reaching he has probably not sanded with corse 40 as recommended.

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The XPS that is available to me in Europe is 50% more dense, 33kg per m3 and has 250kpa (36 psi) or 300kpa (43.5psi) compressive strength. He is also using 1" foam which limits strength of the sandwich i plan to use . Remember that doubling the core (foam) thickness will give 300%-400% increased bending resistance.

He did go the same route as I have in regards to surfacing with a 9oz roving and surface veil for smooth surface. I am going for 10.7 oz roving and 1oz veil and I plan to hand laminate not using vacuum. The price really dictates the choice of fiberglass, a 200g (7oz) woven is 200-300% more expensive per square meter compared a roving 300g (10.7oz). I paid 131€ (140$) for 150m2 (1516 square feet) for the roving and the 1oz veil is 0.5€ per m2.

I also plan to mix 5% white pigment into my laminating epoxy and see if that removes the need for additional covering layers of paint later. Additionally I will do a thin "hot coat" to make sure the veil does not print through to the final surface. If everything looks good I will coat it with a transparent two part polyurethane coat to protect it from UV
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Re: XPS and Epoxy

Postby McFish1951 » Tue Mar 21, 2023 2:50 pm

I am a complete newbie, so please forgive my stupid questions. In other applications, basaltic fabrics and material are much stronger than fiberglass or carbon. In this application, would the added strength be beneficial? Also, I'm not sure of the cost differential. I'm not sure if you need added compression strength, or more tensile? I found this boat building You tube that seems pertenant.
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Re: XPS and Epoxy

Postby McFish1951 » Tue Mar 21, 2023 3:03 pm

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Re: XPS and Epoxy

Postby kennyrayandersen » Wed Apr 26, 2023 1:33 am

McFish1951 wrote:I am a complete newbie, so please forgive my stupid questions. In other applications, basaltic fabrics and material are much stronger than fiberglass or carbon. In this application, would the added strength be beneficial? Also, I'm not sure of the cost differential. I'm not sure if you need added compression strength, or more tensile? I found this boat building You tube that seems pertenant.


That sounds Expensive and exotic. If PMF works, and fiberglass is stronger, then there seems to be little reason to go chasing exotic materials for some small gain in strength. Could you make the while teardrop, including frame out of Gr/Ep (graphite/epoxy)? Yes, but it would be mind-blowingly expensive for not that much gain. Just my opinion.
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Re: XPS and Epoxy

Postby nbcarey » Sun May 28, 2023 5:05 pm

kstills wrote:
Squigie wrote:Aircraft and hobby aircraft (RC) builders have been doing this for years. More recently, it has become a more popular forming method for custom auto body panels, as well (but usually with an acetone rinse afterward, to remove the foam and leave just the shell if it is the final panel.



This just hit me.

Way cool, my mind is spinning thinking about the shapes that might be able to be formed using this method.

Just off the top of my head, I would suspect you could make some pretty lightweight doors using this method.
Bear in mind that you'll need a lot of acetone, and that the resulting mixture is not dissimilar to napalm. It's toxic, highly flammable, and will need to be disposed of as hazardous waste - e.g., not cheap.
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Re: XPS and Epoxy

Postby kennyrayandersen » Sun May 28, 2023 10:57 pm

fonsan wrote:
He is using 1.5lb/cubic foot XPS which is about 20kg per m3. He does not state but looking at the poor surface adhesion he is reaching he has probably not sanded with coarse 40 as recommended.


Sanding will certainly help, as well there are other methods like poking small holes in the surface that the epoxy can get a grip on. In the industrial world, the facesheets are attached to the core with a layer of adhesive. Facesheets have a strong tendency to peel from foam core.

fonsan wrote:The XPS that is available to me in Europe is 50% more dense, 33kg per m3 and has 250kpa (36 psi) or 300kpa (43.5psi) compressive strength. He is also using 1" foam which limits strength of the sandwich i plan to use . Remember that doubling the core (foam) thickness will give 300%-400% increased bending resistance.


The core reacts shear -- the bending resistance is virtually unchanged. As long as the core shear allowable is not exceeded, the core will not fail irrespective of the bending. The facesheets are very much stiffer than the core. The load in the core relative to the load in the facesheets due to bending is not even used in the calculations (it's so small it's thrown away).

fonsan wrote:I also plan to mix 5% white pigment into my laminating epoxy and see if that removes the need for additional covering layers of paint later. Additionally I will do a thin "hot coat" to make sure the veil does not print through to the final surface. If everything looks good I will coat it with a transparent two part polyurethane coat to protect it from UV


As I understand it, epoxy is not good with the sun. Personally I'd just go ahead and put actual paint on the outside in order to really block the UV, but that's me.
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