Macgregor 26D deck repair, what fiberglass to use?

I have a soft spot on my starboard cabin top. The core is gone so I need to replace that. After grinding off all the non skid the deck seems really springy. So I want to strengthen it up. I was thinking of adding two layers of 1708. Since I want to add 2 layers of fiberglass on my deck to strengthen it up, my original plans where to use two layers of 1708. Since the weave is 45+/-, would it be better to have one layer 45+/- and the next 90+/-, or both layers as 45+/-? 1708 and 1208 run 45+/- and 1808 runs 90+/-. So should I run 2 layers of 1708/1208 or run one layer of 1708/1208 and a layer of 1808?

 

Hi Ken,
The core is doing most of the work of making it feel sturdy. Since you don't have core right now the deck glass will feel soft, especially after being ground .
Are you going to pull the old deck skin, replace the core, and then re-adhere the old deck skin with extra layers and a beveled and taped seam or make all new deck skins?

 

Tops, this is exactly what I plan. But there are other areas with good core. Like the front deck that isn't soft. Core is good i checked but still deflects enough feel when you are walking on it. I feel it could benefit from additional strengthening layers.

 

Adding layers on top to firm up the deck is only half the solution.
There’s two sides to a sandwich .

 

The interior of this boat has fiberglass ceiling liner. So no access to the bottom of the deck unless I cut through the liner and that's not a possibility. So this "sandwich" will have to be built up "open faced".

 

The core is really what is providing the rigidity.

The old core. Was it balsa? Or blocks of plywood?

If you want a stiffer core; stiffer deck the best solution is plywood. If the deck has camber; this is best achieved by building up thinner laminations of plywood. Use weights to hold them down; it will tale a few days and it will ise quite a bit of resin and cabosil. Doing the lamination should use great care because the plywood will like to drysuck the resin from the cabosil at the bond. So precoat the panels after dryfitting or before laying the mud. I'd use 1/16" or 1mm vee trowel on both sides. The resin use is great and will surprise you.

For a 3/4" deck; the three layers at 1/4" with epoxy between would end up thicker.

Adding an extra layer of glass to the top won't offer much because that layer is in compression which means when you stand on it the force is pushing the fibers closer. If you want to add any extra glass, it must be done to the bottom for benefit.

@kapnD remark is very accurate, but lacking in detail (sorry kapn)...hopefully I filled in some of it

Tell us about the existing core and extent of the repair. If you only want to fix an area of rot; the best you can do is the top glass, but it won't offer much.

 

The rotten core is plywood. Easy enough to remove and replace. The section that slopes from the cabin top to the front deck is not cored. The cabin top and front deck are cored.

I’m waiting for Andy from Boat Works Today to respond as well. But in one of his videos he laid down two layers of 1708 on his Bertram deck and it strengthen it up a good bit. This is why I wanted to try.

There is no access to the backside of anything, except small holes to access hardware. The top side is the only area where any repair can be completed.

 

It would be best to put chop strand down. The best way would be 1708 and 1808 with the tows out. If you need the chop strand out; then flip one. The mat offers little in terms of adding strength.. For the weight added; you'd be better off with db1700, a uni and db1700

the mat backed glass is about 25oz per yd

so two layers is 50 oz, where 3 layers of 17oz glass is 51 oz

 

I thought the 1708 was 17oz biax and the 08 =3/4oz mat.

my plan was mat down on the first and mat up on the second layer to prevent print through plus it gives a sacrificial layer if I sand through the fairing compound.

 

3/4 oz is per sqft

9 • 3/4 = 27/4 or about 7 oz per yard

 

Fallguy, thanks for the education. I’ve followed some of your build and comments on the seasled builds.

I’ve read that with 1708 it’s best to put the first layer mat down as it helps to adhere better? Your thoughts? Also any issue with print through from db1700 if I went that route? I know three layers will use more resin but overall more strength.

 

it will print thru some, but what is going on it?

non-skid?

 

After fairing it will be painted and non skid paint.

 

I have db1700 on cabin surfaces no post cure with minor print through on the cabin sides which are painted to a high gloss The issue of print through on a sole/deck is not worth considering. You'd never see it through non-skid. The printing on mine happened when the summer sun heated the cabin up and is only visible at the intersection between roof and hullsides. Mine is all epoxy.

DB1700 should get stitching knocked down, but this or peelply would be a matter of normal course before fairing.