changing a plastic through hull
- Thread starter Brad9210
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Removing the old thru hull
If you have an old thru hull that was put in with 5200 or some other material that is nearly impossible to remove here is a way to get it loose. It basically takes Tom's idea one step farther. Run down to you loal hardware store, Home Depot or Lowes,and get you one of the wire saws made for cutting PVC pipe. Has little handles on each end, and works pretty good.
If you have an old thru hull that was put in with 5200 or some other material that is nearly impossible to remove here is a way to get it loose. It basically takes Tom's idea one step farther. Run down to you loal hardware store, Home Depot or Lowes,and get you one of the wire saws made for cutting PVC pipe. Has little handles on each end, and works pretty good.
Bedding compount
I feel most people (including me) in their responses were being politiacally correct or just flat out shy about their choice. What is the prefered "bedding compound" for below and above water line...... Personally, I do not use 5200 and rairly 4200 on the boat.
I feel most people (including me) in their responses were being politiacally correct or just flat out shy about their choice. What is the prefered "bedding compound" for below and above water line...... Personally, I do not use 5200 and rairly 4200 on the boat.
Remove
1. Remove plastic through hull. 2. Discard. 3. Install bronze through hull, either by or with the advice and inspection of a qualified professional. 4. Repeat for all underwater through hulls. The money spent will be forgotten. The piece of mind stays with you forever.
1. Remove plastic through hull. 2. Discard. 3. Install bronze through hull, either by or with the advice and inspection of a qualified professional. 4. Repeat for all underwater through hulls. The money spent will be forgotten. The piece of mind stays with you forever.
I like 3M 4000 UV
for all the bedding except plastic or PVC ports. Then I use 100% silicone. r.w.landau
for all the bedding except plastic or PVC ports. Then I use 100% silicone. r.w.landau
Sikaflex 291 LOT
Quote: "I feel most people (including me) in their responses were being politiacally correct or just flat out shy about their choice. What is the prefered "bedding compound" for below and above water line......Personally, I do not use 5200 and rairly 4200 on the boat." Most of the top notch boat yards/builders here in Maine use Sikaflex products and more specifically Sikaflex 291 LOT. It's not as tenacious as 5200 and more along the lines of 4200/UV4000 but this stuff has an elasticity at break of 700% where 5200 & 4200 are 350% according to 3M. The only 3M product I use is 101 but that has been quickly been replaced by Sikaflex 291 LOT. 3M has not kept up with the technology or the times. Yes 3M is still better than the Boat Life products but that's not saying much. I've re-beded a lot of products over the yeas most of them done with 5200, 4200 or Boat Life products but I have yet to find a product I bedded with Sikaflex 291 LOT leak. Not to say they eventually wont but with a 700% elasticity at break why would they leak. Figure a stanchion base has roughly 1/32 film of sealant between it and the deck slightly more if you counter sink the bolt holes to create a gasket/o-ring. If you use a product that only flexes at 350% before it breaks your twice as likley to have a leak as one with a 700% flex at break. 350% of 1/32 is not a lot of movement and stanchion bases flex! Even a thru-hull flexes. Every time you open and close the valve it's subject to flexing forces. If you use wood backing plates they swell with moisture also exposing your thru-hull to slight movements. I always laminate my own backing plates out of solid fiberglass to prevent this expansion/contraction when I replace a thru hull. Trust me you want a product that is as flexible as possible and 291 LOT is the most flexible product that still offers a decent bond.
Quote: "I feel most people (including me) in their responses were being politiacally correct or just flat out shy about their choice. What is the prefered "bedding compound" for below and above water line......Personally, I do not use 5200 and rairly 4200 on the boat." Most of the top notch boat yards/builders here in Maine use Sikaflex products and more specifically Sikaflex 291 LOT. It's not as tenacious as 5200 and more along the lines of 4200/UV4000 but this stuff has an elasticity at break of 700% where 5200 & 4200 are 350% according to 3M. The only 3M product I use is 101 but that has been quickly been replaced by Sikaflex 291 LOT. 3M has not kept up with the technology or the times. Yes 3M is still better than the Boat Life products but that's not saying much. I've re-beded a lot of products over the yeas most of them done with 5200, 4200 or Boat Life products but I have yet to find a product I bedded with Sikaflex 291 LOT leak. Not to say they eventually wont but with a 700% elasticity at break why would they leak. Figure a stanchion base has roughly 1/32 film of sealant between it and the deck slightly more if you counter sink the bolt holes to create a gasket/o-ring. If you use a product that only flexes at 350% before it breaks your twice as likley to have a leak as one with a 700% flex at break. 350% of 1/32 is not a lot of movement and stanchion bases flex! Even a thru-hull flexes. Every time you open and close the valve it's subject to flexing forces. If you use wood backing plates they swell with moisture also exposing your thru-hull to slight movements. I always laminate my own backing plates out of solid fiberglass to prevent this expansion/contraction when I replace a thru hull. Trust me you want a product that is as flexible as possible and 291 LOT is the most flexible product that still offers a decent bond.
Sikaflex - absolutely the best sealant.
3M tried to copy the formula, but just never quite got it right.
3M tried to copy the formula, but just never quite got it right.
Backing plates
Brad - This isn't a direct answer to your question, but earlier posts have covered that pretty well. Adding to Tom S's comments, you should consider a backing of some sort for just abt. ANYTHING that you bolt thru or fasten to a f'glass laminate. The idea is to eliminate the point loading or hard spots by spreading the loading over a larger area. I'd use marine ply as Tom has: remember to radius the back side to match the curvature of the hull & give it 2-3 coats of unthickened epoxy to seal it from moisture. I'd bed it to the hull with thickened epoxy, but I guess a good grade marine caulk/bedding is OK too. If your hull is cored where the thru-hull is located, the recommended 'drill' is to remove a bit of the core material around the hole and replace it with thickened epoxy, to seal the core from water and future rot problems. This may not have been done by the manufacturer originaly as it cost $$ and takes time. None of the holes thru the cored deck of my O'Day were sealed this way and there is some core deterioration at almost every opening as a consequence: fortunately my hull is solid glass, so there are no issues there. The caulking/bedding compound you apply cannot guarantee that a tiny amt of moisture won't get thru in time. I'd use 3M-5200 below the waterline, but Main Sail's comments abt. Sika have got me thinking & I'll check out their products in future.
Brad - This isn't a direct answer to your question, but earlier posts have covered that pretty well. Adding to Tom S's comments, you should consider a backing of some sort for just abt. ANYTHING that you bolt thru or fasten to a f'glass laminate. The idea is to eliminate the point loading or hard spots by spreading the loading over a larger area. I'd use marine ply as Tom has: remember to radius the back side to match the curvature of the hull & give it 2-3 coats of unthickened epoxy to seal it from moisture. I'd bed it to the hull with thickened epoxy, but I guess a good grade marine caulk/bedding is OK too. If your hull is cored where the thru-hull is located, the recommended 'drill' is to remove a bit of the core material around the hole and replace it with thickened epoxy, to seal the core from water and future rot problems. This may not have been done by the manufacturer originaly as it cost $$ and takes time. None of the holes thru the cored deck of my O'Day were sealed this way and there is some core deterioration at almost every opening as a consequence: fortunately my hull is solid glass, so there are no issues there. The caulking/bedding compound you apply cannot guarantee that a tiny amt of moisture won't get thru in time. I'd use 3M-5200 below the waterline, but Main Sail's comments abt. Sika have got me thinking & I'll check out their products in future.
That Sikaflex product sounds pretty good
I am going to have to try it next time I do a project of this sort. I guess I just use what I have on hand or grab what I see out there at the local West Marine. Maine Sail. Have you ever tried "Boat Seal" for stanchions and ports? Its a combination blend of Polyurethane (like 5200 & Sika 295) and Silicone. Its elasticity is very high (like Silicone) but it claims to stick to anything (like Polyurethane). I doubt it ever will be as tenacious as 5200 but it seems to be doing well. I used "Boat Seal" on the bedding around my extreemely leaking opening ports about 5 years ago and they have be dry ever since (knock on wood...knock...knock...knock). It goes on and cures much quicker that some products and is easy to work with. Its like working with Silicone. I have been very happy with this product above the waterline ( As opposed to the Boat Life polysulfide caulk. That stuff is way too messy and seems to take a lifetime to cure. Never been a fan of that stuff and stopped using it)
I am going to have to try it next time I do a project of this sort. I guess I just use what I have on hand or grab what I see out there at the local West Marine. Maine Sail. Have you ever tried "Boat Seal" for stanchions and ports? Its a combination blend of Polyurethane (like 5200 & Sika 295) and Silicone. Its elasticity is very high (like Silicone) but it claims to stick to anything (like Polyurethane). I doubt it ever will be as tenacious as 5200 but it seems to be doing well. I used "Boat Seal" on the bedding around my extreemely leaking opening ports about 5 years ago and they have be dry ever since (knock on wood...knock...knock...knock). It goes on and cures much quicker that some products and is easy to work with. Its like working with Silicone. I have been very happy with this product above the waterline ( As opposed to the Boat Life polysulfide caulk. That stuff is way too messy and seems to take a lifetime to cure. Never been a fan of that stuff and stopped using it)
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