Filling in "dents" on a fibreglass top

[floating bee]

I have a fiberglass top-Its in very good condition. However where the previous owners have removed quite large windows there are "dents" where the large windows were. Does anyone know what I could use to fill in the undulations.

[Charlotte Burnett]

U-pol - it's commonly sold as car body filler. If it's too thick, you can thin it a bit with resin. Depending on the depth, you might need to build up layers of it. Best to over fill though and then sand back. Give it a good paint on top when you are done, it's hydroscopic - as is primer - so top coat as well.

[bigste]

Fibre glass repair kit from a car accessory shop or a motor factors if you need a lot. Make sure you use rubber gloves

[floating bee]

U-pol - it's commonly sold as car body filler. If it's too thick, you can thin it a bit with resin. Depending on the depth, you might need to build up layers of it. Best to over fill though and then sand back. Give it a good paint on top when you are done, it's hydroscopic - as is primer - so top coat as well.

Something like this:

http://www.ebay.co.uk/itm/290136676154?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649

[Charlotte Burnett]

Yes - but I've fallen out with P38 - it's pretty claggy to apply. U-pol is the pro version, although also available in smaller tins. Fibreglass repair kits are really for bridging holes.

 

http://www.expressautopaints.co.uk/product/upol/easy_7_filler_3.html

 

Thin it with this http://www.building-supplies-online.co.uk/u-pol-fastglas-resin-250ml--tin-16033-p.asp

[RLWP]

I'd second the 'professional' filler vs P38. It sands better and is somehow easier to use. Another bonus - I have a tub in my workshop which is nearly four years old. It still works perfectly where the P38 would have gone off

 

Richard

[Ex- Member]

Yep any good car body filler would suffice. When I trained as a car sprayer Plastic padding was the favoured brand, some years ago now but I've always used it as it does the job perfectly.

 

I note now they make plastic padding for marine applications even one specifically for fibreglass. It's made by Loctite

 

http://www.force4.co.uk/b/109/Plastic-Padding.html

 

Avoid cheap fillers though, some are pretty naff.

[Phil Ambrose]

I have a fiberglass top-Its in very good condition. However where the previous owners have removed quite large windows there are "dents" where the large windows were. Does anyone know what I could use to fill in the undulations.

 

There is a certain amount of truth in all of the above posts, but cherry pick what suits you, ignore the post about GRP being hydroscopic. Fill below surface and finish the job with Gelcoat Filler, this can be sanded/polished to match your existing GRP. ( 10 years living on a 40ft X 12 GRP cruiser)

 

Phil

[floating bee]

Thanks everyone-I will have a look at your suggestions.

[boathunter]

There is a certain amount of truth in all of the above posts, but cherry pick what suits you, ignore the post about GRP being hydroscopic. Fill below surface and finish the job with Gelcoat Filler, this can be sanded/polished to match your existing GRP. ( 10 years living on a 40ft X 12 GRP cruiser)

 

Phil

He said filler is hydroscopic which it is, not the GRP.

 

How deep is the question? You don't want filler too thick or it may crack, but it's the easiest stuff to get a good finish, so if the recesses are more than a couple of mm deep use fibreglass then car body filler on top.

[floating bee]

He said filler is hydroscopic which it is, not the GRP.

 

How deep is the question? You don't want filler too thick or it may crack, but it's the easiest stuff to get a good finish, so if the recesses are more than a couple of mm deep use fibreglass then car body filler on top.

The indents are quite deep-some 1 cm and maybe more.

[Ex- Member]

The indents are quite deep-some 1 cm and maybe more.

 

Wow that's deep,I was assuming more of an imprint rather than a dent that deep. You need to buy some fibreglass mesh and resin. Cut the fibreglass to the shape of the dents with scissors, scratch dented area apply resin then lay on fibreglass. repear process untill 1 to 2 mm from the surface. Where fibreglass resin goes off, smooth & scratch the surface with 40 grit and apply body filler to smooth over the resin. Rub down filler using rubber block first 40 then 80 grit production paper. you might need to fill again if there's areas that did not rub down using the rubbing block or any dints or nicks remaining.

 

Basically with dents filled, and rubbed down, begin the painting process. Smooth body filler with 150 grit wet & dry, prime with several coats of primer, When dry, inspect, you'll probably need to fine fill over the applied primer as you can be sure pinholes will exist in the filler, use a cellulose primer stopper for this.Nick in any imperfections Re-smooth wet and dry up to 360 grit wet & dry, re prime then overcoat with chosen top coat.

[boathunter]

Are we talkin window sized 1cm deep indentations? Maybe you could post up a picture?

 

If you manage to make these invisible by using GRP and filler, I'll doff my cap to you. I don't think you'll do it and what's more you're likely to make it look far worse. I repair classic cars and use filler looking for an invisible repair. I wouldn't atempt what you're suggesting. I could spend a whole week on one large flat panel and that's what you're looking at here per window. What's more you won't have a chance of shaping it flat with anything smoother that 80 grit which will mess the surrounding gelcoat. From what you've said, I'd live with it or make it into a feature somehow.

[Ex- Member]

Are we talkin window sized 1cm deep indentations? Maybe you could post up a picture?

 

If you manage to make these invisible by using GRP and filler, I'll doff my cap to you. I don't think you'll do it and what's more you're likely to make it look far worse. I repair classic cars and use filler looking for an invisible repair. I wouldn't atempt what you're suggesting. I could spend a whole week on one large flat panel and that's what you're looking at here per window. What's more you won't have a chance of shaping it flat with anything smoother that 80 grit which will mess the surrounding gelcoat. From what you've said, I'd live with it or make it into a feature somehow.

 

Agreed a picture is needed, i'm assuming these are small indentations resulting from something previously fitted. possibly recesses for fitting bolts lugs etc no longer required. I dont think the OP is referring to the full surface area of a window as the OP uses the term indents (in the plural) so I'm assuming several small. Could be wrong though

 

Photo's really do help other members solve problems or give advice quicker.

[RLWP]

 

 

Floating Bee's challenge is around the edges of the blanks that were fitted to make the windows smaller. This is a pretty old fibreglass top and was not made smooth and shiny. It is, however pretty strong and waterproof, except for the cracks around the edges of the blanking plates (whatever they are made of)

 

I think I would want to gouge out the existing filler where it is loose, make sure the blanking plates are firmly fixed, seal up the cracks and then use filler.

 

Richard

Edited March 17, 2013 by RLWP

[smileypete]

A good sandable non hygroscopic filler can be made from epoxy resin, micro balloons or glass bubbles, plus colloidal silica, read all the handling precautions/horrer stories on epoxy first though.

 

They can be had from Ebay or an online suppler like CFS fibreglass, or a local boat builder/repairer may be able to sell some on. AFIAK epoxy sticks to cured polyester resin a bit better than more polyester, but in this case more polyester may work OK if the surface is well roughened.

 

cheers, Pete.

~smpt~

Edited March 17, 2013 by smileypete

[Phil Ambrose]

He said filler is hydroscopic which it is, not the GRP.

 

How deep is the question? You don't want filler too thick or it may crack, but it's the easiest stuff to get a good finish, so if the recesses are more than a couple of mm deep use fibreglass then car body filler on top.

 

I did'nt say that filler is not hydroscopic, just ignore the instruction to paint. Correct use of Gel Coat Filler will ensure a perfect water resistant finish, unless of course the GRP has already been painted. I assumed that original Gel Coat finish of the boat remains.

The whole point of using Gel Coat filler is to effect a invisible repair ie replacing damaged Gel Coat with Gel Coat. Oh and I would use Marine Filler, I believe the formulation differs from that of Auto based products.

 

Phil

[RLWP]

The boat has been painted several times

 

Richard

[Phil Ambrose]

The boat has been painted several times

 

Richard

 

In that case paint it. (The repair of course)

 

Phil

[bizzard]

Applying body filler is an art not unlike plastering. A good vehicle body worker can apply it in one swoop leaving it almost perfectly level and smooth with virtually no waste in application or sanding afterwards and needing very little stopping after priming. Be bold use a good wide clean edged plastic spreader and swoop from low down upwards or at an upward angle using uniform pressure.

Don't pat about with little trowel fulls cos it'll take a month of Sundays to get it smooth and level.

[floating bee]

Had a close look today-the surface is a bit undulating-the fiberglass is quite difficult to sand back but I could try scraping it-another idea is to install marine ply; 3-4mm on the sides.