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Author Topic: MDF  (Read 7132 times)

CK

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MDF
« on: May 06, 2006, 08:02:45 PM »

Has anyone had experience of using MDF to make a hull?

I only ask as I've got tons of the stuff in the garage and there are no suppliers of liteply in my area.


Craig
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dougal99

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Re: MDF
« Reply #1 on: May 06, 2006, 09:42:14 PM »

Hi Craig,

How is Kinloss these days? ( I was there from 75-79. The favourite car sticker was 'Happiness is Kinloss in the rear view mirror')

I used MDF for the keel of my Brittany Trawler and all seemed well for 18 months or so then I noticed that it had started to swell in places due to water ingression, despite having used epoxy resin, several coats of paint and varnish. I cut the affected pieces out and replaced with plywood however, I have had to repeat the process twice since (on different parts of the keel) and the boat is now waiting further work for the same problem. Needless to say I wouldn't recommend MDF for any part that will spend most of the time submerged. As you may be aware MDF starts to swell and disintegrate when wet - not a pretty sight in a hull  :(

Having said that Hobbies sell wood packs for their plans that are totally MDF, so presumambly it must be possible to waterproof the stuff, but I'll not risk it again.

HTH

Doug
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anmo

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Re: MDF
« Reply #2 on: May 06, 2006, 11:20:40 PM »

I haven't used MDF a lot, don't like working with it at all, and it always reminds me of Lawrence Llewellyn Bowen and Lynda Barker, but I can offer one bit of advice, always wear a mask when sanding the stuff. The dust is very bad for your lungs, it could even be carcinogenic if you breath in enough of it.
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CK

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Re: MDF
« Reply #3 on: May 06, 2006, 11:50:00 PM »

Hi Doug,

Kinloss is the still a little bit of a sleepy hollow, but you definitely wouldn't recognise the place now. Full of nice shiny new buildings, with no-one in them!!  I've now reached the dizzy heights of Lossiemouth, but since I don't really like Tonka's I wasn't going to put a picture of one on my profile.

The only "proper" aircraft in the RAF are ones where you can make your own brews and eat doughnuts!!!


On the subject of MDF, I am aware of the swelling when it gets wet, and that Hobbies supply hull kits made from it.  That's where the dilemma crept in.  I'm not sure if several coats of varnish would be suitable to seal the hull?

Craig
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DavieTait

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Re: MDF
« Reply #4 on: May 06, 2006, 11:58:07 PM »

Hi CK,
       I used MDF for the navigation boards on my own 25ft ferrocement fishing boat and they only lasted for 2 years before they had to be completely replaced. I guess using MDF for a hull would be ok if you then went on and gave the hull a good coating of fibreglass resin ( or even a couple of layers of fibreglass over the hull ) and made sure that you had a good coating of varnish on the hull afterwards too.

Davie
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MikeK

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Re: MDF
« Reply #5 on: May 07, 2006, 08:51:05 AM »

Surely by the time you have slapped umpteen coats of waterproofing on, any advantages will be lost. I wouldn't put MDF and water anywhere near each other.

MikeK
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dougal99

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Re: MDF
« Reply #6 on: May 07, 2006, 09:59:37 AM »

Hi All,

I've tried the resin, fibreglass, undercoat, paint, varnish route. It only seems to last 18 months or so. I was going to treat an offcut and leave it in a jar of water to observe but never got round to it.

Having said I wouldn't use it again, I have used it for internal frames and to date (fingers crossed) no problems.

Doug
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anmo

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Re: MDF
« Reply #7 on: May 07, 2006, 10:50:35 AM »

It seems to me that as far as we're concerned, the biggest problem with MDF is the lack of continuity in the wood component. If plywood, even the very cheapest stuff gets wet, you still have the wood fibres holding everything together, even after the adhesive softens. MDF is made from sawdust, so once the adhesive softens or breaks down, all cohesive strength is gone. Also because the powdered wood has so much more glue/wood contact area than the wood veneers used in thin plywood, it expands far faster and more readily than ply. It may be OK for cheap furniture, but I''d never use it for anything that was going to get wet.
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Roger in France

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Re: MDF
« Reply #8 on: May 08, 2006, 06:57:28 AM »

Nasty, cheap stuff that works nasty, looks nasty and lasts nasty! Leave it to MFI!

Seriously, I would NEVER use it for construction that goes anywhere near the water no matter how well treated/covered. It has its uses as building boards and construction jigs but otherwise I loath the stuff.

Roger in France.
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MikeK

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Re: MDF
« Reply #9 on: May 08, 2006, 08:05:48 AM »

Nasty, cheap stuff that works nasty, looks nasty and lasts nasty! Leave it to MFI!

Seriously, I would NEVER use it for construction that goes anywhere near the water no matter how well treated/covered. It has its uses as building boards and construction jigs but otherwise I loath the stuff.

Roger in France.


Totally agree !! Couldn't have put it better
MikeK
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CK

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Re: MDF
« Reply #10 on: May 08, 2006, 06:31:45 PM »

Thanks for all the input, guys.

I think I'll forget about the MDF idea and hunt for a plywood supplier in the local area.

Cheers,
Craig
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Colin Bishop

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Re: MDF
« Reply #11 on: May 08, 2006, 07:05:16 PM »

Make sure you get decent exterior quality plywood. There is a lot of nasty cheap stuff about. I recently saw a particularly bad batch in Homebase, warped and splitting on the racks.
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DavieTait

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Re: MDF
« Reply #12 on: May 08, 2006, 09:00:02 PM »

Even better would be the more expensive Marine ply , thats the stuff they stiched and glued sheets of together to make the Mirror sailing dingy's in the 1970's-1980's and I know of a couple of them that are still going strong 25 years after they were built with only normal painting every season. I used Marine ply to repair the transom on my 25ft Ferrocement fishing boat and it lasted without any problems at all. I would build a hull out of Marine Ply anytime without worrying about it rotting or splitting.

Davie

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Colin Bishop

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Re: MDF
« Reply #13 on: May 08, 2006, 09:19:37 PM »

Yes, Marine ply is certainly the best but it's also usually the most expensive. However suppliers like Robbins (link below) will ship small quantities.

http://www.robbins.co.uk/
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anmo

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Re: MDF
« Reply #14 on: May 08, 2006, 09:59:02 PM »

Marine ply is great stuff for big boats, but not much use for models. It's all stamped BS1088, they don't make it any thinner than 6mm, or occasionally 5mm, it's heavy as anything, expensive, and it blunts your tools as it's b****y hard to cut. All we need is good quality ply, preferable birch. The stuff to look for is stamped WBP which means 'water and boil proof'. That means that the adhesive is 100% waterproof, at least as far as modellers are concerned. Places like B & Q sell cheap 3mm & 4mm ply for flooring purposes, it may seem like an economy, but the wood is poor quality and the adhesive isn't waterproof, so it will cause problems eventually. Many of the original Aerokits kits were made from ply like this, and most of the surviving examples are suffering from delaminating bulkheads now. Spending a bit extra on materials like plywood makes construction a lot easier as well, even an old skinflint like Bluebird avoids the very cheapest stuff.
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Colin Bishop

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Re: MDF
« Reply #15 on: May 08, 2006, 10:32:00 PM »

Anmo, at the risk of contradicting you I do have a sample of 4mm lightweight boatbuilding plywood! However, I would totally agree with you that the standard WPB Birch ply you get in model shops is beyond question the best type to use in modelling applications. It isn't all that expensive, comes in handy sizes and takes a superb finish. I prefer it to plasticard every time as it will last virtually forever.
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boatmadman

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Re: MDF
« Reply #16 on: May 08, 2006, 11:13:40 PM »

Hi,

These are pics of the dinghy I am building out of marine ply supplied by Robbins. Its good stuff

Ian
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anmo

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Re: MDF
« Reply #17 on: May 08, 2006, 11:35:18 PM »

Anmo, at the risk of contradicting you I do have a sample of 4mm lightweight boatbuilding plywood! However, I would totally agree with you that the standard WPB Birch ply you get in model shops is beyond question the best type to use in modelling applications. It isn't all that expensive, comes in handy sizes and takes a superb finish. I prefer it to plasticard every time as it will last virtually forever.

No problem CB, I don't doubt you for a moment, but it isn't genuine BS1088 marine ply is it? The word 'lightweight' should tell us that. I can't really see that genuine marine ply has any use at all for modellers, the stuff is so heavy for a start, as well as being difficult to work, especially with ordinary hand tools. You're right about ordinary WBP ply being the best stuff for modelling applications, as you say it will last almost forever, and this may be a good time to mention 'liteply', which isn't one of my favoured materials either. Any weight saving is minimal, and it has a distressing tendency to warp and split, so stick with good quality WBP birch plywood.
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Colin Bishop

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Re: MDF
« Reply #18 on: May 09, 2006, 10:19:01 AM »

Anmo, at the risk of being a sad awkward anorak..(!) the sample I have got is Robbins Tiger Elite Sapele Faced Marine Plywood marked BS1088:1966. My micrometer measures it as 4.14mm. The other sample I have is described as Teak Faced Boatbuilding (WPB) plywood. It's fractionally thinner and lighter than the other one. I don't think either would take such a good finish as modelling WPB birch ply as the grain is rougher.
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Daryl

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Re: MDF
« Reply #19 on: May 09, 2006, 10:30:39 AM »

I have found a copy of BS1088-1:2003, the thickness are as listed.

4mm +.02/-0.6
6mm +.04/-0.65
9mm +.06/-0.75
12mm +.09/-0.82
15mm +.1/-0.9
18mm +.12/-0.98
22mm +.16/-1.08
25mm +1.8/-1.16


As with most BS documents its not light reading, it does waffle on about thickness of veneers, type of adesive, type of wood used in construction etc etc. If anyone is registered withthe BSI as we are at work we can get accsess to any standard document, and then fall asleep reading it. Still the printed copy is useful for proping doors open with!

Apparently this standard is under review, this is the norm with the BSI.

Daryl
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