Fiberglassing USOM

Just seeking out more advice! Seems like everytime I turn around I have a question or two. I have asked/posted this question among several groups/people, so please forgive me if you recieve a double post :stuck_out_tongue:

I have some 0.6 oz sq yd fiberglass I want to use on my USOM hull. I was wondering if I need to do two layers (for 1.2 oz sq yd covering) of it or if I can go with one? This is prolly a debateable issue, but the direction in the construction manual for USOM says to use 1oz fiberglass (it really didn’t say if it is oz per sq yd or sq ft (seen reference to fiberglass in both when measuring FG weight))


The trick is to not over do the epoxy. I wouldn’t hesitate to go with a laminate of two layers on the outside of the hull. 0.6oz is, IMHO, very light, and may not give you the puncture resistance desired for a balsa hull in a single layer.

I’ve used 2.4oz on one hull (because it was what I had on hand) and the boat still came out light enough. You want the glass to be thoroughly wetted out - but no more. It actually takes very little resin to achieve that.

Good luck.

The .6 oz glass is definetly to light. In my latest USOM I’ve always used the 1 (or 1.2) oz fiberglass.


I used 1.4 oz per square yard on my 3R.

kewl beans, i’ll try to use 3 layers and vacum bag so i get 3 tight layers totalling 1.8 oz with a high fiber to epoxy ratio…

just hope i get my vacume system working :stuck_out_tongue:



Your hull is balsa planked over stations correct? Do plan on just laying the glass/epoxy over the hull on the building board, and then just sliding the entire thing into the bag? If so I wouldn?t recommend this, because even if you only pull 1 or 2 PSI of vacuum your hull will deform or crumble.

If you are balsa planking over stations, how many stations are you using?

And even if you get the vacuum bag on properly, be careful bagging balsa core stuff. I would say no more than 10 or 12". I crushed a balsa core keel fin with 25" and it was pretty dense balsa.

I noticed that you use PSI for vacuum. Does this equate with in. of mercury? It seems that it would but I thought I would double check.

actually i am in the process of glassing jnow

So far what i have done, and is working out well,

1st layer (of 2) I laid the glass out dry, trim to fit . Wet it out completly (used excess epoxy/resin) use an old credcit card and squeege out all the epoxy and made sure there was no air bubbles… right now the glass is clear and is tacking up very well. i see no airbubbles, and only 2 minor wrinkles. I even made sure that the edges didn’t have ‘bubbles’

just waiiting a few hours from now to lay up my second layer… i decided against vacum bagging. for the light weight sruff I have its so easy to wet out and remove excess epoxy.

anyways I should have my second layer on tonight, then saturday i move onto microballons and sanding.


Do you plan to do this to fill the weave? If so special considerations need to be made before you try and paint the hull. Since the microballons are hollow, when you sand them they will open up and make your paint job look like it has little pin holes in it.

Yea I was planning on using them for filling and final shaping. I was planning on priming before painting to fill up any ‘pin holes’ that might happen after sanding.

I use system three resin?s and they recommend that after you fill and fair the micro balloons that you apply a thin coat of epoxy again using a foam brush, I have never tried this though.

When I built my boat I used strait epoxy. I applied 3 thin coats with a foam brush.

wow nice lines :stuck_out_tongue:

I may paint a thin layer of epoxy after i micro, but i don’t see the point of that if one is going to be primming prior to painting (the primer should be filling those holes)

I found that the primer would pinhole also and just compound the problem. Pinholes are a bi**h. You wind up using so much paint trying to fill them that all your weight reduction goes out the window. I even tried rubbing primer into them. When I sanded that I just opened new pinholes. Do everything you can to avoid them. One way I found to get rid of them, if you’re stuck, is to rub thin drywall mud into them, let dry, repeat and then sand just enough to get rid of the mud without opening new pinholes, then prime. It sounds kind of Mickey Mouse but it’s the only thing I have found that works. Do you get the impression that I HATE pinholes. Very observant.

AS someone suggested already and as per the directions from Epoxy System Epoxy, after you are done sanding your fairing media your suppose to

“7. Apply several coats of resin/hardener to the area with a disposable brush or roller after you are satisfied with the fairness. Allow the final coat to cure thoroughly before final sanding and finishing”

I am sure other epoxy companies suggest the same to fill in those ‘pinholes’


Adding “several” coats of resin adds weight and I have never had resin applied with a brush or roller go on nice and smooth. When you sand that smooth you will probably uncover more pinholes. The big problem with pinholes is that you can’t see them until you apply paint and then when you sand all the paint off so you can put on a coat of resin you uncover more pinholes. I spent a week on one hull and finally used the drywall mud. If I had used it right away it would have left the hull smoother and lighter. I pull my hulls out of a mould and the factory resin rep suggested preping the mould and the spraying it inside with a thick primer coat and then apply the glass and resin. The pinholes may still be there but they are under the primer where it doesn’t matter. His logic was that if you are trying to go light on resin to save weight you will get pinholes. It only takes 1 or 2 pinholes to ruin a paint job and your day.

To get rid of the pinholes just do a “flotation/leak” test once the hull is done.
With the fiberglass work finished on the outside and the inside waterproofed just place the hull in a water tub with water and push it down beyond the designed waterline. Water will be forced through the pinholes, all you have to do is mark them in the inside and use a little 30 min epoxy (I’ve been told that the 5 minutes one is not water proof) to seal them from the inside. Once the epoxy is cured repeat process again……


Some pinholes don’t go all the way through the hull. They don’t leak but thet screw up the paint job.

What kind of epoxy did you use? Most of the kayak people swear by this method, and after how easy it worked for me on my 3R I would have to say I do as well.

It’s called Industrial Formulations Epoxy. I believe it is made around Vancouver B.C. You probably aren’t familiar with it. It’s formulated for use in lower temperatures. I think the problem with getting a smooth coat is, I mix it and paint it on and as it starts to go off it warms up, thins out and runs or sags. Maybe I should thin it out a little so it will go on thinner. Next time I will try that.