Cabin top repair

Hi I have an Ohlson 35 that needs the fibreglass on the cabin top re done. Can you advise me on which fibreglass would be best to use for this job? I have very minimal experience so any help will be appreciated.

 

Remove all delaminated glass.

Sand the substrate which appears to be strips of wood with 40 grit.

Sand the paint off any glass that remains bonded. This part is tricky and you must be disciplined. No loose glass will work. It will keep on delaminating.

Is the top painted or is that really bad gelcoat?

 

Thankyou! At this stage it looks like the whole top is delaminated or at least enough of it that I want to remove it all. I think it’s painted? Is there anyway to tell?

 

If you are removing it all; you want to sand all the wood with 40 grit. Precoat it with epoxy because it will drink resin. Then glass it with epoxy and paint.

Must you use epoxy? No. But it is user friendly.

Probably someone will disagree. I don't care.

I'd use some 10 oz cloth. 6 oz woven will get drysucked on old wood if you don't precoat the wood...10 oz probably as well... then after you get the glass down, a neat coat or two to weave fill.

 

I don't like voids in my laminates; so I would sand, precoat the wood with epoxy; then use a light density filler in the grooves and sand it and then glass.

 

Download the Gougeon brothers book about epoxy and boatbuilding.Pay particular attention to the warnings about epoxy sensitisation because it is a serious matter.You will need to determine how much area to apply glass to ans which parts need to be removed,for instance would you tke off those hatch coamings and glass beneath them or would you add a fillet radius and glass up the sides?Likewise the Dorade boxes and anything else that sits on the surface.It is not particularly useful to glass into a corner and hope that water never finds it's way in because movement of the wood will frustrate your expectations.

 

Ok thankyou that sounds do able!

 

I was thinking of removing the hatch coaming etc and glassing underneath as I think this was what was done previously?

 

It may well be,but it might not be much fun and it could take a while to complete.You will need to use glass cloth and not mat and it might be wise to use two light plies with the joints staggered.You can paint it after carefully removing the amine blush and when any equipment is reinstalled you can give it a second coat of paint with non-slip grit added where necessary.

We cross posted,I agree that removing the hatch coaming is a good idea.It will leave the boat open to the elements for a while so rigging a cover could be added to the job list.

 

2nd epoxy safe handling

do not allow it to touch bare skin

I am sensitized to it after using 300 gallons. I made the mistake of wearing a pair of briefs with a spot of epoxy on and used a heating pad and post cured it into my skin.. got a serious blister and perm scar. I also degloved and made a small contact area that also blistered. Not to be messed with...throw away contaminated clothing as well..

 

To me it looks more like a traditional canvas top instead of a fiberglass job, but it doesn't matter, the repair is the same. (Even for a traditional canvas job, wich I asume you are not interested in.)

First you remove everything bolted down, including the side trim, hatch coamings, etc. Then you rip off the covering exposing the wood and give it one pass with the sander to clean it. Now you look for rot (soft spots), and depending on what you find there are two ways forward:

1. There is little rot, only in small isolated pockets, the rest of the wood is dry and solid.
You cut out the rotted parts and replace the wood by scarfing (looks to be some sort of pine). Now you must stabilize the wood in preparation for fiberglassing. This can be done in two ways:
a.) Splining:
This means glueing the battens to each other by means of thin battens or thickened epoxy alone. For this you need to chase all the seams between the existing battens with a handheld circular saw or a router. If the existing wood is sized more like boards then battens you split it in two. Measure the depth with a wire in several places and set the tool slightly higher so you don't cut into the beams, nail a batten parallel to the groove as a guide for the tool. The grooves you just cut are filled with either a thin batten set in thickened epoxy, or thickened epoxy alone. In this step you also use thickened epoxy to fill over any holes, grooves and fastener heads. After it's cured you sand it fair, down to at least 80 grit and round over any sharp edges. You are now ready for fiberglassing.
b.) Plywood:
Sand the cabin top to 80 grit, then glue on one layer of 3 or 4mm plywood. Glueing is done with thickened epoxy, you fasten it down with temporary screws, staples or weights. You will probably have to scarf the ply, you can place the scarfs wherever you like. After the epoxy cures you remove any existing temporary fasteners and fill the holes with thickened epoxy. Sand the repairs flat and round over all sharp edges. Next step fiberglass.

2. There is a lot of rot and wet wood.
Remove the entire cabin top and replace it. This is done by removing the fasteners, or by cutting the battens each side of the cabin beams and chiseling away the remains. Remove all fasteners and asess the condition of the beams. If they are solid give them a quick sand, fill any holes, sand the filler flat. If they have rot, replacement is in order before you can proceed further.
The above procedure is likely to destroy the existing overhead (unless it's something removable from the inside), so you get to choose a new one in the style you like. This can potentially influence your choice of the new cabin top material.
The new cabin top can be: solid wood + plywood, plywood only, balsa or foam sandwich (this can eliminate the cabin top beams).

To answer your actual question, what fiberglass to use depends on the substrate. If you choose to spline the existing top, fiberglass with one layer of 400gr/sqm biaxial and one layer 200gr/sqm plain or twill over it. For plywood one layer of 300gr/sqm is enough. If you decide for a sandwich then you need more glass.

 

I agree. The only way to do a proper and neat job is to remove all the hardware first.

 

Thankyou so much for going into such detail, that really helps a lot! I think you are correct about it being a traditional canvas top, I initially thought it was some kind of vinyl. Fingers crossed there’s not too much rotten wood and I can go with the first option! I’m going out to her tomorrow to hopefully start removing the top. I’ll post back in here to let you know how I go

 

Try to keep it dry...you don't want to encapsulate damp wood

 

A traditional alternative that might be suitable if the wood plank deck is still serviceable would be to not stabilize the wooden deck with battens, glue, or ply; and instead use a floating canvas cover. This is particularly a good idea if the whole hull is plank on frame and moves quite a bit. The way this is done is to use Irish felt on the wood deck, then doped canvas on the felt. It's a pretty straightforward decking method that is also able to be refreshed without a huge amount of grief. On a wood planked hull, trying to stabilize the entire hull by battening the deck or using an overlayment is going to be futile.

https://schoonerchandlery.com/irish-flax-felt/

I want to second or third the notion that you want to remove anything and everything that can be removed and reinstalled without destroying stuff. Bedding hardware on a canvas deck may take a bit more thought than on a monocoque deck, so work through any hardware reinstalls or upgrades carefully before laying the canvas.

"What canvas do I buy???

what has been traditionaly used in the past is raw, non shrunk, cotton duck. It has no fillers and is not Sanforized. Once the canvas is tacked in place, boiling water is poured on it. It will shrink drum head tight and should be immediatly painted with piss thin semi gloss oil based paint in order to set it. Paint is applied directly to the wet canvas. See earlier posts on this subject.
Jay

https://forum.woodenboat.com/forum/...-canvas-do-i-buy?171240-What-canvas-do-I-buy=