Update On GRP Moulding

[Lakesailor]

Warning. Contains pictures of non-boats!

Anyway I decided to go along with my first plan to cover my plug with mat and resin and use that as the finished item, filled and faired. I watched the mould-making video and decided it was far too much work for a one-off.

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I painted the plug in undercoat and then flatted that off to try and get a decent finish.

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Then I covered it it parcel tape

Then the lay-up, using two layers of csm and plenty of resin.

Hell of a job getting the plug out of the moulding, but it now sits on the bonnet. It'll be bonded to the bonnet and I have some self-coloured flowcoat which is as near as dammit the right colour. There is some detail edge laminating still to do.

Question here. Will the flow coat bond to car body filler or do I have to fair it with resin (eeek!)?
Also the bonnet is in two pack I think. Will flowcoat react with that? I do have some bits of bonnet I cut out that I could practice on.

 

[sarabande]

many many years ago, a flatmate did something similar to an Imp Special. He had problems with the GRP near the exhaust manifold with embrittlement of the resin due to high radiant temps.

In the end he rivetted a piece of shaped aluminium about 1/4 inch from the GRP to act as a heat barrier.




I like the 'panel' at the back end. How about a boaty style bubble inclinometer ?

 

[Lakesailor]

Too frightening. Ian would keep pointing at it

 

[nigelmercier]

Since I first saw the original thread, I've been thinking this was a ride-on lawnmower

 

[Lakesailor]

It does have a critical effect on grass.

 

[Avocet]

Most body fillers are polyester resin, so the flowcoat should stick to it with no trouble. Best rough it up first though.

 

[30boat]

Flow coat will bond to the filler providing it's polyester(it would bond to well cured epoxy if it were well abraded).Two pack paint won't react with flowcoat (polyester).
So if I understand right you're going to fair the part with filler and then apply flow coat on top?Flow coat won't give you a good finish especially if it's brushed on.Why don't you fill and fair and then spray it with a two pack paint?That's what I always do and it works perfectly.Flow coat will still have to be sanded smooth and polished.Added work.

 

[TQA]

Flow coat will bond to the filler providing it's polyester(it would bond to well cured epoxy if it were well abraded).Two pack paint won't react with flowcoat (polyester).
So if I understand right you're going to fair the part with filler and then apply flow coat on top?Flow coat won't give you a good finish especially if it's brushed on.Why don't you fill and fair and then spray it with a two pack paint?That's what I always do and it works perfectly.Flow coat will still have to be sanded smooth and polished.Added work.

The main reason for using flow coat is that it will cure fully in contact with air. It contains some wax addititve. Laminating or gel coat will have a sticky uncured surface layer that is a right pain to deal with.

Polyester resin does not stick well to cured polyester resin. Perceived wisdom is to use epoxy where you want something to stick to cured polyester. But in this case you could give polyester a go as it is non structural. It is not like you are retabbing a main bulkead or reinforcing a skeg.

 

[rivonia]

Flow coat will adhere -no problem. Do not forget to add the hardener/accelerator to it.

Flowcoat can be brushed on, however it is not such a good finish as spraying on. If you decide to brush it on then you would have to do some wet/dry sanding with the finest paper to get the smooth finish. Then lost of elbow grease to polish.

Good luck

 

[nigelmercier]

I've had reasonable success applying flow coat using a foam roller. Slight orange-peel, but could be polished out.

 

[Lakesailor]

Good thinking. I could use a foam roller. I've got a compressor and spray gun, but don't really want the hassle of cleaning it after testing and then after spraying the flow coat. If push comes to shove I'll spray the bonnet with paint once the flowcoat has cured (that's the reason I am using it, to get a fully cured finish) and I've flatted it.

 

[oldsaltoz]

The main reason for using flow coat is that it will cure fully in contact with air. It contains some wax addititve. Laminating or gel coat will have a sticky uncured surface layer that is a right pain to deal with.

Polyester resin does not stick well to cured polyester resin. Perceived wisdom is to use epoxy where you want something to stick to cured polyester. But in this case you could give polyester a go as it is non structural. It is not like you are retabbing a main bulkhead or reinforcing a skeg.

This is true if applying new over old, however this is new on new. The term old poleyester resin in fact means 6 weeks or more since curing.

So I would expect the flow coat to adhere very well provided the surface is properly prepared.

Good luck and fair wings.

 

[Lakesailor]

Yes it will be all done and dusted within 2 weeks.

I've just tried some flowcoat on the original 2 pack on a bit of bonnet I removed.
It didn't react (some forums suggest it would) It didn't flow very well either, mucho brushmarks. I'll try a foam roller. I did wet'n'dry it with 240 to see if it would flatten and it came out pretty well (more elbow grease needed) but it's very hard. Perfect colour match though. You can still see some of the brush marks near the edges. Perhaps less activator would let it flow a bit more. You can thin it down apparently but it loses it's hard-curing properties as you do that.

 

[Hugh Foulis]

I like the 'panel' at the back end. How about a boaty style bubble inclinometer ?

We tried an experimental version of this last season when Lakey sprayed the seat with silicone polish. It wasn't calibrated but there was a direct correlation between the list on the car and how far I slid across the seat. Had we progressed the experiment then there was also the possibility of measuring the g force under braking depending on how much of the footwell I occupied!

 

[30boat]

This is true if applying new over old, however this is new on new. The term old poleyester resin in fact means 6 weeks or more since curing.

So I would expect the flow coat to adhere very well provided the surface is properly prepared.

Good luck and fair wings.

What you're saying is of course true.It is however perfectly possible to achieve a very good mechanical bond between old polyester laminate and new.It's all down to preparation and application schedule.Given the choice I'll always use epoxy however.
I once had an unfortunate encounter with a steel mooring buoy 500 miles from home and the tip of the bow including the forestay attachment was broken off.What kept the mast standing was the forestay.I couldn't source any epoxy resin so the whole thing was rebuilt with polyester, matt and rovings and faired with epoxy filler.That was in 2003.

 

[Avocet]

It's worth keeping all this in perspective, I think. Although I agree new polyester doesn't stick to old polyester as well as epoxy, people have been repairing crash-damaged polyester sports cars for more than 50 years with more polyester and the new bits don't fall off!

 

[30boat]

It's worth keeping all this in perspective, I think. Although I agree new polyester doesn't stick to old polyester as well as epoxy, people have been repairing crash-damaged polyester sports cars for more than 50 years with more polyester and the new bits don't fall off!

And boats.If well made there won't be any problems.I attached the chainplate webs to my previous boat with polyester in1990 and the boat is still sailing happily.

 

[Lakesailor]

I do have a litre of epoxy resin, so it would be easy enough to bond it to the car with that. However it's just a cover. Even if it falls off it's not a drama. I'll probably use polyester as the csm strips I'll use to blend it in with rely on something in the resin to break down the bond and make it flexible. Not sure it works quite like that with epoxy, unless you use proper epoxy mat.

 

[30boat]

I do have a litre of epoxy resin, so it would be easy enough to bond it to the car with that. However it's just a cover. Even if it falls off it's not a drama. I'll probably use polyester as the csm strips I'll use to blend it in with rely on something in the resin to break down the bond and make it flexible. Not sure it works quite like that with epoxy, unless you use proper epoxy mat.

One thing to bear in mind is that if the area is going to get hot then Polyester might be better as it softens a lot less with heath.

 

[Lakesailor]

Good point. I'll carry on with polyester.