Easy question for woodwork specialists

A couple of years ago I ordered a sheet of 12mm marine ply for a tawny owl nest box from a well known building materials supplier. I have only just got around to making the damn thing . After completing the carcass it I put it outside to let the preservative dry. It rained gently for a couple of days which I didn't think would be a problem. Today I went to finish it and found the ply was delaminating badly in several areas !

This makes me think that this material was not marine ply. There was no marking on the sheet to suggest it was or wasn't. Should there be, and how would I know that I have the proper stuff next time ?

Gerry

What type of preservative was it? Is there a chance it reacted with the laminating glue?

Apologies if I'm stating the obvious to you, but worth mentioning to any reading this who are interested in making nest boxes. General guidance on nest boxes and preservative is: "Any rough wood, planking or exterior ply wood will be suitable. Try to use at least 15mm thick wood, to ensure better insulation. You can protect the exterior of the box with water-based wood stain, but do not use any wood stains or preservative inside the box or round the entrance hole. Fenceguard and Sadolin Classic (a wood stain, not a preservative) are recommended by the manufacturers as being suitable products for use on nest boxes. Cuprinol TimberCare (for use on rough sawn timber) is also safe to birds when dry. As with any preservative, do not paint the inside of the nest box or around the entrance hole."

When I used to buy ply for my boat the marine ply standard 'BS 1088' and 'WBP' standing for weather and boil proof were stamped on the sheets.

John

You don't buy marine ply from a "well known building materials suppler". Try a proper wood yard, waterproof board as Johns says above is marked as such.

Don't forget your box will need cleaning out for each new season.

Hi Gerry,

If it has no markings on it, I suspect it wasn't "marine ply". If that's the case, It's at best, likely to be "exterior ply".

Just guessing, but being in storage for a couple of years, might have affected the glue holding the plies together, especially if it got a little damp in that time. The couple days in the rain may just have been the straw that broke the Camels back.

I suspect an unscrupulous building materials supplier might have been to blame.

+1 for markings on sheets of Marine ply as Sandgrounder notes. also Marine ply is made of hardwood plies which are heavier than the softwoods typically used in exterior ply, the surface plies of marine ply are usually smooth rather than the rougher finish on exterior ply and there are more ( thinner) plies.Typically the outer plies in marine ply are a mahogany type hardwood which has a darkish reddish colour with fewer knots, compared with the paler and knottier appearance of exterior ply. So chalk and cheese really, big difference in price too!

Rod

By its price ye shall know it !

If memory serves marine ply is a lot heavier because its been impregnated, it has a really good quality feel and look about it

Ordinary ply tends to be light and strong

Even buying from panel speacialists as I often do you have to be careful these days as a lot of the imported stuff can be suspect even if it does come marked. As an example two summers back I had about 80 sheets of 12mm and 10 of 18mm marine ply for a job from a large panel products suppliers. The 18mm off cuts that were left out started delaminating after one night of rain, some of the 12mm stuff has been in the elements for two years and is as good as the day it was bought if a bit grey looking now.

It's not impregnated and can look much like WBP, only when you start paying for LLoyds registered stuff does the quality and price go up.

I made a top bar type beehive out of genuine Marine ply, it was a mahogany colour on the outside. I applied a mixture of linseed oil and beeswax as preservative for the outer surfaces. I made the mixture by using pure linseed oil (not boiled) warmed enough to absorb a small amount of beeswax, paint it on while still warm and allow 24 hours to dry and apply another coat, warmed up as well. When dry the surface will be coated with a thin layer of wax and it withstands the weather very well and protects the wood. This mixture is non toxic to wildlife and of course contains no dangerous chemicals, ideal for beehives, nest boxes etc. Dave W

I agree with many comments about marine ply having a redish colour as in mahogany. You can't go by price as Cabinet grade plywood is very expensive having no voids.

I have made bird nesting boxes but have only ever used untreated pine then sealed the outside only with a stain/preservative finish, I did however paint the hole which I should not have done. This one and the feeder have lasted from when I made them in 2014 until last year not sure if they are still going as my Mum passed last year and not sure what happen to them after that

Edited By Derek Lane on 15/05/2021 14:44:20

You can’t judge plywood by its colour,have a look at the cheaper grade supplied by Fyne Boat kits(usual disclaimer) which is to BS 1088 and also FSC certified. And I’ve had some with a very rough surface ,from a trusted local supplier,which also complies and has been perfectly ok in use.

I'm not sure how much this stuff costs, but North Cave nature reserve had a new hide/viewing screen made from a waterproof MDF; not waterproof, not water resistant; I think it is Medite Tricoya Extreme
https://mdfosb.com/en/products/medite-tricoya-extreme

It sits there outdoors untreated in all weathers, and was tested my leaving it submerged for a year or two.

Bill

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Genuinely waterproof MDF ... That’s astonishing !!

Thanks for the link, Bill

MichaelG.

I built a boat out of Robbins real marine ply over 20 years ago. It's as good as new. I've only ever oiled it, never varnished. It lives on a trailer but no problems with the ply or the epoxy holding together. Mind you the stuff costs a fortune. I don't know what it costs now , over £150 a sheet for 12 mm I should imagine. You get what you pay for.

AFAIK, BS1088 for marine ply covers the glue, WPB, commonly phenolic resin as for exterior ply, also the wood species, ie hard-wood, and number of voids in the interior layers. Otherwise it does not guarantee much else.

There is a variety of "qualities", Robbins being at the top level and priced accordingly.They control the production I believe.

However, a lot of ply is produced a long, long way away, so who knows what lies under the stamp!

I can certainly agree with this statement - I purchased sheets of "Marine" ply from Jewsons a few years ago - paying about three times what they were charging for "WBP' ply at that time. I spent a day carefully cutting the boards to size (not for bird houses) and left the parts in the Shed overnight. The next morning some of the parts had badly delaminated.

I called the branch manager to complain and was told it was my fault, as I should have sealed the edges immediately after cutting. I told him this was complete nonsense but he would not offer a refund because I'd already cut the boards. We finally agreed a 50% refund.

The boards were required for a portable/modular Gauge '3' project I was working on and the agreed 'spec' was really just for a level of weather proofing, sufficient for a weekend set-up outside. So the marine ply was really an overkill (belt & braces) on my part.

Having cut the parts (and spent the money) - the delamination problem was solved by spraying water into the gaps and then dripping Gorilla glue into it - which foamed and filled the gaps. The boards were then quickly clamped and thankfully have been fine since then.

I haven't purchased any marine ply since but I do use quality birch ply occasionally. These days I order from a local hardware store that still runs a timber yard. They don't stock the quality birch ply I use, so order it in for me and cut it (very accurately) to my requirements on their vertical panel saw. I could probably find it for less elsewhere but they don't charge for the cutting and I'm very happy with their service.

Regards,

IanT

Thanks all for your comments and advice. The sheet I was 'sold' did have a mahogany skin which convinced me it was genuine, but on the quiet was always concerned by the lack of any marking confirming the fact. I will have to buy another sheet, this time from a 'proper' supplier and look for some some marking on the product. Even then I will do a test sample !

It's the second box I have made. My first one did get occupied successfully. But I used standard ply and after two years the bottom had dropped out and the rest was in a sorry state. I plan to put a camera in the 2nd box so want to make it survive. I've already decided the first one is going to finish its life as yet more garage shelving.

Gerry

I am under the impression that one of the factors that marine ply has is that it is guaranteed to not have any voids as well as the wood and adhesive properties. Shuttering ply must surely be very water resistant to do the job it is intended for but it’s appearance is poor, I doubt any birds will be be too worried about knots and poor finish.

Mike

I'm pretty sure this Meter Box was not constructed from Marine Ply

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MichaelG.