Apply cascamite glue to one or both surfaces?

[Harrris303]

Hi all, I've never really used cascamite glue before but I just bought a tub of powder and was quite surprised to read in the instructions that the glue should only be applied to one surface.
I was taught joinery using mainly PVA and religiously told to apply it to both surfaces. Admittedly I was never really told why that was the best way, but I assumed it was just to ensure the glue was spread thoroughly into texture of the wood and got a good grip on both parts of the joint.
I've got a feeling it's probably one of those things which just comes down to personal preference but I thought I'd check on here and see if anyone has any little nuggets of info which might be useful.

Thanks in advance.

 

[deema]

I've only ever with Cascomite coated on one surface as per instructions, never had a problem. Although it says its dry in a day, I would wait until it turns to a glass like finish before sanding it. If when you start to sand down its a little soft, wait a little longer.....another night! When it's like gkass it's very easy to sand down / chip the excess off.

I always glue up a couple of scrap pieces when I first start building something to test the glue. I use the hammer and see where it breaks routine to check that the glue is OK. I also repeat when mixing up for the real stuff, especially when its cold. If it freezes, it's scrap. Better to find out before you deliver it than after you've installed it.

 

[Phil Pascoe]

If you read the instructions on (most,afaik) PVA they'll tell you to apply to one side only.

 

[Harrris303]

Oh right do they? I just did what I was told by my tutor so never bothered reading the instructions on PVA! I'm pretty sure my textbook said apply to both sides too. I can safely say with PVA it doesn't do any harm to glue both parts, and having trawled the internet it seems maybe it is just a matter of personal preference. Of course gluing both parts you use twice as much glue and more time, so there is that to be said for just doing the one side.
Thanks for the tips Deema, I'll bear them in mind. Luckily I've found a big enough space inside to get it glued up so the temperature shouldn't be a big issue this time. Good to know all that with winter coming though!
Cheers.

 

[Jacob]

I always do both sides 100%. You can't rely on it spreading evenly - try pulling a few pieces apart before it goes off and you can see for yourself.
Some joints are very weak if there isn't 100% glue in the join - not enough glue spread is much the same as a crack in the material. Conversely it'll be very strong when there is 100% glue.
e.g. edge glued boards - more likely to break in the wood than along the glue joint, and no need for dowels, dominoes etc except as locators. Best avoided if poss as they themselves become weak spots.

 

[RobinBHM]

Applying glue to both surfaces is almost certain to yield the the best joint since there can be no areas which are not fully wetted. Of course it depends on the application, I would always prefer to apply glue to both part of a M&T joint, but may not bother when butting up boards to form a table top.

UF glue is easy to clean up (with a wet rag) and has a long working time.

I remember visiting a Spanish bed slat making factory many years ago and they added a percentage wheat flour to extend its coverage, so it must be pretty strong anyway!

 

[Phil Pascoe]

Yes, I always coat both sides well - I've never heard any valid reason given for not doing so. (Or any invalid reason, come to that.) I've raised the question here before, but no one seems to have an answer to why that is the instruction given.

Robin - "Applying glue to both surfaces is almost certain to yield the the best joint" - I agree 100% - but why do manufacturers specifically tell you otherwise? There has to be a reason.

 

[Kalimna]

In answer to the 'Why are we told one surface only?' question, I also suspect (but have no evidence for) that there is a good reason why. Two thoughts spring to mind :
1) If it really didn't matter, then there is no reason for manufacturers to suggest using, effectively, half the quantity of glue per join. i.e. they would be advocating fewer sales of their own product.
2) If, in general, it's the case that thinner glue lines lead to stronger joins, then would it not place greater emphasis on clamping pressure to squeeze out the inevitable excess? I'm not sure whether this has much effect in most cases, but it's just a thought.

Cheers,
Adam

 

[Jacob]

Applying glue to both surfaces is almost certain to yield the the best joint since there can be no areas which are not fully wetted. Of course it depends on the application, I would always prefer to apply glue to both part of a M&T joint, but may not bother when butting up boards to form a table top. ...

I do it the other way round - a M&T is partly mechanical and not 100% dependent on the glue but board edges are wholly dependent. If the table top shifts at all a weak glue joint is the most likely place to go first, but a strong one may survive. Bin there dunnit.

 

[RobinBHM]

I've always believed that the reason is because some glues are single application, such as PVA, UF, PU whilst UF glue with a hardener may be separate application (glue on one surface, hardener on the other) or contact adhesive which is of course applied to both surfaces.

 

[Sgian Dubh]

I strongly suspect the 'apply to one surface only' guidance is to help bring the two parts together quicker so that necessary pressure can be applied within the approximate ten minute window available with most of the adhesives mentioned so far. Most manufacturers indicate the maximum allowable working time from first application of the adhesive to parts to the time you need to walk away from the completed glue-up, and in most cases this is the ten minutes I mentioned above. After this ten minute window, if you're still fiddling to get clamps in place and the job sucked up tight you're breaking the adhesive bond.

I've seen quite a few inexperienced workers assemble fairly complex bent laminated work in multi-section male/female formers, for example, with urea formaldehyde adhesives (Cascamite being one type) and fail. The failure in almost every case I can think of has been down to the time required get pressure on, up to 45 minutes in some cases, which is about 35 minutes too long, and the failure shows up as layers simply not bonded.

Having said all that, I quite frequently apply glue to both surfaces to ensure full coverage, and as others have said, M&Ts are a good examples for doing this, whereas plain panel edge joinery only needs adhesive applied to one surface, followed perhaps by rubbing the mating edges together to spread the viscous liquid evenly, then clamping the job up. Slainte.

 

[Phil Pascoe]

I think I'd used Cascamite for about 20yrs before I realised there was a hardener for it. Phosphoric acid? Formic acid? One or the other- I used to have both, one for Aerolite and one for Cascamite although they appeared pretty much interchangeable.

 

[Max Power]

I was reading a wheelwrights blog where he was laminating blanks from 1 1/4 " boards to make into hubs using cascamite and recommended sanding the faces with 60 grit to improve glue absorption. Is there any benefit to be gained from this ?

 

[Mike.S]

When making up boxes from MDF I found I had to apply cascamite to both surfaces, otherwise the MDF 'sucked up' the glue and left a dry joint. Joints still strong 12 months on.

As well as making it go further, I believe Wheat flour is sometimes added to cascamite to give it 'body' - i.e. more viscous so that on, for example, vertical surfaces it doesn't run so much.

 

[dickm]

I think I'd used Cascamite for about 20yrs before I realised there was a hardener for it. Phosphoric acid? Formic acid? One or the other- I used to have both, one for Aerolite and one for Cascamite although they appeared pretty much interchangeable.

Are you sure you are thinking of CascaMITE, rather than CascoPHEN? Had never heard of using a separate hardener for 'mite, but the 'phen (a phenol-formaldehyde rather than urea formaldehyde) only worked with a hardner, with the adhesive on one surface and the hardner on the other. Unless, of course, memory is playing tricks .

 

[Phil Pascoe]

Yup. Definitely Cascamite. Handy for rapid repairs - if mixed with the powder rather than put on the opposite side, it goes rock hard in about two minutes. I've not used Cascophen.

I should have said - this was about twenty five years ago, it doesn't follow the stuff's still marketed. Nothing to stop anyone trying another acid on some scrap, of course.

 

[Chrispy]

Yup. Definitely Cascamite. Handy for rapid repairs - if mixed with the powder rather than put on the opposite side, it goes rock hard in about two minutes. I've not used Cascophen.

I should have said - this was about twenty five years ago, it doesn't follow the stuff's still marketed. Nothing to stop anyone trying another acid on some scrap, of course.

K10 was I believe sold as an accelerator for cascamite put on one side of the joint, but a friend of old just used oxalic acid either mixed in or on the other face.

 

[Peter Sefton]

I have K10 in the workshop but more for an example than for use. I did used to use it before we got involved with low voltage and RF (back in production days). We stopped using K10 as I felt it weakened the joint.