How to get dent out of rotomold 'yak

My 16 ft kayak got moved to the yard for a week while the garage was being worked on. It sat in the partial sun on 2 picnic benches, upright.

We just went to move it back to the garage. It dented on the bottom – a big dent. I assume it happened from the heat/sun, as it in the 80s all week. Dent’s on the bottom, in the bow area, forward of the seat area.

I flipped it over for now. How can I get this big dent out? Hair dryer? Weight on it from the inside? Lost cause?

It’ll pop out…
Same thing happened to mine in the same location after sitting on two sawhorses in the garage. I put it on top of the car, went paddling, loaded it back up at the end of the day, dent gone. I don’t put it on sawhorses anymore.

Those Amish do some poor work?

No, damn electrician

– Last Updated: Sep-06-08 7:21 PM EST –

It's taken him 3 visits and he's still not finished. I had to get all the boats out of the garage for him to work. They were sitting in the yard for a week (well maybe a little longer).

We put them back in the garage on their racks today, even though the guy has to come back one more time to finish.

The Amish garage is a great building. But the Amish don't do electric.

maybe this will help , maybe not …

– Last Updated: Sep-06-08 9:37 PM EST –

...... first check out rotational , blow and injection "moulding" processes , on say Wiki. .

if you haven't done this already , it's an interesting read for basic info. .

What I'm getting at is that I believe I remember that the construction process requires a heat that will bring the plastic to somewhere between 200 and 210 degrees to polymerize (molecular orientation ??) the different components that end up as the "plastic" .

Perhaps if you can bring the dent areas to the correct temp. you may have the ability to reshape the dents (I'm thinking the proper temp. will re-polymerize the plastic to a great extent) .

I remember that the unused particles that had gone through the heat process of roto moulding , were reusable (recycle) ..

You will probably need something the take the place of the mould shape when the boat is heated up in that area .

also remeber the cooling phase is critical , but I would guess just add a low heat a couple of times as it cools , to slow the cooling process some .

I think as the plastic nears 200 degrees it will become very malable (soft) ..

But even if one can determine the correct temp. to re-polymerize the plastic , how would you be able to measure and maintain the heated plastics temp. correctly ??
That seems to me like the "key" to a successfull job ..

I also thought about that some before .
If I were going to attempt it , I would do some preliminary testing first with the heat gun and a high temp. thermometer .

My thought was to start the heat gun at a distance from the thermometer and hold it there until the highest attained reading remained constant . Then move it a little closer . Then a little closer , until a constant heat on the thermometer gave me a reading of about 205 degrees without further rise . Note the distance the heat gun is from the thermometer at that temp. . My thinking is that if that distance is maintained , the plastic should never exceed the target temp. no matter how long the heat is held in place . The plastic may as well become a heat sink and the temp. may not acually reach the 205 target precisly but be lower in practice .

All I did with my plastic Necky was to
cut a piece of 2" foam, wedge it between the deck and hull bottom, and put the boat in the sun for several hours. If your boat bottom has not been severely stretched, it should go back in place fairly readily.

Try approaching it in stages . . .
First, as others said, you can try just leaving it out in the sun, dent up, and the rest of the kayak well-supported to avoid new dents. If your boat’s like mine, the “memory” in the plastic will allow the dent to come out by itself.

If this does not work, or only works part way, you can pad a board at both ends, cut to size so that wedging it inside will push the dent out to the original shape. Then, leave it in the sun for a few days. An option of this approach is to wedge the board in and while the wedge is keeping the boat in its proper shape, go over the dented area with a hair dryer, or lightly with a propane torch.

I have heard of people placing the boat right-side up and pouring water inside (even hot water) to push the dent out.

Let us know how it works out.

good hair dryer
A few years back a friend had a tree limb come down on the front of his roto-molded boat. BIG limb. What we found out was using a good hair dryer in stages will bring back the memory of the poly material. Start with warming the outer most section of the dented area, and slowly work inward. This can take patients as you may have to do this several times. I think our first warming took almost 1/2 hour. Let it rest, and repeat the process after the material has cooled for a few hours. Don’t hold the heat sourch in one spot, but make circular motions around the dented area. It takes a while, but you should be able to slowly lift the dent. A hair dryer works better than a heat gun as it doesn’t get the material over hot. Let me know if you have any questions. I work in a research facility where we frequently weld poly. Interesting material. Good luck.

BTDT, I have answers
I’ve got two different answers for you.

IF your boat has has the dent worked into it for a good while, it may want to think that’s the way it is supposed to be shaped. That’s okay though, since it started out as something completetly differently shaped anyway :wink:

You CAN fix this.

The first method I tried worked very well. The dent had appeared because I had the boat hull-down on a half-trailer. The dent was right under the front of my seat, and it was large.

I went to Lowes and picked up a cheapie heat gun that I’ve needed forever but never had a good excuse to get. $25 later I was in the garage with the gun in my hand, feeling a little worried.

Not to worry though, the operation is simple and unless you’re a complete idiot you won’t hurt anything. Just apply the heat (pref on a warm day) to the area of the dent, especially to the outer edges of it, where it starts to become concave. Keep moving the heat around; nice, slow motions but not slowly enough to cause the plastic to go shiny. The dent will become plenty pliable enough to push right back out, and it’ll likely pop right back into shape. After you do this, support the area for a bit until things cool down. Let it sit, then re-cook it again once more to set everything.

Now, you’d think I’d learned my lesson, huh? Nope, not this guy. I guess the padding I used in the back of my truck wasn’t keeping the hull off the bed as much as I thought, and I wound up with a big dent in nearly the same place. This time I tried filling the boat up with water. No dice. The pressure wouldn’t overcome the dent and the plastic didn’t re-form. I figured I’d be getting the heat gun out again. In the mean time, I flipped the boat over and supported the decking as the hull sat in the sun. When I came out of my garage, the dent was gone (90F+ day and in the sun).

So, my advice is to play around with sitting it in the sun first, especially after cooling the whole boat (water inside) to get a good thermal inconsistency between deck and hull. That’ll probably do it. Also, go ahead and get the heat gun. A bit of heat applied to dents makes them easier to work (especially in cooler weather) and if you get a scuff, you can melt it just enough to set the plastic back down without trimming it off. I’ve done a lot of hull repair on my boat using this method and it has not made the boat thinner anywhere (because you don’t keep the heat on it for that long).

Good luck, and happy dent-popping. You’ll get it out, so don’t give up! It isn’t rocket science, just be patient and careful, and remember that the plastic on these boats is surprisingly thick; they can take a good bit of abuse and muscle applied to them before things start to be a concern.

Ness my answer is true & cute

Not being a pet lover I finally found a use for them.

During my 49 day trip I noticed a major dent in the middle of my kayak which I figured came from the weight in the bow and in the dry storage. When I finished the trip I was afraid it was permanent.

My sister has cats so I took 3 - 50# bags of litter and put one under each end and one on the dent. I still used the kayak every day but when I got home I stored it on the litter bags with the bag on the dant.

It didn’t take long and the kayak was back to normal.

Everything turned out great. The kayak is fine and I realized “Cats do have a purpose”.

See ya next month!!!

Paddlin’ on


I thought you were going to say have the cats sleep on the dent, then warm it up with their bodies til the dent comes out. :slight_smile:

We have 2 cats AND bags of litter, also a hairdryer and a heatgun…so I can try many of these options.

Right now I have the Eskia with the hull up outside. Hoping for some SUN. It was cooler and overcast for 2 days now. Want to see if dent pops out first. It doesn’t look as bad as it did, but it is still pretty obvious.

You can’t use live cats

they move around too much.

Let me know if the sun works cause I got 3 cans of Beanee Weenees that say …it won’t.

Now quit foolin’ around and use the bag trick. It works, tried and proven.

Paddlin’ on


Polymerise is not the correct term
The solid particles “fuse” or liquify.

‘for sale’ sign works well

Foam Blocks
Ness; If you need some foam blocks give me a hollar. I’ve got a ton of em.

Yeah , technically you are correct …
… the term is “coalesce” of the polymers .

Hey Ness,

Hope all is well in your neck of the woods. Vince uses bricks to get the dents out of his rotomolded Sealution. He just puts some bricks inside of the boat, over the dents, and leaves it in the sun for several days. Works just fine.


Sell it

It popped out!!!
A few days in the semi-sun…and it finally popped out almost completely today. I have now moved it into the garage and stored it properly.

Thank you for all the suggestions for the next time this happens, when the dent will no longer pop out!

GK, you owe me some Beanie Weeenies!

When the boat is back to normal, hit it with the heat gun, gently. That’ll ‘set’ the shape again.