Advice on attaching marine ply to fibreglass

[josh28]

Can anyone give me some advice as to the best products/system to use to fix a marine ply daggerboard housing (which I am rebuilding and replacing) to the GRP hull of my express dinghy.

Any advice/experience would be much appreciated thanks!

 

[rjp]

I'm surprised that nobody has responded to this but I'll have a go having had some limited experience of once rebonding an detached ply bulkhead to a grp hull.

You could probably get away with using polyester resin and CSM as I did though nowadays I would use epoxy and woven glasscloth designed for that resin (CSM doesn't work well with epoxy). I think the key is to roughen both surfaces well and degrease by wiping with acetone (care - very flammable and noxious fumes, good ventilation required). I then painted the resin on the surfaces to be joined - at least 50mm each side of the joint, applied the glass cloth and stippled in more resin to wet it out thoroughly. Leave to set tacky and repeat with as may layers as you think necessary making each new layer overlap the last by a reaonale amount either side (10-20 mm). I envisage that your ply is meeting the grp at right angles or thereabouts so best to avoid a right nagled joint by using a fillet of thickened epoxy beforehand (or perhaps beading or suitable foam).

The WEST handbook gives lots of tips about using epoxy.

Hope this helps,

John

 

[sailorman]

I'm surprised that nobody has responded to this but I'll have a go having had some limited experience of once rebonding an detached ply bulkhead to a grp hull.

You could probably get away with using polyester resin and CSM as I did though nowadays I would use epoxy and woven glasscloth designed for that resin (CSM doesn't work well with epoxy). I think the key is to roughen both surfaces well and degrease by wiping with acetone (care - very flammable and noxious fumes, good ventilation required). I then painted the resin on the surfaces to be joined - at least 50mm each side of the joint, applied the glass cloth and stippled in more resin to wet it out thoroughly. Leave to set tacky and repeat with as may layers as you think necessary making each new layer overlap the last by a reaonale amount either side (10-20 mm). I envisage that your ply is meeting the grp at right angles or thereabouts so best to avoid a right nagled joint by using a fillet of thickened epoxy beforehand (or perhaps beading or suitable foam).

The WEST handbook gives lots of tips about using epoxy.

Hope this helps,

John

on old fibreglass epoxy is better as polyester resin doesnt adhere well to old lay-up

 

[rhumlady]

Epoxy best here as polyester isn't a glue which will stick well to the ply or wood.

 

[snowleopard]

Epoxy will stick to both wood and grp. Polyester does bond to old grp contrary to popular myth - you just have to be sure to abrade the old laminate back to a clean surface.

Polyester/wood bond works well for a time, especially if protected from moisture but in a plate case the water is bound to creep into the bond and long-term failure is inevitable.

Epoxy is a lot more expensive that polyester in bulk but for a little job like this it's a minor consideration. Epoxy does not react correctly with the binders in standard chopped strand mat so woven/stitched fabric is essential.

 

[footsoldier]

josh

Welcome to these hallowed halls.

PM sent

 

[oldsaltoz]

Here's what i did last time I built an new dagger board box.

Cut all ply to shape and dry fit to ensure is going to right, sand off any corners and edges then pull apart and lay out on a sheet of plastic.

Mix epoxy resin (about half a cup) in a wide shallow container then add a quarter cup or up to 30% by volume of Methylated Spirits and mix again, this will thin the resin and help penetration.

Extra coats will be required on all cut ends and edges because of the exposed end grin in the ply, so keep feeding it.

When have sealed all areas with the thinned resin add another 4 coats on the internal surfaces using un thinned resin.

Now lightly sand any mating areas, just enough to remove the gloss, Mix another half cup of resin and apply a thin coat the the sanded areas, then add Micro balloons to the mix to get a toothpaste consistency.

Apply this balloon resin mix to the box corner joints and assemble the box: making sure you leave a least a 3 mm thick layer between ply joints, anny thinner will weaken the joint.

Clean up any material when still wet, this stuff is very hard to sand off later. Use a small wooden dowel to form a rounded gusset on the inside joints of the box.

Let this cure overnight in area above 18*C and with humidity below 74%.

Joining ply to glass:
First clean the fibre glass area with some Acetone to remove contaminants, then grind the area with a disc grinder and a 40 grit disc. clean the area of all dust and wipe with acetone, allow 15 minutes to dry.

make up some braces to hold the box in the required position now and have them ready to fit.

Sand the bottom and lower sides of the box, wipe with Acetone and coat with fresh resin.
Mix another half cup of resin and after coating as above, add balloons as above, apply this along the joint.

lower the box into the required position making sure you retain the minimum gap of 3 mm at the joint with bracings, again using something like a broom handle of small fish paste jar make a gusset right around the box. Clean up to remove any excess balloon material.

When still wet or tacky start adding you cloth, applying the thinnest strip first, the next strip should overlap all edges by 15 to 20 mm, if using bi directional 300 gram you should apply 4 layers, then to cover any exposed fibres add a layer of 100 gram woven rovings, this will give a smoother finish.

Let this cure overnight as above and sand off any high spots or dags.

As epoxy is not UV stable you must coat it to protect it. I use High build epoxy primer, you then add almost any paint of your choice.

The other alternative is to apply a coat of epoxy flow-coat, do this with a standard nap 80 mm wide roller and tip off with 2 inch (or wider) long bristle brush or foam if you get one that will not melt.

Make sure have good PPE, latex gloves and spare containers, I use 1 litre ice cream containers, easy to clean and re use after the resin cures, put 2 pairs of gloves on, when things get sticky you just pull the outer glove off.

There, I think I covered most of it.

Hope this helps.

Good luck.