Polyurethane glues- the foam is not for filling gaps - Router Forums
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 14 (permalink) Old 02-27-2015, 06:58 AM Thread Starter
Moderation Team
 
Cherryville Chuck's Avatar
 
Join Date: Sep 2010
Country: Canada
First Name: Charles
Posts: 14,992
 
Default Polyurethane glues- the foam is not for filling gaps

I've seen quite a few people say that they like using polyurethane glues because the foam fills gaps. The foam does fill gaps but it has very low strength because it is mostly air bubbles. Manufacturer's used to say so on their websites but seem to have taken it off all the ones I checked tonight. Maybe because they found out that the foam sells glue. I did find this info:

"Gap Filling - Polyurethane glues will fill small gaps of 1 to 2mm. For larger gaps, the air bubbles in the expanded glue create a weaker bond which will fail, so they are not advised for areas where strong bonds across gaps are required." That quote came from this website: How to Use Polyurethane Glues for Miniatures and Models

Polyurethane is recommended for tight fitting joints. The foaming action does promote stronger bonds in tight fitting joints by forcing the glue into the wood fibre creating a stronger bond that PVA (poly vinyl acetate) glues.

If you have a loose fitting joint that needs filling you should use a gap filling epoxy or a PVA glue with high solids content like Lee Valley's 202GF (the GF stands for gap filling). Gap filling glues shouldn't be used in tight fitting joints. I've split joints using 202GF because it was too thick and I got a hydraulic lock in the bottom of the joint and the excess glue couldn't squeeze out. There is no one glue that satisfies every situation you'll come up against sometimes even in just one build.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
Cherryville Chuck is online now  
Sponsored Links
Advertisement
 
post #2 of 14 (permalink) Old 02-27-2015, 09:02 AM
Registered User
 
Join Date: Jun 2011
Country: United Kingdom
First Name: Andy
Posts: 577
 
Default

Matthias at Woodgears did some testing on this, and found exactly what you described Chuck:
Gorilla glue sucks (at filling gaps)
The polyurethane glue is very weak if the joint is slightly gapped.
Remarkably, an ordinary aliphatic resin (yellow) wood glue actually gives slightly improved strength if the joint is loose! So there is definitely truth in the principle of not clamping too hard and squeezing all the glue out.
AndyL is offline  
post #3 of 14 (permalink) Old 02-27-2015, 11:33 AM
Registered User
 
PhilBa's Avatar
 
Join Date: Sep 2014
Country: United States
First Name: phil
Posts: 1,046
 
Default

Not only that but it takes time to master the amount of glue to use as you will get lots of squeeze out (more like ooze out).

The one place where it's foaming makes sense is for gap filling for insulation.

Last edited by PhilBa; 02-27-2015 at 11:36 AM.
PhilBa is offline  
Sponsored Links
Advertisement
 
post #4 of 14 (permalink) Old 02-27-2015, 12:14 PM
Registered User
 
OPG3's Avatar
 
Join Date: Jan 2011
Country: United States
First Name: Otis
Posts: 1,985
 
Default

Very good info Chuck! Thanks for posting that.

Otis Guillebeau from Auburn, Georgia

OPG3

Tweak everything!
OPG3 is offline  
post #5 of 14 (permalink) Old 02-27-2015, 02:54 PM
Registered User
 
Ghidrah's Avatar
 
Join Date: Oct 2008
Country: United States
First Name: Ronald
Posts: 1,466
 
Default

I agree, it takes practice to know how to apply Gorilla glue, If one has done a poor job of creating joints and uses Gorilla glue thinking it will solve gap problems one would be correct and that has nothing to do with the bonding strength of the glue.

I've been using Gorilla glue for about 14yrs for exterior bonding in particular. I do/did a lot of work on the ocean, none of the other glues have held up like Gorilla glue. This includes segmented load bearing columns, flower boxes, trim and for a lack of an appropriate term, applications, (wood on wood build outs to form 3D designs). For some reason I it has probs with high moisture areas, cold, salt, wind, and fir wood products in one of my work areas, Woods Hole Ma.

I love Titebond, I have and use II and III, I also use both versions of gorilla glue, along with epoxy and cyanoacrylate. I'D use PL 400 if wasn't so thick and spread resistant. I've done remodel work on houses built after 1985 where PL 200 and 400 is used to lock subfloor to joists.

I have segmented octagonal VG fir columns holding up a 14X 26 roof over a patio in the historical district facing the sound since 2003, I used Gorilla glue and biscuits to align and hold the seams together, they are still together. The previous contractor used Titebond III, biscuits and nails on a north side column rebuild, protected by the Inn less than 2 yrs earlier, the seams were separating and the nails were pulling away.

It could be an anomaly but I believe the area is a mean testing zone for materials.

Never bite the hand that looks dirty!
The more you know the more you're worth
Ghidrah is offline  
post #6 of 14 (permalink) Old 02-27-2015, 06:45 PM
Registered User
 
Phil P's Avatar
 
Join Date: Jul 2010
Country: United Kingdom
First Name: Phil
Posts: 2,117
 
Default

Hi Chuck

I'd say that if you have to fill gaps you maybe need to practice joint making a bit more (alright, maybe that's being a perfectionist, but it is true - wood fibres are far, far stronger than glue). Of course the original joint filling glue was hot hide glue, where you actually needed your joints to be a bit looser than the fabled piston fit - or you'd end up starving the joint. This slight looseness also allows for a minute swelling of the adjacent wood fibres before the glue sets

I started using industrial PU glue in the 1990s (Fuller), before "brand name" PUs came on the market. The main reason I used them was speed. I found that I could assemble and install stuff in tens of minutes rather than having to wait up to 6 hours or more for so-called (at the time) "fast setting PVA" (aliphatic) glues to go off. In recent times that has change somewhat and we now have some D-4 (water and weatherproof) cross-linked PVAs which set in under 20 minutes (the bottles say 5 or 10 minutes, phooey!). So the need for PUs has somewhat diminished. For high durability of joinery products made in a workshop environment, though, you still can'y beat a urea formaldehyde (UF or plastic resin) glue such as Cascamite - the downsides though are that it has to be mixed, there is a limited pot life and your cramps need to stay on for 12 hours, sometimes longer

Regards

Phil

"Unfortunately there is lots of bad information online; some of it is really scary. It's probably not intentional, but I've seen some content that sets up the illusion that you can do whatever you want and get away with it" - Norm Abram in an interview with Jefferson Kolle
Phil P is offline  
post #7 of 14 (permalink) Old 02-27-2015, 09:36 PM Thread Starter
Moderation Team
 
Cherryville Chuck's Avatar
 
Join Date: Sep 2010
Country: Canada
First Name: Charles
Posts: 14,992
 
Default

Ron I agree with you about using "gorilla" type glue outside like that. It's labeled as waterproof whereas Titebond 3 is really only water resistant.

Phil you are correct about getting joints too tight. If you have to beat it together and then beat it back apart it's too tight. A tenon will scrape away all the glue on the way in. It should be a slip fit, not a mallet fit.

PVA glues have improved for sure. Clamp time is way reduced but unfortunately so has open time which is not always a good thing. Although T3 claims waterproof I don't really buy into it. I would still use a PU or an epoxy. I tried the dry powder mixed with water, equivalent to your cascamite but from a hobbyist's point of view they are too much a PITA, especially when there are viable alternatives that are easier to use.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
Cherryville Chuck is online now  
post #8 of 14 (permalink) Old 02-28-2015, 09:41 AM
Registered User
 
paduke's Avatar
 
Join Date: Mar 2010
Country: United States
First Name: Bill
Posts: 1,184
 
Default

Quote:
Originally Posted by PhilBa View Post
Not only that but it takes time to master the amount of glue to use as you will get lots of squeeze out (more like ooze out).

The one place where it's foaming makes sense is for gap filling for insulation.
What is the best method to apply the glue? Was the quantity the difficult part to master?

Learning is an exciting adventure
paduke is offline  
post #9 of 14 (permalink) Old 02-28-2015, 02:02 PM
Registered User
 
PhilBa's Avatar
 
Join Date: Sep 2014
Country: United States
First Name: phil
Posts: 1,046
 
Default

Quote:
Originally Posted by paduke View Post
What is the best method to apply the glue? Was the quantity the difficult part to master?
Different formulations have different amounts of expansion and different rates of curing so you first have to try it out. I've used PU glues for building model airplanes (where lightweight gap filling can be very useful). First you need to experiment with the glue to see how much is enough but usually it is probably half what you would use with PVA style glues. Secondly, the ooze-out happens as it cures so you need to keep an eye on it. I usually scrape off the first wave after about 5 minutes and then the second wave about 10-15 minute later. You may get more even later so keep an eye on it. Cured PU cuts pretty easy. It also sands but it isn't pretty. I try to scrape it off with a knife. That said, I've never used it for woodworking - titebond uber alles.
PhilBa is offline  
post #10 of 14 (permalink) Old 02-28-2015, 04:25 PM
Registered User
 
Phil P's Avatar
 
Join Date: Jul 2010
Country: United Kingdom
First Name: Phil
Posts: 2,117
 
Default

Quote:
Originally Posted by Cherryville Chuck View Post
I tried the dry powder mixed with water, equivalent to your cascamite but from a hobbyist's point of view they are too much a PITA, especially when there are viable alternatives that are easier to use.
Hi Chuck

As you know I come from a more "industrial" woodworking background. Certainly for joinery such as laminated spars and structural woodworking components there is just no alternative in terms of strength. The downsides, however, make them a lot less attractive to hobbyists as you have stated. Plus you need to use masks when mixing the powder (though only when handling the powder forms) and some people (very few) need to wear gloves as they can be sensitive to skin contact

Quote:
Originally Posted by PhilBa View Post
Cured PU cuts pretty easy. It also sands but it isn't pretty. I try to scrape it off with a knife. That said, I've never used it for woodworking - titebond uber alles.
The biggest issue with it is that if it foams out onto an open-grain timber such as oak or ash you will never get it out of the grain unless you've already lacquered/varnished the wood. No matter how hard you sand or scrape as soon as you put a clear finish over the top that scraped-back glue foam-out just screams at you. Personally, even after 20 years of using the stuff, I've never found an accurate way to estimate how much glue I should apply to a joint to avoid squeeze-out - there are just so many variables from air temperature to air moisture content to species of timber and looseness of joint - and I do this for a living, so I've had a lot of practice using the stuff. So for work to be clear finished I'd say apply with caution - and preferably do your finishing before assembly

Regards

Phil

"Unfortunately there is lots of bad information online; some of it is really scary. It's probably not intentional, but I've seen some content that sets up the illusion that you can do whatever you want and get away with it" - Norm Abram in an interview with Jefferson Kolle
Phil P is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Router Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
Turning foam on a lathe? Bulldogg629 Woodturning and Lathes 9 07-01-2012 03:16 AM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome