Weight of MDF and MDF Lite

[MrSplosh]

Hi all,

I need to make a removable door/panel for built-in storage - there is no space for it to be hinged. The cupboard is under the stairs and will store things that are only used occassionally, it will not be used every day, more likely only once a month, hence it is OK for the panel to be removable and if slightly awkward then that's not a problem.

The panel will be 810mm x 930mm and will rest on the floor when closed, so I am planning to use push-release magnetic catches at the top and simple fixed magnetic catches at the bottom. I have calculated (by weighing an offcut of 12mm MDF) that this is 773kg / m3 so my 810x930x12 panel would weight 7kg. That might be a bit heavy so I am considering using 9mm MDF. Assuming that this is 3/4 of the weight of 12mm the panel would be 5.25kg which is just manageable.

My questions are:
1) Am I right to assume that the density of 9mm board is roughly the same as 12mm, so that for a panel of the same size it would weigh three quarters of the 12mm panel?

2) I have seen some places that sell MDF Lite (e.g. Jewsons) and was wondering if this would be suitable. They give no detailed product information so I cannot work out the actual weight per kg3 and hence the weight of my panel. Does anyone have info MDF Lite? Does it hold screws as well as standard MDF or is it really only good for glueing?

Thanks,

Mr Splosh
{first post on Lemon Fool after moving from Fool.co.uk}

[jfgw]

MDF is usually harder (and, therefore, probably more dense) near the faces than in the middle. I would guess, therefore, that 9mm MDF is, on average, more dense than 12mm.

I have handled quite a bit of MDF in the past and have found that the density can vary from batch to batch.

Julian F. G. W.

[jfgw]

Travis Perkins provide data on some sizes. For a 2440mm x 1220mm sheet, 9mm is 20.35kg and 12mm lite is 22kg.

For a piece 810mm x 930mm:
12mm standard weighs 6.99kg (based upon the density value provided by you);
12mm lite weighs 5.56kg;
9mm standard weighs 5.14kg.

I have no experience of the lite stuff but have found that denser is tougher so would hold screws better. The denser MDF is still sold for a reason; lite MDF has not completely replaced the denser grades.

Have you considered a thin sheet on a wooden frame? A frame sandwiched between two thin sheets should be very rigid (think of hollow doors).

Julian F. G. W.

[redsturgeon]

I think that for this purpose ply would be a better bet, lighter and stronger than MDF.

John

[quelquod]

Finishing the edges of ply is difficult though and I'd say it was more prone to warp. You'd likely get away with just a panel of mdf but I'd be inclined to frame plywood which is a bit of work (and it'd still likely warp).

[redsturgeon]

I'd say ply is highly unlikely to warp at that size used indoor in a low humidity environment.

John

[jfgw]

Whatever you use, treat both sides the same. If you paint or varnish one side but not the other, the panel will end up bowl-shaped.

Julian F. G. W.

[quelquod]

I'd say ply is highly unlikely to warp at that size used indoor in a low humidity environment.

John

You may be right, I'm a little surprised though as I've had plenty of plywood doors (kitchen cabinets in the main) which warped steadily over the years,as the construction stresses worked out. I had expected that a composite with no 'grain' would be more resistant.

[redsturgeon]

I'd say ply is highly unlikely to warp at that size used indoor in a low humidity environment.

John

You may be right, I'm a little surprised though as I've had plenty of plywood doors (kitchen cabinets in the main) which warped steadily over the years,as the construction stresses worked out. I had expected that a composite with no 'grain' would be more resistant.

There is no doubt that plywood has more tendency to warp than mdf although as has been said they both must be treated on both sides or they all will bow. But plywood has alternate layers of grain set at 90 degrees which does stabilise it somewhat and in my experience, indoors I have not had a problem.

A panel of the size in question though, in a hallway, indoors, treated both sides would probably be OK for many years though and be lighter than MDF.

John

[Imbiber]

http://www.hse.gov.uk/woodworking/faq-mdf.htm

[MrSplosh]

Thank you jfgw, redsturgeon, quelquod and Imbiber for your useful help and information. I decded to go with MDF as I am not an expert (yet) at finishing fine detail so thought that a simple panel would be easier to make neat than a frame or using ply. I did not find a local supplier of MDF Lite so I got the standard density 9mm.

Just for the record, the final cut piece is actually 920 x 807mm and weighs 5.3kg (my bathroom scales only measure to 0.1 kg). This gives a density of 5.3 / (0.920 x 0.807 x 0.009) kg/m3 = 793 kg/m3, which is slightly more than my calculated density for 12mm (see above). At the extremes of my scales accuracy if the weight was 5.25kg this would be 785kg/m3 and if it was 5.34kg the density would be 799kg/m3

Thanks for the tip about treating both sides to avoid warping. On the visible side I'll be using MDF primer followed by the same wall emulsion as the rest of the hall and stairs. Would it be sufficient to just use the primer on the inside, or should I also finish it with emulsion to match?

Jonathan

[ElectricFeet]

Thanks for the tip about treating both sides to avoid warping. On the visible side I'll be using MDF primer followed by the same wall emulsion as the rest of the hall and stairs. Would it be sufficient to just use the primer on the inside, or should I also finish it with emulsion to match?

Primer should be sufficient, as it should make the surface watertight.

[MrSplosh]

Thanks ElectricFeet, that's really helpful.
The panel is all made and working nicely, but not painted yet. You have saved me some work