Fiberglass overlap bumps

I don't see that you have described exactly how and with what materials you plan to build this boat with.

Depending on the laminate thickness you can possibly butt the glass instead of overlapping it. Or add an extra layer and do all the fairing on that.


You seem to be using Bondo as a generic term, the actual Bondo brand product is not designed for use around water. And adding fibers to fillers does make them stronger, but complicates their use as an actual fairing compound. Plus there is no exact formula for making a putty, filler or fairing compound, only generalities that vary by how you want it to perform. Also every different resin base you add it to will require a slightly different blend of products to work as expected, and some resins will work much better than others.

When working large surfaces to achieve a perfect finish you will run into the problem of different materials printing through to the surface with a different look depending on how far they are from the painted surface. The deeper they are, the less they may affect the surface profile.

Whether it's building a mold or putting a new finish on an older part, people frequently say they want perfection in the finish, it isn't easy.

I will have them build several small panels with different materials and methods to show them what is possible, then we examine the finished panels after they've cured.

At first there may not be a huge difference between each one of the panels, but let them sit a few days and the surface will start to change. The big changes comes after you put the panels outside in the sun for a day or so. Panels that looked smooth and almost perfect may turn into an uneven mess, while others will have performed much better.

Normally when they see what it takes to make the surface look "perfect" they pick a panel that is "good enough", but requires less than half the cost and effort.

And the better you make it look, the more every tiny defect will stand out like a huge blemish that can destroy some people's self-worth and ego.

Let us know exactly how you plan to to build it, and with what materials and you'll get better answers.

Edit. I just read your other thread, you have many major hurdles and concerns to overcome before surface profile comes into play

 

Thanks man. I'm aware. Hopefully can get the geometry right. Might even do a mock up of the steps of how to dress the cloth to reduce those spots. They say that fiberglass sands easy but my experience has been the opposite and I do everything I can to prevent small bits of build up. With surfboard ding repair I actually drop a small amount on the surface and put thicker aluminum foil over it and tape it down to ensure the gel layer is exactly smooth to the surface. Substantially reduces Sanding times.

 

Added strips of torn (not sheared) Matt along the edges of overlapped layers helps smooth them out,and reduces chances of sanding through the laminate layer. Tearing the Matt effectively feathers the edge.
What this discussion really points up is the beauty of using a female mold!

 

I completely agree and have been encouraging the use of bonding strips with torn edges for years.It has always surprised me how few laminators have encountered the technique.I still advocate staggering the overlaps though.There used to be a supplier of bare hulls over here whose products were well known for having a substantial ridge every 34" because they didn't adopt this policy.

As has been mentioned,the initial fairing may leave a fair surface and as the resin cures and shrinks a little,the surface will be pulled and lose some fairness.There are some colours that don't help.

 

If you are using "boat cloth", that is in the range of 800 gr/m2 or over then definitely you are going to have problems with overlaps, the necessary evil. Plan your work carefully so that the finishing layers are in the 600 or less even if you have to do a double layers. Plan your WR overlap so it is staggered.

Secondly, the outer layer is supposed to be a resin rich layer before gelcoat or paint. A minimum of 2x CSM 450 + 1X CSM300 is needed if the boat is mostly in the water. CSM is not meant to be cut but teared at the seams, blending it.

Thirdly, the outermost layer is meant to be "in excess of required strength" and the only purpose is improved waterproofing. Sanding it will not affect the structural integrity, only the reduction of water/moisture permeability. So sand it to fair but not so much that nothing is left.

If you have to use a filler to fair, use the same type of resin you use and add some microbaloons or plastic filler. Cab o Sill is too tough to sand. Use sparingly.

 

I noticed the mention of dark colors. It maybe counterintuitive but we use to paint the outside of our mold with black or lampblack. Neutral gray or darker than gray is usually allowed if the environment is not so severe.

Black reduces the penetration of UV light which could degrade the resin. Of course a light color is required after the dark color to prevent the laminate from heating up and softening the resin. Red is the min dark color allowed for heat absorption. Others absorb a lot of heat.

 

Thanks. What a great tip!

The problem with the female mold is there is shapes I can't do with it. It's also very expensive, and super time consuming.

 

The more I look into it, I'm guessing I can't use dark colors which kinda is bumming me out. I guess it's only feasible with carbon hulls. Which I can't afford.

 

So glad i made this thread. Everyone has wonderful tips and advice. Tha KS so much!

 

Dark color only on the outside to prevent UV penetration and needs to be painted over with a light color to prevent heat migration. We use darker than neutral gray as a primer before paint.

 

So you think like a month at 80 degrees is enough and then finally fairing. or should I cure it longer?

 

We fair as soon as the last layer has cured and shrunk. one to two days. A month is too much.

 

Nah man. I'm well prepared and have all of the contingencies. I'm doing other fiberglass projects right now as well.

 

The materials as I have outlined are fiberglass on wood frame with metal flanges and c flex.

 

The uv degrades the resin quickly then. So inside curing. Got it. I can't do a very high heat treatment as my build space isn't setup for that, but I do have an industrial heater and industrial fans which I used for curing car paint and such.