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Plywood - Standard or Exterior?


mick
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I've just about settled on the use of plywood as the base for the new Worsley Dale and had intended ordering 'exterior' grade, however, although it recommends that all surfaces and edges are sealed when used for outdoor purposes, the same recommendations are also given for the standard grades which are somewhat cheaper per sheet and also 'suitable' for outdor use. I don't wish to go to the additional expense of using marine ply but if properly sealed and protected, do you think I could get away with using standard grade rather than exterior grade or would that be false economy?

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Ive got a shed in the front yard with a ply roof Mick an all its covered with is thin felt I didn’t seal it when I made it and that was eight

Years ago, you can see the wood inside it hasn’t swelled or anything, so if you were to seal it and felt it I would say it would last a very

Long time :)

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Would that just be standard grade plwood Dave?

I'm satisfied that plywood can last for a long time. I had some old sections out in the garden at Selby that had been in use as shelves in the garage when I moved in there 9 years ago. I removed the shelves to make way for the washing machine or something like that and the redundant shelves found their way out into the garden (as you do). They were left unprotected, unsealed, and exposed to the elements for quite some time but amazingly they were still holding together without any sign of the leaves separating. I'm not sure if they were standard grade or something better.

It seems silly to ponder the cost of an additional £7 or so per sheet when we spend fortunes on our rolling stock, but that's the difference I have been quoted between sheets of standard grade and exterior grade plywood. Is the additional £7 worth it or could I get by with the cheaper grade?

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IanR said:

I used 18mm structural spruce plywood....

Thanks for that Ian. The Wickes website lists that one as being suitable for outdoor use providing it is sealed correctly and it is somewhat cheaper than the corresponding exterior grade. Reckon that will suit me just fine.

Takes a bit of working out when 'structural' is suitable for outdoor use if properly sealed (same recommendation goes for the exterior grade) but the exterior grade isn't suitable for structural use.

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mick said:

Thanks for that Ian. The Wickes website lists that one as being suitable for outdoor use providing it is sealed correctly and it is somewhat cheaper than the corresponding exterior grade. Reckon that will suit me just fine.

Takes a bit of working out when 'structural' is suitable for outdoor use if properly sealed (same recommendation goes for the exterior grade) but the exterior grade isn't suitable for structural use.

I had the same problem as I ordered my plywood from Wickes. I went with the 12mm exterior grade in the end, as the amount of load I'll be putting on the ply with a OO railway is not going to amount to a structural weight and all of my use of ply is as the top surface which is all covered over with felt anyway. Most of my concern was about moisture attacking from below. I've not seen any evidence of this yet, but its only be up a couple of months. I guess we'll just have to wait and see if I made the right choice!

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Yes I was more concerned about the potential problem of moisture from beneath the track bed as my current thinking is to have a large section of the new layout just above ground level. I recall IanR suggesting that masonry paint would be a good sealant for the plywood (is that correct Ian?) so I may take a look at that. Like Ian I'm also looking at using 18mm thickness - the only problem being that Wicke's delivery charges are as much as one whole sheet of plywood and because I live 0.6 miles too distant from my local Wicke's store in Doncaster, there's an additional £5 charge on top of that. Wonder if they would drop it off at the end of the street instead to save the extra £5?

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I'm not sure how good masonry paint is as a sealant Mick, It's just that I've used it on timber before and it seems to adhere to it well. It is also quick drying in good weather, you can get three coats on in the day during summer.

I suppose the best treatment would be a good timber paint system consisting of primer, undercoat and a couple of finishing coats if you have the time and patience!... or maybe a few coats of yacht varnish.

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mick said:

I live 0.6 miles too distant from my local Wicke's store in Doncaster, there's an additional £5 charge on top of that. Wonder if they would drop it off at the end of the street instead to save the extra £5?

The delivery charges are quite high - I assume you're looking at 8'x4' sheets? It was less of a problem for me as my nearest Wickes is 39 miles away anyway and I did order 5 sheets and a whole load of 2"x1" batons (or whatever it was in mm), because I used the same for mkaing shelves and brackets for the garage.

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IanR said:

You could get it cut to more convenient sizes at B&Q and then maybe get it in your own vehicle??

I'd thought about that but the full sheet, although a little unwileldy perhaps, means I could get away with fewer cuts/joins on the layout itself. The Wickes delivery charge is steep but by the time I've added up my own costs and time, getting it straight off the lorry and into the garage doesn't look too bad providing I order enough material at the one time to justify the cost.

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Hi Mick,

As you know, I'm using plywood exclusively on my layout. I've opted for the exterior grade WBP plywood because I needed the extra protection afforded by this grade of ply. Although the wood used in the ply itself isn't waterproof, the adhesive is, and I think its worth the few extra pounds. In fact apart from the higher grade hardwood "facing" timbers used in Marine Ply, WBP is identical in every other respect.

Either way, whichever grade of ply you go for, it needs to be adequately sealed - especially on the cut edges. As I mentioned in my earlier post, I've opted to go down a similar route to Roy and use paint as the main protection for the track baseboards. This coupled with a previous coat of Dulux exterior preservative / primer should be more than enough to protect the baseboard, but as they say only time will tell.

Duncan

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Thanks for that Duncan - I wasn't entirely sure of the properties for the different types of plywood. I had seen the astronomical price of marine ply and discounted that as a viable option some time ago but was confused by structural and exterior grades, both of which are stated as being suitable for use outdoors providing they are adequately sealed. To be honest I'm still somewhat confused (the word 'structural' is perhaps a clue with one) and I expect that exterior has waterproof glue whereas structural doesn't? It would seem either would suffice for my requirements but that exterior may be slightly more resilient.

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I think the only difference apart from the adhesive, is the timber used for the facings on the sheet. I think standard and structural ply use spruce or other softwood facings as they not expected to be put on display. Whether structural ply uses waterproof adhesives or not I couldn't say, but as you know, Wales has a naturally wet climate and I thought the extra protection afforded by the waterproof adhesives used in WBP ply worth the extra cost.

I don't know what you intend to mount the track bed on, but if you're considering posts I can tell you now that although I started using 1200 x 200 x 18mm support rails, 1200 x 100 x 18mm would be more than sufficient. In fact as I mentioned in my own thread - I purchased a sheet of 6mm WBP ply for the rails on the curves as I thought is would bend naturally into the correct radius around the pre-installed posts. I can tell you now that not only does it do the job I originally asked it to do perfectly, but it's also suitable for the support rails on the entire layout, and a third of the costs of a sheet of 18mm ply.

The only draw back with the 6mm is the lack of depth for screw when attaching the track bed - but I'm sure some scraps of 18mm ply where the screws will be used will do the trick...

Duncan

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  • 3 weeks later...

This is when one needs to think if they have a friend who has a good vehicle for this kind of work. I have friends with trucks that I call for favors and then buy a six pack of their favorite drink as a thank you.

Unrelated anecdote follows:

My vehicle is a toyota station wagon and you'd be amazed what things I've fit in there. I had a girl friend a few years back who drove a SUV type vehicle, but it was actually for work. To do her garden we drove to a horse ranch for some free manure. When we had it loaded on plastic sheets with the back seat down,oh it smelled fertile in the vehicle, all the windows fogged up because the manure was actually hot and releasing moisture.

B&Q must be your equivalent to our Home Depot mega hardware stores. HD does free cuts on plywood so that you can fit it in your car too. Width is the real issue with loading my station wagon, I can fit 10 foot beams in it otherwise.

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  • 1 year later...

search out a local timber supplier. Much cheaper than wickes or b&q. Recently built a workshop/shed for my indoor part and as an example wickes osb was nearly 10quid a sheet more than the merchant I used. kent blaxhill, plus it was free delivery too

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