Applying the cloth and resin –

First put the cloth down in place – make sure you are ready to go because one things are mixed, it’s go time!

Second, know how long you’re going to have before the resin hardens. Assuming roughly 20c in your workshop, polyester is going to give you about 15 minutes before it kicks in the pot. You get a few minutes more if you spread it out thinner. Epoxy varies – for regular hardener, you can assume 20-25 minutes before it starts to kick on you. For “fast” hardener, it’s more like 10 minutes. I don’t know how long the “extra-slow” takes. I’ve never wanted to wait that long for my epoxy to cure!

A warm room or a cool room will make a tremendous difference. Too much heat is a headache because the resin kicks too fast. If the room is too cool, everything will happen quite a bit slower (though pot life will still be surprisingly short – it’s heating up from the inside. There is a minimum temperature below which you shouldn’t even start. With West System and slow hardener that’s 16c. You can go down to 4c with West and fast hardener. If your workshop gets up into the 25-30c range – use slow or extra slow hardener or prepare to work fast and keep your resin bathes small.

Resin gets hard to work with once it starts to kick. If you try to push it too far, then the finished job will be lumpy. Just mix up some more resin and pick up where you left off.

Work from the middle out!

The glass cloth is very light and flexible. If you pull on it, it will distort and twist. Just dab it into place with a small, stiff brush you’re prepared to throw away. And, watch as you move outward that you aren’t pulling it out of place in the middle. In a real emergency, you can dab a tiny spot of CA through the glass cloth to tack it down in a spot. It’ll wet out around the CA just fine – but there may be a slight discontinuity to sand in that area.

As to the brush to apply it with – my local hobby store carries “resin brushes” – they’re inexpensive and great for the process. They’re flat, about 18mm wide, and fairly stiff. And, unlike “acid brushes” they don’t lose hairs. You can really control the amount of resin you apply, because you do NOT want to put on more than you have to. A foam brush or a disposable “acid brush” also work – and are a lot faster – but the result is nowhere near as good – it’s just about impossible to control the amount of resin – because the brushes are simply too uneven in shape and soft.

The idea is to put on only enough resin to “wet out” the cloth. You do NOT want to fill the weave. If you find you’ve put on more than you need, then the cloth will float up on the resin and will not be smooth and tight on the surface. Work slowly. If you have a bit too much resin, work it out towards the edge. If you run out of time, get another cup and brush, and mix fresh resin. You can see when the resin is “wet” as I said – take your time and get it right. A few extra minutes putting it on will save you hours later when it comes time to smooth it out and fix the errors.

Note that sometimes there are flaws in the cloth – perhaps you got your cloth shipped to you and it came folded, so it won’t sit down perfectly. Just do your best. When it’s all done, so long as you didn’t use any extra resin, it’s not hard to sand off any “bubbles” and fill the cavity – unless it’s too big for your comfort, you don’t have to patch in cloth – a little resin or putty will do the job. If you see something wrong – and the resin may have started to kick – just leave it. You’ll fix it later.


Trimming the cloth –

After some time, which can vary a lot depending on the resin and the ambient temperature, the resin will become “leather hard” – it’s still a bit sticky, and somewhat flexible, but has mostly solidified. Experience will guide you here, but it’s a significant period of time, not something that comes and goes in a few minutes.

At this stage, the extra cloth can be cut off easily and precisely with little effort. If you wait until the resin is fully cured, it’s a lot more of a pain. I find the best way to do it is to grip the resin-free outside edge of the cloth gently, pull gently – don’t pull away from the hull – and slice the cloth with a brand new x-acto blade.

Especially if there are no heavy resin drips, it should cut right on the edge and with ease. If there’s a section you can’t get, or you think it’s going to pull away – leave it. If you DO start to pull the cloth away from the hull – STOP! It won’t adhere well if you put it back and that’s hard to fix. You can always cut excess un-wet cloth with scissors and grind down the excess that has cured with resin after it’s fully cured.

If you’re going to put on an additional layer of glass, either do it while the previous coat is still a little tacky or wait until it’s fully cured and then sand the surface, otherwise there will be adhesion problems. Putting a second layer on a tacky hull is tricky. It’s usually best to wait and do it the slow way.

Then, walk away and let it fully cure. Preferably until the next day. If you start sanding early, it’ll just clog the sandpaper.


Finishing the job –

After the resin is fully cured, you can sand back any irregularities and give the surface a good tooth for filling the weave and getting a smooth contour.

If you’ve done it right, you now have a cloth textured surface that closely adheres to the shape of the hull below. If there’s too much resin, you’ll have a shiny surface and some bumps and hollows – just sand back as best you can. You may have to sand through the occasional bubble of cloth if it’s too high, but everything is fixable!

In a small area, if you sanded through a bubble, you can often ignore it, but if it’s bigger and you feel the need, just cut and patch in a little more cloth – it’s no big deal. You just have to wait until the patch is fully cured to move on.

Now, if you need it, you can use the filler of your choice to fix any shape issues. A filler like Bondo, epoxy filled with microballoons, or System 3 QuikFair will just a little bit be softer than the resin so you can sand it without worrying about destroying the fiberglass unless you’re really ham-handed. I’m not sure about using Bondo over an epoxy glass job – I’ve never tried it, but the 2 part Bondo is the filler of choice on polyester glass jobs – it’s just polyester resin with filler in it.

Don’t use too much. It’s often better to use a couple of applications than to glop it on and spend a ton of time getting it all off again.

Then, lastly, you can brush on and sand back as many additional coats of resin (usually 2) that it takes to get you a smooth surface with no visible grain. If you didn’t use filler, the glass should be just about invisible at this point – so if you went for a clear coat over wood, you can put any kind of top coat on it to give the shine and depth you want.

Note that resin may develop an “amine blush” – this is a waxy coating that curing resin can exude. It wrecks paint jobs, but is easily removed with a gentle scrub with soap and water. I sand heavily, so I’ve not had to do this, but if you’re just touching the resin and then painting, it’s a good idea to give it the water/soap washdown.


One of the beauties of fiberglass is that pretty much everything is fixable. If you need more, put it on. If there’s some in the wrong place, grind it off.

Please take precautions. This is nitrile glove and dust mask territory! This stuff is nasty to breathe.

You can also lay glass patches on the inside of a hull that is either weak or damaged – just let ‘em dry as is and you’re good to go.

I don’t have any experience completely fabricating parts from fiberglass, unfortunately.

Best of luck!