noobie fiberglass repair questions

[muncedog]

Hi all,

So looking to do some fiberglass repair on the boat over the off-season. Just had a few hopefully quick answer questions that will hopefully help many people:

Structural or cosmetic - other than common sense to the size of damage and wood staining visible are there any other damaged parts that should be left to the professionals - in my case the very bottom of the transom below the plug is somewhat damaged (surface broken) where its scrapped the sand bed.

Outside Corner repair tips - This mentioned section below the plug is on a corner under the boat/transom. Youtube repairs show some corners but not when repaired from the outside only. Any tips?

Is Gel-coat required and matching old faded coat? - Being under the boat at the back and hard to match a faded old colour ? is gel coat even required at all for sealing or can I leave the repair without gelcoat?

Filler uses - If I have understood correctly fillers can be used for very light cosmetic scratches and possibly on top of other repairs for an easy to sand down surface?

Water absorption on trailer boat - Given the climate here in Auckland NZ, and the boats only in the water a few hours a week, is water absorption (wood rot) likely or is this only an issue for boats moored in water?

Thanks in advance!

 

[DeepBlue2010]

Hi all,

So looking to do some fiberglass repair on the boat over the off-season. Just had a few hopefully quick answer questions that will hopefully help many people:

Structural or cosmetic - other than common sense to the size of damage and wood staining visible are there any other damaged parts that should be left to the professionals - in my case the very bottom of the transom below the plug is somewhat damaged (surface broken) where its scrapped the sand bed.

This needs a picture to access the damage and give you the correct answer. If it is only from beaching the boat, the sand will act like a sand paper and remove the gelcoat layer only (around 1 mm in total thickness). You should see no obvious damage to the fiber glass layer underneath the gelcoat. If this is the case, it is cosmetic. If the fiberglass itself is broken - if you hit a submerged log or rock, this is structural and require grinding and reglassing.

Outside Corner repair tips - This mentioned section below the plug is on a corner under the boat/transom. Youtube repairs show some corners but not when repaired from the outside only. Any tips? Again, without pictures, it is hard to say.

Is Gel-coat required and matching old faded coat? - Being under the boat at the back and hard to match a faded old colour ? is gel coat even required at all for sealing or can I leave the repair without gelcoat?

Gelcoat is defiantly required. Fiberglass is porous and will absorb water (very small amount over very long time) and subject your boat to bigger problems such as blistering. The color match accuracy and the perfection of the gelcoat totally depends on how much of a pain in your own nick you are Do you care if there is a slight difference in the color that can be seen only by the driver of the car behind you on the highway and the fish under your boat? If you do care then yes, you need to match the color and spend hours sanding, compounding and polishing. if you don't, you can spray the gel and rough sand it to the best of your ability and go boating.

Filler uses - If I have understood correctly fillers can be used for very light cosmetic scratches and possibly on top of other repairs for an easy to sand down surface?

In general yes. Just be careful when selecting the type of filer you will use. They vary depends on the type of resin they made out of and depends on the location they will be used (above or under waterline) Epoxy filers (and resin for that matter) will go over anything BUT. If you use epoxy filers, you will not be able to gelcoat. Gelcoat is made out of poly resin which in general can't be used over epoxy (some poly product is better than others when it comes to how will they bond with epoxy but I don't want to muddy the water with this argument. If you intend to use gel, make sure you get poly filer and for below waterline use. Don't use Bondo. By the way, you can also make your own filers. Let us know if you want to know how.

Water absorption on trailer boat - Given the climate here in Auckland NZ, and the boats only in the water a few hours a week, is water absorption (wood rot) likely or is this only an issue for boats moored in water?

You are mixing two scenarios, boats that are maintained well and don't leak water inside should - in theory - be as equally resilient to wood rot whether they are moored or trailered. The difference however is the need to protect the bottom from marine growth. Moored boats need bottom paint otherwise will have your own private reef start growing under your boat in a matter of few weeks.

Boats that are neglected and leaky however will both rot. Moored ones will go faster than trailered ones but at the end, they will both rot.

Thanks in advance!

Best of luck to you

 

[muncedog]

No Title

Thanks for your reply - super helpful answers. After a second look there is more damage than I thought - the glass has been damaged at the back. I have attached some photos. See what I mean about an outside corner...

The other photo attached is down the centre of the bow. Would a new gel coat suffice here?

So for both of these sections of damage anything is better than nothing and so am not that fussed with gel coat matching!

 

[Woodonglass]

That's pretty typical! Here's what I'd recommend. Use a dremel tool or a Drill with a Rasp type bit and grind out the rough areas. Sand the rest with 40-60 grit then clean it all well with acetone. Mix up a bit of "Hairy Peanut Butter" That's resin, cabosil, and 1/4" strands of CSM to fill the real rough areas and OVER build them Once that sets up sand it and reform the edge. You could lay down a layer or CSM and 1708 if you wanted to build the area up dependin on how much sanding you do and if a straight edge reveals the area is a bit low. Might not hurt anything to do this. Tape some plastic over the patch to ensure it cures well. Next day, sand everything well and feather the edges. and then lay down 3-4 heavy coats of gel coat and again cover it with plastic so it will cure. Or you can spray the gel coat with PVA or Add wax to the last layer. Your choice. DONE!!! That's how and Old Dumb Okie would do this repair!!!!

 

[DeepBlue2010]

The damage in the first picture requires some grinding and reglassing work. If you are going to tackle this job yourself here is what I would do..

1- Get a 4.5 inch grinder with a 40 grit flap disk
2- Grind down the damaged area until you see clean & damage free layer of fiberglass. Keep in mind that small areas or pinholes with sight yellow discoloration is normal. Don't try to chase these with the grinder or you will end up on the other side of the hull. You just need to remove the damaged fabric until you get relatively smooth and uniform glass.

3- feather the edges and try to blend the repair area with the rest of the surroundings
4- Trace the areas of the repair on a sheet of transparent laser printing sheet. Trace the areas based on their depth. The middle area with normally be the deepest and an outer area that is more shallower and so on.

5- Use 1708 fabric (some prefer to use an alternating layers of CSM and 1708. I don't personally do that because 1708 already has a 0.08oz layer of CSM attached to it. As a matter of fact, that is what the name stands for 17oz biaxial fabric and .08oz csm)

6- Cut the 1708 to match the areas you traced. The inner layer is the smallest (surface area wise) and the outer one will be a little bigger such that it engulfs the first layer and go a little beyond the first layer's borders, and so on

7- after the resin cures, sand down and fair the area, wash the heck out of it with Acetone and gel

Some people would fill the area with thickened resin to fair it and build back thickness and completely skip the glassing part. I never do that myself and I don't claim to be an expert or hold the keys to the truth. I just simply don't do it and I have my reasons. IMHO, the mixing ratios for a thickened resin (a.k.a peanut butter) doesn't comply with the resin to glass ratios that are required for structural integrity and strength. Even for deep gouges, I prefer to use strands of fiberglass from woven fabric but, again, this is just me

 

[muncedog]

Thanks fellas for your help -sounds like some learning/practice somehow would be a good idea first!

Just a few quick questions on your replies:

That's pretty typical! Here's what I'd recommend. Use a dremel tool or a Drill with a Rasp type bit and grind out the rough areas. Sand the rest with 40-60 grit then clean it all well with acetone.

I assume any areas which are no longer covered with the white gel coat will need sanding due to compromised fiberglass. As for the Acetone I guess I need to be careful not to damage surrounding gelcoat?

1/4" strands of CSM to fill the real rough areas and OVER build them Once that sets up sand it and reform the edge

I assume you mean long strips 1/4" wide or do you mean 1/4" squares? This approach of building the corner back up sounds like I will need to sand/feather out over a fair amount of the back surface (where the plug hole is) even though the gel coat is currently in tact there, to ensure a good bond?

3-4 heavy coats of gel coat and again cover it with plastic so it will cure. Or you can spray the gel coat with PVA or Add wax to the last layer.

Should each coat be dried independently or just tacky? Is the final cure important considering I am not fussed with cosmetic appearance here (likely to become damaged again!) e.g. if you didn't cover with plastic or wax/pva would the tacky finish cause any issues with the coats integrity?

If so, what would you reccomend for this upside down job e.g. pva/wax/plastic cover?

Cheers

 

[muncedog]

No Title

Cut the 1708 to match the areas you traced. The inner layer is the smallest (surface area wise) and the outer one will be a little bigger such that it engulfs the first layer and go a little beyond the first layer's borders, and so on

Trying to imagine this approach on a corner - is it something like my attached photo below?

Some people would fill the area with thickened resin to fair it and build back thickness and completely skip the glassing part. I never do that myself and I don't claim to be an expert or hold the keys to the truth. I just simply don't do it and I have my reasons. IMHO, the mixing ratios for a thickened resin (a.k.a peanut butter) doesn't comply with the resin to glass ratios that are required for structural integrity and strength. Even for deep gouges, I prefer to use strands of fiberglass from woven fabric but, again, this is just me

Interesting to hear two different approaches. If I have understood correctly one is more like a 'filler' - thickened resin with small cuts of unwoven (CSM), although I think woodonglass was suggesting long strips amongst the thickened resin?

The other is with resin and woven sheets.

I am reasonably new to boating and wondering how likely this is to happen again and so perhaps a quick 'filler' approach might be right, and then when I have learnt my lesson apply properly woven sheets.

That said it sounds like both approaches may take as long as each other. The gel coat itself from a quick read seems like the time consuming part (wax/PVA/plastic coating etc) sounds challenging to get right?

First things first I might start with the minor damaged areas and sand back and apply just new gel coat or do you think these need resin/glass also (the other original photos)

 

[DeepBlue2010]

WoodOnGlass is one of iBoats top authorities on the subject and I can't say - for sure - that the enforced filler approach wouldn't work. I am only sharing with you the approach I would take. I know myself, I am a pain in my own nick. As an engineer, I am more inclined to build "right" and never take shortcuts. So, instead of open it up to possibilities and learning leasons which might be more costly than I can afford, I just prefer to get it right the first time. If I take the filler approach on a place like this which is under consistent stress from the propulsion force of the engine, I would lose sleep keep asking myself "will it hold"

By minor areas, are you refering to the areas on the keel near the bow? If so, please try to post more clear picture of the damage, I can't tell from the ones you posted. If you still talking about the corner of the transom. I am not sure what are you referring to by "minor damage areas"!

This entire area - IMHO - is very structural. It is where the transom meets the hull. This whole area is under consistent force from your engine and it should be reinforced properly. If you mean some other areas than the seem, please highlight them.

One more approach to consider is ....

If you have access to the damaged area from the back, you can reinforce with multiple layers of 1708 from the inside of the boat. In such case, the filler approach on the outside would be much less risky .

 

[Woodonglass]

Thanks fellas for your help -sounds like some learning/practice somehow would be a good idea first!

Just a few quick questions on your replies:



I assume any areas which are no longer covered with the white gel coat will need sanding due to compromised fiberglass. As for the Acetone I guess I need to be careful not to damage surrounding gelcoat?
Yup but Acetone will NOT harm gelcoat so no Worries.


I assume you mean long strips 1/4" wide or do you mean 1/4" squares? This approach of building the corner back up sounds like I will need to sand/feather out over a fair amount of the back surface (where the plug hole is) even though the gel coat is currently in tact there, to ensure a good bond?
No, I mean 1/4" long Thread like Fibers. CSM is comprised of Loosely woven Fibers. Make your own or buy the fibers ready made. Yes sand up to the drain plug but the filler will mostly go on the "Edge" and feather on the side.




Should each coat be dried independently or just tacky? Is the final cure important considering I am not fussed with cosmetic appearance here (likely to become damaged again!) e.g. if you didn't cover with plastic or wax/pva would the tacky finish cause any issues with the coats integrity? Not but the final gel coat MUST be covered or waxed or PVS'd or it won't cure properly. Sanding any Polyester product that has not fully cured ends up in a GUMMY MESS!!!!

If so, what would you reccomend for this upside down job e.g. pva/wax/plastic cover?

Since its so small I'd tape it off with plastic.

Cheers

See my responses above and...

Your transom is 1 1/2" thick. It's "Glued" to the outerskin of your boat which is what's damaged. With the Transom being in place there's not much chance of a puncture at this juncture and it's pretty solid here. This outerskin is typically anywhere from 1/8" to 5/16" thick. Sometimes thicker. The bottom of the hull can be the same. The bottom is where the concern should be. If the glass has worn thin then it needs to be built back up with 3-4 layers of CSM and or 1708 glass. I'd prolly lay down a couple of layers of CSM just to be on the safe side and feather them in. The corner junction is always problematic to fix because wrapping fiberglass mat or fabric/cloth around a corner is not the easiest thing to do but if you pre bend/fold/crease it, it's a lot easier. Your repair is seen quite often. As I stated previously, Structural PB (Thickened Resin) will build the area back up. You only use 1/4" fibers of CSM "Threads" If you've seen CSM you know it's made up of Hair like fibers and you just separate these "Hairs" and cut them up to make your own or you can BUY these 1/4" fibers already made in a can. For your repair you'll only need about 1-2 cups of this Structural PB and your Mixing ratio would be 500 ml of resin, 5 ml of MEKP, 50 ml of Chopped fibers and then add Cabosil until it's as thick as Peanut Butter. Apply to the clean surface and Over Build it so you can sand it to shape. Then Sand the surrounding area back about 2" all the way around and apply a couple of full layers of CSM using plain resin and extend these layers out the full 2 inches onto the sanded areas and Tape a sheet of plastic over all of it to make it cure. Polyester resin is Air Inhibited Cured. The next day it will be fully cured. The plastic makes the cure happen.

 

[DeepBlue2010]

This is not a fight someone has to win. You are making assumptions about the health of this transom with no validation or inspections just to be right. In my book, this is irresponsible. The outer skin doesnt magically transfer the propelling force into the transom. Forces has to pass through, it is simple physics. Any tear or wear combined with hull flexing, as an engineer who stuided mechanical and structural engineering, i find it hard to accept your claim that "there is not much chance for puncture in this area" how do you think it was punctured in the first place?!!!

I also dont know where did you come up with the term "structural peanut butter" is adding a scoop of 1/4 inch long glass hair to a quart of resin makes it structural?!!

the mixing ratios of glass to resin are not secret, look them up and do the math and you will find it easy enough to scientifically - as opposed to egotisticaly - conclude that this mix is weak and dosnt come even close to the description "structural". True structural fillers from reputable companies like 3M are not even sandable, that is how strong they are. The only use i would personally consider for the thickened poly resin mix known on this forum as peanut butter is to make round transitions for fiber glass and that is it. And the only person i would accept another perspective from on the subject is Ondarvr because he has the expertise and the rationality to discuss it. If he tells me that this above mentioned mix is actually structural, i would stand corrected. Until then, i stand by what i said.

On a final note, moderators, please take a closer look at the members dynamics and code of conduct. Some attitudes here are becoming unbearable and intolerable. Some other members are becoming flat out disrespectful.

 

[muncedog]

As an engineer, I am more inclined to build "right" and never take shortcuts. So, instead of open it up to possibilities and learning leasons which might be more costly than I can afford, I just prefer to get it right the first time. If I take the filler approach on a place like this which is under consistent stress from the propulsion force of the engine, I would lose sleep keep asking myself "will it hold"

I am also an engineer although electronic so not quite my forte! I totally appreciate this point although I guess I am viewing the repair to this area as a medium term 'consumable' repair e.g. next season some further damage to it! That and if the quick fix is a 2 hour job and the long one a 2 day job... Id happily re-apply the quick fix many times!

By minor areas, are you refering to the areas on the keel near the bow? If so, please try to post more clear picture of the damage.

Yea I was refering to the area on the keel or some even smaller 'stone chip' areas just for practice/building confidence sake! Perhaps you view the keel damage area not minor either - it looks like its sand scrapped just past the gel coat about 1 ft long but very shallow damage, e.g. no strands of fibre exposed - the hull is a good 25 years old remember!

That said I'm sure the glass is also compromised there also!

If you have access to the damaged area from the back, you can reinforce with multiple layers of 1708 from the inside of the boat. In such case, the filler approach on the outside would be much less risky.

Interesting point, I do have access to the damaged area and so could reinforce! Would certainly be less visible also if I make a mess - What kind of coating is required on the inside of the boat -it does obviously get very wet here given its the drain hole but looks like its a plain coloured coating currently e.g. not gel coat?

I presume that any half decent repair approach is better than none at all, I can't reduce its strength from a bad repair.... I hope...

Did my cut out shapes make sense on that last attached photo?

 

[muncedog]

No, I mean 1/4" long Thread like Fibers. CSM is comprised of Loosely woven Fibers. Make your own or buy the fibers ready made. Yes sand up to the drain plug but the filler will mostly go on the "Edge" and feather on the side.

aha - so you literally mean individual fibers - like what the CSM cloth is made from. I guess you make your own by cutting up CSM cloth?

Not but the final gel coat MUST be covered or waxed or PVS'd or it won't cure properly. Sanding any Polyester product that has not fully cured ends up in a GUMMY MESS!!!!

I guess my question was do you need to sand/fully cure the final coat if you don't care about cosmetic appearance but reading that back I guess that's asking for trouble structurally also!

The bottom is where the concern should be. If the glass has worn thin then it needs to be built back up with 3-4 layers of CSM and or 1708 glass

So I a little confused, are you saying build the flat underside up near the transom with csm/1708 then fill the corner with peanut butter before covering with the feathered CSM? Also both this resin and the gel coat must be covered(e.g. plastic) to be cured ?

 

[muncedog]

This is not a fight someone has to win. You are making assumptions about the health of this transom with no validation or inspections just to be right. In my book, this is irresponsible. The outer skin doesnt magically transfer the propelling force into the transom. Forces has to pass through, it is simple physics. Any tear or wear combined with hull flexing, as an engineer who stuided mechanical and structural engineering, i find it hard to accept your claim that "there is not much chance for puncture in this area" how do you think it was punctured in the first place?!!!

I also dont know where did you come up with the term "structural peanut butter" is adding a scoop of 1/4 inch long glass hair to a quart of resin makes it structural?!!

the mixing ratios of glass to resin are not secret, look them up and do the math and you will find it easy enough to scientifically - as opposed to egotisticaly - conclude that this mix is weak and dosnt come even close to the description "structural". True structural fillers from reputable companies like 3M are not even sandable, that is how strong they are. The only use i would personally consider for the thickened poly resin mix known on this forum as peanut butter is to make round transitions for fiber glass and that is it. And the only person i would accept another perspective from on the subject is Ondarvr because he has the expertise and the rationality to discuss it. If he tells me that this above mentioned mix is actually structural, i would stand corrected. Until then, i stand by what i said.

On a final note, moderators, please take a closer look at the members dynamics and code of conduct. Some attitudes here are becoming unbearable and intolerable. Some other members are becoming flat out disrespectful.

I apologise for initiating a heated debate on this topic. I don't know if some posts have been moderated or removed but I don't think anyone was meaning to be disrespectful.

I aim to learn as much as I can before proceeding and hope others can learn from this thread. As an engineer also rest assured I won't be jumping into any solution before carefully thinking it through - if needs be I will take to a local professional if the job becomes out of hand.

I'm probably mistaken, but for the sake of peace, it sounds like WoodOnGlass was not suggesting the filler is the only part, more that it is also just for rounding the corner before applying sheets over the top?

However, that said, perhaps I shouldn't open the can of worms but you mentioned the structural fillers from 3M - even if these are at a high price, perhaps this is an avenue for me to consider here....?

 

[muncedog]

Hey guys,

So I bought some CSM, resin and flow coat - I realise its not the 'correct' way of gelcoat and covering but given its an area where appearance doesn't really matter and any repair better than none right - any other reasons to avoid flow coat? If I understand correctly its gelcoat with wax in it?

Also, was wondering on the areas where gelcoat has been damaged but fiberglass only damaged by moisture, how much should I sand back - how to know when you reach good dry fiberglass?

Im hoping its a thin layer and I can just sand that back and add gelcoat without having to build up fiberglass?