Smooth finish on fibreglass floor?

rbcoomer

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Haven't posted here for a while, but as my rebuild project enters it's 5th year (don't ask - lack of time :rolleyes: ) I'm about to enter a new phase and after some tips please!

I've replaced the transom, stringers, ribs and floor and now currently completing the resin/mat overlay on the two side floor sections (these are higher than the central floor section which I will do last). All the timber was treated and the voids under the floor filled with 2 part foam. All the reconstruction has been done with polyester resin (after extensive testing of bonding with that which was cut out and removed) - various reasons but primarily cost and as an asthmatic, working undercover I couldn't risk epoxy. As a first project of this kind, I've not done too badly in terms of air bubbles or decent adhesion - mainly I think due to preparation/cleaning of surfaces and starting with smaller quantities, but the one aspect I've not yet cracked is getting a smooth, level finish! I have 3 layers of 450gsm CSM (which, with hindsight, would have been easier with 300gsm!)

I've ended up with a textured finish where the strands are embossed in places and thickness varies by perhaps as much as 1mm. I've yet to do the tissue layer but wondering how much this will smooth the finish? The final objective is to flow-coat all of the interior prior to application of eventual floor covering (probably a teak effect) to the walked areas. Will the tissue mat and eventual flow-coating level the surface or should I attempt to sand this flat first? Finally, do I need to add a gel-coat layer prior to the the flow-coat or, assuming smooth enough, can I apply the flow-coat to the resin layer?

Many thanks,

Robin
 

Tranona

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Skim it with a fairing compound such as International Watertite or make your own using epoxy and a fairing filler - high density but soft enough to sand easily. This is what is used when hulls are sheathed in glass and before final painting. Then you can flowcoat if you wish or you may find just paint will be OK. If you are going to stand on it you may want to finish with a non slip such as Kiwi in which case no need for flowcoat.
 

rbcoomer

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Skim it with a fairing compound such as International Watertite or make your own using epoxy and a fairing filler - high density but soft enough to sand easily. This is what is used when hulls are sheathed in glass and before final painting. Then you can flowcoat if you wish or you may find just paint will be OK. If you are going to stand on it you may want to finish with a non slip such as Kiwi in which case no need for flowcoat.


Many thanks, will get some and try :encouragement:

I was intending to use flowcoat as some surfaces are vertical and wanted an even finish first and then cover the walked areas with a harder wearing finish like a fake teak etc
 

prv

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Finally, do I need to add a gel-coat layer prior to the the flow-coat

Flowcoat and gelcoat are basically the same thing, the main difference being that flowcoat will cure in contact with air and gelcoat tends to stay tacky. So no need for gelcoat first.

Although if for some reason you were doing multiple coats, only the last should be flowcoat with the rest gel. Flowcoat cures with a waxy surface, which you'd have to remove to get the next layer to stick.

Pete
 

rbcoomer

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Flowcoat and gelcoat are basically the same thing, the main difference being that flowcoat will cure in contact with air and gelcoat tends to stay tacky. So no need for gelcoat first.

Although if for some reason you were doing multiple coats, only the last should be flowcoat with the rest gel. Flowcoat cures with a waxy surface, which you'd have to remove to get the next layer to stick.

Pete

Thanks Pete.

Yes, I was aware of the wax in the flow-coat - I was thinking that more layers might help smooth the final finish but was also aware I couldn't add another layer of flow-coat and expect to stick! I'll press on with the CSM and then a layer with the tissue on the bits I want smooth. If that's not enough (suspect it won't be) then I'll use a filler layer before flow-coat. Some of the areas will be covered with a grippy floor material (probably a fake teak or similar) but some sections are vertical (Bulkhead etc) or non-walking areas and I'd like these to be smooth with a decent aesthetic finish. It seems to make sense to flow-coat the lot and then apply other finishes to just those areas where needed... :) Long way to go yet.
 

William_H

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Flow coat is used for the inside of GRP hulls especially smaller hulls as a sort of decent finish to the otherwise rough CSM finish. It is usually white polyester resin with thickeners. However it does not present anything like a smooth finish. I think the only way to get that smooth finsh would be a layer of resin with filler like microballons or similar which is very easy to sand smooth. I suggest you start with an area not so obvious to the eye and see how you go. It will take a lot of work to get a smooth finsih like GRP gel coat (from inside a smooth mold) I think you might be going for a standard too high for the practicalities of the job. in other words slap on flow coat and ge the boat int he water. good luck olewill
 
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