peel ply question

i want to make my flat floor smooth. using polyester and csm 2 layers . do i used cloth and resin with something like peel ply? i just want to cut down on sanding before i gel coat the floor

 

You would be much better off using a woven cloth (plain or biax) or woven roving to get a flat or smooth surface. CSM usually gives you a rougher surface and is not as strong. Your last coat ie the one under the gelcoat should be as fine as you can get probably around 200gsm to stop 'imprinting' when the resin shrinks over time. If you roller well it should be pretty flat, but do not over saturate.

Gelcoat will sit fine on this. Aim for 0.5-1.0mm gelcoat thickness and don't forget the 2% monomer/wax as well as the hardener. See one of the other threads about application if you need to - recoating f/glass canoe.

 

the reason for the csm is to strengthen the deck, light sand and ill put the 200 cloth. just thought the peal ply will make less sanding . i see its not really needed

 

CSM will not strengthen anything, only cloth or a knitted fabric will. CSM is a bulking agent and helpful with rough bond situations.

 

see still learning. so im sealing the plywood and bonding the cloth to it. the roving tab around the edge holds it. will the peal ply work with poly? also do i seal the ply on the bottom with a layer of mat? i have had people say it causes rot but more say its a good idea

 

It is very important to seal the ply prior to bonding glass on to it. I come across many, many failures where the ply has gone rotten inside the glass because it has been laid up dry. To save time the builder has not sealed or pre coated the timber parts, just laid the glass on the outside and put the resin on. In 90% of rotten cores on dinghies this is the fault. Recently I have had side benches, thwarts, jib sheet turning block mounts, inner stem fitting blocks and others all disintegrate from lack of basic attention to detail. Recently did a part new king plank because there was no timber to screw the stem/jib attachment fitting to other than a small bit of WR Cedar!. After 25 years it cried enough. Of course had to cut hole through stem to access as in built buoyancy tank with 4" hole was not good enough to work through.

Of course sometimes the ply quality is questionable....

However whatever resin you use, polyester or epoxy you must seal the ply surface and especilly the edges (end grain) which may require 2 sealing coats. Normally with ply I seal then sand after curing then apply cloth/roving. You know from the sanding that the surface is flat and good. The resin has already keyed into the wood pores and filled them so you should have a mechanical and chemical bond if done inside reasonable time frame.

The edge treatment will depend on the application. Glass will not easily bend 90° around an edge without leaving air pockets. If you need glass at the edge I would put a tape around it and cut this flush to the flat face prior to surfacing the main flat sheet. This will give a good seal and prevent water entering.

I've only used peel ply with epoxy but I can't see why it should not work with polyester. However I still think it is unecessary as a good cloth/roving surface will flat out really fast with an orbital sander and 80 grit or even a good fairing board and a couple of small hand blocks. PAR is completely right CSM is only any good for bulking out repair areas or bulking an area in the build. Also for tooling. Use cloth or roving for quality smooth strong surfaces.

 

Jimmy - peel ply will work wonders with either CSM or fabric.

"an orbital sander and 80 grit or even a good fairing board and a couple of small hand blocks. " is not something I like to do if I have some peel ply on hand.

Once problem with peel ply is that it doesn't handle compound shapes well, unless you use smaller pieces over the whole area.

It is a great way to get glass to lie down tightly and smoothly - like around the curved coamings of kayaks. Use gloved hands to smooth it tightly onto the underlying surface.