Glueing MDF - latest and greatest?

G'day brains trust,

--Problem--
Its wisdom extraction time! This time it's trying to obtain the latest and greatest method of glueing MDF together.

--Background--
I've been making a lot of MDF things recently. LOTS of MDF things. I've been using Titebond2.

No real reason to use this over and above TB1 or TB3. I've plenty of all. All give me good glueing performance and there's no real reason to complain.

But, I have had a few occasions where there've been tricky joints (angles and multiway) that resist efficient clamping and the joints fail.

Failure is invariably due to glueing ends, or parts of machined ends, and the glue being ravenously sucked into the edges. Copious glue, squeeze out collection and a wet rag solve it, but it's a messy PITA I'd rather avoid.

--Hoping to obtain--
Is there a magic MDF glue out there? Fast acting, MDF loving, edge filling, sandable, quick setting.... And other wishful thinking attributes.....

-- seen--
Part of the hunt is obviously to hit google. It shows few results.... It's all old info. One that keeps appearing is Bostik AV180 http://www.bostik.com.au/_upload/res...v180__0914.pdf

Perhaps there are people here who work for kitchen companies or an MDF using manufacturer who would know what's used?

Have you tried PU glue???

Epoxy with fast hardener is about the only thing I can think of that combines edge filling, sanding and reasonably fast setting into one package, as well as being thick enough not to be sucked into MDF end grain dust.

Try sealing the edges with glue first. Wait for it to set before joining. This way the adhesive will not be sucked into the board.

Quote:

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Originally Posted by Handyjack

Try sealing the edges with glue first. Wait for it to set before joining. This way the adhesive will not be sucked into the board.

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I use watered down left over or near end of shelf life Titebond II as a log end sealer and to seal the edges of MDF table saw jigs. Sealing the jointed surfaces with glue first is an old trick for very dry/porous timbers.

Perhaps I'm over thinking it.

The last few weeks have been pretty hectic. Much more is being asked to be made with this.... Stuff. I admit it's quick, but it's cursed material. The dust is foul, it's heavy and my space is very limited.

To make things with a minimum of faffing around, I'd thought there might be a resin-friendly or MDF specific glue. It seems a bit odd considering how much it's used that there isn't such a glue. The properties of MDF are distinct. Not many material exhibit them, so it's odd some chemical combine hasn't come up with a specific solution. Given MDF is bound with "various" glues, binders, fillers and resins, it seems a bit odd the manufacturers don't specify a specific glue for their products (maybe ill go ask them!).

Delving into AV180 shows it to be not dissimilar to any other PVA on the market. The Titebond 1, 2 and 3 are good... It matters not which are used.

BUT all 3 leave a yellowing glue line or overspill and neither offer any form of filling capacity. I'll give the foaming PU a crack....

I'm still curious what kitchen and cupboard manufacturers use. It certainly wouldn't be Titebond!

nuke the glue lines with radio frequencies to achieve a strong initial bond (maybe even a cured bond, not sure of that though).

the woodwelder
http://www.workriteinc.com/003.html

I havent used this woodwelder thing or any other radio frequency devices, seems like its just a portable microwave used to excite the water molecules in PVA creating heat.

PU glue MUST be well clamped to work; the foaming as it sets can push the join apart and it's not gap filling beyond about 0.5mm. Even if it's just a whole pile of masking tape holding things together, you have to use something.

From my experience.. I had very good result with PU glue
I've been using Sika from bunnings.. bit exy comparing to your standard PVA but dont need to use as much..
Clamping wise.. it needs half decent clamping I've done test sample where I've glued two veneered MDF piceces to a 90 deg... so cut edge mdf straight onto the veneer... no prepping no sanding or anything.. Just applied onto the one side a line of glue and placed it on top of the other piece.. since I didn't have any clamps I've held it together for about a minute or two and then left it for couple of days (done it on friday at work and left it over the weekend)
When I tested the strength.. I've managed to actually peel off the veneer of the MDF ... the glue did not give...
Main pain with PU is the foaming.. have to be very careful how much you apply... From my experience.. lets say I'm gluing up 50 mm thick wood.. I would run one 15mm wavy line through the middle and two straight lines roughly 10 mm of the edge ,,, as glue foams and expands it pretty much reaches out but not too much...
Clamping it as usual and leave it for 24 hours (although even after 2 -3 hours you can do some limited work on the piece ) I prefer full curing.
Done several MDF pieces with PU and had very good glue joints... factories using MDF generally use contact glue... Doesn't foam and doesn't get absorbed by MDF too much either....
When it comes to gap filling.. It will fill small gaps .. even larger ones... but with larger gaps once filling is sanded down.. it leaves spongy surface (full off small pockets of air) so on a nice piece of wood it looks bit ugly ... like using builders bog on a clean slab of oak... just doesn't go well together.. so do your best to fill gaps by other means (timber putty, resin, small wood inlay etc)
Another thing you have to watch for is... in contact with skin it leaves dark marks and it a bit tedious to clean off.. .Marks usually clean of with fair amount of solvol combined with a brush and water as hot as you can bear.. or with fair amount of pure acetone.. which has its own issues but at least cleans off the glue residue.... (acetone really dries of your skin)...
Highly recommended to use gloves when working with PU glue...

Quote:

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Originally Posted by Evanism

I'm still curious what kitchen and cupboard manufacturers use.

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screws or contact cement

if you search around there's probably a product like double sided tape sold in rolls the same width that MDF is thick

Quote:

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Originally Posted by Handyjack

Try sealing the edges with glue first. Wait for it to set before joining. This way the adhesive will not be sucked into the board.

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Ditto
lve got into the habit of brushing all cut edges of MDF with watered down glue, usually out of date TB. It makes end grain glue joints much more reliable and also prepares the MDF for later painting.
This solved my then 2 problems of poor end grain glueing AND the MDF swelling when I painted it with water-based paint.
BTW, l once had a batch of "wet area" MDF which was more expensive but didn't seem to have any of the above problems?
Fletty

Quote:

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Originally Posted by Prle77

When it comes to gap filling.. It will fill small gaps .. even larger ones... but with larger gaps once filling is sanded down.. it leaves spongy surface (full off small pockets of air)

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While the foam will fill the gaps, it will not actually provide any structural bond

That is correct... One PU cures it is actually bit flexible (you can dint big runout lumps quite easy) the main strength of the PU is that when it foams it actually goes into every crevice or pore (thus works very well on porous material like MDF) and then it hardens establishing very good bond.. Also it is a bit aggressive so you can glue some hard to glue materials like merbau ... I've glued few pieces with just lightly sanding gluing sides and I've forgot to clean them with acetone.. Glue joint was firm and did not fail.... The main trick with PU is ... more is not better... with PU ... less is more... When applying.. you need to take into consideration that it will foam and expand.. If you apply it the same way you apply PVA you will have a lot of fun taking off the foamed run out.... ..
In response for gap filling.. it will fill the gap but due to its flexibility it will not be structural and will most likely fail.. but then again... who will use PU for gap filling.. we have epoxy for that :)

Quote:

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Originally Posted by Evanism

G'day brains trust,

--Problem--
Its wisdom extraction time! This time it's trying to obtain the latest and greatest method of glueing MDF together.

--Background--
I've been making a lot of MDF things recently. LOTS of MDF things. I've been using Titebond2.

No real reason to use this over and above TB1 or TB3. I've plenty of all. All give me good glueing performance and there's no real reason to complain.

But, I have had a few occasions where there've been tricky joints (angles and multiway) that resist efficient clamping and the joints fail.

Failure is invariably due to glueing ends, or parts of machined ends, and the glue being ravenously sucked into the edges. Copious glue, squeeze out collection and a wet rag solve it, but it's a messy PITA I'd rather avoid.

--Hoping to obtain--
Is there a magic MDF glue out there? Fast acting, MDF loving, edge filling, sandable, quick setting.... And other wishful thinking attributes.....

---

up early this morning and now waiting for the sun to rise, so thought I'd take a look at 3M's info and came across their VHB tapes.
The info's a bit dense, but it appears 3M have a "magic" double sided adhesive tape (less than 3 hundredths of a mm thick) strong enough to replace spot welding, rivets and screws which, after some surface prep, essentially gives an instant bond. Being 3M it's probably too exy for all but joints that are difficult to clamp.
inter alia, 3M also appear to recommend spray on contact adhesive as an alternate MDF glue.

Another product is Instantbond (TM) -- described as an industrial strength cyanoacrylate adhesive -- appears to have similar instant grip properties.
Instantbond doesn't appear to be a 3M product.

don't know about sanding either product.
also, given that they essentially are instant grip -- there will likely be little opportunity to align teh joint once the contact surfaces have touched.