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Preparing and finishing MDF

Help with choosing the right coloured milkpaint to slather all over your new project.

Preparing and finishing MDF

Postby greeno » 13 Jan 2017, 16:26

I've got a little toy box/book shelf to knock up for Jr.

18mm MDF looks to be the material of choice on this.

I've always had a problem getting a good hand painted finish on MDF. I've had a Google and there are a lot of answers on this but I just wondered what the wisdom of the forum was?

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Re: Preparing and finishing MDF

Postby RogerS » 13 Jan 2017, 16:45

Are you talking about having problems with the surface or the cut edges? If the latter then most people use moisture resistant MDF as it gives a cleaner cut.
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Re: Preparing and finishing MDF

Postby Tusses » 13 Jan 2017, 16:48

Depending on size .. consider 12mm
as it gets heavy quickly !
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Re: Preparing and finishing MDF

Postby Pinch » 13 Jan 2017, 16:55

Surfaces: at least 3 coats (denib in betweenie) roller applied using small dense foam roller - just the job! 8-)

Raw edges: a few brush applied coats, sand back between coats until surface is lovely jubbly and apply final coat - just the jobby! 8-)

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Re: Preparing and finishing MDF

Postby Robert » 13 Jan 2017, 17:00

As well as using moisture board if you can it needs to be sealed before painting.

I have some Morrels MDF primer/sealer and it smells and looks just like sanding sealer - a cellulose based thin varnish like stuff that dries quickly. Once it is dry you sand it smooth before painting. The sealer locks all the fluffy fibres together so you get a neat surface and edges.

I'd guess any primer would work for a one off but it will need sanding when dry. Water based stuff will make the fluffiness worse and may need a repeat to get a result.

Or what Pinch said as i type too slow :)
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Re: Preparing and finishing MDF

Postby greeno » 13 Jan 2017, 18:03

Thanks for the ideas.

Yes, my problem mainly was the cut edges.

There's been the odd instance as well of a cock up and I've over worked/got to aggressive with the board face and it got a bit messy. But that is my fault.

Think I'll give MR MDF a go this time.
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Re: Preparing and finishing MDF

Postby tracerman » 13 Jan 2017, 18:10

Greeno - I also think 18mm will be too heavy , even 15mm as well . I would opt for 12mm so long as you use good joining and good glue , PU perhaps . For exposed edges I have in the past applied some PVA to the edges with a small brush and sanded it down .
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Re: Preparing and finishing MDF

Postby greeno » 13 Jan 2017, 18:22

Seems that 18mm is generally considered overkill. I'll give 12mm a go then.

I was just concerned about the amount of abuse it was going to get and potential for sagging.

I also saw in my Google-ing that watered down PVA was a good option for edge prep.
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Re: Preparing and finishing MDF

Postby Tusses » 13 Jan 2017, 20:12

greeno wrote: potential for sagging.
.


It depends on the span (you didn't say ? ) .. if it's quite wide, then maybe think about edging the front
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Re: Preparing and finishing MDF

Postby Phil » 14 Jan 2017, 08:37

Robert wrote:As well as using moisture board if you can it needs to be sealed before painting.

I have some Morrels MDF primer/sealer and it smells and looks just like sanding sealer - a cellulose based thin varnish like stuff that dries quickly. Once it is dry you sand it smooth before painting. The sealer locks all the fluffy fibres together so you get a neat surface and edges.

I'd guess any primer would work for a one off but it will need sanding when dry. Water based stuff will make the fluffiness worse and may need a repeat to get a result.



Agree on the sealer.

When I have used this MDF 'stuff', generally just sealed the edges with some PVA glue watered down (cheap than sealer) and some light snading afterwards.
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Re: Preparing and finishing MDF

Postby Salmon's lair » 15 Jan 2017, 13:34

Greano,

On the making side you could use 9mm MR MDF by making a box from 9mm with butt and glued joints and then
Overlay with 9mm x 80mm strips on all the outside edges (sand internal edges first) overlapping the edges, this will give panelled look and give you an 18mm thickness at the joints and reduced weight. You could use the same method on the lid, but put the strips on the underside.

I would have a look on Amazon.com for some toy box hinges so the lid would not slam on mini greeno's fingers

Painting wise if you wanted a dark or bright colour I would use something like oil based primer and eggshell as follows

Mix 2 parts primer- 2 parts eggshell- 1 part white spirit as your primer one coat.

De-nib between coats by hand using 240g finishing paper

Finish with 2 coats eggshell

Using this method it tints the base coat to the same colour as the top coat and it forms an excellent primer, I have used this on hand painted
Kitchen for many years without any problems

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Re: Preparing and finishing MDF

Postby RogerS » 15 Jan 2017, 13:39

Welcome to the forum, Paul, and many thanks for a very helpful post.
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Re: Preparing and finishing MDF

Postby Salmon's lair » 15 Jan 2017, 13:58

Thank you Roger,

I'm happy to help
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Re: Preparing and finishing MDF

Postby Andyp » 15 Jan 2017, 21:12

Welcome Paul and thanks for probably the most informative first post ever.
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cheers
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Re: Preparing and finishing MDF

Postby TrimTheKing » 15 Jan 2017, 21:39

Andyp wrote:Welcome Paul and thanks for probably the most informative first post ever.


What he said, welcome Paul.

Take yourself over to the 'Welcome' forum and do us a proper introduction.

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Re: Preparing and finishing MDF

Postby greeno » 16 Jan 2017, 15:32

Thumbs up to Paul, I reckon that's the way I'll go.

When I said "toy box", it is not a classical design and hence my concern about sagging.

It'll look a bit more like a church pew. The bottom will be partially covered so toys can be stuffed in. The seat part of the pew will be a bookshelf - that's the bit I was worried about sagging as it'll probably get sat on as well.

I think I'll just frame underneath a put a facing strip on. Width is probably ~1200mm.
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