MDF SEALER

[LESNPAM]

HI ALL
im going to be making a couple of bedside cabinets in mdf finishing with a painted white gloss paint will it be sufficient to just seal the edges with mdf sealer proir to painting
regards
les

 

[Ollie78]

MDF is a nightmare to paint.
To answer your question. No it will not be sufficient.
I have recently made a few built ins with MDF with simple rounded over edges on the doors.
During these builds I experemented with a few things.

1: Knifing putty (very fine filler used for fine filling car bodywork)
This is very good at sealing the edges, but it is hard to sand so be very sparing with it. Time consuming but you can acheive a glass smooth egde.

2: Painting the edge a couple of times ( dulux MDF primer ,water based) then sanding back and painting the whole thing.
Not very good, caused more work for myself in the end.

3:Sand the edges with 320 grit sandpaper, just sort of polishes the edge smooth.
This worked surprisingly well, seriously reduces the excess paint absorbtion and reduces fluffyness ( is fluffyness a technical term? ).

I found that 2 coats of MDF primer, sand with 320 just to de nib, 1 coat of undercoat, 1coat of topcoat, de nib again and then final topcoat was a pretty decent finish. I was using Dulux trade waterbased paints.
Also either use very good brushes (Purdy are my favourite) or preferably a small roller on the flat areas.

Good luck
Ollie

 

[mailee]

I think you will find the best stuff for MDF edges is Morrells high build primer. It is a 2K paint and is not cheap but is brilliant on MDF. It does help if you use MRMDF as this isn't as 'fluffy'. I use two coats of it sanding between with 320 grit. (It dries in about an hour) and then over with the top coats, smooth as silk. I also spray the top coats on. It really is that good! :wink:

 

[LESNPAM]

HI
thanks very much for the info will post again when i have finished them
best regards
les

 

[Allylearm]

Best tip is do not use MDF if edges are exposed and want a finish. Go for the Machine quality HDF this is finer particled and denibs best and lets the machined profiles be crisper and lets the paint seal the edges as the particles it is made up from are tighter nit so easier sealed so to speak.

The other way is curtain coating, but you still need better board and you need to denib. I have only seen this used in industrial setting, very high gloss finish is achievable with feed speed.

 

[brimham]

Hello i'm new to wood working and as a result i don't know some of the terms that are used. De nibing is mentioned a few times in this thread what's it mean?

 

[CHJ]

Hello i'm new to wood working and as a result i don't know some of the terms that are used. De nibing is mentioned a few times in this thread what's it mean?

Removal of raised fibres, usually caused by moisture/solvents swelling fibres, usually done by light sanding.

 

[brimham]

Thanks for the quick reply. Today was the first time i have cut mdf. I made a jig to sit a guide bush in.

"Removal of raised fibres, usually caused by moisture/solvents swelling fibres, usually done by light sanding."

Once again sorry for my ignorance, would the "nib" be the slightly raised edge around the cut, or would it occur on the face of the material?

 

[CHJ]

or would it occur on the face of the material?

Normally refers to raised grain or fibres on the cut/finished surface that can be felt/seen as a roughened surface after sealer or finish has dried.

 

[brimham]

thanks.

 

[chippy1970]

When I get a spare minute I will take some photo's of my latest job, two sets of wardrobes with shaker doors 10 in total. I had all the exposed edges of the mdf edges edged with preparation tape. That way it can be painted with no problems whatsoever, its the first time I have seen this stuff and it looks good. Im sure the decorator will love it.

 

[mailee]

That's a new one on me Chippy? What is preparation tape? :?

 

[RogerM]

I think you will find the best stuff for MDF edges is Morrells high build primer. It is a 2K paint and is not cheap but is brilliant on MDF. It does help if you use MRMDF as this isn't as 'fluffy'. I use two coats of it sanding between with 320 grit. (It dries in about an hour) and then over with the top coats, smooth as silk. I also spray the top coats on. It really is that good! :wink:

Would you use the Morrells High Build primer for MRMDF if there were no edges to paint? An MDF panel set in a tulipwood or beech framed shaker door for instance?

 

[chippy1970]

That's a new one on me Chippy? What is preparation tape? :?

It's brown tape edging that can be painted just the same as the surface.

here it is cant really see it that well in the photos, my supplier does the edges square or slightly rounded mdf-wardrobes-t54351.html

 

[mailee]

Yes Roger I use the Morrells primer on all of it. I brush a coat on the edges and then once it is sanded pray the down I then give the whole lot two sprayed coats of the primer. You can actually just spray the edges by coating them each time the panel is sprayed front and back so they get four coats on the edges. But I like to use it like a stopper to make sure. Two coats is sufficient for MRMDF and it sands down very easily so is no problem.

I have never heard of the tape Chippy. Is it self adhesive or is it glued on and whats it made of?

 

[chippy1970]

Hi Alan , its like some sort of paper tape they put it on with a huge edgebanding machine then I had it slightly rounded put you can leave it with a sharp square edge if you want.

Heres a better photo

 

[mailee]

Ah I see now. It has to be fitted with a machine then? I have seen it before but didn't realise what it actually was.

 

[Allylearm]

Hi Alan , its like some sort of paper tape they put it on with a huge edgebanding machine then I had it slightly rounded put you can leave it with a sharp square edge if you want.

Heres a better photo

The issue with taping is you have to watch for expansion due to moisture absorption on the edge and the other issue is saw chatter from misaligned teeth on saw cut. As such the better edge banders, they have a trim cut prior to gluing the edge on with the scraping the top and bottom face of board the most important aspect for finish.

In hand finishing it is worth thinking about the edge preparation prior to ironing or gluing your tape on prior to trimming.

For flush edges the tape is good idea, but for shaped edges denibbing is requirement or unless you solid wood edge the profile on with Edge bander or by manual method saves time in painting or matching grain/timber finish.

 

[mailee]

I see, so it's not really a DIY sort of application to get a good edge. I shall stick to priming the edges as my doors are often rounded or ogee profile. Thanks for all the info on it though guys, at least I know what it is now. Thanks. :wink:

 

[chippy1970]

The issue with taping is you have to watch for expansion due to moisture absorption on the edge and the other issue is saw chatter from misaligned teeth on saw cut. As such the better edge banders, they have a trim cut prior to gluing the edge on with the scraping the top and bottom face of board the most important aspect for finish.

Yeah they have a pre-miller on their edgebander, state of the art by the looks of it take a look http://www.wrightscarpentry.com