Advice regarding Hardwood for battening

[chibb]

Hello all,

I thought this question was best for the classic forum as it is "wood related"!

So...

Currently working towards getting the inside of a steel boat (Tom Thumb 24) spray-foamed.

Our current thinking for the hull fixings is:
1" thick insulation therefore will have battens or blocks about 2" thick to leave a bit of an air gap and allow for thicker bits of insulation (e.g. over stringers)

would prefer to stick battens/blocks to the hull with polyurethane sealant (Sikaflex type stuff) to minimise the amount of welding and metal bits sticking through the insulation, so if wooden they need to be non-oily.

battens/blocks must need very little maintenance as they'll be partly buried in the foam

they must be soft enough to screw into them to attach the lining and interior fixings.


Seems like some kind of hardwood will be best to cut down on the maintenance - can anyone suggest one that's non-oily and you can actually screw into. Any other suggestions welcome.

Thanks in advance for any advice.

 

[srp]

Why not consider pressure treated softwood?

 

[ccscott49]

I ewould go for pressure treated softwood, as reccomended, or something like pitch pine, which would be very rot resistant.

 

[Peterduck]

Pressure-treated softwood is fine if you're using it in the sizes in which it was treated. The biocide doesn't go into the wood very far, even under pressure, so when you cut a long piece into short blocks you expose untreated end grain on the inside of the wood. Not good. Go for a durable species and sleep well.
Peter.

 

[Blueboatman]

In the states there is a polyurethane material called Starboard or kingboard available in sheet/strip form in variuous thicknesses.it is uv stable and will take screws,tension,compression etc and impervious to moisture and decay.And bonds with Sikaflex/5200 well...Might be worth a thought for your 'fit and forget'application when cut into blocks with a jigsaw or handsaw.

 

[SwedishLass]

There is a group dedicated to metal boats on this link http://www.metalboatsociety.com/
Pm sent re forumite nearly finished larger task.

 

[misty56]

I must admit I like that idea better. The one thing you need to ensure the health of wood is a good flow of air and it does sound like the OP's plans would mean that it would be difficult to arrange this.

If I were going to use a timber solution I'd look at iroko or elm, which stands wet conditions well. Oak would be fine as long as it is well sealed from the steel, as it is acidic and will promote corrosion otherwise. Don't think I like the idea of softwood unless it's naturally resistant/durable like pitch pine (very hard to get and not easy to work) or larch (tends to split.)

Not convinced by pressure-treating-- fine for houses, not for boats.

 

[Blueboatman]

Actually I dont think it is polyurethane,more likely a polyethylene,sorry,my sloppy posting there..
I am wondering whether it would actually be simpler to weld localised flanges to the stringers and 'risk' the localised corrosion of screwing self tappers directly to them,minimised by dipping each s/steel screw in sikaflex..?
Here is one link anyway to a supplier of Kingboard with product description

King Board

 

[misty56]

Presumably he's trying to prevent cold bridges which could cause condensation to form and damage to his linings (as well as not encouraging corrosion) by minimising the amount of uninsulated steel that is in contact with the interior air and fittings. I like the idea in principle but I think on balance, welding on lugs or flanges seems more manageable.

 

[chibb]

Yes misty, thats exactly what we're trying to achieve... some good thoughts here, thanks guys.