Friday, 1 July 2016

MYOG - Tyvek Groundsheet

Tyvek Fact Storm

Tyvek is high density polyethylene (HDPE), also called "spun-bonded olefin". Tyvek is not the lightest material for constructing a groundsheet but it is tough, versatile and fairly easy to work with.

The two types most commonly seen are the soft structure 1443R and HomeWrap. Tyvek has a higher strength-to-weight ratio than paper and is rip-resistant. It absorbs little or no moisture but allows water vapour to pass through. Liquid water will not pass through.  It shrinks 5% when washed.

Tyvek is brilliant white. The HomeWrap and soft 1443R types have an embossed rectilinear surface texture but it is not woven. It is structurally an amorphous matrix of densely packed polyethylene fibres and air - which gives it holding power to bond to paint, glue and silicone - and dirt.  It is opaque and reflects light well so it offers shade and UV protection. UV will degrade it, with a useful life of 3 months high UV exposure, but opaque UV inhibitor coatings may be applied. Some grades of Tyvek have UV inhibitors built in.

It is a noisy material. It creases well and doesn't stretch much. Toughness and flexibility remain down to -73C and it  is 100% recyclable. There is a Tyvek Seam Tape, for joining sections together.

Tyvek HomeWrap cuts easily with scissors. Both sides of the fabric have the same surface structure and breathe the same, however the plain side will reflect sunlight better.


Making a Groundsheet
I have glued both 1443R and HomeWrap with PVA but the adhesion has not been tested under wet conditions.  Hem the edges by folding over about 4cm and gluing.  Apply glue evenly with a brush to both sides.  Apply a light weight and allow 2 days to dry.  This hemming should make it harder to rip and provides a more substantial substrate for grommets. To join sections I overlapped by about 6 or 7cm and applied glue evenly with a brush to both pieces.  I then sandwiched the material between wood slats and applied a light weight for at least several hours and left to dry for 2 days.

I've made a small groundsheet/tarp out of 1443R Tyvek. 1443R is a much softer, quieter material and probably not as protective against sharp objects as HomeWrap.  It is a better choice of material for making a bivvy bag or clothing.

Thinned silicone can be applied to clean new 1443R Tyvek.  This might be useful to do around regions with PVA glue to block the ingress of water.  Use mineral turpentine, not odourless turps, in a 2:1 dilution to seam seal silnylon tent flies but for surface DWR function the dilution factor should be more, say 5:1 or thinner.  Shellite will also act as a solvent.  Stir it well, adding the turps or Shellite slowly.  The 1443R type has a rougher surface and seems to absorb the silicone better and resists peeling afterwards. You can also apply this mix to new paper maps to waterproof them. You run a risk of tearing old maps that have creases with this treatment.  Apply and spread the diluted mix with a foam block or cloth. If necessary repeat.  There are no shortcuts with a thicker mix as you run the risk of the whole application peeling off.



Cut and Glue Hems
This project uses Tyvek HomeWrap. I chose a 1 piece 2-axis symmetrical hexagonal shape.  I cut 2 long sides 156cm at each end and 4 short sides 122cm.  Width is 275cm (being the width of the roll it came from) and length is 212cm. The area is then reduced by folding and creasing the hems about 4cm. With the offcuts I made a smaller tarp using PVA glue.
Tyvek HomeWrap groundsheet for a Tarptent Stratospire 2.  300g.

Choose a clean dust and lint free area to do the gluing. I applied PVA glue evenly with a brush to both pieces to ensure 100% contact.



Optional Extra: Grommets

Adding grommets means the groundsheet can double as a tarp.
 
Chain hardware stores have 10mm grommet kits which will fit walking pole tips.  The kit costs $20 and extra grommets cost $5.50 for 25.  Get a kit which has a hole punch since you need to make the hole in the fabric before you can hammer the grommet together using the supplied swage and die.
Grommet Swage and Die with grommet pieces in place


The hole punch that was supplied was blunt.  This punch was a 10mm rod with a concave end.  A conical sharpening stone attached to a drill easily sharpened its inner edge to give a clean hole.

Set the hole well back from the edge with the punch.  Do this after the glue dries.  Place a flat piece of soft wood under the tarp and tap the punch through.

Site the grommet pieces on the swage and die and fit to the hole.  Use several light to firmish taps with the hammer on the die to set the grommet evenly.  More lighter taps give the metal a chance to warm up as it turns over. Avoid splitting the grommet as it turns over.  The grommet is through 2 or 3 layers of Tyvek and not too close to the edge.



Packing


The result is a bit bulky, but the tent this is built for is big enough for 2 or 3 users.


Scrunching it up or washing will make it quieter and more pliable but may shorten its life.  Keep any offcuts as you may be able to use these to glue patches on any holes that develop. 

This is a fairly sizable tarp/groundsheet and will catch a lot of wind, so it may be advisable to add more grommets than shown.

Deployment as a Tarp
Taut pitch! Note the blown highlights on the top surface due to the high reflectivity of Tyvek
I set up the large groundsheet with 6 pegs and 4 guys here.  The poles were set below 100cm height since I pegged one side directly to the ground.  This makes a great sun shade if you get stuck in high UV. The deepness of the shade is greater than that provided by lighter, more expensive and UV prone Sil/Nylon tarps.  Not sure if it would survive rain or drizzle on the glued hems. Don't skimp on guy outs. The more used the less stress is placed on each one.  The hexagonal shape probably helps to spread stress around the shape.

The tarp ridge is about 270cm long and each wing is about 100cm wide. About 150cm along each wing tip with a guy point at each end.

I used the 4 large corner offcuts to make a smaller hexagonal version of the tarp, bonding them to a rectangular piece.

Cool, deep shade in summer with a Tyvek tarp, Mt Townsend. Take a tarp if there is no shade where you are going.

I used 2 trekking poles plus a light vertical tent pole about 1.2m tall to set it up.  I used 6 long pegs and 6 guys: at least 3 about 2.5m and another 3 about 1.2m long with toggles for adjustment.  Setting up requires a few adjustments but it is a skill that is quickly learned and gets better with practice. While it is fun setting up in good weather, it could get old quickly under rainy, windy conditions. You need to know the bowline and tautline hitch if not using toggles.

The grommets have taken several hours wind on exposed sites with no problems. The smaller tarp above is made of 5 PVA glued sections, with overlaps of nearly 3". The glue appears to be holding exceptionally well. I have washed it by hand with a quick scrub and reglued a few loose flaps of hemming.  It is pretty hard to clean so don't sweat it, just make another when it has done it's time.


You could spray the Tyvek with UV Proof, but I suspect this may be incompatible with later treatment with a silicone coating. I don't think either are needed except around glued regions.  Further testing in rain and wind are required.  For this reason I am not about to rely on it as a primary shelter.


Conclusion

In brief: Sil/nylon tarps for rain, Tyvek for shade 

Tyvek works great as a groundsheet and is a very effective sun shade!  Forget silnylon tarps for shade. The stiffer HomeWrap is a little more bulky to pack so I fold and roll it into a "folded tent pole" sized package for easier access in and out of the pack.  It can flap and make a noise if the wind picks up a corner. Big questions are: will the glue in the hems weaken with a thorough soaking after several hours of rain and will the grommets hold over time if used as a tarp?  I have washed this tarp by hand and the PVA glue held, but a few small sections needed a reglue in any case.  Grommets are holding well but it remains to be further tested in sustained wind. The small tarp has been out for over 10 days as a sun shade in the wild and is holding up well. I am surprised with the result of PVA gluing of polyethylene. If I am expecting rain rather than sun I would take a lighter silnylon tarp.

Total cost is about $20 for the HomeWrap Tyvek and grommets and construction time was about 2 hours.  While it won't last forever, it is cheap and easy to make another.

I've seen some arched pole tents with grommeted nylon groundsheets that cost $40 or $50. You may be able to make a cheaper Tyvek version of these but make sure the grommets are the right size. You may need a 7, 8 or 9mm grommets to stop the tent pole from slipping all the way through (or attach washers to the pole tips with some gaffer tape).
Continental divide high camp sun shelter at Mt Townsend in light winds. PVA glue holds it together.
Tyvek works great as a sun and UV shade.  Amazingly great. The reflectivity of the white surface is blinding. It is brilliant white! It feels cool to touch on the underside and, get this, while others were sweltering in stifling windless tents as they watched the UV attack their silnylon flies I had to put on extra clothing to keep warm when resting in its shade and enjoying the view for hours. Winds over 20kmh may put a lot of stress on the grommets and a lower profile rigging in a more protected location than what I have shown should be employed.

It is worth noting some ultra-lighters use painter's drop sheets and polycryo window film for groundsheets, which may be a moisture barrier of sorts, but others note that Tyvek Homewrap is much more robust and more protective from sleeping mat puncture. 
 

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