what type of roller for gelcoat thinned with acetone

[redfox]

I am doing a gelcoat repair job on a rudder.

I've succeeded in applying two coats so far with reasonable results, but about two minutes into the rolling I start to get what looks like thin plastic strings coming off the roller. I suspect it is the roller material being dissolved by the acetone / gelcoat combination.

I think my current roller material is a polyester fibre.

Are there any other types of material that I could select for a roller?

Would West System polyurethane foam rollers behave any differently ?

 

[duhmey]

Re: what type of roller for gelcoat thinned with acetone

Hello redfox! I am wondering this same thing, I hope someone chimes in!

 

[Woodonglass]

Re: what type of roller for gelcoat thinned with acetone

I'm just wondering why you find it necessary to thin it with acetone when you are rolling it. That is not the norm. Even when spraying it you don't normally thin it. You are correct in that the acetone will pretty much melt most roller material. It is Not the gelcoat that is causing the problem. Acetone will break down pretty much any mfg's polyurethane rollers.

 

[chriscraft254]

Re: what type of roller for gelcoat thinned with acetone

I'm just wondering why you find it necessary to thin it with acetone when you are rolling it. That is not the norm. Even when spraying it you don't normally thin it. You are correct in that the acetone will pretty much melt most roller material. It is Not the gelcoat that is causing the problem. Acetone will break down pretty much any mfg's polyurethane rollers.

X2^^^^ Also, never heard of gelcoating a rudder before. Interesting. You should not be thinning the gel coat with acetone.

 

[redfox]

Re: what type of roller for gelcoat thinned with acetone

Hello Woodonglass !

Thanks for the reply. I could try an application without thinning with acetone.

My thinking regarding thinning was that I would get a smoother application. So far I am getting nice smooth layers.

I'm working at low temperatures at the moment when applying (about 5 C), leave the job outside for 3 hours or so, then bring inside at 20 C for proper curing after the fumes have dissipated.

Takes one day between applications after touching up previous run with wetpaper.

I have a problem with quick lumping of gelcoat after mixing in hardener if I use without thinning.

Any suggestions ? Can I use some other type of thinner that would not destroy the roller ?

My rudder area is approx. 30" x 9" x 2", so I can cover the entire area in 2 - 3 minutes.

 

[Woodonglass]

Re: what type of roller for gelcoat thinned with acetone

First off your substrate should always be at the same temp as your gelcoat. Having said that, 5c is too low to be applying gel coat. You will not get good results. What you could/should do is use a tarp and build a tent and then use heat lamps to heat the area up to a minimum of 13-15c. The heat of the lamps will not cause the fumes of the gelcoat to ignite. Mix the gelcoat inside the house and do not add the Catalyst until the very last minute and make sure the heat lamps have done their work. Then rush out to the boat and apply the Unthinned gel. What ratio of catalyst are you using in your gel? What Brand of Gel are you using? When rolling gel you're always going to get somewhat of a textured surface but if you use a foam brush to "Tip it Off" you can make it a bit smoother, but you will always need to sand and buff to get a smooth surface with gel. I am assuming you are speaking of the rudder on a Sail Boat...Correct???? Pics always help us to See what you are dealing with.

 

[redfox]

Re: what type of roller for gelcoat thinned with acetone

Hi Woodonglass !

Thanks for the advice. It IS a sailboat rudder, gelcoat above water, approx 9" x 2" x 30 ", rough 9" x 2" rectangular cross section above water, approx. 38" below water, proper sailboat rudder shape. The below water portion is covered with multi-layer Interprotect 2000 with VC 17 antifouling. I'm using Evercoat Marine One Step Finish Premium Gel-Kote, White. (Isophthalic Polyester Gel Coat).

I'll see if I can try some of your suggestions by setting up in my garage. So far my results appear to be good. The coating is still "wet" when I bring it inside and it does appear to cure and harden properly inside.

I see that you are in computing too. I'm a retired IBM mainframe systems programmer, still working on contract on the same IBM equipment that will be "retiring" early next year if all the conversion goes as planned.

 

[Yacht Dr.]

Re: what type of roller for gelcoat thinned with acetone

I'm just wondering why you find it necessary to thin it with acetone when you are rolling it. That is not the norm. Even when spraying it you don't normally thin it.

There is no Norm in Gel .. and yes when spraying "it" you would thin it unless its already ready to be fed into a pump gun for mass production.

X2^^^^ Also, never heard of gelcoating a rudder before. Interesting. You should not be thinning the gel coat with acetone.

Where do you get that information from ? I hope you understand that there are boats ( like a cat ) that have rudders out of the water most of the time. .. Gelcoating a rudder or two has not been "unheard" of by some of us that are in the Biz. Thinning with Acetone and other solvents have been used before you got your boat m8. ( direct from the factory ).

Hi Woodonglass !

Thanks for the advice. It IS a sailboat rudder, gelcoat above water, approx 9" x 2" x 30 ", rough 9" x 2" rectangular cross section above water, approx. 38" below water, proper sailboat rudder shape. The below water portion is covered with multi-layer Interprotect 2000 with VC 17 antifouling. I'm using Evercoat Marine One Step Finish Premium Gel-Kote, White. (Isophthalic Polyester Gel Coat).

Good Call redfox .. IP2000 and VC17 is a Very good combo..

As far as your rolling out gel on an exposed rudder is use a brush. Rollers Suck up Too much gel IMO. Very costly.

You can brush your rudder one side .. flip it and brush the other side..flip rinse and repeat until you get what you are seeking ( sandable/buffable or just sand and apply other epoxy coatings ).

Pics really help m8 .. you have a 25+ catalina ? ..

YD.

 

[chriscraft254]

Re: what type of roller for gelcoat thinned with acetone

Yacht Dr. I wasn't saying gel coating a rudder was unheard of, I simply said I have never heard of it done. Also if gel coat is thinned to much with acetone it can greatly effect the viscosity of the gel and not let it perform as it should. I would think if rolling or brushing there is no reason to thin the gel.

 

[ondarvr]

Re: what type of roller for gelcoat thinned with acetone

When "small" amounts of acetone are used while spraying, most of it flashes off during the spray process. When brushing or rolling, the acetone doesn't have the opportunity to flash off, so it stays trapped in the gel coat. Acetone inhibits the cure of the gel coat, that's why it doesn't get lumpy as fast, the problem is if it doesn't escape it can cause a poor cure, leaving the gel coat soft and with less water and UV resistance.

Sounds like the gel coat you have has wax in it, that means it should cure tack free on the surface. This is a problem if you want to apply more coats because you need to sand the surface very well for the next layer to bond. Gel coat without wax can be recoated without doing anything to the surface, the final layer should wax added though.

To get a smoother surface, use a brush or roller (for something this size us a brush) on the first coat and let it get hard, you can apply another coat with a brush and again let it get hard. Now use a small squeegee (Bondo spreader) and skim-coat the surface with gel coat. This will fill the low spots and not build up on the already high spots.

 

[oops!]

Re: what type of roller for gelcoat thinned with acetone

just to add......doing gell in 5c can be done if you keep a quatrz halo work light on the substraight....(rudder) you have to fool the gell into thinking it is at normal temps ....or it wont cure properly. mix your stuff indoors.....and run it out to the boat when you are ready

also.....i have done the approach suggested by ondarvr in several repairs......works like a charm....
remember ...you are building up[ the area...so dont press too hard with the brush on any coat.

as far as "lumpy" gellcoat without acetone....never seen it......perhaps the product you are using is really really old????.... (i never add acetone unless i am spraying...and then only at a max of 10% acetone)

ondarvr....what is up with the lumps...any idea????

 

[ondarvr]

Re: what type of roller for gelcoat thinned with acetone

I assumed the lumps he was referring to were from it gelling too quickly

 

[oops!]

Re: what type of roller for gelcoat thinned with acetone

e-gads...in cold temps....he is catting too hot

to the op......if you use the quartz light......you dont need to cat hot.....go at 2%....

if ondarvr is correct....you are cat ing too hot and have little working time...., dont mix a big bucket of stuff.....300 ml (a coffee cup full) will take you about 10 minits to apply. and it will all go on before it starts to gell..... 300 mil is 6 mil of MEKP

btw....when it starts to gell.......times up....throw the batch away.

so.....no acetone.....use a brush......unwaxed resin till the last layer.....use a quartz halogen work light to warm the substraight... use small batches.......and caytlize at 2%.