Polyester resin shrinkage. Is this a real concern?

[thinwater]

Just a small polyester project from a while ago.


The top layer just pulled off once the edges were cut loose.




Before painting. I use the same fillers I use with epoxy.





That said, I used epoxy for some rudder repairs done the same day.


Sail Delmarva: Rudder Rebuild and Adding a Fence



BTW, you can get bi-ax cloth with a thin mat attached (1708). Nice product, epoxy or polyester.

[Cadence]

Originally Posted by Wind River

Thanks everyone for the input.

Steve (and others) - I think you really said what I felt in my gut was correct. I had referred to several deck recore thread here on this forum where Miraret and other professionals were giving advise to another DIY member with a similar project. Not to leave out any of the reputable professional members of this forum (thank you all and you know who you are), but I have followed Minaret's work and advise here for quite a while have grown to trust his recommendations, but all of you pro's seem to agree on most things fiberglass.

In my down time I kept reading and seemed to find more of the #NeverPoly and #NotMyResin kind of posters arguing the benefits of epoxy to the pro's and the pro's just were not taking the bait. As Steve points out, many of these posters were amatuer DIY guy's like myself and probably want to err on the side of the most tenacious bond they could get, maybe, just in case they didn't really understand what the mechanics were of what they were doing as they don't have as much experience with it.

"Experience is something you get only after you need it"

There is no argument that epoxy adheres better than polyester and that is my concern..... making sure the new glass never detaches from the old glass. This is a huge project for a pro, let alone a DIY'er like me. I don't want to ever have to redo this. I have the 12:1 scarf, I have sanded the surface with 36 grit sandpaper and it will be cleaned with Acetone before the new glass is applied. Another pro on this forum (JohnMardall) has suggested adding a series of holes in the old laminate to add a "geometric bond" as well. I really like this idea, thanks John. (see his recommendation here: http://www.cruisersforum.com/forums/...ck-209370.html )

It seems idle minds create their own demons and that is what happened here with me. I never read any discussion of this shrinkage issue before and when I read this article, the alarms went off. I thought I was pretty well read on the subject until that.

I will do it like the pro's and use Polyester.

Thanks everyone.

Re: holes a good idea but make them closer the dimples in the old glass. Getting resin in anything more would be a problem and remember resin in itself has little strength.

[MartinF]

Just a math point (which doesn't really affect the practical discussions above). If you (eg) increase the size of an object such that its length increases by 50% the the new length is Lx1.5, new area is Vx1.5x1.5, and new volume Vx1.5cubed. So if the volume shrinkage is 7% the new length of 30ft is 30x(cube root .93), about 9" shrinkage.

I hope your job goes smoothly,
M

[Wind River]

Originally Posted by MartinF

Just a math point (which doesn't really affect the practical discussions above). If you (eg) increase the size of an object such that its length increases by 50% the the new length is Lx1.5, new area is Vx1.5x1.5, and new volume Vx1.5cubed. So if the volume shrinkage is 7% the new length of 30ft is 30x(cube root .93), about 9" shrinkage.

I hope your job goes smoothly,
M

I love math, it doesn't lie and doesn't have an opinion. I just kind of suck at it.

So, since I don't know how to apply what you have added here, does you think that the shrinkage within larger area/volume is more of a stress on the bond line as the Epoxyworks article suggests?....... Or less?

It's still seems irrelevant though, as the pro's here seem to all agree this is a non-issue. Just curious.

[MartinF]

The math says that shrinkage in 30ft is 9", not 25". But I agree with you; its irrelevant. You should follow the pros.

PS. I envy your courage in undertaking such a big job yourself.
Good Luck,
M

[TeddyDiver]

Originally Posted by MartinF

The math says that shrinkage in 30ft is 9", not 25". But I agree with you; its irrelevant. You should follow the pros.

PS. I envy your courage in undertaking such a big job yourself.
Good Luck,
M

Besides the shrinkage is not equall to all directions. If it were think what would happen for a boat laminated in a mould, just pop of so fast as the resin cures
But instead it's practically only thickness which chances and becouse of the fibers in the laminate it just makes a visible imprinting of the fabric which of course you fill with filler. The same applies for epoxy too.

[Wind River]

Originally Posted by MartinF

The math says that shrinkage in 30ft is 9", not 25". But I agree with you; its irrelevant. You should follow the pros.

PS. I envy your courage in undertaking such a big job yourself.
Good Luck,
M

Like I said, I suck at math.

I am a professional in my field and with the right tools and good information most people can do what I do. I believe I can do the same with my boat.

[coopec43]

Originally Posted by Wind River

Like I said, I suck at math.

I am a professional in my field and with the right tools and good information most people can do what I do. I believe I can do the same with my boat.

Windriver

I think you are doing fine.

You are not like the young bloke who decided to build a boat and sail the world. He built a ply yacht and sailed but the yacht fell to bits in Africa(?). He built a new yacht but this time using marine ply. ( He hadn't heard of "marine ply" before!!)

Clive

[thinwater]

Originally Posted by Wind River

Like I said, I suck at math.

I am a professional in my field and with the right tools and good information most people can do what I do. I believe I can do the same with my boat.

Are you good at calculating big tips?

[Wind River]

Originally Posted by thinwater

Are you good at calculating big tips?

If purchasing one of your books counts as a tip, then yes!

[sainted]

When I was having the trailing edge of my keel repaired a while back, the fiberglass guy said that shrinkage would be a problem if he laid up the two sides at different times. He said that the one side shrinking would cause the end of the keel to pull to the side with the newly laid laminate, causing it to curve.

I think the effect of shrinking was only an issue with this specific application, though: a thin structure that was not well supported, unlike your deck.

[Toccata]

A question for the professionals
Re your preparation phase:
Is there an issue with acetone creeping along the old glass fibres and contributing to a weaker job in the end???? OR is this old thinking and the volatility of the product is so great that it is not an issue???

[thinwater]

Originally Posted by Wind River

If purchasing one of your books counts as a tip, then yes!

I'm much obliged!

[clockwork orange]

Originally Posted by Toccata

A question for the professionals
Re your preparation phase:
Is there an issue with acetone creeping along the old glass fibres and contributing to a weaker job in the end???? OR is this old thinking and the volatility of the product is so great that it is not an issue???

I never wipe down a ground laminate such as a scarf with any solvent since it is absorbent, just grind and vacuum or blow off with filtered compressed air. If you are not laminating right away cover it to protect from contaminates. The only time for a solvent wipe is on non absorbent surfaces such as in paint prep. You wouldn't solvent wipe wood either when prepping for gluing. A ground laminate is quite porous which makes for good bonding, the scarf ratio provides adequate surface area, exactly like working with wood. Pre-coat the scarf with resin before starting the laminate to give it time to soak in so you don't starve the joint. Its exactly the same as scarfing wood. The same applies regardless of the resin system used.

Steve.

[Wind River]

Originally Posted by sainted

When I was having the trailing edge of my keel repaired a while back, the fiberglass guy said that shrinkage would be a problem if he laid up the two sides at different times. He said that the one side shrinking would cause the end of the keel to pull to the side with the newly laid laminate, causing it to curve.

I think the effect of shrinking was only an issue with this specific application, though: a thin structure that was not well supported, unlike your deck.

I will be rebuilding/building my rudder. I will be using epoxy for this though. Curious if this an issue with building rudders?