Polyester resin: life & thinning with styrene

Am making some composite panels using polyester laminating resin. Store and used at 65F. My container is 3 years old and seems a bit thicker. Is it recommended to add a small amount of styrene to renew the viscosity?

Also, would adding a small amount of styrene to fresh new resin help the fabric adhere better to a pine 2x6 beam?

Thanks

 

The reason for it being thicker is because it's begining to cross link, adding styrene will reduce the viscosity, but it's not that good for the resin. The bigger issue is being that old it may not cure well, so while it may seem to get hard, it could have significantly reduced physical properties.

Adding styrene to new resin to get a better bond to wood seems like a good idea up front, but the chemistry starts working against you rather quickly. Adding more than a very small amount of styrene (2% or so) can have a big effect on physical properties, this includes water resistance and crack resistance, plus the penetration into the wood is only marginally better.

Pre coating the wood and allowing it soak in does a better job, or buy some infusion resin for pre coating the wood.

 

Thanks,

For the first resin application of wood, maybe it will help warming the jar (100F), catalyzed for a slow cure and let it tack up before applying resin and fabric. Again, I would be using laminating resin.

 

Yes, the first coat needs to begin to harden before applying the laminate, otherwise the laminate can suck resin out of the wood.

 

The previous coat needs to "stiffen" up enough, to support the weight and chemical realities of subsequent applications (regardless of what they might be). This is true of most things, such as subsequent layers of varnish, being applied over previous layers, not sufficiently stiff enough to support it's weight, without sagging, etc. Polyester adds a chemical activity window to the equation.

 

Some boat builder, some epoxifier ( I can't think of his name, he had that shallow draft tunnel drive boat, Rescue Minor, and built his first boat from a sheet of roof tin,) would heat up the wood first, and then apply resin. Claiming that as the wood cooled it would suck the resin in deeper than it would by applying warm resin to room temperature wood, I think he would turn off the heat and open the windows to cool the wood down after coating with resin.

 

3 yr old poly should be ok and probably seems thick just from low temps. Try warming and see what happens. Prep polyester, not wood, with a styrene wipe down. Like already posted, use laminating resin. Brush a coat on the wood and let soak a few minutes before lamination begins. Pine will not (enough to be concerned) soak much resin but the reason for coating the surface first is to keep it from sucking resin from the cloth, resulting in a dry layup...and usually a "pin" bubble at every weave. Foam sucks more and is where the dry lamination concern really is. "Peck" the wood with an ice pick before glassing if you are concerned with adhesion of the laminate. I made a tool to do it faster but an ice pick will work.

Good luck

E

 

The name of the guy who used the thermal gradient routine is Rob White, a really clever and well educated marine biologist type country boy from Thomasville Georgia. He was a profane writer and skilled raconteur who was a fun guy to be around. He was known for his exploits with the unique Atkin tunnel stern boat; Rescue Minor. It was a remarkable piece of work. Rob used a small Kubota tractor diesel to make the thing go.

 

Endarve,

What did you mean to "prep the polyester with a styrene wipe down?"

Thanks

 

With 3 year old resin that may be starting to cross-link, definitely do a test piece on some scrap. Use EXACTLY the conditions you will be using in the actual wet layup.

Test the piece for a while thoroughly before you procede with the actual workpiece.

Otherwise, buy new resin.

 

I kept thinking 'Ron White, no...it can't be him'.

 

When laminating new polyester to old polyester, clean and degrease the surface first and then do a final wet wipe down with styrene before glassing the two together.

E

 

What does a stryrene wipe do, be specific.

 

Not sure where to go with this one, lots of not so accurate info here.

 

Agree with the evaluation that 3-year-old resin that seems thick "should be OK", etc. , is not accurate. That is why I suggested the test on scrap, but looking back at it, you're talking about a lot of work and probably expense, so just buy fresh new resin, period.

Regarding pine "NOT sucking up a lot of resin" is highly variable - some pine does and some pine does not. The previous advice to coat the wood with thinned resin (a 2nd coat of normal viscosity resin may be in order if it sucks up a lot) until green stage and THEN adhering laminate wet layup is good advice.

I'll add the advice to slap the whole shebang under a vacuum bag (or wrap it under tension with strips of bicycle inner tube or shrink wrap) until fully cured. Are you familiar with vacuum bagging?