Which is better? Being on top or bottom?

[SEVEN]

I can just see this as a messy way to re-core. Imagine the resin dripping down your arms if you do it from below.

 

[Triskele]

I have done my fair share of fiberglass and coring work in the past. I find working upside down a real PITA. when laying in the core you need to be sure that you don't trap air into the layers. If your coring isn't sticking properly and falling down and not laying tight and flush it's a problem. Ive always used balsa which it little square blocks that are bound together with a mesh fabric to form a sheet. I have no knowledge of different coring materials and how they react. If you take a sheet of balsa and put it over a saw horse you can open up the blocks to apply the resin into all the balsa surfaces which is a must. After you apply your thickened fiberglass putty with a v-notch trowel you stick the two surfaces together. The problem is that the resin will start to drip out of the cracks And the balsa and will not stick very well to the putty upside down. If you work in small sections that will be your only option You will also have this problem when laying up the cloth or mat. From the top side it will be much easier to get the coring and mat down but shaping and fairing is labor intensive Most of the materials don't sand like drywall. Lol. And you will need to be careful that you don't have air bubbles and voids in your upper skin, over time this will cause surface failures. If you see white when grinding or shaping That is an indication of voids you need to grind them out. Also don't let the fiberglass hairs pop thu your final layer of resin. If I was doing the work I would work from the top on flat surfaces and from the underside if the fairing and shaping has a lot of curves and valleys. Sanding glass in tight curves and radiuses sucks most of that will be hand work and not machine It helps to hit it with 36 grit before it kicks rock hard. I buy all my stuff from mertons in Springfield ma. He is very informative and will answer all your questions and set you up with the best products for your project. The guy will spend lots of time walking you thru the process and how it relates to products and he ships nationwide. Hope this helps. It's just my prospective and others may think different. Good luck Have fun. Pete.

Pete...thanks for your input. Great stuff. You obviously speak from experience. Any reason why you haven't chosen plywood over balsa for the core material? I'm thinking for the deck that plywood might give a bit more structural integrity. As well, laying one large piece rather than several smaller blocks (balsa) might cut back the tediousness of making sure all the pieces are epoxyed and layed in correctly. You mention one of the drawbacks of working from the top side is that shaping and fairing can be labor intensive and once hardened, the resin and glass don't sand easily. I was thinking that I would save the skin peeled back from the top, reuse it, and then only have to reglass and resin the seams. Is that also your experience? If so, would it really be that much work to sand and fair. On a fairly flat surface, can't the sanding be done with an orbital sander. I ask because I have never done this before and am probably minimizing the difficulty. Also, you had concerns about air bubbles and voids in your upper skin, I would see this being a similar issue working from the bottom with the exception that any fails or problems are less detectable on the bottom side.

Thank you for suggesting Merton's Fiberglass. It's one I had not run across so far, but looks to be a good resource and source of product.

 

[Triskele]

I would never go back to balsa. Indeed it was challenging from the bottom up. I can almost guarantee that the bottom laminate will give you some grief working from the top down. It doesn't have half the substance of the top side and you may find supporting it to be challenging. If you go from the top down make sure to have an arch in the supports. That would be the first thing to install. Get it in, and crank it into position some how so that it mates up with the existing laminate well. I am thinking some 1/4 inch ply "T" over an arched frame to spread things out. Since you saw my post you saw the frame and screw jacks I used. Working from the top something similar could work but all of the pads pressing up should be joined together (1/4 inch ply) to prevent shifting IMHO.

Good points and suggestions Dan! Thanks! I think I am okay with figuring out how to support the bottom glass in the area forward the bulkhead and over the rode locker. Where I am having some doubt is along the gunwale. I do not wish to pull down the headliner to either support or take out the bottom glass. In consolation, the area is fairly narrow, maybe no more than 20 inches wide, so perhaps there won't be so much sag. As well, unlike the bow, there is no cambre to the shape. Oh, btw...any thoughts on the use of plywood as the core material. I'm sort of leaning that way.

 

[rwappleton]

Jay, My weather deck (read lower helm) has several soft spots and has been opened up sometime in the boats past for repair. Vincent C had an area virtually the same as mine that he fixed himself. From what I see it's long, messy and did I mention time consuming. Vincent C I believe did use some plywood. My concern would be adding a lot of weight up high or on just one side. Hatteras used balsa because it was light. I am thinking of sandable foam. Might get wet but wont rot. I have read here that is very important to support the lower side as the decks strength comes from both side plus the core as a unit. Supporting is pretty simple and I know of a few who put carpet between support and headliner and it worked just fine. I can not bring myself to pay for what most yards call fiberglass repair. I want it done right so I guess I gotta do it. I am going to do it in sections starting with the weather deck. Not going to be anytime soon but I will take lots of pictures and notes. Good Luck

 

[rsmith]

I'd look at using this
http://www.loctiteproducts.com/tds/TITE_FOAM_tds.pdf

 

[Top Hatt Craig]

"surfaces can be moist" very interesting, I'm wondering if a skillful application of this product would result in delaminated decks then passing hammer tap tests? Thanks

 

[Toolsntoys]

Jay, I've always used balsa because that was what I was taking out. I think balsa is a good product and is made to to the job it's designed for. The problem is when holes get drilled and hardware is added, but there are proper ways to deal with that besides 3M 5200. In my opinion plywood is not the right product for the job. It sounds like your stuck on using it. Balsa comes in small blocks for a reason, it confirms to the shape you need and won't allow air to be trapped. Laying a big sheet of plywood will be challenging good luck with that. Also usually a DA isn't aggressive enough to shape fiberglass. I usually us a flat 9 inch grinder with 36 sticky paper.

 

[Triskele]

Jay, My weather deck (read lower helm) has several soft spots and has been opened up sometime in the boats past for repair. Vincent C had an area virtually the same as mine that he fixed himself. From what I see it's long, messy and did I mention time consuming. Vincent C I believe did use some plywood. My concern would be adding a lot of weight up high or on just one side. Hatteras used balsa because it was light. I am thinking of sandable foam. Might get wet but wont rot. I have read here that is very important to support the lower side as the decks strength comes from both side plus the core as a unit. Supporting is pretty simple and I know of a few who put carpet between support and headliner and it worked just fine. I can not bring myself to pay for what most yards call fiberglass repair. I want it done right so I guess I gotta do it. I am going to do it in sections starting with the weather deck. Not going to be anytime soon but I will take lots of pictures and notes. Good Luck

Hello RW...thanks for the info. Good stuff. When you say put carpet between the headliner and support, are you saying that it is not necessary to remove the headliner when set up support on the bottom? Agree with your thinking on the type of core material to use, however, for a forward deck seems like plywood might be the better option because you can attach hardware to it. According to others, balsa sounds like it is least favorable. Coosa seems to be a preferred by others. May look into it. Besides being light weight and water resistant, Coosa is also easily shaping and formable to contours of the boat.