Fibreglass laminating query

[Avocet]

I need to lay up a small area of GRP about 12mm thick. Does anyone know how much I can put on at once before risking it going up in smoke? I'm using 2% catalyst and it's ordinary polyester resin.

If I can't do this all in one go, will I have to sand the previous layer as soon as it is cured before putting the next one on or can I let each couple of layers partially cure and then slap the next couple on while the first ones are "green"?

Any thoughts gratefully appreciated!

<hr width=100% size=1>

 

[30boat]

Hi
If the area you are laminating is reasonably flat and well ventiladed , you can do it in one go.If it is shaped in such a way that the curing heat can't escape easily it would be better to do half first and when the first layer starts to cool then laminate the rest.There is no need to sand between layers providing you don't wait for more than two days or so.In the first few days after hardening the curing process is still going on and there will be a chemical bond with subsequent layers.
Remember to thoroughly abrade the base fiberglass before you begin.
Hope this helps.

<hr width=100% size=1>

 

[oldsaltoz]

G'day Ian,

Sounds like this might be below the waterline at 12 mm thick; if this is the case then I would use only epoxy resin, as it will provide a much stronger bond. Appling a standard wax resin over standard laminate will not give you a chemical bond if the original material is old (8 weeks max) but an epoxy will, also note that below or above the waterline, epoxy is lighter and stronger.

Most of the heating will be towards the end of the reaction in standard or epoxy resins, if it overheats it will crack and be very weak, both epoxy and standard resins leave a residue as a result of the curing process, so they should cleaned off prior to sanding, as sanding will end up spreading the contaminant if not removed first, and may cause delamination down the track.

I hope this helps.

Andavagoodweekend....



<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[Avocet]

Thanks chaps.

Just to give a bit more detail, it's not below the waterline, it's the underside of the coachroof. The reason it has to be thick is that it's directly under the mast "shoe" and is repacing a wooden plank. Last season, I noticed a hollow in the coachroof as if my mast was "sinking" through it. That's exactly what was happening! At that point in its construction, the builders laminated a 1/2" piece of plywood about 6" wide into the layup to give it a bit more stiffness. Over the last 30-odd years, water must have been seeping down the bolts that held the mast shoe through the coachroof and the wodd had rotted. Once I cut away the GRP underneath, I was able to scoop most of it out with a teaspoon! I decided I'd replace the plywood plank with a GRP "plank" so in answer to some of the questions, it doesn't need to "stick" particularly well - it just needs to fill a 1/2" gap. I can't lay it up out of the boat because it passes over an internal stiffener running athwartships so I wouldn't be able to bend the finished item enough to feed it in.

The reason I was asking about laying up in stages was because I'd heard that laminating resins have wax inhibitors in them which form a skin over the exposed surface (the one away from the "mould") so that the resin cures. Apparently, it won't cure if it is exposed to the air so I was wondering whether I'd have to grind the surface between successive layers to remove this "wax" (if it's true!) I don't know if I'll be able to lay up too much in one go because I'm working upside down. On the other hand, grinding GRP upside down in a confined space isn't right up there with the most pleasurable experiences I've had in my life so far! Finally, You're right Oldsalt, I think I'll use epoxy when I come to put the "bottom" skin back. because this obviously will have to be strong. The "plank" doesn't - it just needs to stop the bolts crushing into it when tightened.

P.S. Don't panic! this doesn't take the downward load on the mast exerted by the stays - that's done by the main bulkhead!

<hr width=100% size=1>

 

[simisoon]

Delaminating a laminate

Dear Friends,

Could someone be kind to advice as to how do i post a new query. I have an issue of delaminating and using a molded laminate which is 8 years in the mold to protect the mold.

Thanks chaps.

Just to give a bit more detail, it's not below the waterline, it's the underside of the coachroof. The reason it has to be thick is that it's directly under the mast "shoe" and is repacing a wooden plank. Last season, I noticed a hollow in the coachroof as if my mast was "sinking" through it. That's exactly what was happening! At that point in its construction, the builders laminated a 1/2" piece of plywood about 6" wide into the layup to give it a bit more stiffness. Over the last 30-odd years, water must have been seeping down the bolts that held the mast shoe through the coachroof and the wodd had rotted. Once I cut away the GRP underneath, I was able to scoop most of it out with a teaspoon! I decided I'd replace the plywood plank with a GRP "plank" so in answer to some of the questions, it doesn't need to "stick" particularly well - it just needs to fill a 1/2" gap. I can't lay it up out of the boat because it passes over an internal stiffener running athwartships so I wouldn't be able to bend the finished item enough to feed it in.

The reason I was asking about laying up in stages was because I'd heard that laminating resins have wax inhibitors in them which form a skin over the exposed surface (the one away from the "mould") so that the resin cures. Apparently, it won't cure if it is exposed to the air so I was wondering whether I'd have to grind the surface between successive layers to remove this "wax" (if it's true!) I don't know if I'll be able to lay up too much in one go because I'm working upside down. On the other hand, grinding GRP upside down in a confined space isn't right up there with the most pleasurable experiences I've had in my life so far! Finally, You're right Oldsalt, I think I'll use epoxy when I come to put the "bottom" skin back. because this obviously will have to be strong. The "plank" doesn't - it just needs to stop the bolts crushing into it when tightened.

P.S. Don't panic! this doesn't take the downward load on the mast exerted by the stays - that's done by the main bulkhead!

<hr width=100% size=1>

 

[nigelmercier]

Dear Friends,

Could someone be kind to advice as to how do i post a new query...

The +Post New Thread button, about half way down the page, under all the dross...

 

[lw395]

Thanks chaps.

Just to give a bit more detail, it's not below the waterline, it's the underside of the coachroof. The reason it has to be thick is that it's directly under the mast "shoe" and is repacing a wooden plank. Last season, I noticed a hollow in the coachroof as if my mast was "sinking" through it. That's exactly what was happening! At that point in its construction, the builders laminated a 1/2" piece of plywood about 6" wide into the layup to give it a bit more stiffness. Over the last 30-odd years, water must have been seeping down the bolts that held the mast shoe through the coachroof and the wodd had rotted. Once I cut away the GRP underneath, I was able to scoop most of it out with a teaspoon! I decided I'd replace the plywood plank with a GRP "plank" so in answer to some of the questions, it doesn't need to "stick" particularly well - it just needs to fill a 1/2" gap. I can't lay it up out of the boat because it passes over an internal stiffener running athwartships so I wouldn't be able to bend the finished item enough to feed it in.

The reason I was asking about laying up in stages was because I'd heard that laminating resins have wax inhibitors in them which form a skin over the exposed surface (the one away from the "mould") so that the resin cures. Apparently, it won't cure if it is exposed to the air so I was wondering whether I'd have to grind the surface between successive layers to remove this "wax" (if it's true!) I don't know if I'll be able to lay up too much in one go because I'm working upside down. On the other hand, grinding GRP upside down in a confined space isn't right up there with the most pleasurable experiences I've had in my life so far! Finally, You're right Oldsalt, I think I'll use epoxy when I come to put the "bottom" skin back. because this obviously will have to be strong. The "plank" doesn't - it just needs to stop the bolts crushing into it when tightened.

P.S. Don't panic! this doesn't take the downward load on the mast exerted by the stays - that's done by the main bulkhead!

<hr width=100% size=1>

The wax is in flow coat, not laminating resin.
I'd do it in 2 or 3 goes, dealing with a 12mm thick liquid mass not in a mould can get messy. A couple of hours between layers should be fine, so long as it's no longer flowing.

 

[lw395]

G'day Ian,

Sounds like this might be below the waterline at 12 mm thick; if this is the case then I would use only epoxy resin, as it will provide a much stronger bond. Appling a standard wax resin over standard laminate will not give you a chemical bond if the original material is old (8 weeks max) but an epoxy will, also note that below or above the waterline, epoxy is lighter and stronger......

That's not really accurate, 'wax resin'? Do you mean flow coat or normal polyester laminating resin?
Polyester resin will bond very strongly to 'old' polyester resin, provided the surface is taken off with abrasives. This leaves enough unbonded bits of the polymer that the new resin will bond to pretty much the same as with uncured resin. With proper cleanliness, a peel strength very close to a new layup can be achieved, and that should be plenty unless the design is downright bad.
Mixing epoxy and polyester for repairs can be more trouble than it's worth, but it's true that epoxy has advantages, particularly when you ned it to sick to wood or metal.
Epoxy, unlike polyester, is prone to producing a wax or bloom on the surface, so once it has set, it often needs abrasion before more stuff is added.

Don't use epoxy with glass mat, only cloth. Mat (usually) is held together with a binder which is dissolved by the polyester resin or the styrene in it. Epoxy doesn't do that and won't stick to the fibres at all well.

The production of heat is increased by two things, one is the number of bonds available to be made, which goes down as the resin sets, but the dominant one can be temperature, more heat = a faster reaction = more heat, so it can run away and even catch fire, but once the resin has gelled, there is not that much energy left to be released so it will cool and it's safe to add more layup.
The risky thing is a cup full of resin, a lot less surface area to cool it compared to a layer in a mould, so the heat can build up if you mix too much in one go and don't get it in the job quickly.
Another thing, wear polythene gloves and don't guess the catalyst, disposable polythene pipettes from ebay are the way to go imho!

 

[Avocet]

The wax is in flow coat, not laminating resin.

Which then begs the question - why does laminating resin not stay tacky? I'm intrigued by this. It's all polyester resin. The gelcoat doesn't stay tacky because it's got the mould to exclude air on one side and the laminate to exclude the air on the other side. Flowcoat doesn't stay tacky because it has the laminate to exclude the air on one side, and the wax on the other... So why does laminating resin not stay tacky?

 

[TQA]

Polyester resin does 'stick' to old cured polyester resin but not well. Epoxy 'sticks' much better. Much research and test pieces prove this.

For a small job the extra cost of epoxy is negligible. Make sure you get the right sort of cloth, some are only suitable for polyester.

Buy laminating resin and not flow or finish resin. If you want a high quality and non sticky surface finish use a sheet of HD plastic film [ drafting mylar or butyl pond liner ] and press down on the surface. Sand bags work.

 

[William_H]

I did something similar on the little boat a few years back. In this case there was an aluminium shoe under the mast base fitting of SS. The ali went to powder. In this case actually on top of the cabin roof. It was a slight wedge shape. I used polyester resin and Chopped strand mat if I remember correctly I di it in one go and over heating was not a concern. 19 degree ambient. The grp thus made is very strong being in compression. I wonder if OP can not cut the deck and do it from the top? Much easier.
if you do it from the bottom consider using something like cling film over the lay up followed by a rag or foam with a brace and jack to press it all into place while hardening. Possibly need a helper if you can get one in to hold the layed up glass in place while you add more then support it. good luck (prepare the bad language before hand just in case). olewill

 

[oldsaltoz]

Have you considers some of plastics available for backing, much the same stuff as the Bread Boards? Drilling a few holes through it will ensure no trapped air and improve stability, neede becuse any fibreglass will bind well but put around it it should be worth considering.

That's not really accurate, 'wax resin'? Do you mean flow coat or normal polyester laminating resin?

Flow coat is a combination of resin an fillers, the same as gel coat but with added wax.

Wax is added to all standard poly resins the resin will not cure if no wax is added, think of gel coat, no wax added.
Flow coat is Gel coat with wax added. gel coat will not cure unless it is covered, normally a bit of plastic sheeting when repairing damaged gel coat.
The wax in the standard resins makes it way to the surface (less density) and forms a thin layer that excludes the air so the curing process can carry on.

Polyester resin will bond very strongly to 'old' polyester resin, provided the surface is taken off with abrasives. This leaves enough unbonded bits of the polymer that the new resin will bond to pretty much the same as with uncured resin. With proper cleanliness, a peel strength very close to a new layup can be achieved, and that should be plenty unless the design is downright bad.

I almost agree with this, however, preparation must be meticulous and the design should include that the new work is not under tension, but rather in compression. So fine for this particular application.

Mixing epoxy and polyester for repairs can be more trouble than it's worth, but it's true that epoxy has advantages, particularly when you need it to sick to wood or metal.
Epoxy, unlike polyester, is prone to producing a wax or bloom on the surface, so once it has set, it often needs abrasion before more stuff is added.

Don't use epoxy with glass mat, only cloth. Mat (usually) is held together with a binder which is dissolved by the polyester resin or the styrene in it. Epoxy doesn't do that and won't stick to the fibres at all well.
Using CSM (Chopped Strand Mat) also uses more than twice the resin to cloth ratio of resin. Epoxy to cloth is a 1 to by weight ratio, Standard reins and CSM is 3 resin to 1 cloth by weight, and at today's price for epoxy resin that's a lot to pay for what may well be a weak repair.
CSM is available with no binder at all and can be used with epoxy, but normally only used to change the characteristics of the finished item.

The production of heat is increased by two things, one is the number of bonds available to be made, which goes down as the resin sets, but the dominant one can be temperature, more heat = a faster reaction = more heat, so it can run away and even catch fire, but once the resin has gelled, there is not that much energy left to be released so it will cool and it's safe to add more layup.
The risky thing is a cup full of resin, a lot less surface area to cool it compared to a layer in a mould, so the heat can build up if you mix too much in one go and don't get it in the job quickly.
Another thing, wear polythene gloves and don't guess the catalyst, disposable polythene pipettes from ebay are the way to go imho!

Use only large shallow containers when mixing, 1% Catalyst is enough for most poly resins (check the data sheet) Any more will faster heating as the Styrene rushes out of the mix.

Good luck and fair winds.

 

[nigelmercier]

You guys know this thread is 10 years old, right?

 

[Avocet]

You guys know this thread is 10 years old, right?

Yes, the OP presumably has a similar problem and used the search facility?

Anyway, as it has surfaced again, I can report that 10 years on, the repair is fine and stable! (Although for 8 of those, the mast has been down)! I did the job in three batches - not so much because of heat build-up but because I was working upside down. I deliberated long and hard about whether I should cut open the top skin and fill from above, or the bottom skin and fill from below. I went for the latter, to avoid the problems of trying to match the gelcoat on the deck, but the price I paid was a boat full of dust and an utterly vile upside-down laminating job! Given that the problem only became apparent when cracks in the gelcoat started to form around the mast base, I still had cracks to fill afterwards and they didn't match, so I might as well have done it from above in the first place.

Strength was never an issue. This was just filling a void left by a bit of plywood that had rotted away and is only carrying loads in compression. I did wonder about a "bread board" solution but was worried about "creep" in the long term. Apart from that, I had a ready supply of polyester and glass.

As far as heat is concerned, there's a "peak exotherm" in the reaction after which it starts to cool again. If the OP was really worried, he could always do a bit, wait for the maximum temperature to have been reached, and whack another layer on top before the previous layer has cured. Laying up just over 1/2" (say 15mm) of fibreglass laminate takes a surprisingly large number of layers!

 

[fisherman]

Three or four layers of 600gm CSM is good, but if you are going to lay up in one go, also good, cut the cat to 1%, the more you lay up at a time the less you need, particularly if you keep using the same container. As you are working upside down I would wet out the mat on a board, 3 x 600gm at a time, then push it up into place with gloves, brush and roller, assuming each piece is not too big, say about 1ft square, otherwise you'll be wearing it on your head. By the time you have the next 3 x 600 ready the first will have gone enough not to cause a heat problem.


I made a mistake and added 0.2% to a mix, took the lot off and binned it.....where it went off, but slowly.

Oh........now I see this is a bit out of date.....never mind.

 

[Lakesailor]

Some forums lock older threads so that anyone finding them can read the advice but needs to start a new thread to address their own issue.
I disagree with those who think it doesn't matter.

 

[nigelmercier]

Some forums lock older threads so that anyone finding them can read the advice but needs to start a new thread to address their own issue. I disagree with those who think it doesn't matter.

+1

 

[Avocet]

Why is it so bad? I sometimes read the odd thread and realise that's an old one that's been resurrected, but so what? Sometimes I even fail to spot it's old and reply to it, but as tragedies go, it's not the worse that could befall me. Other times (as in this one) I replied to it either to update on whether that repair worked or not, or to query something new that has been added to it since. The alternative seems to be multiple treads about the same thing - which I find maybe slightly more dull, but hardly "annoying". Maybe just some forum software that highlighted old threads differently (a sort of papyrus shade maybe...) or some sort of icon for "ancient"?

 

[nigelmercier]

Why is it so bad? I sometimes read the odd thread and realise that's an old one that's been resurrected, but so what? Sometimes I even fail to spot it's old and reply to it ...

Resurrecting old threads leads to a flurry of replies to the OP. If the topic changes, as it often does, this leads to a lot of wasted time and effort for everyone.

Have started a thread in Feedback forum requesting a lock or warning: http://www.ybw.com/forums/showthread.php?396099-Request-lock-on-resurrecting-old-threads