Fiberglass help needed

Hi Wynand,

Sorry I missed your post. I have seen those bubbles before, but only in the free state

That is a not-bond problem you have there. If the previous layer, ie gelcoat has dried some, paint with resin before applying the glass. The problem is not the fiberglass.

Water or wetness will also isolate the wetted glass and pevent it from proper bonding.

If the resin get to gel before it is rolled onto the previous layer properly then that can also happen. If some resin got spilled on the glass and it gelled and the glass is then applied it is what you may get.

Polyester resin in general is not full of nonsense, and I have found you must make some really bad mistakes for it to come out improper. One thing though, do not allow the resin to gel before the glass was worked over completely.

I made a couple of experiments this week. One thing I found that worked well was to cool the resin down. This prolongs your pot life from about 8 to 10 mins to about 30 mins, but the applied resin wants to gel fairly quickly since it heats up once applied.

Looking at those pictures it looks to me like the resin started gelling before it was wetted out onto the bottom glass or gelcoat. The gelled glass was at a different angle and so lifts up to form those bubbles. I would grind it down and just apply small patches of chop to get the thickness even again.

One experiment I did was to check the amount of layers vs thickness. The resin cooled down, I applied the next layer of glass before the previous one started gelling. This caused the excess resin to be taken up by the fresh glass when you roll it on 'dry', and less resin is required for fully wetting the glass out then. I must say I was impressed with the compactness I got with 12 layers.

On your boat - I would precut the glass and all the layers. Roll the glass up, just the first layer lies in place. Then start at the transom and wet the first 1m of bottom layer, then the second, then third. Then do the next half a meter, roll the 2nd layer out a bit and wet that, then the third. This way all the layers gets applied while they are all wet, and you never struggle with dried spots. You will need some hands to hold the layers.

Some more advantages are better bonding between layers, they develop better heat when the layup is thick and when you are finished with the keel the transom should already have gelled. You should never get those bubbles again.

Also, when I do large layups, I use the minimum hardner for max pot life. To apply the resin I use about a 300mm paint roller, one can do quite a big layup in a relative short span of time. They also hold more resin which gets released more by pressing down on the roller, and excess resin gets picked up by it again and spread to elsewhere.

You can wash the roller thoroughly afterwards with washing powder. I use a plastic basin so one can rotate the roller easily in it. Wet the roller properly in the stromg mix washing powder, then shake the water out some and squeeze the resin out of the roller by clamping you hand around it hard and stroke. I know what you're thinking, but this is different The white stuff that comes out is resin that you can discard of. Spin the roller in the washing powder untill the hairs stand out properly and repeat. To rinse the roller I hold it under strong tap water that spins the roller. Dry by spinning it against a wall or flat surface. The hair should be soft and fluffy again. Hang it up to dry, if you put it down that part of the roller will go flat.

Best here in SA is to do glassing at night in the winter. You can work at your leisure and have enough time to do all the layups. The concoction cures the next day only.

 

Wynand
CSM is a pain particulalry 450.
I just built a heavy 12 foot knockabout boat and had similar problems. I found that I could eliminate all the voids by covering the hull with clear thin polythene sheet stretching it slightly over the hull and clipping it down. Then I used a sponge to smooth down on the polythene, you can see exactly whats going on and you dont pull the fibre by trying to roll partly cured mat. Even if you don't clip the edges it seems to work just smoothing out from the centre. Leave the sheet on till the resin has set. For awkward bits with a sharper return I found I coult put polythene then a car wash sponge clamped over the top which worked a treat.

Current thinking is that the principle reasons for the bad blistering of many GRP hulls is the voids left in CSM layup.

 

Thanks to all for the input thus far.

Yes Andrew, this is going to be the female mold for the infusion boat. The flange is only 70mm wide with location pins (half ping pong balls) spaced evenly around the perimeter of the hull flange.
But, this flange is only the base to which the hull sheer to deck mold screws to. The hull has a continuous radius sheer flange inwards and with a slight recess about 60mm from radius edge to which the deck fits into flush. This mold is small and easier to make and fit than to fabricate a split hull mold. On this mold I will leave enough "meat" to attach the envelope snot tape, vacuum and feed lines