Casting Cement Elements

[david s]

I found the original thread ….. https://community.fornobravo.com/for...the-dome/page2
...unfortunately I have just had major surgery so I am laid up at the moment..

I hope it wasn’t caused by oven building. I too had major surgery this time last year following a blood infection and now sport a replacement aorta valve kindly donated by a very generous cow. Fortunately successful I’m now pretty much back to normal. I hope your op goes well too. The medical professionals are just fantastic, follow every recommendation re recovery punctiliously and you’ll bounce back as good as new.

[fox]

Thanks David, I have had my left kidney removed four weeks ago.
There has been a few issues since then but at last, it feels like I am finally on the mend, although I cant even drive a car at the moment let alone handle 50kg pizza oven parts ha ha

Nice to hear you have fully recovered and I agree about the medical people in general and I am very gracious toward them all.

[david s]

You are testament to good design, having been originally fitted with two kidneys. Wishing you a speedy recovery and return to good health.

[david s]

Hi Fox
Yesterday I bought some glass fibres, however considering the epoxy prices I might switch to the polyester alternative. Let's see.

Marvin

Marvin, be aware that any repairs or maintenance on moulds, polyester or epoxy, and there will be plenty, must be done using epoxy. Polyester over polyester produces a very poor bond.
Dave

[MarvinG]

Hi Dave,

Thanks for this helpful information. That basically results in the "big" works done with polyester, and then repairing cracks, adjustments or whatever in epoxy. But the good thing about this is, that I will have to plan better - what anyway worth it. :-)
I'm waiting for a 100 and 120 ball now from china. Polyester, gelcoat and mold release is luckily available. Epoxy too.
Keep you posted when I advance further.

[fox]

You wont need any epoxy at all, you will need ‘wax in styrene’ though as that is the agent that allows for reverse moulding ie using the gel coat on top of the mattering as a non stick top coat.
Any filling required can be done with gel coat, wax and talcum powder.

[david s]

You wont need any epoxy at all, you will need ‘wax in styrene’ though as that is the agent that allows for reverse moulding ie using the gel coat on top of the mattering as a non stick top coat.
Any filling required can be done with gel coat, wax and talcum powder.

Possibly my understanding is out of date, but I have to do maintenance on my polyester fibreglass moulds after around half a dozen castings and always use epoxy. Oiling the moulds also creates bonding issues and the surfaces must be prepared scrupulously before any repairs.

"polyester is only marginally effective as a repair resin for repairing well-cured polyester/fiberglass laminates."


https://www.epoxyworks.com/index.php...s-boat-repair/

[fox]

I have been working with composites for 45 years, I trained as a boat builder and then got involved with mould building car bodies,
To be honest I may no be up to speed with the latest technical sheets but I am still actively using both epoxy and polyester products.

Epoxy is a very good product and most certainly can be used for repairs, with the addition of the correct powders it can both fill and bond many materials.

Polyester, unlike epoxy, is not a glue but it will bond to itself very effectively and is much cheaper and less fickle!

However in this case we are talking about building a mould out of polyester products and I see no use for epoxy repairs at this stage?

The issue with using gelcoat as a surface filler comes from the fact the surface that is exposed to air will remain sticky and only the surface that cures in an air free environment will be properly cured.
So we add a wax that forms a skin on top of the gel and allows a tack free hard surface.
Personally I use gelcoat to repair gelcoat damage but yes of course you could use an epoxy product quite successfully as well.