[Public-List] Strength of Mazonite

crufone at comcast.net crufone at comcast.net
Mon Jul 26 10:54:37 PDT 2010


I am not an expert but have the same vintage boat.  What I plan to do on rebedding my deck hardware is to fashion some type of tool to remove that material, what ever it is, between the upper and lower skins outward perhaps a quarter inch around each fastener hole. Clean surfaces with acetone and then tape the bottom of the hole and fill with Epoxy, keep filling until the hole is completely filled. After curing redrill the hole to the fastener size using each piece of hardware as a template. If I plan to increase the fastener size then I would use the hardware as a template and drill the larger hole prior to removing the 1/4" of core material around each hole. I would use this same process to fill unused holes and for new mounting holes. 

Where ever possible I plan to use a single solid backing plate, made from either Coosa Board or Star board of a foot print large enough to encompass all of the fasteners and extend beyond them an inch.  If clearance is an issue I still plan to use a single backing board rather than fender washers around each fastener, even if I need to make it some strange shape to fit. 

We are fortunate to have no liners in our boats so this system is more possible to accomplish. I believe that the Masonite composite cores have substantial compression strength, assuming that they are not severely delaminated or deteriorated by advanced wetting rot.  

The donuts of Epoxy around each fastener hole should accomplish several tasks, consolidate the edge of the skins of fibreglass, adhear them to the core, seal the core from the fastener hole and provide some measure of compressive resistance to the fasteners.  On the early boats with Masonite coring I would not go to the work to remove and replace bits of core where the fastener holes are to increase compressive strength.  If you inspect our early boats as they came from Whitby.....you will realize that the above proceedure is many degrees better than the factory mounting which in most cases has lasted forty plus years with a few but not too many problems. 

Now on my Cape Dory Typhoon, with 3/8" balsa core.................I plan to recore the deck and use 3/8" Coosa board anywhere there is a planned deck penetration for a fastener, hatch opening.etc. 

The Coosa board will be laid up at the same time as the new balsa core and then a new upper skin laid on top of that. 

Hope this helps. 

Michael #133 
----- Original Message ----- 
From: "Roger L. Kingsland" <r.kingsland at ksba.com> 
To: "Alberg 30 Public List -- open to all" <public-list at lists.alberg30.org> 
Sent: Monday, July 26, 2010 1:06:55 PM 
Subject: [Public-List] Strength of Mazonite 

Hi Folks, 
I will soon be installing the deck cleats on good old #148 and noticed in 
the current issue of Sail Magazine (pg 66) is a description of cleat 
mounting that recommends, with cored decks, cutting out the core around the 
bolt holes and filling w/ epoxy to avoid crushing the core when tightening 
the fasteners.  I am wondering if the Masonite core on our boats is strong 
enough in compression make the epoxy unnecessary?  What do the experts 
Roger 148 
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