Gelcoat not gone off

I have re gelled the outside of a boat seat base. The first coat worked perfectly and went rock solid. I then sanded it down and did another 2 layers (using roller) and this time it hasn't gone completly off. I added was in styrene to final coat. But the electric tripped and the temperature dropped down to less than 10 degrees.

What I have now I tried sanding and it gums up and leaves a mess. I applied some MEK, let it rest then covered in pva but there is no change

Today I have scrapped large proportions off with a Stanley blade scraper. In some places it's solid. Other places rubbery and you can dent it with a nail.

Do I have to keep doing the same and get it all off or will another fresh batch ontop cute it. The bits that come off are solid enough to roll up and feel cured on the airless side but sticky on other side and rubbery

Thanks in advanced gt

 

The only sure way is to take it off. I know, it is a bummer. Scraping may be the fastest way, and then wash with solvent. You can also try a heat gun and scraper.

 

take Gonzo's suggestion

scrape it off and give a good solvent wash with acetone or mek and some terry cloth towels, then sand it again

sorry for the bad luck

 

It maybe that you should have left it longer. In this cold spell we are having in the UK, I have mixed (correct proportions) gelcoat but found much longer setting times. As in 2 hours instead of about 20 minutes to gel. Temperature seems critical to the reaction, at some point the polyester really slows down. It does go off OK but needs the time and try and hold 10 deg C if possible.

Fortunately I've not been doing really large areas!, so relatively local 'dry' heat has come in handy. It also sounds as if the gelcoat was not thoroughly mixed with hard and soft spots? Try a little more mixing, I tend to add the 'wax' (2%) before the hardener and mix that thoroughly before adding the catalyst and repeating mixing. It may help to locally pre warm the gelcoat and wax mix ie stand on oil filled radiator (any heat that is dry) prior to stirring in the hardener. This will ensure the reaction (exotherm) starts correctly. If your gelcoat is at 'room temperature' and that is 5 deg, then it will prefer being warmed up a bit!.
Note the wax will be crystalline at these low temperatures so it must be heated a bit to mix in correctly.

 

Thanks all. Got most of it off today. Just the corners to tackle.

I am worried it will happen again. It's 10 degrees in workshop at the moment so I am dubious at recovering yet. I have read that wax is harder to get right than pva Rosie inhibit. Is that true? I didn't warm the wax up but mixed it at 2%. Catalysed at 2%. I wasn't sure if I need to increase catalist with another substance in it

First batch went off lovely and it's a real shame. I got a very good finish in most places.

Ps it's been 2 weeks now so I can't imagine it's going to do anything now.

 

I'd check the state of the wax. It goes into crystals, or almost a solid state at low temperatures, hence it needs to be warmer to be a liquid. It also needs to migrate to the surface after application so local heat is a boon. A small element blower will work or a small say 0.65Kw oil rad convecting over the surface.

You should be able to 'feel' the mix and maybe see the crystals if they are still there. The mix should be really fluid prior to adding hardener.

 

As mentioned, the wax solution needs to be warm enough to keep the wax dissolved in the styrene, at temps below around 20C it's possible for it to begin to solidify and separate (different suppliers use wax that may melt a different temp, higher or lower).

Not only does the wax solution need to be warm, but so does the gel coat or it will begin to solidify as soon as you add it to the gel coat.

If the reason for it not curing was related to temperature, then warming and recoating would have been fine. If you didn't mix the correct amount if catalyst, then it most likely would never cure correctly. If after warming it up later it didn't cure, then it was most likely not just a temperature issue. Having the surface stay tacky would be a normal consequence of cold temps and the wax not coming to the surface, but what's under that tacky surface should be hard.


Since the first attempt worked well, I will assume all the products are in spec.

Even a common heat lamp will be enough to allow the gel coat to cure correctly, or a simple tent over the part with a heater will work. No need to heat the entire room.

Another thing to check is if there's any wax left in the solution you're adding to the gel coat. What can happen when it cools and the wax solidifies and floats to the surface, is the first time you pour some out almost all of the wax goes out in the first glug or two, after that there is very little left in the container, so all subsequent batches get little to no wax.

 

Might sound like a silly question. How do I tell if the wax in styrene is still waxy enough? I'm confident from what you guys are telling me the wax didn't work. As when I peal the gelcoat off the other side is cured. It's all off now. Off to screwfix to get a bigger heater and try again this weekend
Thanks all

 

What sort of heaters do you use? The boat is in a make shift polytunnel but it can get quite funky in there when the polyester is mixed up. I open vents each end but the fumes can hang around. I presume they are flammable

 

I use mainly oil filled rads, but the small 'fan' type ones are OK too. Avoid like the plague the propane gas ones, they create as much water as the gas they burn. Utterly useless when working with epoxy or trying to get a bloom free finish on paint or varnish. Keep the humidity as low as possible. Tenting a local area with poly sheet or ply panels is fine to hold better local heat.
I'm not so keen on the monster blowers (electric) either as they tend to raise dust and I'm suspicious that they may pull in cold air from under doors etc if on the floor.

 

At 25C the wax solution should be clear, as it cools towards 15C it should become cloudy and then the wax will separate and solidify. Warming it will reverse the results until it's clear again. Do this test in a clear container.

If this doesn't happen then there is a very good chance there's not enough wax in it.