Keel repair - glass reinforcement question

[SailingEcosse]

Any fibreglass experts out there?

I need to repair the keel bottoms (encapsulated) on my boat (colvic bilge keeler) but I'm not sure what glass reinforcement to use?
I've ground the bad bits back to good fibreglass, and have the required epoxy resin, so should I be using chopped strand mat, woven roving, tissue, tape or something else entirely!

Many thanks
Alex

 

[Rigger Mortice]

IIRC you shouldn't use chopped strand with Epoxy. The others are OK, but tissue is really only for the final finishing layer and, on the keels, possibly not worth bothering with.

 

[Quandary]

Ubergeekian had a recent thread on this subject,
Note if you are using epoxy resins you should not use any old mat, it must be powder bound. (So not the stuff you get in Halfords) Rovings give structural strength but mat is good against abrasion and reduces the amount of fairing needed. If the surface is vertical or inverted rovings tend not to hold so much resin so a combination with matt will reduce run out. I general build up with a fairly heavy woven fabric and overlaid with mat then mix a putty with fairing powder if you need a very smooth finish. Calcium silicate is the better filler for under water but is very hard to fair so I only use it where there is a fillet or a big build up. I use a microbubble mix as a finishing top coat as it is very easy to fair but you could use a premixed epoxy filler for this last stage.
My suggestion, shape with a mix of resin and calcium silicate in voids and hollows, lay two to three layers of woven rovings, laid wet on wet if possible, overlay with a layer of powder bound mat, perhaps two if you have room. Smooth off when hard using the mat as a sacrificial layer, then apply fairing mix, smooth as well as possible but leave slightly high for fairing down when cured.
Uber was going to use Kevlar fabric but I would recommend just keeping it simple.

 

[SailingEcosse]

I would recommend just keeping it simple.

I'll go with simple everytime

Thanks for the info, just what I needed to know

Cheers
Alex

 

[oldsaltoz]

First up, do not use chopped strand mat, the voids in this material will more than double the amount of epoxy resin needed and will actually weaken the structure.

Pre cut patches of cloth so each patch overlaps, starting with the smallest patch first, apply wet on wet to start with, then, if needed wet on tacky, till almost level.

When this starts to go off (tacky) mix epoxy resin with 'Q' Cells (Tiny glass bubbles,closed cells) fill any remaining void and cover with peel ply or cover with plastic sheeting and tape.

After curing, sand flush and apply 4 coats of epoxy resin wet on tacky.

If the damage was caused by taking to the stone filled mud, consider using stainless steel angle shaped to fit the keel profile, fit an angle to each side with the angles overlapping along the bottom.

Good luck.

 

[sailorman]

I'll go with simple everytime

Thanks for the info, just what I needed to know

Cheers
Alex

for GRP repairs use epoxy as polyester resins do not adhere to post cured polyester resin

 

[SailingEcosse]

No chopped strand mat...got it, thanks

And just when I thought I knew what I was doing

After curing, sand flush

So I've got to ask..whats a sand flush?

cover with plastic sheeting and tape.

Peel ply I was aware of, but plastic sheeting and tape?
Is this to do the same job as peel ply, and actually sit on the surface of the epoxy while it sets, or is the idea to protect the epoxy from the elements while it sets?

Thanks all

 

[Quandary]

First up, do not use chopped strand mat, the voids in this material will more than double the amount of epoxy resin needed and will actually weaken the structure.

Good luck.[/QUOTE

I know that it is a big risk to contradict an Australian, but I do not agree with this statement; many of the boat builders I know might also want to contest it. I may be using different quality of mat but I get get good build up and a fairer finish and the resin does not drip away as it might with just rovings. I am certainly convinced that adding material does not make a lay up weaker as asserted above. Most of my background is in polyester moulding over forty odd years, starting out with making fuel and oil tanks for competition motor cycles.

 

[TQA]

First up, do not use chopped strand mat, the voids in this material will more than double the amount of epoxy resin needed and will actually weaken the structure.

Good luckI know that it is a big risk to contradict an Australian, but I do not agree with this statement; many of the boat builders I know might also want to contest it. I may be using different quality of mat but I get get good build up and a fairer finish and the resin does not drip away as it might with just rovings. I am certainly convinced that adding material does not make a lay up weaker as asserted above. Most of my background is in polyester moulding over forty odd years, starting out with making fuel and oil tanks for competition motor cycles. .

I agree with oldsaltoz on this. Avoid chopped strand mat if you want maximum strengh with minimum weight.

But in this case does it matter It is a keel! However I would still use mat and apply polythene sheet held on with tape just to halp hold everything in place AND reduce the need to sand off the excess.

 

[oldsaltoz]

First up, do not use chopped strand mat, the voids in this material will more than double the amount of epoxy resin needed and will actually weaken the structure.

Good luck.[/QUOTE

I know that it is a big risk to contradict an Australian, but I do not agree with this statement; many of the boat builders I know might also want to contest it. I may be using different quality of mat but I get get good build up and a fairer finish and the resin does not drip away as it might with just rovings. I am certainly convinced that adding material does not make a lay up weaker as asserted above. Most of my background is in polyester moulding over forty odd years, starting out with making fuel and oil tanks for competition motor cycles.

Epoxy resin will not dissolve the binders used in CSM, the fact that it tries to retain it's original shape helps smooth the work.

However, by nature CSM will take up to 3 times the amount of resin to fill the voids in it, unlike the one to one ratio in epoxy cloth.

The simple rule with epoxy is to roll out as much resin as practical, because epoxy resin is very brittle when cured, having too much resin will contribute to the problem.

Make a simple test sample, one with and without CSM, stick in a vice and flex it, you don't need me to tell you what will break first.

Good luck.

 

[oldsaltoz]

No chopped strand mat...got it, thanks

And just when I thought I knew what I was doing

Quote:
After curing, sand flush
So I've got to ask..whats a sand flush?

Sand the area flush.

Quote:
cover with plastic sheeting and tape.

As this is on your keel I thought peel ply may not flex enough to cover the area without flattening the repair area.
A thin plastic sheet over the area will hold the repair in position and prevent any bleeding.

Peel ply I was aware of, but plastic sheeting and tape?
Is this to do the same job as peel ply, and actually sit on the surface of the epoxy while it sets, or is the idea to protect the epoxy from the elements while it sets?

Good luck.

 

[SailingEcosse]

..whats a sand flush?

Sorry I should have put a smiley at the end of that one

Understand about the plastic sheet now though, I was wondering how I would get all this to stay on the bottom of the keels while I waited for it to set, but that solves the problem nicely, thanks much

Work starts this weekend (weather permitting!)

 

[oldsaltoz]

Work starts this weekend (weather permitting!)

I try to start around 10 AM when I am sure the temperature is on the rise, most epoxy resins need a minimum of 17*c during the cure and humidity less than 75%.

Make sure you wash the repair after curing and befire sanding to remove any residue left by the curing process.

Start at the top and work down, run a hose over the area and rub with a plastic kitchen 'scochbrite' scourer, you will know when it's clean, the water will no longer form beads like that in fresh polished car.

Good luck.

 

[William_H]

Keel repair

Presumably the bottom of the f/g keel has been damaged by grounding or hitting rocks. A better material is kevlar for the basic repair work. It is incredibly tough. In fact hard to cut to shape with scissors.
You need to put a fair bit of filler over the kevlar as again it is so tough it won't sand smoothly but rather produces little hairs of material that stick out of the sanded area. ie don't try to sand the kevlar itself but rather the filler on top of it. If you want a large build up use f/glass with kevlar covering then filler.
I think the kevlar would be easier/cheaper than a stainless steel foot to protect the keel. good luck olewill

 

[Quandary]

If you are doing the job in Scotland you may have to wait a month or two for a daytime temperature above 17C. However, West claim that their fast hardener (205) can be used above 10C so you might be safe enough accepting their advice and going ahead rather than missing a month in the water. It is still worth choosing as warm a day as you can find. They give a lot of advice about lay up too, some different from what you read on here, worth reading it if you have not used epoxy resins,fillers and fabrics before.