Housewrap for skin?

[Mojave Bob]

Good morning! I have read through a whole lot of the foamie threads, but I don't think I've encountered this question. A big topic of discussion is what to use for the skin. Canvas, dropcloth, muslin, etc have all been mentioned. Has anyone tried using either Tyvek or other polyester housewrap? And, if so, what makes the best adhesive for this material? TBII, latex paint, oil paint? Housewrap comes in fairly wide rolls to minimize seams, it handles easily, it is very light, it is pretty strong, and it is cheap. It also repels water, which is good for the camper, but maybe bad for adhering it. What are the thoughts of the experienced?

[KCStudly]

Independent testing (by others) has shown that it does not adhere well; too slick to take glue or paint.

[Mary C]

Polyester and any plastic surface material is not porous enough the glue will bead as water. and yes it has been tried and like KC said didn't work. We suggest that a treated fabric with stain guard will not adhere either. We have taken the last two years experimenting and Reporting back findings in regards to materials and glues in the BIG Thread. and Yes it is long but........It is amazing what you will learn and get to know about building foamies. Everyone here has built with their own ideas and presented it as you have we watch in earnest to see if it works. If you want to try it go ahead you may have different results. But please take pictures.....We love and don't feel like you fail, you have just reinforced previous conclusions.

Mary C.

[Mojave Bob]

Thanks for the reply. I will try to dig around in the the BIG thread, but, as you say, it is pretty long. Anyway, I am specifically curious what adhesives have been tried to date. I saw the following on the the Tyvek website:

"A number of adhesives can be used to glue Tyvek®, either to itself or to other substrates. In general, water-based adhesives that provide quick tack and fast drying are preferred. However, the first step in choosing an adhesive is to determine how it will react with Tyvek®. Laboratory testing is the best way to make this determination.

Natural-product adhesives based on starch, dextrin, casein or animal by-products are preferred to synthetic-based adhesives. Synthetic adhesives often contain low-molecular-weight materials that can act as solvents at elevated temperatures and cause swelling and wrinkling. Hot animal glue is an excellent adhesive for adhering Tyvek® to paperboard. Water-based synthetic lattices also bond Tyvek® to itself and a variety of substrates. Ethylene/vinyl acetate adhesives are especially useful, as are the acrylic pressure-sensitive adhesives. Solvent-based single-component polyurethane adhesives provide optimum adhesion (lap and shear), flexibility and water-resistance for adhering Tyvek® to itself and a variety of substrates."

In particular, I note that they say polyurethane adheres well. I will track down a scrap of Tyvek, and try to find a suitable brush-able adhesive for it.

[KCStudly]

So, I think one needs to consider the application for which they are advising. I would think that they are generally considering how to seal and hold the product in place until sheathing can be applied over the top. (I'm thinking about house wrap products here, so maybe there are other applications that may have different requirements.)

Whereas in our application we are trying to make a composite outer membrane that is part of the structural element of our shell (the outer most fibers that will determine the strength of our structure). As a moisture barrier on a house, the glues only need to hold the skin in place under the load of gravity. Whereas, when used as the hard shell skin of a camper the skin is subject to flex, vibration, and structural loads that will try to separate it from the foam.

By all means, do more research, test and see. Sure would be nice to have a super light weight, ultra strong and water resistant skin material.

[Mojave Bob]

A builder friend of mine is dropping off to me scraps of 4 different types of house wrap, and I will do a little testing. As I see it, the adhesion needs to be good, but the fabric is there to stiffen the panels and provide a dent-resistant surface. It is not really intended to provide the strength in the joints. The joint should be strong in itself, and the fabric just adds to that.

[KCStudly]

It is not really intended to provide the strength in the joints. The joint should be strong in itself, and the fabric just adds to that.

On the contrary. Any joint with foam is only as strong as the foam; which is in fact very weak in tension and bending. Most foam joints that I have personally checked (either in testing or when checking off cuts to see how well they had bonded) have failed at the foam just beyond the glue seam.

The foam is just there to separate the outer fibers (the ones that do the work, in our case the fabric skins) and to hold them far enough apart. It is this separation of the outer fibers (a longer lever, if you will) that determines the strength of a material in bending (look up moment of inertia in static analysis if you what to learn more). It's why box tubing is hollow, and why I-beams are shaped the way that they are. The reason the foam and canvas works so well is because the foam is not easily compressed over broad areas. This allows it to keep those all important outer fibers separated. All of the tensile strength comes from the skin, and for a given skin strength, the farther apart you place them, the more the panel will be able to resist flexing.

So it is absolutly the skin and reinforcements at the corners that are doing the work. Scientifically, mathematically proven.

Here's where it gets a little tricky, it is not just the strength of the fibers, it is also the unity of the composite, so the glue bond between the layers is very important.

Think about it this way, if you have three thin boards and you stack them one on top of the other in a span, they will bend more when a load is applied than the same three boards that have been glued and screwed together. The strength of the individual members doesn't change, but the strength of the composite does, due to unity.

So even if the house wrap fibers are stronger and lighter than canvas, if the bond to the foam is inadequate, the unity may be compromised and the structure may not be as strong.

[mgb4tim]

If you get it to stick adequately to the foam, then what? I don't think you can paint it.

[GPW]

JMHO , I think house wrap is not a very good idea for a skin ...
Do what you will , but don’t complain later .... Everything that we All approved here has been thoroughly tested and works ...

[Mojave Bob]

It could be painted because it would be saturated in polyurethane, and the house wrap would not be getting painted directly.

The primary strength demand that was described is almost entirely shear strength, and that does not require as strong a bond, because it is cumulative per square inch, up to the point of catastrophic failure of the fabric. Tyvek is pretty strong in that regard. As to testing of joints, by gluing two pieces together, and then seeing if I can break the joint, that will put a lot more stress on the joint than a well-designed box would ever experience in the real world -- flexing a test joint 1/2" before it snaps would be akin to flexing a trailer wall 6", which would simply never happen short of an accident.

Anyway, I'm not claiming to be an expert, nor am I discounting the opinions of the group here. I just did a search on the forum, and while I found a few mentions of house wrap, I didn't find any real world experience bonding it in the way that the manufacturer recommends. It seems that it is worth exploring before just discounting it out-of-hand. My biggest initial questions are whether poly will actually saturate Tyvek, or just surface-bond it, and whether the Tyvek fibers get brittle when saturated with poly.

[wagondude]

The first step would be to find out what adhesives they use on Tyvek envelopes. Think a FedEx pack. Whatever that is works very well. A patent search might shed some light there. That way you know you are working with something that works with the skin and you just need to see how it reacts to the foam.

[Mojave Bob]

My research so far has been interesting. I found a few great articles out there. It seems that Tyvek comes in a variety of flavors, house-wrap being one style. House-wrap is perforated to breath, and is not as strong. Another Tyvek is used for clothing, and is soft and flexible. The Tyvek used in envelopes is #10 Tyvek. It is often referred to as Tyvek paper, and is the strongest and most waterproof. The adhesives used vary, but the strongest ones are apparently an acrylic. The manufacturer and the articles I read indicate that the strongest large-area bonding for this type of Tyvek can be achieved with PVA adhesive (poly-vinyl acetate).

It does become clear that it would be important to first choose the right Tyvek, and then choose the right adhesive accordingly. Somewhat of a science. I will do some experimenting with the house-wrap, but I get the feeling that the #10 Tyvek paper is the better solution. It is available in thicknesses up to 10 mil, which would be very strong but less workable, although it can be re-formed/re-shaped somewhat with heat. I have found that listed in up to 60" wide rolls, but I wonder if larger sheets might be available through an outdoor-advertising company. Although, it might be easier to work it in 42" wide, and just have one seam. If it were adhered with PVA, then it could also be primed for paint using PVA primer.

[Mary C]

The whole idea about foamies is $$$$$$$$$$$$ It is using what is at hand to build a well constructed and durable TD. To spend very little to be able to go camping, and traveling and run from hurricanes. If the cost is greater than the canvas and a couple of gallons of TBII then you have wasted time and money. Canvas has been used not just for a year or too but Canvas was used in plane making in the 30's and in trailer making since the 1800's. So my experimentation may be just a few years old but the experimentation has been going on a while. Now tyvec ??? It may work but but it may not do what the canvas does. you may want to think about the ultimate outcome, plastic, on top of plastic, on top of plastic. I hope it would give you the strength you are looking for. I would be afraid that if you got it cold really cold it would shatter, and crack like the inside of a old hot tub. The one thing about the house paints of today is the ability to move without cracking. the canvas even glued on will have ply ability and can move. Try and experiment with both on a large 3x5 sheet of 1x2 inch foam. Let dry for at least 2 weeks in the sun. once nice and dry bend them. No really bend them at least 5 inches. now let them get cold really cold cut into little squares 10x10 put them into the freezer for a week, now bend them. check out the difference now put them in the oven on the lowest heat setting you oven has let it stay for 15 to 20 minutes take it out, how is the bending action. I think this is the nearest summer and winter simulation. I am curious so please make lots of pictures. our canvas covered TDs have been subjected to the real world and have survived very cold winters and snow and very hot wet summers. they bend a lot before they break thus taking a bumpy road, a wet muddy road and now mold and mildew with just soapy water and a brush. Canvas is so easy!! TBII and the paints I use are wash off with water NO harsh chemicals, environmentally safe.

Since you have looked into the different types you can try using them on on curves and foam joints. Also I am interested in any types of safety equipment you may need when using the glues and paints since many people have children and are older and just don't want to jeopardize their health.

I am not trying to dissuade you I just want you to justify your arguments, Like you said Try it see how it works and compares, always compare the Money and the resulting product. I am interested to see your experiments. I am looking forward to it. Please document your experiment taking lots of pictures.

Mary C.

[KCStudly]

Mary, PVA is a generic term for most water based wood glues, like TB2, so nothing harsh or hazardous.

I think the key things stated are the type of wrap (paper based vs. house wrap), and the availability of relatively small quantities of large sizes. We know the canvas is available, but is there a source for the preferred sizes and quantities of the Tyvek (may only be available in large rolls)?

[Mojave Bob]

In the past, I have made a number of tissue-paper-over-balsa-wood model airplanes, and I have built kayaks skinned with canvas. So, I am familiar with some of the pros and cons of canvas. It remains a viable option for me. However, since what I am designing is a little larger (20' overall) and is intended for full-timing, I am just weighing the options. Walls of this size need buttressing, which will be accomplished with interior walls and cabinetry. And, a roof that size needs triangulation and pitch. So, basically, I am not assuming that what works well for a small camper will scale well to a larger one. Or, if it does, that it is my best option. I am trying to design a 20' camper that is lighter than many of the teardrops on this forum. Canvas is rather heavy, so I am simply looking for lighter weight alternatives. Failing that, I'll go with canvas (if I decide this build is viable at all).