...Laminate with Jesmonite AC100 and glass fibre fabric

This How-to will tell you how to laminate an item as a hollow rigid shell using Jesmonite AC100 and glass fibre fabric. This article assumes you already have a mould to make the item from, if not check out the articles on 'moulding it and casting it solid' from the main How-to index.

Of course you could just pour plaster or some other casting resin into the mould and make a solid piece. However, in this example we are going to make a rigid and hollow shell from Jesmonite AC100 and glass fibre fabric. This will be much lighter than a solid object and also be very strong due to the reinforcement.

Jesmonite AC100 is supplied as a liquid and a powder which are mixed together at a ratio of 1 part liquid to 2.5 parts powder. A Jesmonite thixotrope additive is also available to make the mixed resin into a gel which won't be as runny - this is useful for the first coat inside the mould when we are making hollow items.

Jesmonite is non-toxic and non-flammable as it is water based. Although it has no dangerous fumes like solvent based resins it should still be used in a ventilated area as it has some odour. In this example the work has been carried out indoors with a nearby window open.

Firstly we have have mixed up a small pot of Jesmonite as directed. This was measured out with a set of scales and mixed by hand. For large amounts of Jesmonite over 1Kg it is recommended to mix it with a blade in a power drill. This is largely so it can be mixed properly before it starts to solidify which takes around 8-15 mins. However, in this case we used a teaspoon handle.

The Jesmonite thixotrope was added until the resin was no longer runny. This should be added at 2-6g per 1Kg of mixed resin, so this is a very small amount. In order to get this right, the handle of the teaspoon was dipped in the thixotrope about 2cm and then used to mix it into the resin - that's literally all you need.

A nice thick coat of thickened Jesmonite AC100 is applied to the mould, making sure that it went into all the details. You may wish to mix and apply several thickened coats until you can no longer see the rubber mould through the resin, allowing each a few minutes to set in between:

The next coat we will apply will be a thin glass fibre fabric called surface tissue. This weighs approximately 30 grams per square metre, so it is very lightweight as easily conforms to the surface. This coat will bond to the initial gel coat and make a rigid shell which we can apply a thicker fabric to without cracking the gel coat when pressure is applied. The surface tissue is damped down all over with more mixed Jesmonite resin, this time with no thixotrope added:

The next step is to apply some proper reinforcement. Once the surface tissue coat is dry to the touch the next layer of thicker fabric can be applied. In this example we are using Jesmonite Stitched Quadaxial mat. This an open weave multi-axial glass fibre mat which is easy to wet through with resin. Although the manufacturer of Jesmonite recommends only using Quadaxial mat, other glass fibre fabrics can be used. One layer of Quadaxial mat is applied and wet through with mixed Jesmonite AC100 resin, shortly followed by a second layer:

Allow at least an hour for the whole thing to set. Jesmonite AC100 has an active catalyst so it will set solid even in thick layers, it is not reliant on air drying. However, it will be softer for the first 24-48 hours before full strength is achieved, so if you need to sand, drill or trim the piece, this is the time to do it.

Once it has all set, you can remove the item from the mould to reveal the finished piece.

The excess can be trimmed from the piece and it can be generally finished as you wish. Jesmonite AC100 can painted with a wide range of paints from cellulose car paints and lacquer to water based acrylics or even house hold gloss and emulsion paints.

Check out the Jesmonite AC100 Strength Testing page with video of destruction testing.

Here are a few other larger items that have been made with Jesmonite AC100 using Latex moulds. The items have all been sanded, then primed and painted using cellulose car paints. For info on making larger more complex moulds check out the 'mould it and cast it solid - multi part mould' article from the main How-To index.