Polyester resin shrinkage. Is this a real concern?

[clockwork orange]

No problem with epoxy, depending on what the repair involved i would typically use VE or epoxy for a rudder repair

[Toccata]

Re solvent use
Thankyou "Clockwork Orange"
That was the advice I had been given from an "Old timer" (i.e. don't wipe with a solvent.) just wondered if it still applied.
Interestingly the same Old timer (naval architect, John King) specified that my yacht be built with Vinyl Ester Resins to allow sufficient flex and not crack.
Over the 12m hull length, with everything pulled on really hard, (a calculated vertical load on the mast of 15 tonne) the hull will flex about 32mm

[clockwork orange]

Yes, its just common sense really, you do a final wipe down when prepping for paint because there is always some numb nut that has run his hand over it when you weren't looking, they are drawn to the smooth surface like a moth to a flame, but its not a porous surface so you can. I don't usually see folks running their hand over a rough ground fiberglass surface so no problem there but you should cover it to protect it if not doing the layup right away, you never know what is in the air and the longer its open the more potential for contaminates. As I said earlier I don,t really use PE anymore preferring VE as the go to resin for layup, its just better all around and it typically has better tensile elongation than even many of the readily available epoxies and the cost is not too bad. That said poly has proven more than adequate when used properly for many years, I have never seen a failure that could not be traced to obvious bad prep. The same thing goes for the bad rep balsa, gets when it is always, always the fault of the builder or owner when it fails.

Steve.

[Wind River]

How long can I let polyester sit between layers?
For example, I doubt I will get this entire deck laid down in one weekend, especially if my helpers are scarce. If I only have weekends to work on it, can I start again next weekend without having to sand? I would cover it to keep anything from settling on it but other than that, can I just start again?
I planned on peelply for the last layer to completely cure it.
Would you lay up all layers as you move up the deck? Or one layer at a time over the whole thing?

[thinwater]

1. Epoxy also shrinks. Less, but measurably.


2. Most of the shrinkage occurs early in the reaction, while it is still gelling. Thus, the resin moves around just a little, accommodating the shrinkage. The part does NOT end up 2% shorter or with extreme internal stress. Obvious?

[thinwater]

Originally Posted by Wind River

How long can I let polyester sit between layers?
For example, I doubt I will get this entire deck laid down in one weekend, especially if my helpers are scarce. If I only have weekends to work on it, can I start again next weekend without having to sand? I would cover it to keep anything from settling on it but other than that, can I just start again?
I planned on peelply for the last layer to completely cure it.
Would you lay up all layers as you move up the deck? Or one layer at a time over the whole thing?

Sand.


If it were epoxy you would also have to remove the amine blush before sanding. Just sayin'.

[Wind River]

Originally Posted by thinwater

Sand.


If it were epoxy you would also have to remove the amine blush before sanding. Just sayin'.

So for the least amount of sanding, pre cut all the layers and lay them all up as I go leaving only the overlap area to sand.

Still, how long can I wait without sanding
..... overnight maybe? Or as long as it is still sticky, however long that is??

[thinwater]

Originally Posted by Wind River

So for the least amount of sanding, pre cut all the layers and lay them all up as I go leaving only the overlap area to sand.

Still, how long can I wait without sanding
..... overnight maybe? Or as long as it is still sticky, however long that is??

As long as you can dent it with your finger nail is a reasonable rule of thumb. Maybe just a little longer, but definitely sticky (that can be hard to judge with blush).


That said, there are other reasons to do it in separate steps. For example, the core will NOT go down level and you will have fill and level. This is a lot of dust, and you are probably best to do that in one go. It will come out smoother. Same with final fairing. As for laying on the top skin, you may find that goes pretty fast, particularly if you pre-cut most of the glass. Even if you can just get someone to mix resin and hand you the glass.


I'd rather not feel pressed by cure time. I'd rather sand.

[44'cruisingcat]

Originally Posted by thinwater

Sand.


If it were epoxy you would also have to remove the amine blush before sanding. Just sayin'.

With epoxy you would peelply. Any blush comes off with the peelply.

[Wind River]

Originally Posted by 44'cruisingcat

With epoxy you would peelply. Any blush comes off with the peelply.

Since the poly doesnt completely cure when exposed to air, I need to either gelcoat it with wax or peelply to seal it. Any preference?
With peelply I don't have to wash off the wax before fairing. That is why I was leaning that direction. I don't even have to peel it until I am ready to start fairing so it will stay protected until then.

[Wind River]

Originally Posted by thinwater

As long as you can dent it with your finger nail is a reasonable rule of thumb. Maybe just a little longer, but definitely sticky (that can be hard to judge with blush).


That said, there are other reasons to do it in separate steps. For example, the core will NOT go down level and you will have fill and level. This is a lot of dust, and you are probably best to do that in one go. It will come out smoother. Same with final fairing. As for laying on the top skin, you may find that goes pretty fast, particularly if you pre-cut most of the glass. Even if you can just get someone to mix resin and hand you the glass.


I'd rather not feel pressed by cure time. I'd rather sand.

I really want the most chemical bonding I can get. I guess I need to solicit some help and get this all done in one shot.

[Cadence]

Originally Posted by Wind River

I really want the most chemical bonding I can get. I guess I need to solicit some help and get this all done in one shot.

As long as you keep the sun and dew off it you are good for s day or two to maintain a chemical bond. In MHO someone read something about shrinkage, that's not an issue.

[Wind River]

Originally Posted by Cadence

As long as you keep the sun and dew off it you are good for s day or two to maintain a chemical bond. In MHO someone read something about shrinkage, that's not an issue.

Thanks. I am in a shrink wrapped enclosure so I am good.

I was the one who read about shrinkage and started this thread because of it. Happy to hear it is a non-issue.

[Cadence]

Originally Posted by Wind River

Thanks. I am in a shrink wrapped enclosure so I am good.

I was the one who read about shrinkage and started this thread because of it. Happy to hear it is a non-issue.

If you're enclosed you should be as good as gold. Just work it daily. I have said it before, wear goggles MEK peroxide can cause long term damage just a few PPM..

[jimbunyard]

Originally Posted by Wind River

So for the least amount of sanding, pre cut all the layers and lay them all up as I go leaving only the overlap area to sand.

Still, how long can I wait without sanding
..... overnight maybe? Or as long as it is still sticky, however long that is??

I assume you're talking about polyester, not epoxy.

If so, proper laminating resin doesn't have wax in it; it will stay sticky for quite a while, and will be almost impossible to sand. Polyester continues to cure for a long time after it 'kicks', the best 'chemical bond' is immediately after the initial setting, but you'll be good for at least a few days. If you want to sand, you really need to add some wax to the resin before you apply it, or, after laminating, put on a 'hot coat' with wax in it to keep the paper from loading up. I like skimming the finished layup with a coat of fairly runny glass beads (or whatever your easily-sanded-filler-of-choice is) and resin, almost all of which is sanded off. A perforated disc with a vacuum helps a lot.

Better than sanding is to do a careful, logical layup, with a minimum of staggered laps, strategically placed in either hidden or otherwise unobtrusive areas, or in the open so that they can be easily blended in after the lamination is completed.

A competent, educable helper can be invaluable in doing large layups.