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Cut MDF

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Delboy18/03/2013 10:10:13
36 forum posts

In a fairly recent edition of GW, there was an article discussing best ways to treat cut areas of MDF to ensure a smooth finish when painting. I am replacing all the skirting board and architrave in the house with a lambs tongue profile but these are cut MDF boards.

I have tried to find the article by flicking through my back issues but so far have failed. Can anyone help throw any light on this and if you remember, can you let me know the issue number of the magazine pleas.

Many thanks

Delboy

Big Al18/03/2013 10:41:45
1600 forum posts
73 photos

I have always found that the best way to treat MDF sawn edges prior to painting is to either sand it smooth, or lick the edge with a plane, then lightly sand it and then prime it. Once the primer has dried then sand it smooth and either prime it again or apply the first coat of top paint.

Al

Derek Lane18/03/2013 10:57:32
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3219 forum posts
1004 photos

With the Motorbike rocker i made I used PVA glue slightly watered down(Not to much) when dry sand and paint as usual with all under coats primers and top coat. This seals the MDF and helps prevent the paint being sucked into the MDF.

Well it worked for me

daveO18/03/2013 16:13:13
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250 forum posts
32 photos

well I asked this question a while ago and this is the answer that "Mailee" gave

hanks guys. Well Dave it does take some work and money to do it. I use Morrells AC primer for the edges of my MDF, which by the way is MRMDF. I sand the edges down well to 120 grit and then apply a coat of the primer by brush on the edges only. When this is dry (about 1 hour ish) I sand the edges with 320 and then apply two sprayed coats of the primer all over. I then sand it all with 400 and apply the top coats. I have been told that a product named Zinnser bin is a very good sealer for MDF edges but I haven't tried it yet. the only drawback with using the Morrells primer is the cost as it is only available in 5 ltr tins at around £35 per tin. (it does last a long time though) HTH

Dave

Mailee19/04/2013 19:45:33
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1048 forum posts
1235 photos

Yes i still use the same method on my MDF but i would recommend the Zinnser bin which can be brushed on and is available in smaller quantities. HTH.

Ron Davis19/04/2013 20:18:30
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1619 forum posts
201 photos

Watch out when sanding and planing because of the dust, and keep the oilstone handy as the MDF will blunt the blade.

Ron

Michael Yorke 116/06/2013 13:11:52
1 forum posts

I use Zinnser Bin for edging MR MDF and find it the best of all the above options but you still have to sand the edge smooth after application.

Do not use the water based version though as I find it too 'thick' and takes a lot longer than the shellac based product.

It is expensive though so I do not recommend dropping a new just opened tin on the floor like I did some time ago.

Peter Leslie 120/01/2014 22:34:45
4 forum posts

I know this is an old thread but ill chip in my 2p.

I have a CNC router and produce a lot of mdf parts. I deal mainly with 6mm and 18mm mdf

The thickness is important because 6,9,12 mm mdf are consistent in their fiber structure, 18mm + generally has a soft core (there are products like 'deep rout' for cnc'ing which are pretty solid but you'll not find them easily).

I dont worry about sealing 6mm, i just paint, sand, paint, sand, done.

The centre of 18mm is like a sponge and soaks in tons of sealer. I've tried everything for 18mm from celulose spray, to shellac, pva, mdf primer ..etc etc etc. I have been using decorators caulking for years. Its cheap, very very easy to apply, available in different colours, dries in around an hour and is sandable when dry. Gives you a perfect finish to paint over. Did i mention its cheap! I use Soudal caulking, at a quid a tube you can't grumble.

Hope it helps someone.

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