Flow coat problem, advice needed.

NUTMEG

NUTMEG

Well-Known Member
Joined
1 Sep 2009
Messages
1,923
Location
Essex
www.theblindsailor.co.uk
About this time last year I got the brilliant idea of creating a shower in the heads compartment.

The old vinyl lining was removed from the plywood walls and a shower tray was created with a void underneath to accommodate the wate pipe and discharge pump.

The walls and floor were coated with epoxy resin, a single layer of woven roving was applied to the walls and several extra layers to the floor. All was wetted with epoxy and allowed to cure.

The walls were washed with an ammonia based cleaner to remove anything nasty, then a wash with acetone. The lot was sanded to give a key and washed again with acetone.

A flowcoat was applied as per instructions and allowed to cure.

Two of the three walls are/were fine, but one had several areas of about 8" square where the flowcoat lifted, cracked and looked horrible.

Last week (a year later) I decided something had to be done about the horrible patches. So my mate and I sanded the whole compartment with 500, then 800grit and washed everything down with acetone. We then applied another coat of Flowcoat. The boat was left overnight with an electric radiator on. Temp about 15'C.

On returning to the boat today the floor and two walls look great, even better than before BUT that one wall has behaved as it did before, four or five areas of about 8" square have reacted and lifted/cracked.

This sounds like an issue of simple contamination, but the surface of the wood was sealed with epoxy and matting and this problem only happens in these specific areas, nowhere else.

Any ideas would be most welcome.

Cheers

Steve
 
Sounds as though contamination is passing through the epoxy seal - which has apparently not sealed the 8" squares. If the wood had previously been contaminated with silicone (from eg furniture polish) then the epoxy may well have failed to form an effective seal - "fish eyes" form in the liquid epoxy layer before it hardens and you end up with tiny holes. This problem also affects varnish and can be recognised by watching the epoxy/varnish before it goes off - the film starts off smooth then fish eyes appear, looking almost like bubbles. It's a known problem in furniture restoration where even sanding off a 1/16" layer of wood may not prevent contamination and subsequent failure of varnish finishes. Only certain fixes that I am aware of are to replace the ply wall or to cover it with a solid sheet material.
Sorry to be so pessimistic, Steve, I hope someone can offer an alternative solution
 
Thank you for the reply. I think you are on to something, unfortunately:-(

I have no way of knowing what was on the wood prior to my ownership.

Rats. A big Perspex mirror might be a solution. But seeing myself in the shower would be less appealing then looking at the horrible patches I think.

Thanks again

Steve
 
myquest said:
Flowcoat is gelcoat with wax added and my understanding is that gelcoat can't go on epoxy.
Click to expand...
I have heard that too. However West Systems say that polyester flow coat is fine over epoxy so long as the surface is clean and abraded. In my case two out of three walls are fine. Just that one wall has an issue and even then only in small patches. I think Stuey_two may have hit on the problem. Just a gut feeling but...

Thanks for replying

Steve
 
Is there anything behind the defective area which might cause a problem?
Something which might cause it to be different, cold or damp or perhaps a leak of oil or soap?
There has to be something different to cause the problem, contamination with silicon as suggested above is only one possible cause. Other causes may be treatable.
 
Thanks Ian.

No idea to be honest and it would be a hell of a job to strip the epoxy off to have a look. The otheside of the bulkhead is the saloon, so no oil or whatever. I am beginning to think there must have been something on the wall before we epoxied it.

No idea what though.

Is there a sealer or something I could apply to act as a barrier I wonder.

Any suggestions eagerly awaited.

Steve
 
How about rubbing that wall back and applying a tie coat? Polyester based products don't stick to epoxy well without a tie coat.
 
For epoxy to set it, just like flow coat, has wax in it that comes to the surface sealing it from air so it can cure.
Before you apply anything to epoxy resin finish you must remove this blush.
I see you said you abraded it but you need to use three or four sheets otherwise all you do is push the blush around.
Acetone also has the same effect unless you keep changing cloths
I tend to use warm soapy water and a scotchbrite scourer as it tends to be a more reliable method.

As far as using polyester on Epoxy, it really needs to have fully cured.
Polyester is pretty bad at sticking to stuff other than itself and given half a chance it will fail.
Giving a surface a coat of Bonda sealer, which is polyester based and uses moisture in the air to cure can create a good base.
Another is to skim the surface with a very thin coat of car plastic padding as that is polyester based as well.
Flowcoat will have a much better chance to stick.

However for best results I'd apply three thin-ish coats of gelcoat and then add one more coat of gelcoat will a little added wax in styrene or a light coat of flowcoat.
Applying a thick coat of flowcoat is rarely successful as the tiny bubbles created during mixing won't escape and during the polishing phase they will start appearing and cause the Gel to be semi porous.
 
Last edited:
That's brilliant. Just asked the missus and she is up for a day out. We are both off work today. Lunch and Adnams in the harbour in, walk the dog on the beach, spend money in chandlers. Perfect day out.

Thank you
 
You must log in or register to reply here.

Share this page

Top