What plywood and timber?

[rbcoomer]

I am currently replacing flooring, bulkheads and stringers in an early Fletcher Arrowbolt 21' as part of a rebuild project. Unlike the originals that relied on a overall fibreglass layer on top, I will be resin-coating every section prior to glassing in place in order to 'seal' against moisture.

Is there any benefit of marine ply over a hardwood ply in these circumstances?

Secondly, what would be the best choice of timber for the stringers? I realise they can also be constructed from ply, but as the originals are obviously a hardwood*, I would prefer this option. *The boat is over 30 years old and despite the stringers being sopping wet, they are still solid and have only rotted slightly where untreated ends butted up to the plywood bulkheads if they had been softwood, they'd be long gone! The bulkheads were only tabbed in at the bottom, and hence have rotted over the years, allowing moisture to be drawn into the ends of the stringers and get trapped beneath the fibreglass - much like the floor which rotted from beneath/ends. Whilst I don't want to scrimp costs on something that needs to last, budget is a reasonable consideration!

Many thanks,

Robin

 

[rob2]

WBP or exterior ply is manufactured using the same waterproof glues as in marine plies. As your panelling will not be immersed in water, it should suffice. Marine plies are structurally better as they are not permitted any voids in the plies which are permitted in WBP and are generally filled. Just as with marine plies, some are more flexible than others, the most rigid being constructed from equal thicknesses of veneer rather than a thin outside veneer with thicker inner cores. As you are planning to seal thoroughly and presumably all near enough flat panels, I would imagine that a good quality WBP ply would meet your needs. You might like to have a look around the Robbins Timber website for examples.

For framing I would suggest one of the mahogany family as they work nicely and are pretty rot resistant. Again, if you seal them before final assembly, the framing should last some considerable time. If you need to form a curve, such as under the dck, strips can be laminated to increase the strength of the curved beam.

Rob.

P.S. one of the advantages of using epoxy is that it can be used both for varnishing/sealing and when thickened makes an extremely strong glue. Best to varnish over with a UV resistant varnish when finished to prevent long-term degradation.

 

[aitchem]

WPB from the likes of B&Q etc..........WILL have BIG holes in the hidden plies, in EXACTLY the WRONG places.

Don't ask how much waste I had making a battery box.!

 

[LittleShip]

Go for Marine ply. You wont need teak faced as it's for flooring so standard BS1088 ply will suffice.

You should be able to find a sheet 8x4 for around £30 - £40

Listen to the warning above and....Dont use exterior ply

Tom

 

[rbcoomer]

Thanks for the prompt replies - I've done a bit of ringing around on the plywood aspect and can get 12mm 8' x 4' sheets of marine ply for around £40 each - much better than the initial £65 I was quoted so will probably go with that if I can haggle down to £35... I can get the hardwood faced 'far eastern' plywood for around £15 sheet, but as already mentioned, they tend to be full of holes!

Thanks Rob2 for the mahogany suggestion - at least now I'll have an idea what will be suitable, although ultimately I will have to see what local merchants have or can get in the required sizes. The larger of the existing timber sections are quite a large profile at about 20mm x 250mm - and about 4.5M long! Even the smaller ones are about 20mm x 150mm, then there's all the cross-sections...

 

[TopDonkey]

And dont be tempted to by any ply from Selco, i bought a sheet of WBP from them last year, and ended up throwing it away, once i cut it, some of the laminates were simply peeling away, they had obviously used too little glue and the core wood was very very poor quality, its the worst quality ply i have ever seen

 

[LittleShip]

Just as a final bit of information.....

Ply, no matter what type is very susceptible to water ingress over time, true marine ply will last much longer but it will still absorb water given half a chance.

To stop this I now use this product.

http://www.mbfg.co.uk/epoxy-resins/eposeal-300-epoxy-primer.html

It is a low viscosity epoxy which will permanently seal the end grain on plywood or any wood for that matter preventing any water ingress. Many will tell you that normal epoxy will do the same but it wont penetrate in as far as the 300 product.

If you’re looking to prevent future water damage this is the way forward.

Tom

 

[Spuddy]

A chum just renovated his Folkboat - his boatbuilder mate swears by the sort of stuff that Littleship mentioned.
I too would use marine ply; the exterior could well have voids and be non-durable stuff inside. Mind you, there are forumites who've built dinghies out of wbp and they're going strong after years.
For the stringers, ask the merchant; meranti might still be available. It's fairly cheap and durable enough for what you want. Iroko is probably overspecced for this application.

 

[davidej]

Mind you, there are forumites who've built dinghies out of wbp and they're going strong after years.

I think that is the awswer. Years ago I built an A-Class catamaran out of wpb but it was much better quality than you get these days

 

[rbcoomer]

Just as a final bit of information.....

Ply, no matter what type is very susceptible to water ingress over time, true marine ply will last much longer but it will still absorb water given half a chance.

To stop this I now use this product.

http://www.mbfg.co.uk/epoxy-resins/eposeal-300-epoxy-primer.html

It is a low viscosity epoxy which will permanently seal the end grain on plywood or any wood for that matter preventing any water ingress. Many will tell you that normal epoxy will do the same but it wont penetrate in as far as the 300 product.

If you’re looking to prevent future water damage this is the way forward.

Tom

Hi Tom,

Thanks for the link. Do you know if that would be compatible/necessary with a polyester resin? I aim to be putting 2 coats of resin on each section prior to assembly and tabbing into place. I looked at epoxy systems but cost was prohibitive for the amounts I believe will be required. (Committed now anyway as I already have the first 20kg )

I'm now looking at £31.95+VAT a sheet for the marine ply and a little more haggling/phone calls to go...

Regards,

Robin

 

[rbcoomer]

I think that is the awswer. Years ago I built an A-Class catamaran out of wpb but it was much better quality than you get these days

Yes, I fear that's true. I built my own garage in 1996 and used exterior ply under the corrugated roofing sheets - 100% no voids and it's still as good as when it went in. However got some to redo floor in a trailer a couple of years ago and it was rubbish - used it elsewhere and did the trailer in marine ply & varnished!

 

[rbcoomer]

A chum just renovated his Folkboat - his boatbuilder mate swears by the sort of stuff that Littleship mentioned.
I too would use marine ply; the exterior could well have voids and be non-durable stuff inside. Mind you, there are forumites who've built dinghies out of wbp and they're going strong after years.
For the stringers, ask the merchant; meranti might still be available. It's fairly cheap and durable enough for what you want. Iroko is probably overspecced for this application.

Thanks - not heard of either, so will add to my list to look out for!

 

[LittleShip]

Robin

I would never use Polyester resin on wood....Polyester sticks to (and therefore detaches over time) and epoxy tends to bond to as it soaks in to the wood.

Using the 300 as mentioned and then finishing with epoxy coating and matting will give you a hard wearing clean finish that will last for years.

Tom

PS. polyester will sick to the finish of the 300.

 

[oldharry]

Differences between WPB and Marine Ply:

1 Marine ply has all laminates the same thickness, wpb has cores of thicker cheaper timber with a thin hard vebeer on the outside. Styrength depends on what has been used inside.

2 Voids: Marine ply is not permitted to have voids innexcess of a given width, so they do not affect the strength of the board. WPB has no specirfied maximum for voids in the laminates, therefore in cheaper quality may be of considerably lower strenght.

3. Marine ply requires all internal laminates to be of the same quality of timber as the external veneers. WPB does not, and very commonly cheap softwoods are used

4. Marine ply must have glues of a particular grade, and applied to a specified thickeness over the laminates. WPB has no such controls, and although the same glue may be used, it may be much thinner, and have 'holidays where there is little or no glue at all, resulting in rapid delamination in water

Having said all that, not all 'marine' plys comply with the regulations, specially far eastern imports, which may even be marked 'BS1088', but do not bear the 'kitemark'. I have even seen this stuff marked with something that looked like a kitemark, but isn't!

Similarly some of the better WBPs are actually better quality than the cheap imported 'marine' stuff.

And its often very difficult to tell the good from the bad! A stamp BS1088 means nothing without the official kitemark: BS1088 couldy mean it was made October 1988..... funny they choose that particular number for stock control so much!

 

[rakaaw]

Chilton Timber of Hemel Hempstead have 2440x1220x12mm BS1088 for £27.95. Not used it myself but someone on here may have knowledge.

 

[rbcoomer]

Robin

I would never use Polyester resin on wood....Polyester sticks to (and therefore detaches over time) and epoxy tends to bond to as it soaks in to the wood.

Using the 300 as mentioned and then finishing with epoxy coating and matting will give you a hard wearing clean finish that will last for years.

Tom

PS. polyester will sick to the finish of the 300.

Thanks Tom, I'll certainly coat first with the 300 then!

I was assured by the supplier that the Polyester would a) stick to the original hull (provided it was keyed, clean and all air removed by working into joints) and b) be suitable to coat the ply/timber. I've proved the first of these with a test on some of the old sections I've cut out (sticks really well!), but never thought to try on a wood off-cut! They did suggest that I dry all the sections thoroughly (even in the house) before coating but never mentioned that it wouldn't get absorbed.

There are air gaps in the original layup between the timber and the fibreglass, but mostly on top of the stringers where the matting was wrapped over and 'inside' corners. I assumed this was because the timber was laid out and interlocked before the matting and resin was applied? This was clearly how it was done because there is no fibreglass where wood meets wood/ply! I had hoped that by slightly under-sizing all the timber/ply sections (circa 1mm) and then giving a couple of coats of resin, that I'd make a seal and any moisture would be kept out!

Apart from car bodywork in the dim and distant past, fibreglass isn't something I have any experience of, but a couple of forumites have kindly provided a host of advice and tips! The suppliers are also local and in addition to a printed 'how-to' guide have given a contact number for free help and advice. Apart from cost factors, the ability to be able to vary the curing time was key to the polyester decision over epoxy. I'll be working outside and temperatures will obviously drop off considerably at night - plus there is also the the risk of dew/condensation (even though covered). Even though I plan to get this work done in the mornings to allow ample time to cure, shorter curing times as I get more proficient and tackle bigger areas (floors/cuddy etc) will be a big plus.

Thanks once again...

Best regards,

Robin

 

[rbcoomer]

Thanks rakaaw - I'm a long way from Hemel Hempstead, but useful to get some comparative prices...

Thanks oldharry for the ply details - I've ruled out the WPB after talking to the merchant - who said similar. They've also said I can call by for some off-cuts if I want to 'disassemble' to verify quality, but they're confident it's good quality. I'm going over in the morning to pick up a few sheets and see what they have in the way of Mahogany/Meranti/Iroko or similar planks whilst I'm there - I didn't dare enquire as to costs for those whilst on the phone...

 

[maxcampbell]

There are air gaps in the original layup between the timber and the fibreglass, but mostly on top of the stringers where the matting was wrapped over and 'inside' corners. I assumed this was because the timber was laid out and interlocked before the matting and resin was applied?
Apart from car bodywork in the dim and distant past, fibreglass isn't something I have any experience of, but a couple of forumites have kindly provided a host of advice and tips!

Robin

One more tip, perhaps the most important part of glassing in, whatever resin you're using (and epoxy is more durable), is to completely consolidate the glass into the resin, with an appropriate roller - either the type that looks like a cambridge field roller, a row of washers on an axle, or the paddle wheel type - try an inch dia "washers" followed by a small dia paddle, especially around curves - so that there are absolutely no areas of dry mat or air.

If you're getting air, you're probably trying to go round too-tight a radius. Pre-cove any inside right angles with filled epoxy, and round off outside corners to min 6mm radius.

 

[rbcoomer]

Thanks!

One more tip, perhaps the most important part of glassing in, whatever resin you're using (and epoxy is more durable), is to completely consolidate the glass into the resin, with an appropriate roller - either the type that looks like a cambridge field roller, a row of washers on an axle, or the paddle wheel type - try an inch dia "washers" followed by a small dia paddle, especially around curves - so that there are absolutely no areas of dry mat or air.

If you're getting air, you're probably trying to go round too-tight a radius. Pre-cove any inside right angles with filled epoxy, and round off outside corners to min 6mm radius.

Hi Max,

The supplier provided a 'kit', which includes what I would describe as metal rollers with small teeth! In addition to the matting, I included a roll of a much softer/more flexible 'tape' roll of webbed glass-fibre for the tight corners. They too emphasised the importance of getting all the air out and fibreglass covered - basically, keep working it until all the mat is soaked and no air bubbles! I'll start on small bits I think...

Cheers,

Robin

 

[gljnr1983]

I would not go about looking for the cheapest marine ply because when i was sourcing the cheap stuff jewsons sold a marine ply that turned out to be junk separating at the edges after a 2 week soak test.
It was the jewsons and timbnet plys that i tested and the timbnet stuff stayed together so i used that, i also repetedly soaked the ply with ronseal or cuprinol clear preserver,letting it dry properly before glassing it in place.