Polyester Laminating 'outdoors'

[medusaboat]

Has anyone any experience of laminating Polyester FRP outdoors in the UK???

Summer daytime temps are high enough to begin a cure, but will the laminate remain undercured as the evening temps drop???

What would be an acceptable procedure? Start time? dealing with condensation etc??

I realise that this is a very 'open' question - any help would be appreciated.

Cheers

[gonzo]

If you have concerns about condensation, cover the whole thing with a plastic sheet. It won't adhere to the resin.

[medusaboat]

I am talking about the production of a large (60ft ish) sailing yacht, where all of the laminating will not be completed in one day. I obviously do not want to attempt a bond to damp grp layed the day before, but by waiting until the condensation 'burns' off in the sun I am wasting laminating time!!!
Also if I were to begin laminating at say 8:00am and work until 2:00pm my laminate will not be fully cured by the time the temp begins to fall. Will this result in dramatic undercure? Will the cure be reestablished during the warmer temp on the following day? I appreciate that it will never be as good as a 'proper' post cure in a heated building, but needs must etc. Does it REALLY matter in the real world??

[gonzo]

You can cover a very large boat with plastic sheeting. Also, a heater in the inside of the boat will complete the cure overnight. Make sure it is spark proof.

[medusaboat]

My God!!! I feel REALLY stupid - I never even considered a heater!!!
The hull is being built upside down and is moulded over a former made from 16mm (approx.) thick Pine strips. The former is 30ft long. Roughly what kind of heat do you think I will need to be safe assuming an overnight temp of ??? 5 deg C.

[ondarvr]

You say outdoors, do you mean no cover at all? If there is no cover then you are asking for trouble. On small projects that will be finished in a few days it may not be a problem, the weather may stay nice long enough for you to finish it without too many complications. But on a 60' yacht many of those days (months) it will be pouring down rain, with no cover it will be a mess. With a cover ( none leaking roof) you should be OK, many boats have been made over the years that way, not perfect, but will work.

[lewisboats]

With poly you can vary the amount of MEKP that you add and vary the cure time. More juice equals a quicker gel and cure time at equal temps. get a gallon of cheap stuff and do a bit of experimenting... adding progressively more drops per batch then time the results.
Use a board with a few light bulbs under a localized polytarp tent to warm up your immediate working area and burn off any moisture. 2 or 3 60 watt bulbs in cheap fixtures mounted to a flat board, light it for a 1/2 hour or so and the immediate temp around the board under the tent will be about 80-90 f deg, plenty to dry things up. You can use this to help speed cure too.

Steve

[gonzo]

They make infrared bulbs that screw on to a standard fixture. They produce more heat for the same power.

[lewisboats]

I suppose you could use less bulbs with the IR. They are designed to keep stuff HOT so you would need to be very careful.

Steve

[medusaboat]

Do you really think that a few bulbs, IR or not, would be enough to raise the temp of a large surface area, through an insulate (wood) high enough to ensure a full cure overnight in the UK? What do you consider the lowest temp for a full cure and for what time period would I have to sustain that temp?
Cheers

[lewisboats]

Why would you have to go through the wood? And how large an area are you doing in one shot?
Try holding your hand within 25 cms of a light bulb that has been burning for 10 minutes or so, quite toasty.
The lowest temperature would be about 12-14 C (55-60 F) with the right mix of resin and catalyst.
Suspend the lights above the laminate (about .25-50 m) and suspend some polytarp above this by about the same distance to enclose the area. You should get a good 10-20 deg rise inside the tent with say...4 75-100 watt bulbs. Putting a tiny fan (battery?) to circulate the air would even be better yet. With the right mix, you should be quite hard within a few hours, then full cure within 24 hours...but you have the daytime hours to help this. IR bulbs would increase the heat by 5-10 degrees.

Steve
See attached for a diag of what I mean. Left is a profile view of the board, right is an end view showing the board, hull and tent.

[yokebutt]

Don't worry about heater efficiencies, they're all high due to the second law.

Yoke.