cinder blocks

[Bayou Dave]

I will be removng the trailer to do some needed repairs to the bunks and rollers.
Some members have posted not to use cinder blocks as they may explode. Cinder blocks are very strong and can hold up a building as they are laid on edge, not on the flat.
Any ideas why a cinder block would explode?

 

[Bondo]

Re: cinder blocks

I will be removng the trailer to do some needed repairs to the bunks and rollers.
Some members have posted not to use cinder blocks as they may explode. Cinder blocks are very strong and can hold up a building as they are laid on edge, not on the flat.
Any ideas why a cinder block would explode?

Ayuh,.... Usually from an idiot layin' 1 on its side, so's it won't sink into the dirt,...

Uneven loadin' of the block is probably the 2nd reason,.....

Wood blockin' is Much safer,...

 

[Bob_VT]

Re: cinder blocks

Wood will not penetrate the fiberglass. The materials in cinder blocks can harm your gelcoat real FAST. Like the equal of using 40 grit or courser sand paper.

 

[Silvertip]

Re: cinder blocks

Cinder blocks cannot tolerate a "point load" meaning that a couple of square inches of trailer frame coupled with weight is enough to fracture it. In building construction they are also overlapped and in full contact around the perimeter as well as the cross webs. Not the case when resting the trailer frame on just a part of the block. In building construction the blocks are also resting a level "footing". The only way a cinder block would be safe would be to fill the voids with concrete and then rest a 2x6 or 2x8 board on top with the frame resting on it. And by the way, using cheap jack stands is not safe either. The style of stand that consists of a round tube with the bottom end cut into three parts to spread them out to form the legs are dangerous. Yes -- they have a metal band to sort of tie them together to prevent spreading. These stands can bend to the side, forward or backward right where the slits end from forming the legs. The stands may be able to handle a true vertical load, but they cannot handle any amount of side loading. Just ask me how I know that to be true.

 

[Bayou Dave]

Re: cinder blocks

I planned on putting a 4x4 or 6x6 on top of the highest block to protect the hull. A few searches show that a lot of folks use cinder blocks with wood on top. If I only used all wood I probably would have to use 8x8 for it to be stable a couple of feet off the ground. By using 3 or 4 cinder blocks and then a 6x6 on top I think it will be stable enough. I already have a 8' long 4x4 and a 8' long 6x6 I cut into 2' sections.

 

[tpenfield]

Re: cinder blocks

Cinder blocks are fine as long as the load is distributed across the surface of the block and the block is oriented the proper way.

The problem that arises when using cinder blocks for lifting/holding heavy objects is that often there are very concentrated 'point' loads placed on the block(s) which can cause the concrete to fracture and the block to abruptly shatter (explode).

When I use cinder blocks I put plywood in between each layer of block and 2x wood as the top piece. This makes it much safer . . .

If I am going to work underneath something , I use multiple methods of supporting it, each capable of holding up the load.

 

[Bayou Dave]

Re: cinder blocks

Silvertip... I was typing my last post and then I saw your post. What you say makes sense. Looks like I will search for some 8x8's to support it.

 

[GA_Boater]

Re: cinder blocks

I planned on putting a 4x4 or 6x6 on top of the highest block to protect the hull. A few searches show that a lot of folks use cinder blocks with wood on top. If I only used all wood I probably would have to use 8x8 for it to be stable a couple of feet off the ground. By using 3 or 4 cinder blocks and then a 6x6 on top I think it will be stable enough. I already have a 8' long 4x4 and a 8' long 6x6 I cut into 2' sections.

If you plan on stacking 3 or 4 blocks vertically with wood on top, you have a recipe for disaster. If the trailer rocks in the slightest and the blocks separate like a hinge, down it comes. If you insist on blocks, double up with two side by side on the bottom and the next course at right angles. Much safer and stable base that way.

 

[Bayou Dave]

Re: cinder blocks

If you plan on stacking 3 or 4 blocks vertically with wood on top, you have a recipe for disaster. If the trailer rocks in the slightest and the blocks separate like a hinge, down it comes. If you insist on blocks, double up with two side by side on the bottom and the next course at right angles. Much safer and stable base that way.

That thought never occured to me. Sort of like stacking firewood. Thanks....

 

[crabby captain john]

Re: cinder blocks

Why not rent a slip or dry stack for a short period?

 

[Home Cookin']

Re: cinder blocks

So what it comes down to is this: used correctly, cinderblocks are safe. That means hiring a licensed mason to build you a wall or pier. But the general public cannot use them correctly. Hence the warning: don't use them. Even a smart guy who is seldom around cinderblocks would appreciate how fragile or unstable they are.

It's the same with dozens of safety rules: don't stand up in a boat. Don't shoot a gun indoors. Don't play with matches. Don't wear tennis shoes to cut the grass.

And good point about not trusting jack stands, etc. They are all made like crap now and the good old ones are stressed out. Hydralic and floor jacks are worse.

Gravity has no conscience and will not make allowances for how careful you are or how much you trusted your skills or someone else's.

 

[Chris1956]

Re: cinder blocks

Yes, As GA says, two blocks side by side in first course, two blocks perpendicular to them for next course and so on. The last course can be a single block, with a piece of wood (any kind, but at least 3" wide) between it and the hull. Blocks must be laid open end down and plumb, and level.

Mono-hull Boats need to be blocked in the stern corners of the hull and under the keel, 3/4 of the way to the bow. That part of the keel must be parallel to the ground. Normally blocking the stern keel is optional, as it is not usually strong in a molded fiberglass hull, and a pain to get all three blocks level with each other.

 

[steelespike]

Re: cinder blocks

I haven't used blocks a lot of times but have used on a lot of boats.
Always some wood on top.These were all wood boats size 15' to 23 feet.
The stern blocks at 45 degrees to the keel for stability.
Blocks were always stacked flat side but with at least a 2x4 on top.

 

[Texasmark]

Re: cinder blocks

I never had a problem with them. As others said, main objective is reasonable load and even distribution. On the edge, 2x8 top and bottom. Go for it.

Mark

 

[Lone Duck]

Re: cinder blocks

I never had a problem with them. As others said, main objective is reasonable load and even distribution. On the edge, 2x8 top and bottom. Go for it.

Mark

If you must use cinder blocks, Tie port and starboard sides together with a board to help stop sideways movement.

 

[smokeonthewater]

Re: cinder blocks

when I was in my early 20's I rode sport bikes to nearly 200 mph without a helmet many times.... since I am still alive should I tell people to go for it and that it'll be fine? of course not... It was a HIGHLY dangerous thing I did and by the grace of god I'm still here....

Cinder blocks are designed to be used with mortar to build walls.... they are fragile and dangerous for use as cribbing and should NOT be used for that....

need convincing? take an 8" x 8" x 12" wood block and throw it on a concrete floor as hard as you can... it'll bounce ...... now pick up an 8" x 8" x 16" cinder block and throw it down.... the wood will get a dent in it but the block will crush

 

[sphelps]

Re: cinder blocks

They use blocks everyday to block up whole trailers and houses . Solid one on the bottom and wood on top . But I would probably not go more than 3 high at the most ..

 

[Thalasso]

Re: cinder blocks

Concrete and cinder blocks share some basic elements, but a key ingredient makes all the difference. People sometimes use the terms interchangeably, but concrete and cinder blocks are very different.
Cinder blocks have not been made or used in the USA for some decades

 

[bruceb58]

Re: cinder blocks

Cinder blocks(concrete blocks) are fine when they are filled with concrete, reinforced with rebar and sit on a concrete footing. By themselves, they offer little strength.

Go to a boat yard and see what they use. You won't find cinder blocks.

 

[MH Hawker]

Re: cinder blocks

Go to your local lumber yard and buy several 10 ft by 4 x 4 and cut them to 24 in lengths and be safe.