A solution to MDF expansion on joints, translams etc.

ShinOBIWAN

diyAudio Member
2004-02-25 9:13 pm
UK
I see that many folks, including myself are frustrated by the fact that MDF has an annoying tendancy to expand and spoil, be it with veneered or more severly with sprayed and painted finishes.

Some folks have suggested PVA/water mixes, shellac, level filling, resins etc.

I've tried most and still get the expansion to a greater or lesser degree but finally I have found something that truely works.

Its actually used for stabilising rotting wood and uses the moisture within the wood to actually form a chemical bond that looks the fibres in a resin cast that penetrates into the MDF. Once set its water proof and very tough, much tougher than untreated MDF, which also means I'd suggest you do all you sanding and detail work before applying this as it will cause you some extra work. Its excellent for applying spray finishes onto though as its almost like steel in its substrate toughness.

The one that I used is Bonda Wood Hardener:

http://www.decoratingdirect.co.uk/viewprod/b/BONWH/

I'd also highly recommend using void free plywood, its better than MDF by far for jointing and for absolute troublefree finishing use the wood hardener on this also.

Hope this helps folks out there, who like me, probably pull their hair out when they try to spray cabinets when faced with this problem.
 
Very interesting........would one of you guys look a t the declaration and tell me what's in it....??
I do a fair amount of woodworking in general, both house and furniture, and I often envy you guys down there and over there, having access to all sorts of wood and accessories......
I live way up north, and are sometimes able to track down stuff throughout Norway, by phone or internet, but generally, it is quite expensive if I find what i am looking for at all. Often I have to "synthesize" an acceptable solution.....
 

ShinOBIWAN

diyAudio Member
2004-02-25 9:13 pm
UK
AuroraB said:
Very interesting........would one of you guys look a t the declaration and tell me what's in it....??
I do a fair amount of woodworking in general, both house and furniture, and I often envy you guys down there and over there, having access to all sorts of wood and accessories......
I live way up north, and are sometimes able to track down stuff throughout Norway, by phone or internet, but generally, it is quite expensive if I find what i am looking for at all. Often I have to "synthesize" an acceptable solution.....

Its late evening here now but I pop up into the shed tommorow and take a look at the ingredients label.

I remember reading that its a polyester resin on the tin. I should imagine that Bonda/Ronseal has website which have the information also.
 
ShinOBIWAN said:


Its late evening here now but I pop up into the shed tommorow and take a look at the ingredients label.

I remember reading that its a polyester resin on the tin. I should imagine that Bonda/Ronseal has website which have the information also.

seems like a simple resin like a fiberglass resin... just soaks in and makes in harder at the expense of possibly less dampening ability...

just a guess though
 

ShinOBIWAN

diyAudio Member
2004-02-25 9:13 pm
UK
Audiophilenoob said:


seems like a simple resin like a fiberglass resin... just soaks in and makes in harder at the expense of possibly less dampening ability...

just a guess though

No you are mistaken.

The hardener reacts and uses moisture as a catalyst for the hardening process: Once the reaction is complete the resin is water proof.

From the Tin:

"Just think about it - all wood contains some moisture so a resin that actually uses moisture to harden has a distinct advantage over any system that does not"

The fibreglass resins you speak of don't.

MDF is very absorbant so you can see why this trait is advantageous. The hardener uses moisture contained in the MDF to form the resin and thus removing it from the equation, rather than locking it in.

For damping to become significant enough to become measureable yet alone audible would require more than simply sealing the cabinet as I have suggested. You'd need a significantly thicker layer, to claim any such effects.
Better to actually use a composite of woods or thicker walls and bracing should damping be of primary concern.
 

mzzj

Member
2005-07-02 8:17 pm
65N 25E
JohnL said:


Doesn't polyurethane glue(Gorilla Glue) work something similar to this?

Yeap, polyurethane glues rely on moisture in hardening. Sometimes problem at winter as here relative humidity can drop really low when its -35c for 2 weeks :)

quicksift, shinobiwan, what else it says on package? I am intrested to find similar product in here so i would need some clues. Some 1-component concrete sealers comes to my mind first, polyurethane based and very low viscosity. Popular in here for diy-fisherman for coating lures :)

And yes, how smelly it is? :)
 
Box joints that show through a piano-like finish are frustrating!
I'm going to hazard a guess-to provide a little background for what is being witnessed.
MDF is a material manufactured with a great deal of compression. The compression is 1-dimensional. Some of the stresses imparted to the mass of wood fibers, resins & what-all are relaxed over time. The rate and degree of relaxation is affected by changing moisture content in the mdf. Remember, wood expands as moisture content increases. If you really want to see for yourself, place the end of a piece of mdf in water for a few days.
Our constructions with mdf include cross-axis conditions, ie. edge to face.
Several suggestions;
Be mindful of the dimensional changes that are likely to occur.
Limit the cross-axis conditions. Full mitered edges will do this.
Treat the casework, especially the edges to limit moisture changes. The better it is sealed, the less moisture change = more dimensional stability.
The aforementioned epoxy adds strength to the equation.
 
i don't use mdf anymore.i found some high Density particle.it's not the cheap low density stuff.i have only found it in 48"X48"X5/8" sizes.i double them for 1.25".at that thickness and good bracing i'm not worried about vibration!this stuff is very strong and i find it glues and screws much better than mdf.i'm yet to see a piece expand-maybe if it was left in the rain!!i aslo find it's a dream to veneer too.glue does not get sucked in like mdf....my 2 cents..
 

ShinOBIWAN

diyAudio Member
2004-02-25 9:13 pm
UK
chainenoble said:
i don't use mdf anymore.i found some high Density particle.it's not the cheap low density stuff.i have only found it in 48"X48"X5/8" sizes.i double them for 1.25".at that thickness and good bracing i'm not worried about vibration!this stuff is very strong and i find it glues and screws much better than mdf.i'm yet to see a piece expand-maybe if it was left in the rain!!i aslo find it's a dream to veneer too.glue does not get sucked in like mdf....my 2 cents..

HDF still expands when you spray it.

Even hardwoods such as Oak expand a little when you laquer them.

Veneering covers a multitude of sins that you can't pass off when spraying, especially when applying a high gloss clearcoat.

What I prefer to do is use a few coat high build primer then level it back, apply another couple of coats and level again. Then go onto the basecoat and a good few layer of clearcoat, afterwards level the clearcoat and buff out. Take ages compared to veneering but its worth it in the end if done properly.

This trick here still isn't perfect but its the best solution I've found so far.

Now if you were working with metals or plastics then we would need to have a thread like this at all :)
 

ShinOBIWAN

diyAudio Member
2004-02-25 9:13 pm
UK
Vikash said:
Dumb question coming up, what's 1k and 2k? I'm going to try this stuff out Shin. Can you think of a good source for high build spray primers in the UK?

1k is cellulose paint and 2k is two-part paints that use a hardener mixed with the base.

Cellulose paint is relatively safe and you can work with it using just a face mask that filters VOC's(volatile organic compounds). 2k on the other hand is very dangerous and should only be sprayed using a full face air fed mask.

The difference between the two is durability and quality of finish. 2k's are rather better than cellulose, especially when it comes to high gloss finishes or extreme durability.

I get all my paints and supplies from these guys:

http://www.paints4u.com/Default.aspx

Check out the Rage Extreme selection if you want something a little different.
 

ShinOBIWAN

diyAudio Member
2004-02-25 9:13 pm
UK
richie00boy said:
I would also seriously look into acrylic paints as an alternative to cellulose. They go on just as easy, but dry tougher. It is also more 'compatible'.

Celly is yesterdays technology IMO.

Yes Acrylic is definitely better than cellulose. In fact cellulose will no longer be manufactured in the EU after Jan 06.

Everything is moving onto water based paints which have come on massively in recent years. The quality of finish is quite stunning now and up there with Urethane.