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How do I prevent fibreglass to attack my styrofoam mold?



I am Louwrens du Plessis and I stay in Middelburg in Mpumalanga in South-Africa. I am a pilot and busy with the design of a Micro Light aircraft. In the process I have to model and shape several sections of the aircraft before I cover it with fibreglass which I have to finish of to a mirror polished surface to enable me to form a mold over it with fibreglass to be used for the final product.
The problem I have is the fact that Fibreglass resin and polystyrene is what you would call compatible or even long distance pen pals. The resin demolishes my molds in a record time. I need to protect it against the resin HOW?


Louwrens du Plessis
Consumer & Private Pilot - Middelburg, Mpumalanga, South Africa.



I would suggest you switch from polystyrene foam to polyurethane foam. It is my understanding that this is the type of foam used in making surfboards, which involve a similar process to what you are doing. As to where you might find a source of polyurethane foam in your locale, I really don't know.

Danny Uerling

Danny Uerling
- Fort Smith, Arkansas


Hi Louwrens,

Danny You hit it on the head .... SWITCH !

Styrene is one of the components of ANY fibreglass product and, ipso facto, will be attacked with glee by any frp solvent such as acetone [on eBay or Amazon].

Urethane seems the way to go .... but, as you know, the super finish of the end product is always due to the quality of the mould.

freeman newton portrait
Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).


HI Louwrens,

If you're using EPS foam (Polystyrene) like the type used to package electronics, etc. in cardboard boxes, you can't use polyester resin. You need to use epoxy resin instead. It's more expensive, but it would be an answer to your question.
Just make sure that the epoxy resin is compatible with the type of fibre you intend to use.

Paul Swanepoel
- Taiwan

Hi, Can you not just cover your moulds in parcel tape, ensuring the tape is layed perfectly perpendicular with the previously layed piece will leave you with a super smooth finish and will protect your foam from the chemicals.

James Smith
- Coventry, UK
January 24, 2008

Cover the EPS with paper mache.

Tim Bond
- Cape Town South Africa
February 25, 2011

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