veneer sandwich construction: wood and glassing schedule questions

General Discussion
1

Hi there,

for my new 9’6 performance longboard I want to try veneer as the sandwich supporting material.

Last Board I made with a 3mm (1/8’') poplar plywood and I’m not so happy with the durability (only 4oz at the outside) of the Board.

So now I want to build a “proper” sandwich construction with a veneer inside layer.

Now my questions:

  • what is the best veneer (comparision weight, durability, strength, water resistance,…) for a sandwich?

  • what are the pros and cons of e.g. balsa and hard maple (these two I considered already)?

  • what glasing schedule do I need in dependence of veneer-wood and thickness?

 

At the Moment, I tend to 0,9 mm maple with

eps(20kg/m³)->4oz-> hard maple->6oz on Top, and

eps->4oz->hard maple->4oz on Bottom

and a 9mm (3/8’') plywood stringer.

What do you think of this?

 

Best regards,

Andi

2

what thickness of veneer?

Greg’s using like 1/24" -1/42’ paper thin veneer in his builds

I’ve used up to 1/8"-3/16" balsa and paulonia boards

I don’t think plywood is a good choice unless you’re making a hollow like Paul J or Marke

Greg likes poplar

I lean towards paulownia, hickory or cypress or bamboo(water/swamp weeds) and cedar but have used rock maple as a spring stiffener down the middle of the deck or bottom like CMP uses his obeche strips.

being able to get a 20"-24" wide single sheet of thin veneer makes things so much easier. just cut and vaccum on

we usually cut our boards 4" wide by 3/16"-1/4" thick on a table or band saw and then plane it down to about 1/8" on a thickness planer and glue up what ever combination of wood strips we need to create a deck and bottom skin. Sometimes we use decorative worm hole wiliwili or spalted mango decorative strips doen the middle. (check out Haleiwa Surfboards for some insame veneer marquetry work)

we usually glass on the wood shell to the foam with 2oz-4oz glass and the fine tune the wood skin with sanding before glassing the outside like a normal surfboard with 4oz-6oz. Usually double 4oz deck and single 4oz bottom or 6oz deck and 4oz bottom if its a bigger board. the key is managing the resin to glass to wood  weight ratios to keep things light. Jarrod (Shwuz) build some incredibly light wood composite boards.

1/24"-1/42" paper veneer is not allot of strength probably the same as a layer of glass or more but 1/16"-1/8" wood shell skins are like skinning it with 1/8" high density foam only lighter of done correctly which from what I understand is pretreating your wood in an autoclave (pressure/heat). That involves using super thinned out resin to saturate and seal the wood cells kind of like how pen bulder and wood turners stabilize soft wood before turning it on a lathe. Others just use a mix of qcell or microballoons in a paste and squeegee it in hard into to the wood pores before sanding smooth and glassing the outside similar to how you might seal a roucgh EPS shaped blank with spackle.

Greg layed out a glassing schedule on here some where for toughness versus lightness and flex just search for it. 

 

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Always a wealth of info Oneula…

 

To the OP, I’m really surprised you had durability issues with 1/8" plywood!  The first bagged board I made was 2oz under and over 1/8" poplar bender ply and that board is insanely strong.  Not even a hint of a pressure dent after many years of service.  And I have boney knees and a boney butt that just destroy surfboards.

4

I think your issues are with glassing. How can 1/8 plywood not be bullet proof.  I do 1/40 veneer with 4 oz over it and it has held up for 3 years of multi-weekly abuse.  If you want to build a tank use 6 oz under 1/40 veneer with 6 oz over. The issue is that you make it so stiff that the board sucks and feels like you are riding a wooden plank. But then maybe that’s what you want?

5

Thanks for all the replies and the food for thought!!

 

@ oneula: 

I found this from Greg:

2# EPS - Use one layer 6 or 2 layers of 4 bottom… Use 2 layers 6 or 3 layer 4 deck.

1.5# EPS - Use one 4 and one 6 oz for bottoms… Use two 4 and a 6 for the deck.

1# EPS - use two 6 bottom… three 6 deck.

These are minimums. For strength, go up from there. 

 

I think my EPS is between 1# and 1.5# (20 kg/m³ = 1.25 [lb/ft³]).

If I use the 1/24’’ maple you say I can replace one layer of glass, so my glassing Schedule will be:

bottom: eps -> one 2oz -> maple -> one 4oz

top: eps-> one 4oz -> maple -> one 6oz

 

Is that ok or still too much?

What would be the effect, if would use a 1/8’’ balsa core?

What would be the best glassing job with 1/8 balsa?

 

From what point I can do the board stringerless or rather just work with a parabolic balsa stringer?

 

@llilibel03 and resinhead:

Yes, I have issues with my glassing, I know…

I didn’t make a glass-layer between wood and foam, just on top.

Now I noticed, that this is understaffed and for the next board, I have to reinforce the wood a little more.

 

And if I have to reinforce more, then the question is: why use plywood and not a thinner (and maybe) lighter veneer.

6

I use 3mm [1/8] Cedar Veneer over EPS. Been doing so for about  10 years. Collaberating with Chris Garrett in the earlier years… we have together developed a [IMO] superior product. One which requires no egg shell  of fibreglass to stop them breaking in half. One of test riders whom I nicknamed Big Foot had… like the name suggests, a very large heel and It was decided we put a layer of 4oz under the deck to stop deck depressions. Also we put a patch of same under fin area to stop the grain splitting at the tip of the forward plug. 

Some four years ago I left the industry for various reasons … divorse stress burnout etc etc. Sooo the last six months I’ve been relearning all the things I forgot and am back on the page. 

One of the reasons I embarked on the journey in the beginning was my aversion to fibreglass and I no longer use FG at all. I’ve replaced it with a hemp fibre called hession,  burlap in the States. 

Also I am now experimenting with a maple veneer @ 1.2 mm. Silky Maple… Pacific Maple… of the Maranti family. It’s a wonderful timber to work with and far better than Cedar and what’s more half the weight . Some ask me what about the strength? … Well it’s got be a lot better than 500 microns of F/Glass. 

 

PS. Chris Garrett hired me for a number of years to put veneer over his shapes and all the discoveries I/we’ve  made are due to his sponsorship and what we put together is a winner and that’s why we have been copied [in part] by parties un-named. 

 

The board on the right [marked by the Carrowong] has a Maple bottom. Cedar deck. 

Cheers 

DF. 

 

 

 

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1 Like
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@Quanta

 

What resin do you use for bagging the skins and to finish the outside?

 

So if a get it right, you use natural fibres under the skins to stop the skins from cracking, but no fibres on the outside?

 

Interesting

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9

makes senss

1/8 cedar or maple veneer

would be like 12-20 layers pf glass

as long as you eliminate water intrusion like you get with unprepped balsa it would be a great shell/skin

why not paulownia versus cedar?

i find it an interesting choice

cedar/redwood strip fresh water canoes have been around for eons

where do you put the burlap under or over?

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double post

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triple post

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@llilibel03 and resinhead:

Yes, I have issues with my glassing, I know...

I didn't make a glass-layer between wood and foam, just on top.

Now I noticed, that this is understaffed and for the next board, I have to reinforce the wood a little more.

 

And if I have to reinforce more, then the question is: why use plywood and not a thinner (and maybe) lighter veneer.

[/quote]

 

Answer:

Right.. use a thinner veneer.  How the heck are you going to bend 1/8 ply wood?

 

Use a thinner skin with glass under and over......It works fine and you can get a more accurate shape. And you can get better looking wood too.

 

1 Like
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resinhead, I don’t know what you want to tell with your last post…

I read your last post again with more accurate, there you told me how to deal with thin veneer. Thanks a lot!

One more question left: did you do the 4oz on both sides of the veneer or just on top?

14

depends on what I'm after/ Some boards have wood and only 4oz, some have 4oz wood then 4 oz, some have 4oz wood then 6 oz.  the board pictures is 6 wood then 6 over. it is made to travel the globe.

The best boards I think are 4oz wood with 4oz.

15

 

If I could get paulonia at 3mm as easily and as affordable as Cedar I would most definately use it. The Burlap goes under the deck. It would look like shit if it was on top, :wink:

16

Is that picture of what I think I’m seeing?  The inside of a pre formed wooden deck?  Well that’s a new way to build them!

17

Why do you use Burlap?

The material engineer I know sais that it is greatly inferior to flax. Especially the bonding with epoxy, but also the mechanical properties.

However I’m quite interested in why you use it, and why it is good for this application.

18

Well I’m not using it with epoxy. I’m using it with  single pack moisture cure PU glue.  Why? In the beginning I used to use epoxy  but since for about 10 years maybe 100 boards I’ve found the ‘poo’ glue works brilliantly with any fabric. and is way way WAY more flexable than epoxy. I only use epoxy on the exterior with NO glass or fabric.

Flax sounds interesting also but can I buy that as  easy and  inexpensive  as I can Burlap or Hession?

I’d like to hear what your material engineer has to say about my Burlap and poo glue mix. Realy I would. 

BTW when you bond under vacuum pressure the poo glue penetrates the poly sytrene [EPS] up to and beyond 10mm from the surface thus sealing the gaps between the closed cells while still remaining flexable.  That’s an added bonus. A REAL Biggy IMO.

These are my little trade secrets that I no longer covert :wink:

Cheers. 

 

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19

Flexible foaming epoxy exist and with far better mechanicals and chemicals properties than pu.

20

Lemat,

Can you give us a source?