Can I use plaster to make a mold of my front bumper?

I'd like to make a modified fiberglass bumper for my car. Would plaster be ok to use as a mold?

I would think that plaster would be heavy and fragile. Use fiberglass to make a mold,there is something you can cover the bumper with so the fiberglass would not stick to it like they use in making boat hulls,to get the hull out of the mold.Not sure what it is.

No, plaster would be way to fragile. Are you going to use the nose of your own car as a plug to make the mold from? Just be aware that you can generate some serious heat making a mold.

Have a read here...
http://www.fgci.com/howto/ht003fiberglass_mold.html

I have done it with plaster, it's not fragile. Just build soething to support and it mold the shaped with plaster. Make sure it's completely dry. Whyen it's starting to get dry you can smooth out the surface. When dry paint it with dirt cheap paint, lay it on nice and thick and then laminate.
You will have a mold that will need work to make it ncie and smooth.

Twin_Turbo said:

I have done it with plaster, it's not fragile. Just build soething to support and it mold the shaped with plaster. Make sure it's completely dry. Whyen it's starting to get dry you can smooth out the surface. When dry paint it with dirt cheap paint, lay it on nice and thick and then laminate.
You will have a mold that will need work to make it ncie and smooth.

Click to expand...

I've used plaster before to make small molds, but to do a bumper? You'd need a lot of plaster and whatever you made to support the plaster would have to be very rigid - a slight twist and the plaster would crack...

JMO

I used the plaster that they use for walls here, it becomes hard liuke concrete and won't crack very easily. In fact it takes a hammer to break it apart.

A big chunk of plaster will get really hot when it cures. That would not be good for your front bumper.

A fiberglass mold is commonly made to reproduce a part.

If this is only for one bumper I don't believe it's worth the effort, if you want to make a few and sell them then yes, do it :drink:

You can use thin plastic sheeting from the hardware store to prevent the resin to stick to the car. hold the plastic in place with double sided tape, but buy the cheap stuff, the 3M sticks too good and might rip off your paint....

Then you need mold release, good resin (UScomposites for example, not Bondo), $50 a gallon... mat, sealer, primer....

heck, for $300 you can buy a bumper, the materials are going to cost you almost $200 and it's a lot of work (and time).... well it can be a fun project....

Use wax for your bumper and the thing (don't know how it is called anymore) that you put on your bumper and act as a water soluble paint (sorry for spelling). Lay on some fiberglass and make sure you have edges to take it off afterwards (you can use play doh). et voilà it is ready. Did it, but was not satisfied with the results.