A solution to MDF expansion on joints, translams etc.

[ShinOBIWAN]

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.

[richie00boy]

Good tip. Ronseal Wood Hardener is good stuff as well, used it on my rotten porch and it's still standing after 2 years. UK made as well.

[AuroraB]

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]

Originally posted by AuroraB
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.

[Audiophilenoob]

Originally posted by ShinOBIWAN


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]

Originally posted by Audiophilenoob


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.

[JohnL]

Originally posted by ShinOBIWAN

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

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

[ShinOBIWAN]

Not familiar with it, John. Maybe someone else is?

[mzzj]

Originally posted by JohnL


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?

[Ed LaFontaine]

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.