Thickening Gelcote Resin

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robbieg

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Next weekend if the weather gods are kind I intend to deal with one or two dings on my topside.

My boat is offwhite in colour & I've previously spent time mixing gelcote resin & pigments (all bluecote products) to get a reasonable match when I had to repair a small flat area on the deck. When sanded & polished this blends in fine.

The only problem is that the gelcote resin, hardener & pigment mix is quite runny-not a problem on a flat surface but I imagine it will be when trying to fill holes on a vertical surface.

Can I therefore thicken the gelcote mix to a putty like consistence & if so with what. If not how do you approach these repairs-wait until the mix starts to kick & then work like crazy. Any tips appreciated-I've done a search & found lots on gelcote repairs but not anything that addresses this. Thanks.
 
Hi,

You have a couple of options, 1 is to add some glass bubbles (note this does effect the colour a bit so you will have to add a little extra pigment) 2. Build up in layers. 3. Use some stickytape to hold the filler in place.
 
If gelcoat is running then you are putting too much on a small area, you only need to be just above the gell coat thickness, any more is waste anyway as you will have to wet and dry it off again.
Try using cellotape over the wet resin as this will flatten it out and exclude the air so that it dries completely.
 
Just take your time and put it on in thin layers. Any air bubbles will escape properly. You can recoat as soon as it is tacky. Mask around the holes so that you can test the tackiness on the masked areas. I don't use the waxed versions and finish with a film or spayed PVA (blue watery stuff). Most of the gelcoat I have done is with a spray gun and we did about a 1mm in 4 layers with 5-10 minutes between layers.

The hardest part is the sanding, so getting exactly the right amount on in the first place helps. Lumpy saggy blobs just make the sanding harder and there is only so many hour of my life available for that tedious task.
 
Robbie

Gel coats are designed to be used as a thin coat. They are brittle and if applied thickly will end up cracking. The strength in a grp laminate is from the glass resin composite with the gel coat providing the "impervious" top coat. If you are "filling holes" make sure you fill them with epoxy or polyester fillers and then apply the gel coat as the final layer.

I would avoid multiple coats as the styrene in the gel coat can attack a partially cured previous layer. The effect is called aligatoring in the trade.

Best to fill the vertical hole with epoxy filler then get a piece of melanex film bigger than the hole and apply gel coat to the melanex at the recommended thickness (1mm?). Then slap the melanex on the filled hole (resin side down) and smooth out to get rid of air bubbles. Leave in place until gel coat is hard (an hour? dependent on temp) and then peel off. Dont go mad on the catalyst - tempting to put a lot in ie >3% but it can cause discolouration as it can get hot.

Dr Bob
 
Colloidal silica is the generally accepted method for thickening low visosity resins. You should be able to buy from a model shop, sold under the generic name of micro balloons. I have used this successfully in the past on my boat and model aircraft!
 
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