Working with polyester resin to attach wooden components inside GRP fuselage shells, and to apply wing centre section glass fibre bandages, is an almost inescapable task that you're gonna have to tackle at some time in yer aeromodelling career! Here are a few basic 'Feeney Zone' guidelines to help make this 'prickly' but often necessary evil a little less irritating…

THE PAIN OF GLASS!

First, a heartfelt warning: working with glass fibre cloth and polyester resin is a potentially dangerous affair! Those noxious fumes and microscopic needle-like glass cloth offcut strands floating about can irritate one's skin and seriously damage one's 'breathing apparatus' if inhaled. So, wear a good-quality face mask to cover your nose and mouth, and slip on some 'latex protection' over your digits, just in case of the worst! Some barrier cream, available in auto-finishing outlets, lovingly rubbed into your hands in the absence of latex or vinyl gloves, is also a sensible measure.

Tight-fitting swimming goggles, coated with spit before wearing to prevent 'em misting up, help keep one's eyes free of nasty particles. Having suffered a horrible eye irritation in 1996, after wet-sanding GRP, I can confirm that this extra optical safety/protective measure ain't just a 'wet' idea!

MIX-UP

Personally, I like 'Bonda' polyester resin, as it offers an easy-mix system using graduated dispensers; it also brushes well and features a comfortable cure time. Whatever brand of resin you choose, ensure that it's really fresh. Follow the resin/catalyst mixing ratios precisely (make sure that the product offers at least a half-hour drying time), and have plenty of cellulose thinners standing by for brush cleaning afterwards.

BRUSH STROKES

On the subject of brushes, ordinary 1/2" hardware shop 'domestic' brushes and 'low-grade' 1/4" artists' brushes are fine for resin application. The ferrules of cheap and cheerful artists' brushes, which are best suited to resin application in confined areas, may need crimping with pliers to prevent hair loss. The ferrules of these cheapo artists' brushes can be bent at angles also, to stipple tricky internal corners, with the brush taped to a length of square-section 1/4" spruce strip. I have to admit that I frequently 'sacrifice' such crap-quality DIY brushes on 'single use' resin applications; but, as already stated, if you're fastidious about cleaning, they'll last longer!

SHELL SUIT!

Kit ply firewalls come approximately 1/8" over-size to allow for precise trimming to shape, to fit snugly within the GRP fuselage shell nose areas. The firewall edge 'erosion' is a low-tech exercise involving a sharp Stanley knife, followed by 80-grit glass-paper stuck to a hard sanding block. Don't 'fret' if the reduced-area firewall is wavy around its circumference; so long as a good overall friction-fit is achieved, even noticeable localised gaps are easily fixed later on with epoxy, surplus resin, or Deluxe Materials' specialist adhesives.

The exact firewall location within the GRP shell is determined with the engine/mount package attached to the firewall. Bolt the mount to your pre-fitted firewall anchor nuts, then feed the firewall/mount 'module' (with all the plumbing/tank neck holes already drilled by you if they're not pre-cut!) in through the radio bay opening, and jiggle it into its approximate final position. Now, screw or bolt the engine to your pre-drilled mount arm holes, through the fuselage shell's pre-excavated 'powerhouse' nose side/top opening. Some GRP fuselage shells may arrive with the engine opening factory-cut, but this is very rare! Normally, you do the job personally with a drill and Junior hacksaw blade - or a Dremel tool.

A scrap 1/16" ply nose-ring, placed 'twixt the fully-tightened prop-equipped spinner rear, and the GRP fuselage shell front face, maintains a snug but healthy 'operational' engine/fuselage gap. Only tack-glue the firewall solid when totally satisfied that the spinner/fuselage centring and cylinder head/silencer fuselage opening 'protrusion' angles are exactly correct. A mildly under-size firewall will, in fact, aid the overall hardware/fuselage shell alignment procedure, I find.

With the spinner taped securely to the GRP fuselage shell, and the nose-ring doing its spacing job in between, and with everything lined-up nicely, drop a few dollops of five-minute epoxy, 'Super Crylic', or 'Fusion' onto the firewall rear corners where it touches the nose shell most tightly. Let the tacking adhesive blobs cure with the fuselage stood nose-down against a wall so that the glue will 'pool' against both the wood and GRP surfaces in the most effective way possible. Tack-gluing one half of the firewall border at a time, and allowing the glue to form smooth fillets by angling the fuselage as appropriate, is another effective spot-holding technique. When the tacking blobs have cured, remove the engine and mount again. Seal all plumbing/tank neck holes, all captive nut threads, plus the entire front firewall/GRP shell joint area, with lots of well-kneaded Plasticine. The remaining firewall/GRP shell tank bay gaps are now filled from the radio bay opening with any of the adhesives already mentioned; again, the model is placed nose-down as curing takes place.

Now, the actual resin/bandage work begins! One's fibreglass tape width is chosen to suit the model's internal nose dimensions. The tape length is pre-cut to allow a 1/2" overlap onto the GRP shell.