osmosis treatment


New member
27 Oct 2001
We are currently investigating the possibilities of undertaking DIY osmosis treatment on our GRP Warrior 35. Does anyone have any experience of DIY? How easy is it and how good is the end result? Do we need special facilities other than somewhere to dry out and shore power?
Alex and Ash, Celtic Wave.


I did a Hurley 22 on g/friends lawn. After drying out, sanded down to glass with angle grinder fitted with sanding disc ( green h/duty from auto-finishers [ 90 grit] but be gentle its easy to get too deep, and remember a GOOD dust mask. Go over again with higher grit to smoothe finnish. Wash with fresh water a few times then prey for at least 2 weeks of dry warm weather, no frost or dew. I used Blakes O/T, 2x2 coats at set intervals then antifoul keyed in This will be 3rd season on drying tidal mooring using hard cruising a/f. No probs so far. `E` me any Q.
PS lawn was blue/green for a while but soon came back. All forgiven.

<P ID="edit"><FONT SIZE=-1>Edited by harrygreasley on Sat Feb 9 21:58:14 2002 (server time).</FONT></P>


Well-known member
6 Sep 2001
I did mine ..It was hard work...gibsea 126..43ft..would recomend diy but a bit " wish i hadnt" at times..all went ok bit aprensive at times re curing of epoxy and will i get mix right..all worked out ok till now ,,and no sign of any problems....will say though I have asked myself was it realy necessary to strip all....I dont think so ..I wish I had only done the paches...Bill



New member
4 Jul 2001
Australia, East coast.
G'day Ash.
If you can handle an angle grinder, lay up small patches of fibreglass and can fair a hull then you should have no problem.
However, be warned, it takes a lot of your time and a lot of very hard work, particularly when fairing the repairs, depending the quality of finish you set as your standard.

Have a look at this site first, it will no doubt open your eyes and will help you understand what is going on and what you need to do.


The following is a short version of what I did many years ago with good results.
First you need to identify the location/s of the blisters, this is best done at night with a torch shone along the hull so that the raised areas produce a shadow, mark then with a suitable waterproof marker pen.

Remove all anti-foul and gel-coat first to avoid contamination. You need to grind into the glass to reach the liquid, it may be under pressure so wear some eye protection as well as a dust mask; follow the brown staining and remove it completely leaving the edges feathered for a smooth and strong join later. Then wash the area in fresh water, do this several times over a few days. Allow the exposed areas to dry out before the next step.

Cut some unidirectional 2 ounce fibreglass matting to the shape and sive of the depression you ground out, the first layer should just overlap the edges of the depression, now cut another close the shape of the original depression than another small enough to fit inside that so that the depression is filled level as you build up the layers. You should end up with a layer around the edge just proud of the surrounding GRP and the fill material should be just below the finish level, keep this as close as you can. Only use epoxy resins to ensure a good bond and reduce further ingress. Do lay up more than four layers one on one or it may overheat and produce gas bubbles. Before applying more layers after the resin has cured, wash the area with a running hose and rub it with a pot cleaning sponge scourer, this will remove deposits left during curing, you will notice the water no longer beads when it’s all removed.

Sand off all material to fair the hull than fill the remaining low areas with micro spheres and resin, then sand again and put a layer of epoxy resin over the repaired area to protect it.

When all repairs are completed as above give the hull 3 good coats of resin, you should be able to apply them wet on wet if the weather is warm enough, if not you will have to wash and scrub then lightly sand between coats. Finally, apply a coat of paint (I used 2 coats of Interprotect from International paints) then apply you choice of anti-foul.

Avaniceweekend or 4 Old Salt Oz.