Polyurethane glue in a vacuum bag?

[Peter Quinn]

Has anyone used PU glue in a vacuum bag? Any trouble with foam sticking to the bag? Does it cure? Did you have to add moisture to one side of the joint? I'm considering skinning door staves, urethane glue has been mentioned by a few door makers as a reasonable choice due to 100% water proof and zero creep plus no water content in glue to affect MC of the core. But i don't think they were using a vacuum press, so I wonder how that changes things. Not sold on this, just exploring all options.

[Mel Fulks]

No experience with vac bags.We have always used a large old press or ,in the case of just a door or two,clamps and cauls.
One of the telephone techs told me it was better not to add water ,unless moisture content of material is less than 6 percent.

[ian maybury]

Polyethylene is hard stuff to stick anything to, but PU handles a surprisingly wide range of surfaces. It needs plenty of clamping force and good fits so that the foaming doesn't push parts apart - which probably wouldn't be disturbed by the low pressure in a bag but i don't know for sure.

Which all points to it's probably being worth getting to somebody with experience as you have set out to do. If you talk to a maker it can be hard to get to somebody with specific experience - sales guys will claim the sun moon and stars...

ian

[Jamie Buxton]

Epoxy and urea-formaldehyde both work well in a vacuum bag. They don't foam, they make excellent bonds with wood, and neither sticks to the vinyl bags I use. Cured epoxy is waterproof, and urea-formaldehyde is darn near waterproof. They both have nice long open times, so you you have time to wrestle large projects into the bag. An electric blanket speeds curing after you get the bag sucked down. Unibond 800 is a good ureaformaldehyde. West Systems and System Three are good brands of epoxy.

[Peter Quinn]

Epoxy and urea-formaldehyde both work well in a vacuum bag. They don't foam, they make excellent bonds with wood, and neither sticks to the vinyl bags I use. Cured epoxy is waterproof, and urea-formaldehyde is darn near waterproof. They both have nice long open times, so you you have time to wrestle large projects into the bag. An electric blanket speeds curing after you get the bag sucked down. Unibond 800 is a good ureaformaldehyde. West Systems and System Three are good brands of epoxy.


Here in CT the shop won't be back above 70 degrees until end of May earliest. I guess the epoxy may be an option, hadn't even considered it. Can you apply the UF glue to a 60 degree substrate, bag it then bring it up to temp with a blanket? My house is not even 70 degrees, so bringing the wood upstairs wont help. Making a small area warmer than 70 is possible, but thats one more hoop to jump through, maybe a closet just to warm the wood. I can certainly make a warm box or water bath to keep the adhesive up to temp. I guess I'm looking at the tite bond PU glue because it works down to 50 degrees and has 25 minutes of open time. Only problem is the foaming. Pesky New England weather.

[Chris Fournier]

Polyurethane glue will absolutely ruin a polyurethane vacuum bag! A vinyl bag and PU will be fine. I have vinyl sheet on a roll and I make one time use bags if I think that the glue up is gonna be a mess.

Temperature is really a problem no matter what glue you use. I wouldn't use epoxy because it is a bear to clean up and if mixed in larger amounts you have to take the time to ensure that it doesn't "go exo" in your mixing pot and burn up. Besides that the epoxies I have used all like warmer temps for best results.y
Personally I would figure out a way to get the glue up to 70 degrees and then I'd use plastic resin glue (either URAC 85 or the PPR powder that you can buy). It cleans up well and is cold water proof. It really requires at least 70 degrees though!

[Mike Henderson]

I've never used polyurethane glue in a bag so I can't give any advice. I mostly use UF glue for veneer (Proglue) and it just doesn't set below 70*F - it'll get rubbery but never hard. I use an electric blanket and wrap it around the bag (put it under and over the bag). I turn the blanket on high and it works fine. I apply the glue at ambient temperature, which can be maybe 50* on a cold day and the blanket brings it up to well over 70*. It still takes a long time for the glue to set, however - I usually leave the work in the bag for 6 or more hours.

I've used epoxy when the veneer is a type that really expands when water hits it and Chris is absolutely correct - you have to keep the epoxy cool or it'll go off on you (it'll generate heat and harden up very quickly). I take ice cubes, put them in a big container, and then mix my epoxy in a separate container surrounded by the ice. I find that works well. Another way - which I don't like so much - is to mix the epoxy in a large, flat container where you can spread the epoxy out and the heat can dissipate easier. But the ice is safer.

Mike

[Mel Fulks]

Peter ,when you don't add water mist ,it actually doesn't foam much. It is hard to spread. If that is an issue Custom Pak has one that is thinner than other brands.

[Chris Fournier]

Peter ,when you don't add water mist ,it actually doesn't foam much. It is hard to spread. If that is an issue Custom Pak has one that is thinner than other brands.

PU requires water/MC to cure. Bone dry wood and PU are a combination that is bound to fail. I personally belive that this is the reason that most folks diss PU because they use very dry wood with no water. It's been a while but I think that the MC of the wood needs to be 10% or 12% for PU to cure properly.

[jerry cousins]

I use unibond - usually wrap the bag & cauls in an electric blanket set to high - while i'm setting up - mixing the glue - spreading - and securing the piece - maybe an hour total. after i put the piece in the bag i rewrap everything and then put another cover over the whole thing - usually good to take out after 3 hours unless i'm really paranoid about the piece - then i let it go for an xtra 1/'2 hour.
jerry

[Mel Fulks]

Chris, I got that from a technition at custom Pak ,not a sales man.If you have any doubt ,call any mfg and let us know what they say. The directions on packaging are for home owners not likely to have a moisture meter. On most applications a little water is fine,but adding it to stiles is not good .I am not the only one to post it can cause them to bow.I have made a large number of them over many years. Not all the stiles bow with water mixed glues ,but a lot of them do.To those who have not seen that ,you have been lucky.That's good.

[Jamie Buxton]

Here in CT the shop won't be back above 70 degrees until end of May earliest. I guess the epoxy may be an option, hadn't even considered it. Can you apply the UF glue to a 60 degree substrate, bag it then bring it up to temp with a blanket? My house is not even 70 degrees, so bringing the wood upstairs wont help. Making a small area warmer than 70 is possible, but thats one more hoop to jump through, maybe a closet just to warm the wood. I can certainly make a warm box or water bath to keep the adhesive up to temp. I guess I'm looking at the tite bond PU glue because it works down to 50 degrees and has 25 minutes of open time. Only problem is the foaming. Pesky New England weather.

Both those epoxies I mentioned have a selection of catalysts. You pick the one that suits your shop temperture. The "fast" ones can certainly cure at 50 degrees.

When I used Unibond 800 a lot (and most UF glues just don't cure below 55 or 60) I used electric blankets to make it cure. I'd lay out a shipping blanket or two to insulate under the vacuum bag, the electric blankets on top of the bag, and another shipping blanket or two on top of that. That setup can get the workpiece at least thirty degrees above ambient.

[Peter Quinn]

Looks like I'm heading to goodwill store after the holidays to pick up an electric blanket. Or two. I have 20mil vinyl and adhesive to make custom bag sizes but I've been using my large poly bag for everything , I'm thinking it would be easier to wrap a smaller bag, long and skinny for two or three stiles/ rails per shot. I'm not doing enough with epoxy presently to justify buying a hot and cold weather hardener, unfortunately we get plenty of both here. At work we use the fast cure hardener for curved jambs, two guys, room temp, go like the wind. The mc of my oak in winter is around 8%, and I'm not looking to add water to the stiles, I'd just as soon use tite bond. So I'm on the fence in light of that regarding pu adhesive. I have a kerosene heater, but appearantly they cause problems for epoxy glue ups and can lead to failure per west systems usage details.

just did some doors with a guy using my bag, used a cabinet set to make two complete door assemblies, glued them back to back to reach 1 3/4" to match wainscot, used tite bond II, worked great. Flat as can be thus far. But it's interior, controlled environment, not sure I trust that glue for stave core. How is unibond to cleanup? For instance on a shop made stave core glue up for the cores themselves?

[Mike Henderson]

Based on my experience, this is a bad time of the year to look for an electric blanket at a goodwill store (or Salvation Army store). I would go into the stores about once a week to look for one but they were always sold out. I finally found one on Craigslist.

Whatever you do, make sure you get a fairly new one and one in good condition. You don't want any chance of fire.

Mike

[Jamie Buxton]

.. How is unibond to cleanup? ..

It cleans up nicely. It bonds well to wood, but pops off anything else -- the vacuum bag, and metal or mixing and spreading tools. Before it cures, it can be washed off tools with warm soapy water. After it cures, it is nice and hard, so it sands better than PVA, which is softer.

[Chris Fournier]

Chris, I got that from a technition at custom Pak ,not a sales man.If you have any doubt ,call any mfg and let us know what they say. The directions on packaging are for home owners not likely to have a moisture meter. On most applications a little water is fine,but adding it to stiles is not good .I am not the only one to post it can cause them to bow.I have made a large number of them over many years. Not all the stiles bow with water mixed glues ,but a lot of them do.To those who have not seen that ,you have been lucky.That's good.

I'd never use PU for joinery. That's not its strength. I have a moisture meter and use it to prevent disaster.

[Curt Harms]

No experience with vac bags.We have always used a large old press or ,in the case of just a door or two,clamps and cauls.
One of the telephone techs told me it was better not to add water ,unless moisture content of material is less than 6 percent.

I haven't used polyurethane glue for a while and never in a vac bag. However, I recall that people tended to add too much water to the joint prior to clamp-up. Too much moisture makes for too much foaming and a weaker joint. I wonder though if too dry could be an issue this time of year in hot air heated spaces with really low humidity.

[Peter Quinn]

I haven't used polyurethane glue for a while and never in a vac bag. However, I recall that people tended to add too much water to the joint prior to clamp-up. Too much moisture makes for too much foaming and a weaker joint. I wonder though if too dry could be an issue this time of year in hot air heated spaces with really low humidity.


I'm wondering the same thing. Every glue I consider seems to have some imperfections. Epoxy costs a small fortune, real pain to clean, temperature sensitive. I have to match a hardener to my shop environment (which is a moving target) and cross my fingers, never quite sure what the pot life might be. I like certainty more than guess work. And it stinks. Polyurethane may or may not need moisture added, though it seems it won't following Mel's guidelines unless the air is bone dry and the wood is too. I'm making parts for exterior doors, so if my wood is 6% or less, I already have problems when they start picking up moisture in the spring. I don't like working wood that dry frankly. But 8%? Thats pretty normal for my shop, so just where is that line. UF glue is toxic and doesn't work below 70 degrees which describes my basement home shop for nearly half the year. I've got the family looking for a cheap ole electric blanket from the local thrift shops, that may help with any glue. Titebond III has served me well, though I wouldn't mind a bit more open time, and there is always the potential for creep which scares me on a product like engineered door stiles that rely so heavily on the glue bond. Actually with the shop at 55 degrees you get a bit more open time from the tite bond, so thats a plus! We used to keep it in the fridge at work in the summer before we got AC. Others have had success with it professionally doing just what I'm considering, and its easy to deal with on most other levels.

So which glue I've been wondering for years is ideal, and it seem its still an open question.

[Curt Harms]

I think TBII extend is supposed to be good for 15 minutes open time and okay to 60 degrees but there's still the creep issue. I found a tech data sheet one time for TB products, should have kept it. Here's the info on TBII extend:

http://www.titebond.com/product.aspx?id=21051713-5cce-4925-a653-3bff0a0f71ab

TBIII gives 10 minutes open time but good to 47 degrees.

http://www.titebond.com/product.aspx?id=e8d40b45-0ab3-49f7-8a9c-b53970f736af