The Difference between Gelcoat and Flowcoat (Topcoat)

Do you need a gelcoat or a flowcoat for your project? Here we explain the difference between gelcoat and flowcoat, and answer the question "Can you flowcoat on top of flowcoat?"

[@ttnyny]

I am new to fibreglass boat ownership and am trying to learn and understand basic principles. This is the clearest explanation I have heard thus far.

[@ecfibreglassuk]

Thank You

[@Cunningcrow]

Thanks mate, great clear explanation that puts my mind at ease about getting the right product to fix a fibreglass roof. 👍🏼👍🏼

[@ecfibreglassuk]

Thanks for the feedback

[@andrewmunro5154]

Absolutely excellent explanation, thank you.

[@CherylCold]

Brilliant. I have problems with bad repairs and bubbling under the paintwork

[@mapopapo3244]

Best explanation ever to the matter. Thank you !

[@pedrolg]

That is what I needed to know. Thanks so much!

[@Hutchy45445]

EXACTLY the explanation I needed! 😁 TVM!

[@cosf918]

Great vid. Supplied the information I been looking for . Thanks

[@malfunction6993]

Finally. Someone explains it. Cheers.

[@andy1986a]

I've used eastcoast fibreglass for years love this company

[@johngeorge2131]

Really good information ℹ️ I didn't know the difference now I do and how best to use it . cheers 👍

[@dannyjones3840]

In the states, we just call it gel coat with or without wax. And yes, you can use gel coat without wax as a top covering- just let it get tacky, and then spray it with pva (poly vinyl alcohol) and pva will form a skin over the gel coat, keeping air away so it'll harden.

[@ecfibreglassuk]

Ive seen the PVA method used quite a lot on videos from the states. looks like an interesting technique we'll have to do some experimenting here thanks

[@officialWWM]

I'm restoring an old timber boat. I've replaced sections of the deck and glassed over it. Should I flow coat it or just use a 2k automotive paint?

[@mgevirtz]

Great video. Very useful, thanks!

[@theunsvanwyk510]

Thanks for great video could you advise what is the best option to repair blisters in jacuzzi spa Thanks

[@robwilson7654]

Very useful information, thank you.

[@stevenmunslow125]

Thank you great explanation. Wondering what type of silicone will bond to flow coat, as I am wanting to water proof some bolts that are going through the flow coat in a camper trailer nose cone?It’s just to keep water out if we do some deep water crossings.

[@bomberman659]

I’d probably use a neutra cure silicone. (It doesn’t smell like vinegar) it’s less likely to bother the resin etc. P.s I’m not a grp pro. But do know a little about silicone and grp. Hope that helps. Edit auto correct

[@Ranger_Troy]

Hi I have a Fibreglass boat with a small hole. What would you recommend to fix it.

[@jt-rz9up]

Can I add another coat of flow coat over an older laminate? does the wax wash or evaporate away over time on my flat roof?

[@riccigilson5763]

The Gelcoat on the hull of my boat has faded/sun damage over the years from white to yellow ish. If i key/prep the hull can I spary flo coat (1 coat max?) to achieve a new white finish…

[@gta5teame701]

Perfect quality

[@rustykockelman9394]

Where can I find the products? I’m looking for a dark blue metallic gelcoat, is there such thing?

[@chrisb5839]

What is the best product to use when hotcoating a surfboard? The method seems to be to hotcoat, sand smooth, then hotcoat again to get a very smooth finish. If Flowcoat is not suitable for multiple layers, what else can be used? Thanks.

[@Simon-rm7pi]

Good explanation 👍

[@andy1986a]

Would it be possible to add acetone too flowcoat so that it would have better levelling properties

[@technicstim]

i put 10 coats of your gel coat on my boat and a final coat off flow coat then sanded back smooth and polished its amazing now !

[@RalphThielen]

10 coats?? You will definitaly get spiderwebs (cracks), coat must be less then 1 mm thickness.. But agreed, its easy smoothing 10 layers :D

[@technicstim]

@@RalphThielen well i haven't yet.

[@davidedwards1565]

@@RalphThielen Standard is 1.4 - 1.8mm thick who told you less then?

[@RalphThielen]

@@davidedwards1565 When your finished putting on coating its like whatever thickness you want, but after sanding it should be no more then 1 millimeter. When the coating is to thick it will be less flexible and you will end up with stresscracks/spiderwebs/etc.

[@keithstewart8799]

Can flow coat be sanded down to give a smother finish?

[@westrootsindustries9916]

for hull repair on boats, I was going to use the flow coat for the fast drying and ease of use but I have a question...Can you use flow coat as your base...then once you sand it and get the impurities out of it can you put a gelcoat onto the flow coat? or are you strictly relying on the bond between the fibreglass and either of the two parties of coatings? cheers

[@ecfibreglassuk]

Hi, you do need a resin with matt or cloth reinforcement as your base, as this finished with gelcoat is what makes GRP. They're similar chemically but different enough that you cant use one in lieu of another if that makes sense? Flowcoat also has a wax additive, so nothing will bond to it

[@HeetJoshiofficial]

Omg this explanation saved my life 😂

[@GooseDave]

Me too. Was planning to use gelcoat as a finish...

[@ingusskursitis3802]

Can I ad a tinner to flocoat and spray my boat?

[@MedMan3636]

What is the best product to thicken gelcoat for working overhead and adding a little extra fill to a chipped keel?

[@ecfibreglassuk]

Cabosil or fumed silica can be used to thicken the gel into a paste

[@ijkoool69]

I am about 1Lt short of gel coat to finish about1/2 M sq of flat roof. Will flowcoat act as gel coat to laminate glass matting and bond to timber OSB board & then get second coat of flowcoat on top fairly quick before full cure (20 mins) when completing the rest of the roof ?

[@ecfibreglassuk]

No. You can only do one coat of flowcoat as it won't bond to itself.

[@yassinchbani4267]

Hello dear Does flowcoat (topcoat) use for the external layer of composite stone such as Quartz sink ? Thanks

[@ecfibreglassuk]

Hi, it only works on polyester laminate

[@martybulbul8715]

Hi I’m in the process of restoring my boat and want to repaint it… my question is after gelcoating some fibreglass patch ups that I have done can a apply flowcoat over the whole boat after lightly sanding it? Looking forward to any advise thank you

[@ecfibreglassuk]

Hi, rubbing down flowcoat can be quite difficult so I wouldn't like to do a full hull. If it required fairing you may be best off doing this with epoxy mixed with a fairing powder such as west system epoxy mixed with 407 filler. skim the area, sand when cured then apply a further 2-3 coats of epoxy and leave to cure before priming and painting. but also seek advice from a professional boat builder/restorer first. As apart from having some knowledge on boat repairs our main background is in GRP moulding rather than boat restoration so our advice is limited on this.

[@joehunter7]

Hi- so im making a concrete hot tub overlaid in fiberglass. Do you recommend giving it two flow coats for thickness- if so should i post cure? Thanks- great video

[@chickenngeorge]

You can’t flowcoat on top of flowcoat cos of the wax on the surface, one heavy coat

[@joehunter7]

@@chickenngeorge thanks- so if I put a really heavy top coat on, could i polish? I'm thinking start with 100 an early up to 1200+? Is there a better way to get the shine?

[@bomberman659]

Once finished with sand paper, you can use a cutting compound then a polishing compound to a shine.

[@thesaltlifewithmichealsarc867]

Hey great vid thanks for sharing I do have a question To achieve cosmetic finish Do I need two coats and Does this mean first coat gelcoat last coat flow coat so the two will bond??? Or am I safe to just go one coat of flow coat

[@ecfibreglassuk]

It depends on the job. You can use a single coat of flowcoat and polish for a cosmetic finish, but generally speaking you want a coat or two or gelcoat, then flowcoat, to give you the correct thickness to be able to polish it back

[@thesaltlifewithmichealsarc867]

@@ecfibreglassuk Thanks for the reply that's the game plan 👍

[@danssv8]

Can I use flow coat to get a nice dry hard finish to make a cooler box or should I rather use gel coat as I will fibreglass over mdf timber treated with a pva , thanks

[@hippolytelures31]

hey thats what i am doing did you find an answer?

[@ecfibreglassuk]

We don't recommend it for this

[@hippolytelures31]

@@ecfibreglassuk what would you recommend?

[@ecfibreglassuk]

@@hippolytelures31 We wouldn't. No experience manufacturing cooler boxes

[@baldybain]

So my original gel coat has begun to develop cracks, how do I apply a new finish to the outside of the boat.

[@ecfibreglassuk]

Hi, please visit www.ecfibreglasssupplies.co.uk/ for technical advice

[@mattyttv]

My experience: You can put flowcoat in a mold before glassing up and you can put flowcoat on top of a flowcoat and still get a chemical bond, but you have to cheat. At around 10 mins after gel / exotherm, then apply the next layer. You need to ensure the prior flowcoat layer is of sufficient film build and gelled off enough to avoid alligator skin / tripe. The second brew needs to be catalyzed moderately and should not be too slow. The idea is that the sytrene monomer in the second layer gets a chance to bite through the wax while it is green and into the resin polymer before full cure. Seems to work well, but it does have its risks. I have only done this on less critical production when gelcoat was not available.

[@ecfibreglassuk]

Depending on the part and the time and money you've invested into the layup and manufacture, it's not worth the risk in our opinion

[@jameseley3098]

saome paints react putting 1 paint ontop of anther but if u use sanding sealer ur ok a and u can make ur own sanding sealer

[@cooke2585]

It would be better to use gelcoat rather than flowcoat if wanting to repaint over the product because of the wax in the flowcoat ? Should I still sand before painting ?

[@ecfibreglassuk]

Hi If you are trying to reapply a gelcoat and using multiple coats,it is better to do coats of gelcoat first as thes ewillchemically bond together, then finish with a flowcoat (gelcoat with wax), however bear in mind that gelcoat and flowcoats are not designed to be used as a paint and have a specific purpose in moulding applications. they are quite thixotropic and will leave brush lines or pit marks with a roller so therefore the finish wont be pretty. Having said that there are some instances where customers have thinned the products with styrene for spraying or even persevered with cutting it back . cutting back and polishing gelcoat/flowcoat is a hard long winded process and I wouldn't want to do a full hull this way. The other issue with this, that alot of users don't realize, is that when mixing you introduce alot of tiny microscopic bubbles, so that when you cut back you start to expose these as tiny microscopic craters, your newly applied gel coat can begin as a gorgeous polished finish but soon after can look dull and grimy once the dirt gets into those tiny pores. If going over old gelcoat you will certainly need to sand it and wash down with acetone to promote some of the chemical bond. If going over an already flowcoated surface we would recommend sanding the flowcoat off back to fibreglass or as near as possible . Some may argue that this is overkill but I've seen the bond fail after around 2 years or sooner once its been exposed to different hot and cold environments. as shown in the video of that failed bond, that panel was originally machine sanded with 40 grit and washed with acetone, all looked fine until after around 2or 3 years then the peeling started, we should have gone further back into the flowcoat or back to the fibreglass.

[@cyndycuffe8925]

I have a 20-year-old fiberglass swimming pool. I have sanded and painted with epoxy pool paint. The finish has oxidized and needs repainting. Is there a produce that I can apply to pool as final, finish coat that will replicate, restore or give result of original final finish?

[@ecfibreglassuk]

Hi, I'm afraid we can't help with this

[@Lucky-uk1bv]

@@ecfibreglassuk Be afraid, very afraid... LOL...

[@jamesfricchione]

What did you use to paint the pool? I am trying to paint my fiberglass pool as well.

[@francogiachin7214]

Phew, thx for your vid. I didn't know that you couldn't put a flowcoat on top of a flow coat. Sure, as you say, with impeccable preparation, it can be done. I dont think I will try that, thx again.

[@leecambsuk2871]

glad to see this as have put flow coat on top of flow coat before sanding in between coats but for board and boat repairs should i use a coat of gelcoat and then flowcoat to achieve a good bond?

[@ecfibreglassuk]

Hi, build up layers/thickness with gelcoat, and then you use flowcoat. After flowcoat you can sand back.

[@leecambsuk2871]

@@ecfibreglassuk thanks, will give it a go

[@andywarhol.]

If you want to use flocoat as a final surface (aka a "paint" ) I have found that if you: Sand the surface area well Wipe the area well again with acetone which will make it sticky THEN apply Flocoat You won't get peeling or issues. Hope that helps!

[@ecfibreglassuk]

That is correct if onto old gelcoat /fibreglass which has been sanded. however you wont get a chemical bond with flowcoat on top of old flowcoat (gelcoat with wax) . you will initially get a good mechanical bond but usually 1-2 years later , depending on weather exposure such as high heat and extreme cold, or flex, it will most likely fail no matter how much it has been sanded or wiped with acetone unless you sand right back to the resin layer . the top layer containing wax changes the properties of the gelcoat and a 100% chemical adhesion is not possible and the mechanical adhesion properties of polyesters are generally quite poor, they heavily rely on chemical adhesion between layers. This is one of the reasons this is massively debated and argued about on forums as some do not prepare the surface enough in the first instance or some are having success as they are going onto gelcoat and some not so much as hey are going onto flowcoat/topcoat.

[@Isaaydinphotography]

@@ecfibreglassuk So if I need to add 4 layers of coating, I should do the first three with gelcoat and then the last one with flowcoat, right?

[@robertolivarez5742]

so, if i was going to repaint my boat, i would use a flow coat over the gel coat? After preperation

[@ecfibreglassuk]

if you are doing engine bays, lockers or anything non cosmetic you would use this flowcoat. If repainting a boat, from a DIY approach, its best to just use marine primer and paint, you will get a much nicer finish. Or have a professional company/boat builder re-gel your boat as they will tend to have specialist spray equipment, formulas, a crucial temperature controlled environment and years of experience in re-gelling boats. but with standard brush flowcoats the finish will not be pretty or have a moulded look. You will get a brush lined finish at best, even with a roller it will be mottled and we wouldn't advise trying to cut back a large area, chances are you'd rub right back to the original surface just trying to eliminate the low spots.

[@robertolivarez5742]

@@ecfibreglassuk thanks very much

[@geoffreyrhodes]

Great video but I'm unclear why if gelcoat (without wax) will cure tacky in the presence of air then why does the laminating resin not try tacky. - isn't gelcoat resin with pigment and additives to increase the viscosity and reduce air bubbles.?

[@ecfibreglassuk]

They're similar but not exactly the same

[@Mark-gg6iy]

Resin\catylst produces anime which may aid in cutting off the supply of air....I think.

[@rogersmith5167]

What is Top Fast I have not had much success with it, it did not adhere well the first time I actually power washed it off, the second time I ground the deck until the mat fibers were visible it is now starting to lift again other resins have bonded perfectly what am I doing wrong. Top Fast is not your product or not supplied by you.

[@dprkassassin1876]

can you put topcoat over gelcoat to make it set

[@ecfibreglassuk]

Yes you can

[@dprkassassin1876]

@@ecfibreglassuk fantastic. cheers 👍

[@chris3237999]

@@ecfibreglassuk is there at time limit? Does the first gelcoat without wax have to fully cure or be in some sort of inbetween stage? (in regards to the question above... putting a flowcoat over a gelcoat)

[@stephenross1581]

Hi, I got a delivery off you the other day, I have one question please, do I add hardner to the flow coat ? Thanks in advance

[@ecfibreglassuk]

Yes you do, there's a chart on the front label

[@QuantumOfSolace1]

Does flowcoat come in clear?

[@ecfibreglassuk]

Hi, it comes unpigmented but it's not crystal clear

[@QuantumOfSolace1]

@@ecfibreglassuk -Thank you!!

[@darrenjones9180]

All ya have to do is add wax to the gel coat , been doing it for 42 years

[@humanitynow1565]

How , I just put the wax and mix it with gelcoat before applying ????

[@humanitynow1565]

The same wax that we use for releasing the mold ??? What is the ratio

[@shanokhala]

Thanks

[@michaelbruunskovkristensen2509]

Your arm must be tired....

[@craigjones9244]

Wax. 1 second, I win😁

[@handtohandcombat3535]

PVA simple

[@rai4241]

or you can buy 50 cents candle and put inside the thinner and put inside the gelcoat -the same results -budget friendly

[@ecfibreglassuk]

Thanks for the suggestion; however to our customers, I would say this is not something we have tried or would advise , especially if carrying out an expensive project. The '50 cent candle' plus the price of a thinner, not to mention the risk of using the wrong type of thinner and the pointless extra effort, may lead to a very expensive mistake and a big sticky clean-up on your hands. I’m not sure what you pay for thinners, but we do 1 liter of this MW for just under £10 plus VAT, and that’s enough to convert 50kg of gelcoat to flowcoat. mixing candle wax and thinners doesn’t really seem worth the risk? However I'm definitely not saying it wouldn't work and would be interesting to see. maybe do a video on this technique and send the link here in the comments once you’ve uploaded it? Although I would say to all our customers that if you start putting candles and thinners in our gelcoat, your product guarantee will be null and void 😉

[@rai4241]

Yes, I understand and respect your opnion- and your customer do whatever they want - in my personal experience I've been putting candle wax and painting boats here in south Florida for years and never stick and the finish is fabulous. @@ecfibreglassuk

[@xlrationmarine]

Um, not totally accurate. You can shoot gelcoat externally, once it starts to kick, spray it with pva. Pva cuts the air off to the gel and it will cure rock hard, and the pva will be slick when you start to wet sand it out, then continue to sand it out with soapy water, it keeps the sand paper from sticking.

[@Mark-gg6iy]

You sound like you are experienced, I am not. Can I bother you for some advice? Project: a wooden base interface between truck cab & cargo box (imagine U-Haul) built primarily to allow the cab seatbacks to recline. In essence, it is similar to a 16"inch wide section of an airplane fuselage. The exterior is fiberglassed. The bottom is immaterial to my concern. I sprayed Gelcoat on the sides and top successfully. When I sprayed the Gelcoat with wax my supply hardened (I am positive I mixed the correct catylst amount properly) unexpectedly allowing me to only apply a very minimal amount. 1 day later I had ~5 small areas that were tacky. I assumed after 1 day I should reapply the Gelcoat w\wax so I purchased more. 3 days later all dry no tackiness. I am\was planning on spraying this additional Gelcoat w\wax in 12 hours. However, after watching your video it seems you are recommending not to do this. Comments? Thank-you.

[@Lucky-uk1bv]

Can you spray Gelcoat... ? 99% of people will say no... But there is the 1 % of people who know what they are doing....

[@ecfibreglassuk]

The answer will always be "it depends". There are a lot of variables to consider

[@peterkoopman5070]

Lol

[@marcelpopescu8311]

După câți anii doar nu vreți sa stea acolo 100 anii mai trebuie schinbat

[@ecfibreglassuk]

to get a better bond that will last longer, you should at least totally remove the old flowcoat to get a better bond to the resin and fiberglass layer underneath. also give the old laminate a good few washes down with acetone to promote a better chemical bond.

[@goldar4846]

Could you use flow coat as a sort of paint for wood or other materials? I have 20l lying around, may as well make use of it if I can.

[@ecfibreglassuk]

HI Unfortunately it isn't much good as a paint. flowcoat relies on a chemical bond to another polyester , ideally on to a fibreglass/polyester laminate. flowcoat's mechanical bonding properties are not that great on other materials, as the wood starts to expand and contract throughout the seasons, the flowcoat will first start to split then as moisture draws in , it will begin to lift and peel off.