Paul

Employee

From: Gatebeck Cumbria

Registered: 4 Aug 2011

Posts: 130

Re: Skerry built from plans (build log)

I am sorry to hear about this problem.  It is difficult to be sure, without more detail, but it looks like you probably applied an epoxy layer over epoxy that had cured but not been sanded.

Unless you apply the next layer before it is totally cured you have to make a mechanical bond by sanding the area and then removing the dust.  The problem could also be caused if you washed the surface down with solvent.

I am not sure which epoxy you are using so please telephone us, if you can, and someone will talk to you about solving the problem and how to avoid it in the future.

Please rest assured that this will not affect the strength of your boat but it will involve more work.

Good luck with it.

This is from a frequently asked questions section

Can I put another coat of epoxy over cured epoxy?

Yes. Since the epoxy has cured a chemical bond is not possible so what is called a mechanical bond is needed. This simply means that the cured epoxy has to be lightly sanded before the next coat is applied: the first coat should have a matt, almost white, surface. Use glass paper of between 80 and 120 grade, no finer.
If the first coat has developed a blush or bloom this has to be removed before sanding and, in the case of our epoxies, it can be removed by washing the epoxy with warm water containing a few drops of washing-up liquid. Sugar soap solution is another fast way of removing it.

Rob

Member

From: England

Registered: 29 Jun 2021

Posts: 37

Re: Skerry built from plans (build log)

Thanks Paul, I did sand the coat which had cured, then put another coat over a layer that hadn't fully cured, so it's a bit of a mystery. I agree though, it looks like the under-layer is not the sanded layer, which is odd.

waterwing

Member

Registered: 19 Apr 2013

Posts: 10

Re: Skerry built from plans (build log)

I don’t think that it is a common mistake but I had this problem.  Thanks to Fyne I discovered that there are two rules. When re-coating after the first coat has cured

1  Wash the the area to ensure that the bloom is removed

2 Then sand it until it is matt but not sanded away.  I think that this is to provide a key.

I can’t find the actual words that were used when talking about the bloom but this iswhat I understood them to mean.

Test for bloom by placing your fingers on the surface and pull them towards yourself.  If 4 streaks are left there is a bloom.
To test if the epoxy has cured push your finger nail into the surface if no groove is left the epoxy has cured. 

I have always washed it before sanding if the first coat has been on for a few days.

Rob

Member

From: England

Registered: 29 Jun 2021

Posts: 37

Re: Skerry built from plans (build log)

Thank you for the advice. Washing down between coats when it's been curing for a few days is something I will be doing now, just to eliminate that problem. I think perhaps in this case it's the chemical bond that failed, as although still a bit soft, I could stick a fingernail into it when I put the final coat on, it had gone past the stage where that bond would hold. Maybe it was the amine bloom problem also, in which case between them it had no chance.

I've now scraped most of it off, with the bulkheads still to do. I'm sanding it all by hand, which is hard work, but it seems to be doing the job. I'm using the opportunity to sand the fillets a lot more, so I can get them to a standard I wanted them to be, as I always felt they needed more cleaning up - small blessings etc. So at the pace it is taking, it should be ready to move forward by Sunday, or next week at the latest. Once it is ready, I will fillet the seats. The bond holding the short pointed seat sections pointing inwards and jointed to the bulkheads have failed, as they are glued to the delaminating layer, so I will have to ensure the fillets on all parts of the seats and tank tops are sufficient to hold them all in place. I was considering using a heat gun and removing all three seats entirely, but can't face that, but the fillets alone should be sufficient.

Last edited by Rob (15 Nov 2023 11:37 am)

Rob

Member

From: England

Registered: 29 Jun 2021

Posts: 37

Re: Skerry built from plans (build log)

Slow but methodical progress. I’m hand sanding it all, first with 80 grit, then with 120. Though every manufacturer of paper seems to have a different coarseness - I have two 80s for example, one is significantly coarser than the other, whatever is printed on the back, and both are of the same abrasive material.

Rob

Member

From: England

Registered: 29 Jun 2021

Posts: 37

Re: Skerry built from plans (build log)

After six days of scraping and hand sanding Hell, I’ve got the interior back to standard. It needs a new coat of epoxy, but should look far better than it would have done now because I’ve sanded the original fillets and got them much more tidy looking. I’ve also done the fillets under the seats, which I made quite chunky as the epoxy that originally glued them on had failed due to the delaminating problem, but not entirely so I couldn’t take them off and start again. Today I did the fillets on the tops, and will sand them to the same standard as all the others when they’ve fully cured.

Last edited by Rob (24 Nov 2023 6:05 pm)

Rob

Member

From: England

Registered: 29 Jun 2021

Posts: 37

Re: Skerry built from plans (build log)

I’ve been hand sanding the seat fillets today, with the bow and centre seat done. I will get the stern done in the next day or two.

Last edited by Rob (28 Nov 2023 3:37 pm)

Rob

Member

From: England

Registered: 29 Jun 2021

Posts: 37

Re: Skerry built from plans (build log)

Final fillets sanded today. Not sure how much more work will get done before the spring with the temperature now dropping, we’ll see.

Rob

Member

From: England

Registered: 29 Jun 2021

Posts: 37

Re: Skerry built from plans (build log)

First coat of epoxy went on the seat tops today. I’m very pleased with how the fillets are looking now.

Last edited by Rob (9 Dec 2023 7:41 pm)