Replacement deck question

Looking at adding to the fleet with an old colvic 26 open boat. At the moment it has loose ply deck boards. They need replacing so the choices are
1. Straight swap but drench with thinned epoxy
2. Laminate ply
4. Ply deck and totally cover with resin/csm
5. Nidiplast and cover.

Never used nidiplast before but seen a few engine boxes made from it and seems good stuff.
Is epoxy or poly the way to go with a deck?
What weight of csm and how many layers? Its gonna be an open work boat and probably abused.

Any advice so I can make some kinda plan and costing before I buy would be great.
Thanks

 

Welcome to the forum.

My thoughts.

Saturation of wood with resin doesn't work. Thinning the resin significantly weakens it. One report I read stated that 10% thinning reduces strength by over 50%. You will not be able to penetrate past the first glue layer.

Nidiplast resists broad pressure well, but point loads poorly. IMO it will not survive the rough abuse typical of open work boats.

 

I mentioned saturating because its worked extremely well in a few other projects but they have been wheelhouses and engine boxes. Not heavy wear areas. In fact, found an off cut that I tested it on in an old bin full of water, 1' square of 18mm ply. Been soaking for about 2 years and good as new. I thinned 10% meths. But obviously this isn't an option for the deck then.

Few people were pushing me in the nidiplast direction but I was also concerned with it. Feel a little more confidence in 18mm ply.

 

Sorry I was interrupted.

The thicker the CSM and resin the greater its durability.

Polyester is inherently more UV resistant than epoxy. If you use epoxy then it most be painted. If some of the paint is worn away, the underlying epoxy will degrade quickly. A polyester mat will not degrade as quickly when the paint fails.

 

Would probably want to topcoat it all in a grey anyway. Used to use a lot of poly about 20 yrs ago roofing but single ply is a better product for roofing so haven't used it in ages. Remember it being an easier product to work with and saturates csm nicer than epoxy.

 

Yes poly saturates CSM easier than epoxy. Costs less. But needs to be thicker to prevent osmotic water penetration.

 

What would you suggest? Couple of layers of 450g ? Or would 3x 300g?

 

There are some contributing factors which I don't know. (Your skills, your weather, size and complexity of your deck)

450 x two pros: less labor, faster completion.
Cons: greater difficulty because of higher exotherm, so faster gelling. Harder to saturate

300 x three pros( easier to saturate with longer open time for resin.
Cons; much longer time spent head down butt up spreading resin.

A thought, tint resin grey. Increase UV protection while reducing visability of scratched paint. Would make spotting dry zones of CSM impossible.

 

Its about 12ish sqm . summer coming up so usually high teens low 20s most of the time. Can go to high 20s . I'd finish the top with non slip grey flow coat. Would prefer to keep laminating clear to make sure saturated.
Experience is a little old. Spent about 5-6 yrs flat roofing with poly before I ditched it in favour of single ply rubber for flat roofing. But that was early - mid 90's
Stopped using fibreglass for roofing because its so weather dependent which isn't good for roofing. Single ply goes down in all but heavy rain, can work between showers with it.

 

Whatever you do, don't thin resin and don't use resin without fiber on a deck. I just pulled my deck up which had resin only and only had fiber at the edges to tie in to the stringers and hull. Even the parts that weren't rotted were significantly cracked and clear evidence that it was a poor or uneducated practice in years past. Definitely use fiber reinforcement!

 

I only thinned the epoxy for the sheets of ply I used to make engine boxes and wheelhouses. Purely for weatherproofing. It works really well for that but obviously no good for high traffic areas .
Looking like I'll go for 18mm ply with I layer csm on the bottom and then a nice heavy lay up on top with a non slip flow coat. Just like the flat roofs I used to do .

 

It is best to use one coat of pure resin to seal the plywood's surface. Resin will be sucked out of the glass leaving it resin starved when glassing over a porous surfaces.

Since you where working in the 90 s, I assume you're near my age, and extended time on hands and knees is to be avoided. 450 won't be bad to saturate on the horizontal.

Tearing the edges of the CSM will help avoid humps at the overlaps.

 

Kinda envisioned cutting the sheets to size. Priming with a coat of poly in the workshop and then fitting in the boat on a nice day and lay up the day after when the putty has cured, weight the deck down while curing. Would a layer of csm on the bottom be a good idea? Plan to fix in place with resin putty rather than screw down, that a good or bad idea?

 

I suggest some slight additions/alterations.

• Cut to fit
• Resin one side and edges
• Sand and 2nd coat
• Flip sand edges, resin 2nd side and 3rd coat edges
• Glue and screw in place, double coated side down (I suspect too little bond area to rely on glue alone)
• Sand and lay glass
• Rince and repeat

 

Got about 60mm wide bearers for the deck all heavy laid up glass from new. Was originally build as a dock workboat for laying moorings