MINERVA POLYMER UNDERPIN ?

[BRUMMIEFRAMER]

I have superglued a polymer frame ,it feels strong , i am reluctant to underpin and possibly cause gaps, what would you do ?

[framejunkie]

I'd avoid polymer mouldings, but that doesn't help you.

I'd be reluctant to leave a frame held together by adhesive alone. Especially using a cyanoacrylate adhesive('superglue'), as they all tend to be very brittle. It would help if you use a narrow-crown stapler to fit the thing up so you can fire through the backing and it'll hold the thing together if the joints fail, but even so...

[Nigel Nobody]

I've been supergluing plastic frames for many years. Always underpin after around 10 minutes.
It strengthens the joint the same way as in wood joints.

The glue is no more brittle than the plastic!

Test a few joints by gluing, underpinning then break the joint on the edge of a table. The glued joint will not break where there is glue contacting both sides of the joint. It will break at around the extremity of the vee nails in a jagged sort of way.

[Bagel Framer]

I used to be very wary of Polymer frames, but now can't get enough of them and think they're great.

Each one to his own but I glue them with Mitre Mate or Bison - I learnt this week that you can using Mitre Mate with just the adhesive, this gives you five minutes to get things right rather than the standard 10 seconds (this has yet to be tested by me though).

I also found that you have to commit to the underpinner process and it's fine then.

[Martin Harrold]

Very interesting. Let us know here how your tests go.

[Jonny2morsos]

Found a replacement for your Plastibond adhesive yet Martin?

I find it works well in addition to underpinning (in correct position). I am down to my last tub by the way.

John.

[Martin Harrold]

It should be back into stock in the next 2/3 weeks.

[Not your average framer]

I also am not the bigest fan of polymer moulding, however there are some which are so stunning that I have recently relented and started offering to my customers.

Perhaps I may offer a few basic points to consider:

Real wood mouldings derive a lot of strength from the structure and grain of the wood. This means that we get used to what we can get away with and rarely end up with the metaphorical "egg on our faces".

Polymers are very different materials! We ALL need to be extra careful how we join polymer mouldings as the structural characteristics of these materials can be affected our placement of the wedges. That little bend at either end of each wedge is creating a small discontinuity in the structure of the material. As we add more wedges across the width of the moulding, these little discontinuities can form a line of weakness, so go easy on the number of wedges, how close you place them and take care where you place them.

I prefer to use the "hard wood" versions of wedges in polymer mouldings as they have less of a tightening effect on the joint when inserted. This will result in less stress within the material and therefore less vunerablity to a later stress induced failure.

If you are using any adhesives of any sort, in any process as a framer, then you need to understand as much as can, where it is relevent to each and every use you have for that adhesive. These are scientific products with highly defined and specific characteristics, which are worth getting to know about. There is no such thing as an absolutely perfect adhesive for any and all applications. They ALL have pro's and con's.

The solvents in many solvent based adhesive will penetrate and prehaps modify the characteristics of the polymer materials in these moulding and these effects may not be immediately obvious. Generally, there should not be any substance in these adhesives to corrode the steel wedges.

Generally "Superglue" type adhesives can over time absorb moisture from the air and this can effect the structural strength of the adhesive itself. Some later types of this have been reformulated to help improve this problem, but it is a known factor. Again, there should not be any substance in these adhesives to corrode the steel wedges.

Waterbased adhesives do not have the advantages of a solvent based bonding process, but there are not usually any serious clean up issues if you get any adhesive onto the finished surface of the moulding provided you wipe off any surplus immediately. No significant proportion of the water component in these adhesives when applied can be absorbed into the moulding, such as with a wood moulding. As some waterbased adhesives will cure from the outside inwards and may take time for the water to fully escape. There may be some resulting undefined rust issue to the wedges. I have observed this effect for myself, but don't know if it is a significant issue.

In general, most adhesives have self life and service life issues.

If in doubt, try them all and then decide which one works for you. I usually use a solvent based adhesive, but I must try Lion's plastibond sometime, (no clean up issues).

[Martin Harrold]

I'm humbled.

I've learnt more about adhesives in framing by reading this posting than in the past 30 years.

[Not your average framer]

Hi Martin,

It's all there in the small print on the product data sheets, application notes and generic information in books and websites. Sometimes you need to read between the lines, as manufacturers often don't like to admit their products have limitations. I used to be a design engineer, so I had to read a lot of stuff like this.

A lot of the time, most of us don't need to know much about all this, but the extra info can be very helpful in giving us confidence in how we are doing things. Also, there are times when some of us, will need to push the limits to do something particularly difficult and demanding. Sometimes, the right knowledge can be very empowering!

[Martin Harrold]

For info, our Lion PLASTIBOND is now in stock again. Forumers feedback on it always welcome.

[guzzijim]

So are you guys using two-part superglue or coating both surfaces with superglue?

[Nigel Nobody]

I only put spots of superglue one side of the joint, then hold the two parts together with a firm pressure and wait around 30 seconds or so before letting them go. If you try to 'coat' a surface, a lot of the superglue will run off.

[Not your average framer]

Plastibond may just be something you ought to try if you are finding superglue problematic. If as I am led to believe that Plastibond is a waterbased adhesive, then it may perhaps result in a less brittle bond, but this would depend upon the type of adhesive or polymer employed. Many water based polymers have a reasonable degree of flexibilty or elasticity, but not necessarily all as some waterbased adhesives have very little elasticity at all.

It's all to do with a materials "Young's modulus of elasticity". Those who are interested may like to Goggle the subject to learn more. In simple terms, is how far a material may be stretched or deformed before it becomes permanently deformed or fractures. In the case of superglue, it has very little elasticity, so it is brittle.