Problems With Glass Fibre Fabrications

[Ian M]

Nothing to do with boats, but I am hoping that someone on here with more experience than me in glass fibre fabrication may be able to offer some suggestions.
We have had some fibreglass fabricated sections produced. These are a gelcoat outer,/matting/foam/matting/flowcoat sandwich. At this stage I do not know what resin or foam is used, or the manufacturing process. I will get more facts in the coming weeks. I guess the foam is approximately 10-15mm, and I suspect that the foam core is applied 'wet' as the sections are curved in two directions. The foam is closed cell.
We are told that the layup is carefully controlled, as the characteristics and especially thickness of the various layers is important to the finished product.
The problems with these sections are ‘bubbles’ at the outer surface. At this stage I do not know whether these bubbles are just under the gelcoat or affect the fibreglass layer as well.
Despite these sections being produced in a carefully controlled process (so we are told), these ‘bubbles’ are a reasonably frequent occurance, and that a remedial process is to drill the affected area, with a 2 or 3mm drill and inject an epoxy and then clamp the bubble to compress it and hence rectify the problem.
We are not too happy with this problem. Our ‘uneducated guess’ is that something is causing outgassing, but what? Has anyone any ideas, or things that I should check when I visit the manufacturers?

[Dirk Diggler]

Closed cell foam??? not sure what you mean by that.

Are these products being made in a mould, or is it sheet foam being laminated on both sides?

[Ian M]

Originally Posted by Dirk Diggler

Closed cell foam??? not sure what you mean by that.

Are these products being made in a mould, or is it sheet foam being laminated on both sides?

Closed cell means that the individual gas pockets are not interlinked, so that for instance water cannot migrate through the foam. Wet suits and drysuits are made of closed cell foam for obvious reasons.
Each section has an area of very approximately 2 square metres. Yes a mould is used in the manufacture.
I will be questioning the manufacturers on the details of the manufacture later in the week. It is not clear to me how they maintain a uniform thickness unless, as you hint, they are using a slab of foam. If that is the case I want to know how they cause it to bend in two planes at once to fit the required shape.
As I said before, I do not yet know what the foam is or what resin they are using, so lots of questions to be answered. Can you suggest questions that I should be asking?

[Dirk Diggler]

Sorry, I understand what closed cell foam is, when used in laminating. Divinycell or something similar.

Just suprised that it's being used for a "dual plane curve" structure, as it's normally pretty rigid, so I cant see how you would get it into the required shape for laminating.

[colcreate]

I have had problems with flowcoat on occasion when the wax has formed what is commonly referred to as fisheyes, small blisters where the resin has separated on the surface. I was told it was the wax coming out of solution because of an inconsistent resin mix.
Blisters under the gelcoat of a moulded item can be trapped air if it is not rolled firmly when laminating. Too hot a mix or damp conditions can cause all sorts of problems as can some release agents that are not applied properly. You might need to slice a few cross sections to determine at what stage the problem has occurred at; surface, gelcoat, flowcoat, laminate or bond area between any of the above

[C-NUMB]

Temperature control might be one reason. If the mould or the resin is different temperature than ambient during laminating, trapped air might expand causing bubbles. Or if the temperature changes plenty during curing proses.

Laminating timing worth checking. If the gel coat is cured before laminating as it should, bubbles should not occur.

The core might be another issue. Maybe worth checking, is it 100% compatible with the used polyester(?), Divinylcell or other known brand should be ok. Check also is it really closed cell.

[Chris]

Ian why dont you give Mike Whitham a call?

[Cookee]

Without actually seeing a section it's hard to speculate on how it's happening but I can tell you it is possible to make that product without it happening!

[Neville]

It could be expanding air or gas due to heat buildup (exotherm) making the air or gas in the core larger , it forms a bubble under the laminate or gelcoat and gets hardenned in.

I have had problems with this in the past using cores (foam, nidaplas & balsa).

The trick was to get the lads to undercatalyse slightly which will create slightly less heat, or dont apply as much laminate in one go.

Working with cores although not rocket science is a skilled job and if done on a production level in a factory it needs to be supervised carefully by someone who has the correct knowledge and gives a toss !