Classic cars forum & vehicle restoration.

[greenbeam]

Hello all,
I need to make up new firewall, floorboards, etc for a 1930's car (1935 Armstrong Siddeley).

I've heard people talk about marine ply, but have been told that exterior ply is just as good for use on cars. I have also been told that marine and exterior ply made with pine isn't the best for the heat cycling of an engine bay, and that I should use hardwood exterior ply.

I don't want to spend $400 a sheet on marine ply, but just the same I don't want the timber to be delaminating in 5 years either.

Is pine exterior ply really up to the job of withstanding engine bay heat cycling, mud, oil and water for another 50 years?

Are the internal voids in hardwood exterior ply going to cause me grief when I cut the sheet of ply to shape?

Cheers,
Paul.
_________________
1963 Sunbeam Alpine Series 3
1935 Armstrong Siddeley 17HP Sports Saloon
1935 Armstrong Siddeley 17HP Coachbuilt Saloon

[kevin2306]

In my experience within construction I would comment as follows:
softwood (pine) based plywood is mainly used for formwork / shuttering and is suitable for work that requires supporting short term.
Hardwood faced plywood is more suited to the rigors that you need but it would all come down to the adhesive used to bond the laminates together, seen high grade ply debond when exposed to temperature fluctuations (mainly under flat roof covering etc).
if it was my vehicle, id source marine grade and do the job properly and only once.

regards

kevin

[Bitumen Boy]

I agree with Kevin. Most ply these days is pretty poor stuff, I would get the marine grade and save yourself grief if not money.

[greenbeam]

Thanks gents, I appreciate your advice.

It seems though that the $400/sheet marine ply is 'hoop pine', ie a softwood (Austral Marine Ply, F17 stress rating, A-A faces, A-bond glue, minimal internal voids). A technical rep from Austral said it may not cope very well with the temperature cycling in the engine bay, and I'd be better with hardwood exterior ply.

Another company has 'Hardwood exterior ply': International Panels, A-Bond glue, F17 stress rated, but no decorative face rating, no mention of internal voids. So same glue type, same F-rating, but no guarantee of internal voids, and made of hardwoods.

Do you have any insights as to hardwood marine ply, or whether the hardwood exterior ply would be the equal?

Regards,
Paul.
_________________
1963 Sunbeam Alpine Series 3
1935 Armstrong Siddeley 17HP Sports Saloon
1935 Armstrong Siddeley 17HP Coachbuilt Saloon

[alanb]

I found this on the web, it defines the requirements for marine ply, heat and water among them, hope this helps?

Although a British Standard, it is used by marine plywood manufacturers world wide. The plywood does not have to be of British Manufacture. It is an extensive document which details all characteristics of the plywood.

The BS 1088 standard is a marine plywood specification that applies to plywood made from untreated tropical hardwood veneers that have a stated level of resistance to fungus growth.
BS 1088 plywood must use a glue, which has been tested and shown to be highly resistant to weather, micro-organisms, cold and boiling water, steam and dry heat. There are standard BS tests for the glue.
The Face Veneers must have a solid surface without open defects. Face veneers must be free of knots except "sound pin" knots, (no more than six in any one square foot,) the average of pin knots cannot exceed 2 per square foot over the whole surface of the plywood sheet. The grain in the veneers should be reasonably regular. Edge joints are limited, and end joints are not permitted.
Core veneers requirements are similar to face veneers except that slits are allowed as long as they are small. Pin knots and edge joints are also allowed. As in face veneer, end joints are forbidden.
Manufacturing Defects are strictly controlled. Poor bonds, overlaps and pleats, and gaps in faces are not allowed. Gaps may be filled using veneer inserts glued with appropriate adhesive.
The Moisture content of the plywood must fall between 6% and 14% when it leaves the factory.
Boards will be equally sanded on both sides.
Finished size The length or width of a standard sized sheet can not be less than the stated size nor more than 6.3 mm (0.25") larger.
Squareness -- The lengths of the diagonals of a sheet shall not vary by more than 0.25% of the length of the diagonal.
Thickness tolerances:
4 mm +.02/-0.6 ; 6 mm +.04/-0.65 ; 9 mm +.06/-0.75 ; 12 mm +.09/-0.82 15 mm +.1/-0.9 ; 18 mm +.12/-0.98 ; 22 mm +.16/-1.08 ; 25 mm +1.8/-1.16
Face Veneer thickness -- For any three-ply construction, each veneer sheet will not be any thinner than 1/8 of the total thickness of veneers assembled dry. Multi-Ply Construction-- This applies to boards thicker than 4.8 mm (3/16")
Each face veneer shall be a minimum of 1.3 mm and not thicker than 3.8 mm. Each core veneer shall be no thicker than 4.8 mm
_________________
old tourer


Morris 8 two seater

[greenbeam]

Thanks for this Alan.

So BS 1088 specifies 'hardwood' for marine ply. The Australian marine ply (compliant with AS/NZ 2272 - 2006) I checked into is made with 'plantation pine', a softwood. This is the product that the supplier didn't think would cope with engine bay temperature cycling.

I am thinking that I need to track down BS 1088 spec marine ply here in Australia. I have been warned that BS 1088 is only enforced/enforceable in the UK, and some regional suppliers are applying the standard mark to sub-standard product. I suspect it will be a matter of finding a reputable supplier that knows their supply chain well.

So, back to the interwebs and telephone to chase down this avenue of enquiry.
Cheers,
Paul.
_________________
1963 Sunbeam Alpine Series 3
1935 Armstrong Siddeley 17HP Sports Saloon
1935 Armstrong Siddeley 17HP Coachbuilt Saloon

[alanb]

Paul
You may find this helpful. http://www.ewp.asn.au/library/tut_ply/infomarine.html
Look in the table of contents at the bottom of the page, there is more information about other grades of plywood that maybe useful,
_________________
old tourer


Morris 8 two seater

[greenbeam]

That is excellent, thanks Alan.
Regards,
Paul.
_________________
1963 Sunbeam Alpine Series 3
1935 Armstrong Siddeley 17HP Sports Saloon
1935 Armstrong Siddeley 17HP Coachbuilt Saloon

[jp928]

I had a similar decision to make with my car - 26 Rover 9. Measured up the major panels (rear floor, front floor, each around 800mm sq). Looked at normal 19mm ply at bunnings, was advised to go for Marine quality, available at another store. I got a big sheet - 1220x2440 for under $200, and they did the major cuts for me on the spot free. This both made it easy to fit in the wagon, and left me with only a couple of trimming cuts to make to get an excellent fit, with several useful pieces left over. Takes paint well. The 19mm thickness was an excellent fit to replace the existing slats of timber also. Surprised to hear its that pricey.
jp 26 Rover 9

[Paul fairall]

[greenbeam]

JP, thanks for that. How long ago did you make yours? I've found the price of good timber has gone up a lot in recent years, could explain it being double the price now.

Good to know Marine ply worked for you.
Cheers,
Paul.
_________________
1963 Sunbeam Alpine Series 3
1935 Armstrong Siddeley 17HP Sports Saloon
1935 Armstrong Siddeley 17HP Coachbuilt Saloon

[jp928]

Paul, without looking for the receipts, I think it was in the last 6 months. $180-$190 comes to mind for the big sheet. Maybe there are grades of marine I dont know about?
Try this item on ebay...25mm Marine, 1200x2400, $123. 19mm will be cheaper, just need to find it in Adelaide!

good luck
jp

[greenbeam]

Thanks JP, I've found another source at a local timber yard. The $400 sheet is to 'Australian Standard' for marine and aircraft structures. It's cheaper if not to that standard.

Great tip about getting the major cuts done too.
Regards,
Paul.
_________________
1963 Sunbeam Alpine Series 3
1935 Armstrong Siddeley 17HP Sports Saloon
1935 Armstrong Siddeley 17HP Coachbuilt Saloon

[jp928]

Yes, the Bunnings stuff is listed as 'non-structural', so that makes sense.
jp