My choice would be waterproof plywood for two reasons. Ply would offer much better thermal insulation. Metal would suffer badly from condensation forming inside in cold conditions. Probably not much difference weight wise as ply would be much thicker.

Alan

Brenda and Alan wrote:

---

 Metal would suffer badly from condensation forming inside in cold conditions.

---

From a rust perspective do you mean Alan? 

elliemike/Alan - Just noting too I might have confused things re underside versus what you walk on.  When I had Steel CheckerPlate initially in mind the concept was to lay something carpet/lino over the top.  Noting the feedback I'm thinking the concept of buying one product that is ready to go in terms of being (a) waterproof on underside and (b) has some thermal insulation.  So the waterproof plywood concept sounds good.  What specific water proof plywood would you recommend? For example:

• Marine Ply
• Film Face (non structural plywood), type of form ply?

 

 

-- Edited by mixedup on Thursday 11th of August 2016 10:05:29 AM

ok thanks Dougwe

still curious to understand what Alan's comment re "Metal would suffer badly from condensation forming inside in cold conditions"?   would be from a rust perspective?

thanks for the advice macka - hey can I ask:

• re "Plastic coating on inner face" - did you have a product in mind? (e.g. what to get from Bunnings for example)
  
  
• re "seal with epoxy along ALL edges" - did you have a product in mind?

• re bitumin paint something like this? https://www.bunnings.com.au/ormonoid-4l-bitumen-paint_p0964864

 

Re why not Marine Ply - is it just to save on cost/weight I assume?

 

 

Hi mixedup,

Look here at this stuff, structural grade with a plastic covering and a grade A glue. Bunnings would sell it too. As shown usually 17mm is the common size.

Jaahn

FORMPLY - A BOND

Form Plywood from Mister Ply&Wood is manufactured to the structural requirements of AS/NZS 6669. FormPly is available in various stress grades and manufactured with a plastic overlay.

FormPly is a premium quality product designed and manufactured for fixed formwork applications.

The life of the formwork plywood depends on care and maintenance taken at the site and is reusable with good concreting practices. 

FORMPLY - PHENOLIC OVERLAY - HWD STRUCTURAL TO AS/NZS 6669
Sheet size (mm)	Sheet thickness (mm)	Pack size	Approx weight per sheet (kgs)	Code
1800x1200	17	50	24-25	fm181217
2400x1200
2400x1200	12	60	22-23	fm241212
	17	50	32-33	fm241217

Hi

As far as I can see looking at the product code numbers the non structural stuff is seconds ?? Probably OK for what you want if there is a saving. Might depend on what they have in stock. They are often the top and bottom sheets in the bundles that may be a bit damaged .

I might give it a coat of tar too.

Jaahn

FORMPLY - FILM FACE - NON STRUCTURAL PLYWOOD
Sheet size (mm)	Sheet thickness (mm)	Pack size	Approx weight per sheet (kgs)	Code
1800x1200	17	40	24	fm1812172nd
2400x1200
2400x1200	17	40	32-33	fm2412172nd

 

FORMPLY - PHENOLIC OVERLAY - HWD STRUCTURAL TO AS/NZS 6669
Sheet size (mm)	Sheet thickness (mm)	Pack size	Approx weight per sheet (kgs)	Code
1800x1200	17	50	24-25	fm181217
2400x1200
2400x1200	12	60	22-23	fm241212
	17	50	32-33	fm241217

-- Edited by Jaahn on Thursday 11th of August 2016 09:15:14 PM

That paint fine. I use similar
Marine ply is ALL Hardwood layers with Waterproof glues.

Top Formply we use on concrete forming (I used to drive cranes on a lot of Dams/Spillways. Bridges etc.
Is softwood inner layers with waterproof glues and the two outer layers of timber, Hardwood.
we used a lot on boat floors.
I wouldn't recommend anything less for a long term project.

BUT... Being softwood inners, If you don't soak in and seal the edges.Properly
The softwood rots away. fairly quickly.
With Epoxy. get a same size tin of thinners with your two pack. Blend the 3 evenly for first coupla coats.
It'll soak right in.
Then coupla coats of normal mix over top of.

I had a timber yacht yrs ago.
Teak/Mahogany with full length Jarrah planking/Ribs
With ironbark keelson/stempost/sternpost.
Beautiful but 35 yr old when I acquired her and neglected a bit.
with a few(hmmm) soft spots topsides..
I learnt to inject those mixxes quite skillfully too to preserve the beautiful timbers..
after drying out the hand carved/shaped teak with blower first.
I used to love caulking those seams.
I learnt that in '40's with fishing boats and tar on beach rollers back home..

Any 2 pack epoxy mixes will do job. Marine ones better but $$$.
Oh. You'll buy 2+ sheets of A grade Formply for 1 sheet of Marine.

That galv sheet Underlay under van flooring is not really a good idea either.

I know a couple (one of them mine) of Off roaders. that got wet a lot Underneath.

If not 100% sealed from each other, (Impossible)
The water gets through. Can't get back out. so rots the ply...

Good Ply at least 17mm (depending on chassis rail spacing.)
Epoxy sealed ALL round the edges of each sheet, b4 mounting
Bitumined underneath. Chassis rails too. Sealed inside, Will last forever.
A quick light sand over of sheet surfaces a good idea too.
That stuff has an Oily? coating over them. To stop the concrete sticking.
even b4 the crews oil them for job.

If you go to paint supplies. they have blends of plastic type Coatings
that you can Spray.roller, pour. on surface. and it seals completely.

Much easier AND internally waterproofing than most other coating.
VERY much easier, and quicker to apply.

OH.
and use some BOLTS.. as well as screws and glue to fasten body to itself and chassis.
Unless ally. In which case the bolts will be fine by themselves hey.
With a bit of help from Mr MIG.

Have fun

There were posts on line recently I was reading about coating the underside of Plywood flooring (not sure if it was on this  GN Forum !)    The were those against using Bitumen type  Underseal  coatings.   Those for  Plain paint or leave it bare.   Underseals do not allow the ply to breath,  and therefore promote rot was one theory.  

I just paint mine with good quality black paint as it is easier for me to apply (actually did it again 2 weeks ago)   Yearly Routine maintenance for me. 

Interested to see what other peoples thoughts are.  

Although Aluminium and ply on top would be the same not allowing the ply to breathe  ! . But heaps of off roader campers built like that ?   I would have no problem in building it like Ply on Ally myself.

Jaan.

Peolpe have to remember that up here and further North in tropics.
We get rained on a but (quite heavy at times.)
Travelling on roads in those conditions. NO different to submerging in creeks. actually more so.
as it pressure blasted in off wheels and bounce back.

I've bitumined several vans over the yrs. Underneath.Incl this one. All chassis too over galv.
Compass in '98. still fine. Mate owns it. and he goes bush a lot (off roader)

The best stuff I find is that Tar/mastic coating they sell for under wheel arches
In shed too lazy to look.
Ply will ONLY form mould and dry rot (That's a misnamer if ever there one, Caused by fresh water only in marine environment) if moisture accesses it.

I've seen PROPERLY sealed and tarp coated/sealed ply yacht decks 50 /60 yrs and older.
Still 100% dry/good when boat scrapped for timbers.

Treated proper like. It's as good as anything.

Just deteriorates faster than most if neglected or not treated properly in first place.
Structural and std ply is total rubbish timber, glued together.
Don't touch it. (my opinions only)

And DO NOT use SIkaflex for sealing round edges in this applic..
Soaking in epoxy's or . cheaper. Thinned down varnish (Not so good) is the only long lived way.
Then seal joint between sheets with Sika if you like,
ALL Silicons will leak past. SIkaflex and 3M Marine the best ones.

It's an awful shame we can't pass on all our expertises to younger people ain't it.
Some of the things I've done in my lifetime you wouldn't believe.

Yea Robol.

A lot of boat yards have gone over to the 3m and some Bostic Marine adhesives.
Near as good as Sika and half the price (nearly)
Sika Deck seam is still the only one for that job though. but messy as.

Another word of advice.
If starting fresh with making van.
Make the body of in one solid piece. Complete. free standing. Modular.
Then plonk onto chassis and bolt down.

It'll be a much more substantial item and last much longer/less leaks too.
Mate made one. 18ft 6 inside Off roader, almost.

Ally angle frame with same for stringers and ribs. Box section floor section stringers. ALL welded. with Rivetted ally gussett plates in all corners. crossovers.
Ext solid ally sheeting (not interlink sections) rivetted and epoxy'd to framework.
Ply floor. Insulation interior walls and roof with light veneer cladding glued and screwed over.
Single ring beam loom, one high. one low. with LED's to suit at whatever places.
240v in sleeve in chassis with junctions up for wall sockets.
Worked out real well.
Showroom full lounge. leather. Drop down queen bed over the top of..
Bathroom. Kitchen.
He was a ships carpenter by trade. I did a lot of his MIG for him.
He left around 2 yrs ago. Haven't seen him since.
His first one . he converted a horse box truck to motorhome.
Profit from that almost built this one.

I've seen marine carpet on the floor. Not checker plate, just aluminium flooring.